Research ArticlePhysicochemical Performance of Portland-Rice HuskAsh-Calcined Clay-Dried Acetylene Lime Sludge Cement inSulphate and Chloride Media
Jackson Muthengia Wachira 1 Joseph Karanja Thiongrsquoo2 Joseph Mwiti Marangu 3
and Leonard Genson Murithi1
1Department of Physical Sciences University of Embu Embu Kenya2Department of Chemistry Kenyatta University Nairobi Kenya3Department of Physical Sciences Meru University of Science and Technology Meru Kenya
Correspondence should be addressed to Joseph Mwiti Marangu jmarangu2011gmailcom
Received 1 December 2018 Revised 12 March 2019 Accepted 17 March 2019 Published 8 April 2019
Academic Editor Robert Cerny
Copyright copy 2019 Jackson Muthengia Wachira et al is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited
is paper reports leach andor intake of SO42minus Clminus Ca2+ Na+ and K+ from andor into cement mortar cubes made from a novel
cementious material in naturally encountered environmental simulated mediae paper also reports changes in pH of the mediaover time of exposure to the cement mortar cubes e compressive strength changes of the test cement in simulated media arealso reported e novel cement labelled PCDC made from intermixing ordinary Portland cement (OPC) with waste materialswhich included rice husks waste bricks acetylene lime sludge and spent bleaching earth was previously tested and found to meetthe Kenyan Standard requirements for Portland pozzolana cement (PPC) 100mm mortar cubes were prepared and theircompressive strengths were determined after exposure to the sea water e media included sea water distilled water andsolutions of sulphates and chlorides separately for a period of six months e tests were carried alongside commercial PPC andOPC e results showed that the PCDC exhibited comparable selected ions intake andor leach to PPC in sea water sulphatesolutions and distilled water In chloride solutions the cement exhibited the highest leach in the selected ions except K+ and Na+
ionse results further showed that PCDC exhibited lower pH in all the media compared to OPC and PPCe tests showed thatthe novel cement can be used for general construction work in the tested media in a similar manner to PPC
1 Introduction
Cement is a major building binder throughout the worldOrdinary Portland cement (OPC) has been used in vastconstruction activities in the past However OPC productionrequires significant amount of energy [1] is makes theproduct unaffordable especially in low and middle economycounties In addition during the manufacturing processenormous quantities of carbon dioxide (CO2) are emitted tothe atmosphere CO2 is one of the main greenhouse gasesmainly responsible for global warming and climate change
ere is an increasing demand for greener constructionmaterials with low carbon footprint globally [2] Portland
pozzolana cement (PPC) has recently emerged as a suitablealternative to OPC PPC is mostly preferred to OPC due tothe fact that it exhibits high ultimate strength and it is moredurable than neat OPC is is mainly attributed to theinclusion of pozzolanic materials in PPC e pozzolanicmaterials are highly siliceous and aluminous and in thepresence of calcium hydroxide (CH) at ambient tempera-tures they react with silica (SiO2) and alumina (Al2O3) toform compounds processing cementitious properties [3]
Rice husk ash (RHA) and broken bricks (BBs) have beenused as pozzolanic materials for many decades [4 5] In-clusion of these materials in cement production is consid-ered an innovative solution to improve the performance of
HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 5618743 12 pageshttpsdoiorg10115520195618743
cement-based materials and offer an environmentallyfriendly method of waste disposal However substitution ofOPC with these pozzolanic materials above 35 has beenreported to greatly lower the strength of the resultingcement-based materials [6] is has largely been attributedto insufficient CH in PPC containing pozzolanic materialsgreater than 35 percent Previous studies conducted usingPPC made from blending 55 percent of OPC with driedacetylene lime cement and an incinerated mix of rice husksreject bricks and spent bleaching earth showed that a ce-mentitious material is formed [7ndash11] ese showed that thecementitiousmaterial labelled as PCDC in this workmet theKenyan standard [12] requirements for PPC in terms ofcompressive strength and setting times [8] Further testswere therefore necessary to observe its resistivity in terms ofmain ions leach or intake in aggressive media commonlyencountered in the natural environment during the con-struction activities
2 Materials and Methods
21Materials Materials were sampled from their respectiveregions in Kenya Pozzolana material preparation and in-cineration was done in accordance with the procedureoutlined in [8] using a fixed bed kiln Sea water as obtainedfrom the sampling site was stored in clean plastic bottlesTable 1 gives the composition of various materials used inthis study
22Methods About 500ml of it was sampled for analysis ofNa+ K+ Ca2+ Clminus and SO4
2minus using the usual methods inflame photometry (for Na+ and K+) atomic absorptionspectrometry (Ca2+) potentiometry (Clminus) and turbidimetry(SO4
2minus)100mm mortar cubes were prepared using 1 3 cement
to sand ratio and a wc ratio of 046 Commercial OPC andPPC were also used alongside PCDC A vibrating pokermodel B25DS was used for compaction purposes e cubeswere demoulded after 24 hours and then cured for additional27 days in saturated calcium hydroxide solution undercomplete submersione cubes were then submerged into a500ml media in a 2 litre plastic container e media usedincluded sea water distilled water and separate solutions ofmagnesium chloride and sodium sulphate Magnesiumchloride labelled Cl1 and sulphate solutions labelled SO1were prepared to have an equivalent of chloride and sulphateconcentration in sea water respectively ese were 20000and 2342 ppm respectively Similar solutions but withdouble the chloride and sulphate Cl1 and SO2 were alsoused An aliquot of the aggressive media was sampled eachtime for analysis of the selected ions (Ca2+ Na+ Clminus andSO4minus2) An equal amount of the original solution of each
category was replenished after sampling e pH of theaggressive media was monitored by using the pH metermodel number 3405 e analysis was done for a period ofsix months
After about six months of monitoring of Ca2+ Na+ K+Clminus and SO4
2minus ions and pH changes in the corrosive media
compressive strength of the three mortar cubes represen-tative of each category was determined e change in thecompressive strength from the 28th day to the sixth monthwas calculated using the following equation
CSgain CS nth day( 1113857minusCSDW nth day( 1113857
CSDW nth day( 1113857 (1)
where CSgain is the calculated percent gain in compressivestrength CS(nth day) is the compressive strength at thenth day which in this study was 180th day andCSDW(nth day) is the compressive strength of the similarmortar cube in distilled water (which acquired a high pHwithin a short time of exposure) at the nth day
3 Results and Discussion
31 Clminus Analysis of Selected Ions from Chloride SolutionFigures 1 and 2 give the progressive intake and leaching ofthe chloride ions in magnesium chloride-simulated solu-tions against the monitoring period by mortar cubes of eachcategory
In chloride-simulated solution 1 the PCDC had thehighest initial intake followed by an early subsequent leachin chloride ions e high intake in PCDC could be asso-ciated with higher permeability due to the high levels ofsubstitution coupled with the lower pozzolanic reaction
OPC had a higher intake of the chlorides than the PPCfrom Cl1 solution is could be attributed to the higherexchange capacity due to a higher OHminus ions [11] Pozzolanareaction lowers the Ca(OH)2 content and hence the bufferstore of the OHminus ions e additional cementious materialfrom pozzolanic reaction higher Al2O3 phase from thereactive constituents of pozzolana and packaging of poz-zolana grains between cements aggregates lower the diffu-sivity of chlorides into the bulk is in turn lowers theintake of the ions in pozzolana-based cements
Table 1 Compositions of various materials used
Material Description
OPC Commercial ordinary Portland cement (425Nmm)
PPC Commercial Portland pozzolana cement orblended cement (325Nmm)
PCDC A blend of 55 OPC and 45 test ash
Test ash A blend of DALS and a calcined mix of RH SBEand ground BB
SO1 Sulphate-simulated solutions with sulphateconcentration equal to the sea water
SO2 Sulphate-simulated solutions with sulphateconcentration twice the sea water
Cl1 Chloride-simulated solutions with chlorideconcentration equal to the sea water
Cl2 Chloride-simulated solutions with chlorideconcentration twice the sea water
DALS Dried acetylene lime sludge
Corrosivemedia
Sea water 20000 and 40 000 ppm Clminus (MgCl2)solution distilled water 2342 and 4684 ppm
SO42minus (Na2SO4) solution
2 Advances in Materials Science and Engineering
As the concentration of the chloride is doubled in Cl2OPC showed a decreased intake of chlorides than the PPCPerhaps the benecial eects above of denser mortar re-duced Ca(OH)2 levels made PPC less resistant to the MgCl2attack is was attributed to higher amount of Ca(OH)2 inOPC than that in PPC High content of Ca(OH)2 in OPCmade its CSH to be attacked more by chlorides than that inPPC PPC being denser from pozzolanic reaction may haveleft little space for expansive brucite fromMg attack [13 14]
32 SO42minus Analyses in Chloride-Simulated Solutions
Figures 3 and 4 show the sulphate leach and intake from thechloride-simulated solutions Sulphates were observed toincrease in the corrosive media rapidly up to about the 11thand 25th day in the simulated chloride solution 1 and 2respectivelye ions then showed a fast decline to an almostconstant amount
e chloride solutions did not have sulphate ion in therst place and therefore the ions must have been leachedfrom the cement mortars e sulphates may have beenleached as soluble salts of sodium andor potassium or eventhe sparingly soluble calcium sulphatesese sulphates mayhave originated mainly from the interground gypsum
e decrease in the sulphates from the corrosive solutioncould have been due to the precipitation of the sulphate ionsas calcium sulphates e reaction between Ca2+ and SO4
2minus
is as shown in the following equation
Ca2+(aq) + SO42minus
(aq) + 2H2O(l)⟶ CaSO4 middot 2H2O(s) (2)
e sulphates could have also been precipitated due tothe eect of the chlorides and hydroxides on the mediaSulphates especially of alkalis and alkaline earth metalshave a diminishing solubility in the presence of chloridesand hydroxides [15]
As the concentration of the chloride solutions weredoubled the OPC showed the highest sulphate leach ismay have been attributed to a higher level of gypsum in OPCthat became a vulnerable phase as the chloride concentrationincreased e substitution of the OPC with pozzolana re-duces the amount of available sulphate from cements It wasnotable that in both cases of chloride concentrations theamount of leached sulphates from PCDC was about thesame at the early days of subjection in the corrosion media
As the monitoring period progressed it was observedthat the test-mortar cements exhibited a decline in SO4
2minus
leach e decline was most pronounced in PCDC especiallywith increased chloride concentration With timepozzolana-based cements become denser due to pozzolanicreactionsus PCDCmay have become less permeable andhence less vulnerable to the aggressive media
33 K+ Na+ Ca2+ and pH Analyses in Chloride-SimulatedSolutions Figures 5ndash7 show the results of K+ Na+ and Ca2+
050
100150200250300350400
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl2OPC Cl2PPC Cl2
Figure 4 SO42minus analyses in chloride-simulated solution 2
PCDC Cl1OPC Cl1PPC Cl1
7500
11000
14500
18000
21500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 1 Clminus analyses in chloride-simulated solution 1
PCDC Cl2OPC Cl2PPC Cl2
[Clndash ] (
ppm
)
25000280003100034000370004000043000
30 60 90 120 150 1800Monitoring period (days)
Figure 2 Clminus analyses in chloride-simulated solution 2
0
80
160
240
320
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period
PCDC Cl1OPC Cl1PPC Cl1
Figure 3 SO42minus analyses in chloride-simulated solution 1
Advances in Materials Science and Engineering 3
analyses Figure 8 shows the results of pH variation ofchloride-simulated solutions over a period of six months
In the test solutions an increase in the amount of leachedCa2+ from the mortar cubes followed by a decline imme-diately around the 11th day was observed Upon continuedmonitoring of the test cement mortars it was observed that
there was a decline in the Ca2+ leached Ingress of chloridescould have improved the microstructure and hence per-meability and strength of pozzolana-based cements Poz-zolanic reactions consume Ca(OH)2 us blended mortarsas observed were expected to show a decline in the amountof leached ions for example Ca2+ as permeability decreasedbecause their resistivity to aggressive agents had increased
ere was a marked increase in pH of the chloridesolution accompanied by leaching of the alkali metal ionsfrom the test cement mortars Generally contact water withconcrete is expected to attain a pH value above 9 or almost atequilibrium with the pore water is corresponded with theleach of the alkali ions observed in all the test cements
e ingress of Clminus is accompanied by leaching (in ex-change) of OHminus from the cement pasteis introduces OHminusfrom the pore solution into the corrosive media which at-tains a pH equilibrium between the pore water and cementmortar environment is could also be achieved throughionic transfer [16] In all cements the K+ ion was highlyleached from the mortar cubes perhaps due to its higherconcentration than Na+ in the pore solution [17]
e leaching of the alkali ions continued up to a certainpoint where it almost attained a constant amount is is asimilar scenario observed by Herold [18] who analysed forCa Mg Fe Al Si Na and K in solutions where hardenedpastes of OPC with a wc ratio of 05 were immersed eauthor [18] observed that there was a marked reduction inleaching in stationary systems And this was attributed to thegrowth of residual protective layer which changed the dis-solution rate from reaction controlled to a diusion con-trolled process e worker also attributed the decline inleaching of the ions to the growth of temporary concen-tration buildup in the corrosive media which caused a de-pression of the dissolution behaviour of the paste
It was observed that the alkali metal ions were leachedmost from PPCe higher leaching of alkalis in PPCmay beattributed to the observed higher pH in the chlorides so-lutions Perhaps the microcracking associated with Mg at-tack was more severe in PPC is may have made thecement more porous and hence highly leached
e leaching of the alkali and alkali earth metal ions isdeleterious as it may lead to disintegration of the CSH eleach could also lead to loss in concrete strength lowering of
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
0
100
200
300
400
500
600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 5 K+ analyses in chloride-simulated solution
0100200300400500600700800900
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
Figure 6 Na+ analyses in simulated chloride solutions
0
500
1000
1500
2000
[Ca2+
] (pp
m)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl2
OPC Cl1PPC Cl1PPC Cl2
Figure 7 Ca2+ analyses in simulated chloride solutions
OPC Cl1OPC Cl2PCDC Cl1
PCDC Cl2PPC Cl1PPC Cl2
65
75
85
95
105
115
pH
25 99857253 16132 39 46 131
18013106 180 3
Monitoring period (days)
Figure 8 pH measurements in simulated chloride solutions
4 Advances in Materials Science and Engineering
the pore pH and hence leading to breakdown in passivity ofreinforcement It would also lead to disruption of the mediathrough which concrete phases and reactions are held PPCexhibited the highest main ion loss for maintenance of thepore pH for example Na+ an important aspect in theconcrete system
34 Sulphate Analyses in Sulphate-Simulated SolutionsFigures 9 and 10 show the analyses of sulphate ions againstthe monitoring period from the sulphate-simulated solu-tions PCDC showed a continuous intake of the ions up toabout 103rd and 163rd day for the SO1 and SO2 solutionsrespectively After these days a subsequent leach was ob-served Similar observations were made for the PPC (intakewas observed up to about the 163rd day followed byleaching) OPC exhibited an intake up to about 103rd and45th day for simulated solution 1 and 2 respectively afterwhich leaching was observed An increased intake of thesulphates was observed when the concentration of thesulphates was doubled
OPC showed an initial reduced sulphate intake at thelower sulphate-simulated solution up to about the 11th day ofmonitoring Ingress of sulphates results in formation of forexample gypsum and ettringite (3CaOmiddotAl2O3middot3CaSO4middot32H2O)[19] ese are expansive products which may have createdmicrocracks at an early time in OPC that would have pavedway for leaching of the sulphates after ingress
PCDC and PPC showed a similar intake of the sulphatesin both solutions PCDC had a higher substitution level thanPPC e pozzolanic reaction and cement hydration weretherefore expected to be slower in PCDC compared to PPCerefore its resistivity to sulphates may not only have beendue reduction in its permeability from secondary CSH fromthe pozzolanic reaction is may also have been attributedto the packaging of the pozzolana particles in between theaggregates and cement grain which reduces permeability
35 K+ Na+ and pH Analyses in Sulphate-SimulatedSolutions Figures 11ndash13 show the changes in K+ Na+and pH in the simulated sulphate solutions ere wasprogressive increase in K+ ions in the solutions e pH rosefrom the near neutral to higher than 9
It was observed that Na+ ions ingressed the cementmortar cubes initially After sometime the ions were sub-sequently leached K+ exhibited a continuous leachthroughout the experimental period e alkalis pre-dominantly maintain the high pH of pore water eleaching preferentially of K+ ions helped maintain the pHequilibrium between the mortar matrix and the surroundingenvironment e intake of the Na+ ion was mainly due tothe ion concentration gradient between the aggressive media(which was prepared from sodium sulphates salt) and thecement pore system
All the aggressive media except PCDC and OPC sul-phate solution 1 showed an increase in pH to approximately11 upon the immersion of the mortar cubes in the solutionsere was a decline in these solutionsrsquo pH after sometimebut PPCrsquos solutions maintained a higher pH to the end of the
monitoring period Some authors [20 21] observed a steadyrise in pH of the corrosive media in few days to about 12due to release of the OHminus from the pore solution of theassociated concrete e interdependence of sulphate intakeand OHminus to be related as shown in the following equation
SO42minus[ ]
t SO4
2minus[ ]ominus12OHminus[ ]t (3)
e subscripts o and t denote concentrations (in thesolution under investigation) of the bracketed ions at initialand after a given time respectively is shows that there is arise in OHminus and hence pH as the sulphates ingress into acement mortar [20]
PCDC SO1OPC SO1PPC SO1
500700900
11001300150017001900210023002500
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 9 SO42minus analyses in sulphate-simulated solution 1
PCDC SO2OPC SO2PPC SO2
100015002000250030003500400045005000
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 10 SO42minus analyses in sulphate-simulated solution 2
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
0100200300400500600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 11 K+ analyses in sulphate-simulated solution
Advances in Materials Science and Engineering 5
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
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Submit your manuscripts atwwwhindawicom
cement-based materials and offer an environmentallyfriendly method of waste disposal However substitution ofOPC with these pozzolanic materials above 35 has beenreported to greatly lower the strength of the resultingcement-based materials [6] is has largely been attributedto insufficient CH in PPC containing pozzolanic materialsgreater than 35 percent Previous studies conducted usingPPC made from blending 55 percent of OPC with driedacetylene lime cement and an incinerated mix of rice husksreject bricks and spent bleaching earth showed that a ce-mentitious material is formed [7ndash11] ese showed that thecementitiousmaterial labelled as PCDC in this workmet theKenyan standard [12] requirements for PPC in terms ofcompressive strength and setting times [8] Further testswere therefore necessary to observe its resistivity in terms ofmain ions leach or intake in aggressive media commonlyencountered in the natural environment during the con-struction activities
2 Materials and Methods
21Materials Materials were sampled from their respectiveregions in Kenya Pozzolana material preparation and in-cineration was done in accordance with the procedureoutlined in [8] using a fixed bed kiln Sea water as obtainedfrom the sampling site was stored in clean plastic bottlesTable 1 gives the composition of various materials used inthis study
22Methods About 500ml of it was sampled for analysis ofNa+ K+ Ca2+ Clminus and SO4
2minus using the usual methods inflame photometry (for Na+ and K+) atomic absorptionspectrometry (Ca2+) potentiometry (Clminus) and turbidimetry(SO4
2minus)100mm mortar cubes were prepared using 1 3 cement
to sand ratio and a wc ratio of 046 Commercial OPC andPPC were also used alongside PCDC A vibrating pokermodel B25DS was used for compaction purposes e cubeswere demoulded after 24 hours and then cured for additional27 days in saturated calcium hydroxide solution undercomplete submersione cubes were then submerged into a500ml media in a 2 litre plastic container e media usedincluded sea water distilled water and separate solutions ofmagnesium chloride and sodium sulphate Magnesiumchloride labelled Cl1 and sulphate solutions labelled SO1were prepared to have an equivalent of chloride and sulphateconcentration in sea water respectively ese were 20000and 2342 ppm respectively Similar solutions but withdouble the chloride and sulphate Cl1 and SO2 were alsoused An aliquot of the aggressive media was sampled eachtime for analysis of the selected ions (Ca2+ Na+ Clminus andSO4minus2) An equal amount of the original solution of each
category was replenished after sampling e pH of theaggressive media was monitored by using the pH metermodel number 3405 e analysis was done for a period ofsix months
After about six months of monitoring of Ca2+ Na+ K+Clminus and SO4
2minus ions and pH changes in the corrosive media
compressive strength of the three mortar cubes represen-tative of each category was determined e change in thecompressive strength from the 28th day to the sixth monthwas calculated using the following equation
CSgain CS nth day( 1113857minusCSDW nth day( 1113857
CSDW nth day( 1113857 (1)
where CSgain is the calculated percent gain in compressivestrength CS(nth day) is the compressive strength at thenth day which in this study was 180th day andCSDW(nth day) is the compressive strength of the similarmortar cube in distilled water (which acquired a high pHwithin a short time of exposure) at the nth day
3 Results and Discussion
31 Clminus Analysis of Selected Ions from Chloride SolutionFigures 1 and 2 give the progressive intake and leaching ofthe chloride ions in magnesium chloride-simulated solu-tions against the monitoring period by mortar cubes of eachcategory
In chloride-simulated solution 1 the PCDC had thehighest initial intake followed by an early subsequent leachin chloride ions e high intake in PCDC could be asso-ciated with higher permeability due to the high levels ofsubstitution coupled with the lower pozzolanic reaction
OPC had a higher intake of the chlorides than the PPCfrom Cl1 solution is could be attributed to the higherexchange capacity due to a higher OHminus ions [11] Pozzolanareaction lowers the Ca(OH)2 content and hence the bufferstore of the OHminus ions e additional cementious materialfrom pozzolanic reaction higher Al2O3 phase from thereactive constituents of pozzolana and packaging of poz-zolana grains between cements aggregates lower the diffu-sivity of chlorides into the bulk is in turn lowers theintake of the ions in pozzolana-based cements
Table 1 Compositions of various materials used
Material Description
OPC Commercial ordinary Portland cement (425Nmm)
PPC Commercial Portland pozzolana cement orblended cement (325Nmm)
PCDC A blend of 55 OPC and 45 test ash
Test ash A blend of DALS and a calcined mix of RH SBEand ground BB
SO1 Sulphate-simulated solutions with sulphateconcentration equal to the sea water
SO2 Sulphate-simulated solutions with sulphateconcentration twice the sea water
Cl1 Chloride-simulated solutions with chlorideconcentration equal to the sea water
Cl2 Chloride-simulated solutions with chlorideconcentration twice the sea water
DALS Dried acetylene lime sludge
Corrosivemedia
Sea water 20000 and 40 000 ppm Clminus (MgCl2)solution distilled water 2342 and 4684 ppm
SO42minus (Na2SO4) solution
2 Advances in Materials Science and Engineering
As the concentration of the chloride is doubled in Cl2OPC showed a decreased intake of chlorides than the PPCPerhaps the benecial eects above of denser mortar re-duced Ca(OH)2 levels made PPC less resistant to the MgCl2attack is was attributed to higher amount of Ca(OH)2 inOPC than that in PPC High content of Ca(OH)2 in OPCmade its CSH to be attacked more by chlorides than that inPPC PPC being denser from pozzolanic reaction may haveleft little space for expansive brucite fromMg attack [13 14]
32 SO42minus Analyses in Chloride-Simulated Solutions
Figures 3 and 4 show the sulphate leach and intake from thechloride-simulated solutions Sulphates were observed toincrease in the corrosive media rapidly up to about the 11thand 25th day in the simulated chloride solution 1 and 2respectivelye ions then showed a fast decline to an almostconstant amount
e chloride solutions did not have sulphate ion in therst place and therefore the ions must have been leachedfrom the cement mortars e sulphates may have beenleached as soluble salts of sodium andor potassium or eventhe sparingly soluble calcium sulphatesese sulphates mayhave originated mainly from the interground gypsum
e decrease in the sulphates from the corrosive solutioncould have been due to the precipitation of the sulphate ionsas calcium sulphates e reaction between Ca2+ and SO4
2minus
is as shown in the following equation
Ca2+(aq) + SO42minus
(aq) + 2H2O(l)⟶ CaSO4 middot 2H2O(s) (2)
e sulphates could have also been precipitated due tothe eect of the chlorides and hydroxides on the mediaSulphates especially of alkalis and alkaline earth metalshave a diminishing solubility in the presence of chloridesand hydroxides [15]
As the concentration of the chloride solutions weredoubled the OPC showed the highest sulphate leach ismay have been attributed to a higher level of gypsum in OPCthat became a vulnerable phase as the chloride concentrationincreased e substitution of the OPC with pozzolana re-duces the amount of available sulphate from cements It wasnotable that in both cases of chloride concentrations theamount of leached sulphates from PCDC was about thesame at the early days of subjection in the corrosion media
As the monitoring period progressed it was observedthat the test-mortar cements exhibited a decline in SO4
2minus
leach e decline was most pronounced in PCDC especiallywith increased chloride concentration With timepozzolana-based cements become denser due to pozzolanicreactionsus PCDCmay have become less permeable andhence less vulnerable to the aggressive media
33 K+ Na+ Ca2+ and pH Analyses in Chloride-SimulatedSolutions Figures 5ndash7 show the results of K+ Na+ and Ca2+
050
100150200250300350400
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl2OPC Cl2PPC Cl2
Figure 4 SO42minus analyses in chloride-simulated solution 2
PCDC Cl1OPC Cl1PPC Cl1
7500
11000
14500
18000
21500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 1 Clminus analyses in chloride-simulated solution 1
PCDC Cl2OPC Cl2PPC Cl2
[Clndash ] (
ppm
)
25000280003100034000370004000043000
30 60 90 120 150 1800Monitoring period (days)
Figure 2 Clminus analyses in chloride-simulated solution 2
0
80
160
240
320
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period
PCDC Cl1OPC Cl1PPC Cl1
Figure 3 SO42minus analyses in chloride-simulated solution 1
Advances in Materials Science and Engineering 3
analyses Figure 8 shows the results of pH variation ofchloride-simulated solutions over a period of six months
In the test solutions an increase in the amount of leachedCa2+ from the mortar cubes followed by a decline imme-diately around the 11th day was observed Upon continuedmonitoring of the test cement mortars it was observed that
there was a decline in the Ca2+ leached Ingress of chloridescould have improved the microstructure and hence per-meability and strength of pozzolana-based cements Poz-zolanic reactions consume Ca(OH)2 us blended mortarsas observed were expected to show a decline in the amountof leached ions for example Ca2+ as permeability decreasedbecause their resistivity to aggressive agents had increased
ere was a marked increase in pH of the chloridesolution accompanied by leaching of the alkali metal ionsfrom the test cement mortars Generally contact water withconcrete is expected to attain a pH value above 9 or almost atequilibrium with the pore water is corresponded with theleach of the alkali ions observed in all the test cements
e ingress of Clminus is accompanied by leaching (in ex-change) of OHminus from the cement pasteis introduces OHminusfrom the pore solution into the corrosive media which at-tains a pH equilibrium between the pore water and cementmortar environment is could also be achieved throughionic transfer [16] In all cements the K+ ion was highlyleached from the mortar cubes perhaps due to its higherconcentration than Na+ in the pore solution [17]
e leaching of the alkali ions continued up to a certainpoint where it almost attained a constant amount is is asimilar scenario observed by Herold [18] who analysed forCa Mg Fe Al Si Na and K in solutions where hardenedpastes of OPC with a wc ratio of 05 were immersed eauthor [18] observed that there was a marked reduction inleaching in stationary systems And this was attributed to thegrowth of residual protective layer which changed the dis-solution rate from reaction controlled to a diusion con-trolled process e worker also attributed the decline inleaching of the ions to the growth of temporary concen-tration buildup in the corrosive media which caused a de-pression of the dissolution behaviour of the paste
It was observed that the alkali metal ions were leachedmost from PPCe higher leaching of alkalis in PPCmay beattributed to the observed higher pH in the chlorides so-lutions Perhaps the microcracking associated with Mg at-tack was more severe in PPC is may have made thecement more porous and hence highly leached
e leaching of the alkali and alkali earth metal ions isdeleterious as it may lead to disintegration of the CSH eleach could also lead to loss in concrete strength lowering of
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
0
100
200
300
400
500
600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 5 K+ analyses in chloride-simulated solution
0100200300400500600700800900
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
Figure 6 Na+ analyses in simulated chloride solutions
0
500
1000
1500
2000
[Ca2+
] (pp
m)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl2
OPC Cl1PPC Cl1PPC Cl2
Figure 7 Ca2+ analyses in simulated chloride solutions
OPC Cl1OPC Cl2PCDC Cl1
PCDC Cl2PPC Cl1PPC Cl2
65
75
85
95
105
115
pH
25 99857253 16132 39 46 131
18013106 180 3
Monitoring period (days)
Figure 8 pH measurements in simulated chloride solutions
4 Advances in Materials Science and Engineering
the pore pH and hence leading to breakdown in passivity ofreinforcement It would also lead to disruption of the mediathrough which concrete phases and reactions are held PPCexhibited the highest main ion loss for maintenance of thepore pH for example Na+ an important aspect in theconcrete system
34 Sulphate Analyses in Sulphate-Simulated SolutionsFigures 9 and 10 show the analyses of sulphate ions againstthe monitoring period from the sulphate-simulated solu-tions PCDC showed a continuous intake of the ions up toabout 103rd and 163rd day for the SO1 and SO2 solutionsrespectively After these days a subsequent leach was ob-served Similar observations were made for the PPC (intakewas observed up to about the 163rd day followed byleaching) OPC exhibited an intake up to about 103rd and45th day for simulated solution 1 and 2 respectively afterwhich leaching was observed An increased intake of thesulphates was observed when the concentration of thesulphates was doubled
OPC showed an initial reduced sulphate intake at thelower sulphate-simulated solution up to about the 11th day ofmonitoring Ingress of sulphates results in formation of forexample gypsum and ettringite (3CaOmiddotAl2O3middot3CaSO4middot32H2O)[19] ese are expansive products which may have createdmicrocracks at an early time in OPC that would have pavedway for leaching of the sulphates after ingress
PCDC and PPC showed a similar intake of the sulphatesin both solutions PCDC had a higher substitution level thanPPC e pozzolanic reaction and cement hydration weretherefore expected to be slower in PCDC compared to PPCerefore its resistivity to sulphates may not only have beendue reduction in its permeability from secondary CSH fromthe pozzolanic reaction is may also have been attributedto the packaging of the pozzolana particles in between theaggregates and cement grain which reduces permeability
35 K+ Na+ and pH Analyses in Sulphate-SimulatedSolutions Figures 11ndash13 show the changes in K+ Na+and pH in the simulated sulphate solutions ere wasprogressive increase in K+ ions in the solutions e pH rosefrom the near neutral to higher than 9
It was observed that Na+ ions ingressed the cementmortar cubes initially After sometime the ions were sub-sequently leached K+ exhibited a continuous leachthroughout the experimental period e alkalis pre-dominantly maintain the high pH of pore water eleaching preferentially of K+ ions helped maintain the pHequilibrium between the mortar matrix and the surroundingenvironment e intake of the Na+ ion was mainly due tothe ion concentration gradient between the aggressive media(which was prepared from sodium sulphates salt) and thecement pore system
All the aggressive media except PCDC and OPC sul-phate solution 1 showed an increase in pH to approximately11 upon the immersion of the mortar cubes in the solutionsere was a decline in these solutionsrsquo pH after sometimebut PPCrsquos solutions maintained a higher pH to the end of the
monitoring period Some authors [20 21] observed a steadyrise in pH of the corrosive media in few days to about 12due to release of the OHminus from the pore solution of theassociated concrete e interdependence of sulphate intakeand OHminus to be related as shown in the following equation
SO42minus[ ]
t SO4
2minus[ ]ominus12OHminus[ ]t (3)
e subscripts o and t denote concentrations (in thesolution under investigation) of the bracketed ions at initialand after a given time respectively is shows that there is arise in OHminus and hence pH as the sulphates ingress into acement mortar [20]
PCDC SO1OPC SO1PPC SO1
500700900
11001300150017001900210023002500
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 9 SO42minus analyses in sulphate-simulated solution 1
PCDC SO2OPC SO2PPC SO2
100015002000250030003500400045005000
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 10 SO42minus analyses in sulphate-simulated solution 2
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
0100200300400500600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 11 K+ analyses in sulphate-simulated solution
Advances in Materials Science and Engineering 5
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
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Journal ofNanomaterials
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As the concentration of the chloride is doubled in Cl2OPC showed a decreased intake of chlorides than the PPCPerhaps the benecial eects above of denser mortar re-duced Ca(OH)2 levels made PPC less resistant to the MgCl2attack is was attributed to higher amount of Ca(OH)2 inOPC than that in PPC High content of Ca(OH)2 in OPCmade its CSH to be attacked more by chlorides than that inPPC PPC being denser from pozzolanic reaction may haveleft little space for expansive brucite fromMg attack [13 14]
32 SO42minus Analyses in Chloride-Simulated Solutions
Figures 3 and 4 show the sulphate leach and intake from thechloride-simulated solutions Sulphates were observed toincrease in the corrosive media rapidly up to about the 11thand 25th day in the simulated chloride solution 1 and 2respectivelye ions then showed a fast decline to an almostconstant amount
e chloride solutions did not have sulphate ion in therst place and therefore the ions must have been leachedfrom the cement mortars e sulphates may have beenleached as soluble salts of sodium andor potassium or eventhe sparingly soluble calcium sulphatesese sulphates mayhave originated mainly from the interground gypsum
e decrease in the sulphates from the corrosive solutioncould have been due to the precipitation of the sulphate ionsas calcium sulphates e reaction between Ca2+ and SO4
2minus
is as shown in the following equation
Ca2+(aq) + SO42minus
(aq) + 2H2O(l)⟶ CaSO4 middot 2H2O(s) (2)
e sulphates could have also been precipitated due tothe eect of the chlorides and hydroxides on the mediaSulphates especially of alkalis and alkaline earth metalshave a diminishing solubility in the presence of chloridesand hydroxides [15]
As the concentration of the chloride solutions weredoubled the OPC showed the highest sulphate leach ismay have been attributed to a higher level of gypsum in OPCthat became a vulnerable phase as the chloride concentrationincreased e substitution of the OPC with pozzolana re-duces the amount of available sulphate from cements It wasnotable that in both cases of chloride concentrations theamount of leached sulphates from PCDC was about thesame at the early days of subjection in the corrosion media
As the monitoring period progressed it was observedthat the test-mortar cements exhibited a decline in SO4
2minus
leach e decline was most pronounced in PCDC especiallywith increased chloride concentration With timepozzolana-based cements become denser due to pozzolanicreactionsus PCDCmay have become less permeable andhence less vulnerable to the aggressive media
33 K+ Na+ Ca2+ and pH Analyses in Chloride-SimulatedSolutions Figures 5ndash7 show the results of K+ Na+ and Ca2+
050
100150200250300350400
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl2OPC Cl2PPC Cl2
Figure 4 SO42minus analyses in chloride-simulated solution 2
PCDC Cl1OPC Cl1PPC Cl1
7500
11000
14500
18000
21500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 1 Clminus analyses in chloride-simulated solution 1
PCDC Cl2OPC Cl2PPC Cl2
[Clndash ] (
ppm
)
25000280003100034000370004000043000
30 60 90 120 150 1800Monitoring period (days)
Figure 2 Clminus analyses in chloride-simulated solution 2
0
80
160
240
320
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period
PCDC Cl1OPC Cl1PPC Cl1
Figure 3 SO42minus analyses in chloride-simulated solution 1
Advances in Materials Science and Engineering 3
analyses Figure 8 shows the results of pH variation ofchloride-simulated solutions over a period of six months
In the test solutions an increase in the amount of leachedCa2+ from the mortar cubes followed by a decline imme-diately around the 11th day was observed Upon continuedmonitoring of the test cement mortars it was observed that
there was a decline in the Ca2+ leached Ingress of chloridescould have improved the microstructure and hence per-meability and strength of pozzolana-based cements Poz-zolanic reactions consume Ca(OH)2 us blended mortarsas observed were expected to show a decline in the amountof leached ions for example Ca2+ as permeability decreasedbecause their resistivity to aggressive agents had increased
ere was a marked increase in pH of the chloridesolution accompanied by leaching of the alkali metal ionsfrom the test cement mortars Generally contact water withconcrete is expected to attain a pH value above 9 or almost atequilibrium with the pore water is corresponded with theleach of the alkali ions observed in all the test cements
e ingress of Clminus is accompanied by leaching (in ex-change) of OHminus from the cement pasteis introduces OHminusfrom the pore solution into the corrosive media which at-tains a pH equilibrium between the pore water and cementmortar environment is could also be achieved throughionic transfer [16] In all cements the K+ ion was highlyleached from the mortar cubes perhaps due to its higherconcentration than Na+ in the pore solution [17]
e leaching of the alkali ions continued up to a certainpoint where it almost attained a constant amount is is asimilar scenario observed by Herold [18] who analysed forCa Mg Fe Al Si Na and K in solutions where hardenedpastes of OPC with a wc ratio of 05 were immersed eauthor [18] observed that there was a marked reduction inleaching in stationary systems And this was attributed to thegrowth of residual protective layer which changed the dis-solution rate from reaction controlled to a diusion con-trolled process e worker also attributed the decline inleaching of the ions to the growth of temporary concen-tration buildup in the corrosive media which caused a de-pression of the dissolution behaviour of the paste
It was observed that the alkali metal ions were leachedmost from PPCe higher leaching of alkalis in PPCmay beattributed to the observed higher pH in the chlorides so-lutions Perhaps the microcracking associated with Mg at-tack was more severe in PPC is may have made thecement more porous and hence highly leached
e leaching of the alkali and alkali earth metal ions isdeleterious as it may lead to disintegration of the CSH eleach could also lead to loss in concrete strength lowering of
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
0
100
200
300
400
500
600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 5 K+ analyses in chloride-simulated solution
0100200300400500600700800900
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
Figure 6 Na+ analyses in simulated chloride solutions
0
500
1000
1500
2000
[Ca2+
] (pp
m)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl2
OPC Cl1PPC Cl1PPC Cl2
Figure 7 Ca2+ analyses in simulated chloride solutions
OPC Cl1OPC Cl2PCDC Cl1
PCDC Cl2PPC Cl1PPC Cl2
65
75
85
95
105
115
pH
25 99857253 16132 39 46 131
18013106 180 3
Monitoring period (days)
Figure 8 pH measurements in simulated chloride solutions
4 Advances in Materials Science and Engineering
the pore pH and hence leading to breakdown in passivity ofreinforcement It would also lead to disruption of the mediathrough which concrete phases and reactions are held PPCexhibited the highest main ion loss for maintenance of thepore pH for example Na+ an important aspect in theconcrete system
34 Sulphate Analyses in Sulphate-Simulated SolutionsFigures 9 and 10 show the analyses of sulphate ions againstthe monitoring period from the sulphate-simulated solu-tions PCDC showed a continuous intake of the ions up toabout 103rd and 163rd day for the SO1 and SO2 solutionsrespectively After these days a subsequent leach was ob-served Similar observations were made for the PPC (intakewas observed up to about the 163rd day followed byleaching) OPC exhibited an intake up to about 103rd and45th day for simulated solution 1 and 2 respectively afterwhich leaching was observed An increased intake of thesulphates was observed when the concentration of thesulphates was doubled
OPC showed an initial reduced sulphate intake at thelower sulphate-simulated solution up to about the 11th day ofmonitoring Ingress of sulphates results in formation of forexample gypsum and ettringite (3CaOmiddotAl2O3middot3CaSO4middot32H2O)[19] ese are expansive products which may have createdmicrocracks at an early time in OPC that would have pavedway for leaching of the sulphates after ingress
PCDC and PPC showed a similar intake of the sulphatesin both solutions PCDC had a higher substitution level thanPPC e pozzolanic reaction and cement hydration weretherefore expected to be slower in PCDC compared to PPCerefore its resistivity to sulphates may not only have beendue reduction in its permeability from secondary CSH fromthe pozzolanic reaction is may also have been attributedto the packaging of the pozzolana particles in between theaggregates and cement grain which reduces permeability
35 K+ Na+ and pH Analyses in Sulphate-SimulatedSolutions Figures 11ndash13 show the changes in K+ Na+and pH in the simulated sulphate solutions ere wasprogressive increase in K+ ions in the solutions e pH rosefrom the near neutral to higher than 9
It was observed that Na+ ions ingressed the cementmortar cubes initially After sometime the ions were sub-sequently leached K+ exhibited a continuous leachthroughout the experimental period e alkalis pre-dominantly maintain the high pH of pore water eleaching preferentially of K+ ions helped maintain the pHequilibrium between the mortar matrix and the surroundingenvironment e intake of the Na+ ion was mainly due tothe ion concentration gradient between the aggressive media(which was prepared from sodium sulphates salt) and thecement pore system
All the aggressive media except PCDC and OPC sul-phate solution 1 showed an increase in pH to approximately11 upon the immersion of the mortar cubes in the solutionsere was a decline in these solutionsrsquo pH after sometimebut PPCrsquos solutions maintained a higher pH to the end of the
monitoring period Some authors [20 21] observed a steadyrise in pH of the corrosive media in few days to about 12due to release of the OHminus from the pore solution of theassociated concrete e interdependence of sulphate intakeand OHminus to be related as shown in the following equation
SO42minus[ ]
t SO4
2minus[ ]ominus12OHminus[ ]t (3)
e subscripts o and t denote concentrations (in thesolution under investigation) of the bracketed ions at initialand after a given time respectively is shows that there is arise in OHminus and hence pH as the sulphates ingress into acement mortar [20]
PCDC SO1OPC SO1PPC SO1
500700900
11001300150017001900210023002500
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 9 SO42minus analyses in sulphate-simulated solution 1
PCDC SO2OPC SO2PPC SO2
100015002000250030003500400045005000
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 10 SO42minus analyses in sulphate-simulated solution 2
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
0100200300400500600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 11 K+ analyses in sulphate-simulated solution
Advances in Materials Science and Engineering 5
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
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Submit your manuscripts atwwwhindawicom
analyses Figure 8 shows the results of pH variation ofchloride-simulated solutions over a period of six months
In the test solutions an increase in the amount of leachedCa2+ from the mortar cubes followed by a decline imme-diately around the 11th day was observed Upon continuedmonitoring of the test cement mortars it was observed that
there was a decline in the Ca2+ leached Ingress of chloridescould have improved the microstructure and hence per-meability and strength of pozzolana-based cements Poz-zolanic reactions consume Ca(OH)2 us blended mortarsas observed were expected to show a decline in the amountof leached ions for example Ca2+ as permeability decreasedbecause their resistivity to aggressive agents had increased
ere was a marked increase in pH of the chloridesolution accompanied by leaching of the alkali metal ionsfrom the test cement mortars Generally contact water withconcrete is expected to attain a pH value above 9 or almost atequilibrium with the pore water is corresponded with theleach of the alkali ions observed in all the test cements
e ingress of Clminus is accompanied by leaching (in ex-change) of OHminus from the cement pasteis introduces OHminusfrom the pore solution into the corrosive media which at-tains a pH equilibrium between the pore water and cementmortar environment is could also be achieved throughionic transfer [16] In all cements the K+ ion was highlyleached from the mortar cubes perhaps due to its higherconcentration than Na+ in the pore solution [17]
e leaching of the alkali ions continued up to a certainpoint where it almost attained a constant amount is is asimilar scenario observed by Herold [18] who analysed forCa Mg Fe Al Si Na and K in solutions where hardenedpastes of OPC with a wc ratio of 05 were immersed eauthor [18] observed that there was a marked reduction inleaching in stationary systems And this was attributed to thegrowth of residual protective layer which changed the dis-solution rate from reaction controlled to a diusion con-trolled process e worker also attributed the decline inleaching of the ions to the growth of temporary concen-tration buildup in the corrosive media which caused a de-pression of the dissolution behaviour of the paste
It was observed that the alkali metal ions were leachedmost from PPCe higher leaching of alkalis in PPCmay beattributed to the observed higher pH in the chlorides so-lutions Perhaps the microcracking associated with Mg at-tack was more severe in PPC is may have made thecement more porous and hence highly leached
e leaching of the alkali and alkali earth metal ions isdeleterious as it may lead to disintegration of the CSH eleach could also lead to loss in concrete strength lowering of
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
0
100
200
300
400
500
600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 5 K+ analyses in chloride-simulated solution
0100200300400500600700800900
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl1
OPC Cl2PPC Cl1PPC Cl2
Figure 6 Na+ analyses in simulated chloride solutions
0
500
1000
1500
2000
[Ca2+
] (pp
m)
30 60 90 120 150 1800Monitoring period (days)
PCDC Cl1PCDC Cl2OPC Cl2
OPC Cl1PPC Cl1PPC Cl2
Figure 7 Ca2+ analyses in simulated chloride solutions
OPC Cl1OPC Cl2PCDC Cl1
PCDC Cl2PPC Cl1PPC Cl2
65
75
85
95
105
115
pH
25 99857253 16132 39 46 131
18013106 180 3
Monitoring period (days)
Figure 8 pH measurements in simulated chloride solutions
4 Advances in Materials Science and Engineering
the pore pH and hence leading to breakdown in passivity ofreinforcement It would also lead to disruption of the mediathrough which concrete phases and reactions are held PPCexhibited the highest main ion loss for maintenance of thepore pH for example Na+ an important aspect in theconcrete system
34 Sulphate Analyses in Sulphate-Simulated SolutionsFigures 9 and 10 show the analyses of sulphate ions againstthe monitoring period from the sulphate-simulated solu-tions PCDC showed a continuous intake of the ions up toabout 103rd and 163rd day for the SO1 and SO2 solutionsrespectively After these days a subsequent leach was ob-served Similar observations were made for the PPC (intakewas observed up to about the 163rd day followed byleaching) OPC exhibited an intake up to about 103rd and45th day for simulated solution 1 and 2 respectively afterwhich leaching was observed An increased intake of thesulphates was observed when the concentration of thesulphates was doubled
OPC showed an initial reduced sulphate intake at thelower sulphate-simulated solution up to about the 11th day ofmonitoring Ingress of sulphates results in formation of forexample gypsum and ettringite (3CaOmiddotAl2O3middot3CaSO4middot32H2O)[19] ese are expansive products which may have createdmicrocracks at an early time in OPC that would have pavedway for leaching of the sulphates after ingress
PCDC and PPC showed a similar intake of the sulphatesin both solutions PCDC had a higher substitution level thanPPC e pozzolanic reaction and cement hydration weretherefore expected to be slower in PCDC compared to PPCerefore its resistivity to sulphates may not only have beendue reduction in its permeability from secondary CSH fromthe pozzolanic reaction is may also have been attributedto the packaging of the pozzolana particles in between theaggregates and cement grain which reduces permeability
35 K+ Na+ and pH Analyses in Sulphate-SimulatedSolutions Figures 11ndash13 show the changes in K+ Na+and pH in the simulated sulphate solutions ere wasprogressive increase in K+ ions in the solutions e pH rosefrom the near neutral to higher than 9
It was observed that Na+ ions ingressed the cementmortar cubes initially After sometime the ions were sub-sequently leached K+ exhibited a continuous leachthroughout the experimental period e alkalis pre-dominantly maintain the high pH of pore water eleaching preferentially of K+ ions helped maintain the pHequilibrium between the mortar matrix and the surroundingenvironment e intake of the Na+ ion was mainly due tothe ion concentration gradient between the aggressive media(which was prepared from sodium sulphates salt) and thecement pore system
All the aggressive media except PCDC and OPC sul-phate solution 1 showed an increase in pH to approximately11 upon the immersion of the mortar cubes in the solutionsere was a decline in these solutionsrsquo pH after sometimebut PPCrsquos solutions maintained a higher pH to the end of the
monitoring period Some authors [20 21] observed a steadyrise in pH of the corrosive media in few days to about 12due to release of the OHminus from the pore solution of theassociated concrete e interdependence of sulphate intakeand OHminus to be related as shown in the following equation
SO42minus[ ]
t SO4
2minus[ ]ominus12OHminus[ ]t (3)
e subscripts o and t denote concentrations (in thesolution under investigation) of the bracketed ions at initialand after a given time respectively is shows that there is arise in OHminus and hence pH as the sulphates ingress into acement mortar [20]
PCDC SO1OPC SO1PPC SO1
500700900
11001300150017001900210023002500
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 9 SO42minus analyses in sulphate-simulated solution 1
PCDC SO2OPC SO2PPC SO2
100015002000250030003500400045005000
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 10 SO42minus analyses in sulphate-simulated solution 2
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
0100200300400500600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 11 K+ analyses in sulphate-simulated solution
Advances in Materials Science and Engineering 5
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
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Submit your manuscripts atwwwhindawicom
the pore pH and hence leading to breakdown in passivity ofreinforcement It would also lead to disruption of the mediathrough which concrete phases and reactions are held PPCexhibited the highest main ion loss for maintenance of thepore pH for example Na+ an important aspect in theconcrete system
34 Sulphate Analyses in Sulphate-Simulated SolutionsFigures 9 and 10 show the analyses of sulphate ions againstthe monitoring period from the sulphate-simulated solu-tions PCDC showed a continuous intake of the ions up toabout 103rd and 163rd day for the SO1 and SO2 solutionsrespectively After these days a subsequent leach was ob-served Similar observations were made for the PPC (intakewas observed up to about the 163rd day followed byleaching) OPC exhibited an intake up to about 103rd and45th day for simulated solution 1 and 2 respectively afterwhich leaching was observed An increased intake of thesulphates was observed when the concentration of thesulphates was doubled
OPC showed an initial reduced sulphate intake at thelower sulphate-simulated solution up to about the 11th day ofmonitoring Ingress of sulphates results in formation of forexample gypsum and ettringite (3CaOmiddotAl2O3middot3CaSO4middot32H2O)[19] ese are expansive products which may have createdmicrocracks at an early time in OPC that would have pavedway for leaching of the sulphates after ingress
PCDC and PPC showed a similar intake of the sulphatesin both solutions PCDC had a higher substitution level thanPPC e pozzolanic reaction and cement hydration weretherefore expected to be slower in PCDC compared to PPCerefore its resistivity to sulphates may not only have beendue reduction in its permeability from secondary CSH fromthe pozzolanic reaction is may also have been attributedto the packaging of the pozzolana particles in between theaggregates and cement grain which reduces permeability
35 K+ Na+ and pH Analyses in Sulphate-SimulatedSolutions Figures 11ndash13 show the changes in K+ Na+and pH in the simulated sulphate solutions ere wasprogressive increase in K+ ions in the solutions e pH rosefrom the near neutral to higher than 9
It was observed that Na+ ions ingressed the cementmortar cubes initially After sometime the ions were sub-sequently leached K+ exhibited a continuous leachthroughout the experimental period e alkalis pre-dominantly maintain the high pH of pore water eleaching preferentially of K+ ions helped maintain the pHequilibrium between the mortar matrix and the surroundingenvironment e intake of the Na+ ion was mainly due tothe ion concentration gradient between the aggressive media(which was prepared from sodium sulphates salt) and thecement pore system
All the aggressive media except PCDC and OPC sul-phate solution 1 showed an increase in pH to approximately11 upon the immersion of the mortar cubes in the solutionsere was a decline in these solutionsrsquo pH after sometimebut PPCrsquos solutions maintained a higher pH to the end of the
monitoring period Some authors [20 21] observed a steadyrise in pH of the corrosive media in few days to about 12due to release of the OHminus from the pore solution of theassociated concrete e interdependence of sulphate intakeand OHminus to be related as shown in the following equation
SO42minus[ ]
t SO4
2minus[ ]ominus12OHminus[ ]t (3)
e subscripts o and t denote concentrations (in thesolution under investigation) of the bracketed ions at initialand after a given time respectively is shows that there is arise in OHminus and hence pH as the sulphates ingress into acement mortar [20]
PCDC SO1OPC SO1PPC SO1
500700900
11001300150017001900210023002500
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 9 SO42minus analyses in sulphate-simulated solution 1
PCDC SO2OPC SO2PPC SO2
100015002000250030003500400045005000
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 10 SO42minus analyses in sulphate-simulated solution 2
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
0100200300400500600
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 11 K+ analyses in sulphate-simulated solution
Advances in Materials Science and Engineering 5
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
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Submit your manuscripts atwwwhindawicom
PCDC showed the lowest leach in K+ than the PPC andOPC as shown in Figure 10 is corresponded to the ob-served least pH as can be seen from Figure 12 is could beattributed to the high replacement of the OPC by the test-ashhence lower leacheable alkalis from the cement pore solutione lower leach of the K+ ions maintains the PCDC poresolution pH from the fact that blended cements have loweralkali content with K+ taking the larger portion of the alkalis
36 Sulphate Analyses in Distilled Water Figure 14 showsthe analyses of sulphate ions versus the monitoring period indistilled water
Leaching of the sulphates was noted in all the test ce-ments With time the amount of leached sulphates got to aconstant level is could be compared to a scenario where aprotective layer development on cement mortar and aconcentration buildup in the solution are observed [18]
PPC and PCDC exhibited a continued leaching with PPCshowing a higher leach PCDC had a higher substitutionlevel than PPC It was therefore expected as observed thatPPC would exhibit a higher sulphate leachis is because ofits initial higher amount of sulphates added as gypsum tocontrol poundash set
37 Ca2+ K+ Na+ and pH Analyses in DistilledWater Figures 15ndash18 show the analyses of Ca2+ K+ Na+and pH from distilled water versus the monitoring periode Ca2+ ions were only detectable for a few days in OPC
and PPCmedia Ca2+ levels in PCDC varied from one testingday to the other
Ca2+ either as CaO or Ca(OH)2 leaching through watercan be through its slight solubility or through attack viasolubilization of atmospheric CO2 [22] as shown in thefollowing equationH2O(l) + CO2(g) + Ca(OH)2(slightly soluble)⟶ Ca HCO3( )2(aq)
(4)
PCDC SO1PCDC SO2OPC SO1
OPC SO2PPC SO1PPC SO2
500700900
11001300150017001900210023002500
[Na+ ] (
ppm
)
30 60 90 120 150 1800
Monitoring period (days)
Figure 12 Na+ analyses from simulated sulphate solutions
PPC SO1PCDC SO1PPC SO2
OPC SO1OPC SO2PCDC SO2
775
885
99510
10511
115
pH
10 20 30 40 50 60 70 80 90 110
160
1500
140
180
130
100
170
120
Monitoring period (days)
Figure 13 pH measurements in simulated sulphate solutions
PCDC DWOPC DWPPC DW
0
20
40
60
80
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 14 SO42minus analyses in distilled water
PCDC DWPPC DWOPC DW
0
05
1
15
2
25
3
35
[Ca2+
] (pp
m)
50 100 1500Monitoring period (days)
Figure 15 Ca2+ analyses in simulated distilled water
PCDC DWOPC DWPPC DW
050
100150200250300
[K+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
Figure 16 K+ analyses in simulated distilled water
6 Advances in Materials Science and Engineering
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
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Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
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Volume 2018
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ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
e leaching of Ca2+ from OPC and PPC declinedimmediately after the rst few days e lower Ca2+ leachcould probably be explained from a pH point of view Asdiscussed earlier the solubility of Ca2+ decreases with in-crease in pH thus higher leach in K+ and Na+ fromOPC andPPC would have inhibited the leach of Ca2+ from the poresolution of the hydrated cement matrix
As observed in other experimental results above Na+and K+ were least leached from PCDC e lower leach ofthese alkalis from the PCDC could explain the lower pHobserved of the PCDC cementrsquos aggressive media as com-pared to OPC and PPC PPC exhibited the highest leach ofthe alkalis combined and correspondingly the highest pH inits aggressive media was observed
Distilled water was not as deleterious as had been ob-served of the chlorides and sulphates especially in theleaching of the main cement constituents for example Ca2+Na+ and K+ among otherse leach of these constituents indistilled water could have mainly been due to concentrationdierence between the cement matrix and corrosive envi-ronment as opposed to chemical attack More so with timehydration of the cement mortar progresses thus making themortar less permeable and hence less vulnerable to attack
38 Chloride Analyses in Sea Water Figure 19 shows theanalyses of chlorides against monitoring period in sea water
It was observed that the test cements showed an intake ofClminus that was continued up to the 103th day After this the testsamples showed an increase in the chloride content in the
corrosive media e leaching could be attributed to thesaturation of the chlorides in the mortar cubes Someworkers [23] attributed the decline in Ca(OH)2 due topozzolanic reaction to increase in solubility of the chlor-oaluminateis may lead to the formation of soluble salts ofthe chlorides of calcium aluminium and iron from de-composition of the same [24] e salts may leach from theconcrete mass A similar trend of intake and subsequentleaching was observed in [25]e author [25] attributed thisto the saturation of the chlorides in the mortar
PPC showed the lowest intake of Clminus PPC is known tocure over a long time compared to OPC It is well docu-mented that a majority of blended cements show a greaterresistance to aggressive media [13 26ndash29] such as sea waterIt was therefore expected as observed that PPC would showgreater resistance to ingress in the constituents of the seawater
e high intake of chlorides by PCDC could be attrib-uted to its high level of substitution is could be attributedto a lower hydration rate of cementus the cement showeda higher permeability than OPC and PPC
39 Sulphates Analyses in Sea Water Figure 20 shows theresults of analyses of sulphates in sea water media against themonitoring period OPC showed the highest intake of thesulphates after which the cement mortar showed leaching ofthe same evidenced by increase in the sulphates in its ag-gressive media
All the cement mortars showed intake of sulphates OPCshowed an intake up to about the 45th day after which itshowed subsequent leaching OPC is known to be easilyattacked by sulphates [30ndash33] In sulphate-simulated solu-tions OPC showed higher intake especially at higher con-centrations of the sulphate solutions (Figure 10) It wasobserved that at the higher sulphate concentration the OPCexhibited leach after intake of the sulphates In simulatedchloride solution OPC showed the highest leach in thesulphates especially at the higher chloride concentration(Figure 4) It would then appear that the combined eect of
050
100150200250300350400450
[Na+ ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 17 Na+ analyses in simulated distilled water
775
885
99510
pH
30 60 90 120 150 1800Monitoring period (days)
PCDC DWOPC DWPPC DW
Figure 18 pH measurements in simulated distilled water
7500
10500
13500
16500
19500
22500
[Clndash ] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 19 Clminus analyses in sea water
Advances in Materials Science and Engineering 7
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
the two ions (sulphates and chlorides in sea water) exhibitedthe same trend where they were more aggressive to OPCthan the blended cements But the severity of attack in theseparate aggressive solutions was noted to be higher com-pared to sea water
ere was no signicant dierence between PCDC andPPC in terms of sulphate intake in sea water is wasdespite the high intake of chlorides by PCDC from the samesolutionis could be accounted for the pozzolana includedwhich makes them less permeable to aggressive agents orintake of chlorides suppressing the intake of the sulphates
310 Ca2+ K+ Na+ and pH Analyses in SeaWater Figures 21ndash24 show the results for analyses of Ca2+K+ Na+ and pH in sea water against the monitoring period
e cements were observed to leach K+ with the highestleach observed from PPC ere was an initial intake of Na+
and then a subsequent leach is is a similar trend asobserved in the above experimental resultse high leach ofthe K+ ion corresponded to the observed pH in the ag-gressive media PPC aggressive media exhibited the highestpH
PPC had the highest intake of Na+ followed by PCDCand least OPC especially toward the end of the monitoringperiod e intake of Na+ may have been to counter for theleached K+ on an ion exchange point of view
e corrosive media was shown to exhibit a decline inCa2+ ions a similar scenario to the chloride-simulated so-lutions PCDCmaintained a higher amount of the ions in itscorrosion media Ca2+ ion solubility decreases with theincrease in pH us the observed least pH in PCDC mediafavoured a higher concentration of the same as opposed toPPC which exhibited the highest pH with least Ca2+ con-centrations in its aggressive solution
e corrosion media was observed to have attained a pHgreater than 9 A rise in pH from about 752 to 917 in seawater into which concrete was immersed in a monthrsquos time
had been observed elsewhere [34] is has been attributedto Ca(OH)2 leach from the concrete Oxides of potassiumand sodium have also been found to be leached fromconcrete immersed in sea water simulated sea water and tapwater [27]
311 Compressive Strength Changes in Mortars
3111 Compressive Strength Changes in Mortars Immersedin Chloride Solution Figure 25 represents the percent gainand loss in compressive strength of cement in simulatedmagnesium chloride solutions
1000
1400
1800
2200
2600
[SO
42ndash] (
ppm
)
30 60 90 120 150 1800Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 20 SO42minus analyses in sea water
300400500600700800900
1000
0 30 60 90 120 150 180Monitoring period (days)
[K+ ] (
ppm
)
PCDC SWOPC SWPPC SW
Figure 21 K+ analyses in sea water
9900
10200
10500
10800
0 30 60 90 120 150 180
[Na+ ] (
ppm
)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 22 Na+ analyses in sea water
200
250
300
350
400
450
0 30 60 90 120 150 180
[Ca2+
] (pp
m)
Monitoring period (days)
PCDC SWOPC SWPPC SW
Figure 23 Ca2+ analyses in sea water
8 Advances in Materials Science and Engineering
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
ere was an observed increase in strength for the testcements immersed in Clminus-simulated solution but it de-creased when the Clminus concentration was doubled in PPC andPCDC (TCal minus1503 and minus750 respectively) PPC had thehighest strength gain in simulated solution 1 is can beattributed this to ingress of the chloride ions Chlorides areactive in enhancing the strength gain because of both theirsmall charge and ionic sizes which enhances its diffusivityChloride ions activate pozzolanic reactions and initiateresidual cement hydration [6] thus increasing their strength
ere was a marked decrease in compressive strengthwhen chloride concentration was doubled is could beattributed to the formation of brucite [Mg(OH)2] as a result ofincreased ingress of MgCl2 on mortar which introduces bothchlorides and Mg ions Brucite [Mg(OH)2] is formed via themagnesium ion attack as shown in the following equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (5)
Brucite is an expansive product and can lead to crackingand hence lowering cement strength Pozzolanic reactionmakes blended cements denser is leaves little space forthe expansive brucite in case of Mg attack on the mortar
is exaggerates the damage due to Mg-attack in thepozzolana-based cements is may have explained whyalthough at the lower chloride concentration PPC had thehighest strength gain and it showed a decline in simulatedchloride 2 solutione results thus suggested that at higherchloride concentration the medium was more aggressiveand hence an earlier Mg attack
Pozzolanic reaction leaves limited Ca(OH)2 for the Mgattack e reduced Ca(OH)2 leaves the CSH as the im-mediate culprits e result is the formation of non-cementious MSH e attack was not severe in PCDCcompared to PPCe less severity could be attributed to thelevel of substitution us the pozzolanic-Ca(OH)2 reactionwas not expected to have consumed all Ca(OH)2 or made themortar as dense as PPC More so it would seem that theintroduced Ca(OH)2 as DALS may have offered a phase forMg attack prior to silica
3112 Compressive Strength Changes in Mortars Immersedin Sulphate Solution e percent gain in the compressivestrength of mortar cubes immersed in sodium sulphate-simulated solutions was also determined after about sixmonths of subjecting the mortar cubes to the corrosiveagents e results are presented in Figure 26
PCDC and PPCmortar cubes under this corrosive mediaregistered a significant gain in compressive strength egain was even more pronounced with increase in sulphateconcentration (TCal 449 for PCDC SO2 versus PCDC SO1TCal 1840 for PPC SO2 versus PPC SO1 way above TCritvalue of 430) e strength gain in OPC was also notable inthe sulphate solution but there was a significant decline ingain when the solution concentration was doubled(TCal minus559 for OPC SO2 versus OPC SO1 the negativesign indicating a decline in strength gain) Sulphates havetwo effects on hydrated cements first they raise the pH ofpore water in cement matrix owing to ion exchange asshown in the following ionic equation [7]
SO2minus4 (aq) + Ca(OH)2(s) + 2H2O(l)
⟶ CaSO4 middot 2H2O(s) + 2OHminus(6)
is increases the concentration of OHminus in the porewater hence increasing the pH of cement mortar matrix ehigh pH results in increased dissolution of pozzolanicmaterials in PPC and PCDC hence promoting the pozzo-lanic reaction Enhanced pozzolanic reaction subsequentlyincreases the early compressive strength of cement mortarsdue to increased formation of CSH that is responsible forstrength [8 9] Secondly sulphates react with aluminiumoxide in the glass phase of pozzolanic materials to formettrigite (AFt phase) Ettrigite formed at early ages of curingresults in a significant densification hence forming a lessporous structure and subsequently leads to higher strength[6] Increase in compressive strength of OPC can be at-tributed to the presence of Na+ which promotes the hy-dration residual cement phases OPC is the most susceptibleto the deleterious effects of sulphates e two effects tend togive an increase and then a decline in physical propertiessuch as strength in mortars or concrete
775
885
99510
10511
0 30 60 90 120 150 180
pH
Monotoring period (days)
PCDC SWPPC SWOPC SW
Figure 24 pH measurements in sea water
ndash15
ndash10
ndash5
0
5
10
15
20
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
Cl1Cl2
Figure 25 Percent gain in compressive strength versus test cementin chloride solutions
Advances in Materials Science and Engineering 9
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
PCDC registered a lower strength gain than PPC Asobserved from even the 28th day compressive strength insaturated calcium hydroxide solution PCDC had the leastcompressive strength development is perhaps could bedue to the high substitution level coupled with slow de-velopment of strength from pozzolanic reaction AlthoughSO4
2minus and Na+ may have activated pozzolanic reaction thereaction is still slower compared to the PPCrsquos High levels ofsubstitution of OPC have been observed elsewhere to havelow-strength gain
e lower strength in OPC as the sulphate concentrationwas doubled could be inferred from the three stages ofsulphate attack classified as early attack transition and laterstages At the early stage densification of mortar or concretedue to sulphate products increased strength but in transi-tion and later stages the deleterious effects of the sulphateswere observed e deleterious effects brought about declinein physical properties such as the compressive strength Anincrease in sulphate concentration in this study may havecaused an earlier lapse of the early stages compared to thelower sulphate concentration is may be attributed to theobserved decline in strength gain as the sulphate concen-tration was increased
In general the PPC had the highest strength gain fol-lowed by PCDC in the sulphate solutionsis is expected ofblended cements compared to OPC is is mainly attrib-uted to low permeability from the resultant secondary CSHfrom pozzolanic reactione packaging of pozzolana grainsbetween the cement grains and aggregates also reducepermeability e reduction in Ca(OH)2 content throughpozzolanic reaction reduces a phase that is most vulnerableto sulphate attackese factors make blended cements to beless vulnerable to the sulphate form of attack
3113 Compressive Strength Changes in Mortars Immersedin Distilled Water e change in the compressive strengthof the cement mortars subjected to distilled water for sixmonths was compared to their respective strength of the28 days of curing in saturated calcium hydroxide solutionFigure 27 shows these results
ere was observed strength gain for all the test cementsin watere increase in the compressive strength in distilledwater could mainly be attributed to a continued hydration ofthe cement without activators for example Na+ Clminus andSO4
2minus as experienced in other aggressive solution e waterdid not contain these activators that initiate residue cementhydration or pozzolanic reaction and thus strength devel-opment increase as observed was expected to be low
PCDC had the highest strength gain which is signifi-cantly higher than OPC (TCal 517 against TCrit 430)ere was no significant difference in strength gain betweenPCDC and PPC (TCal 217) Pozzolana-based cement hasslow development in strength as compared to OPC if ag-gressive ions are not encountered is is attributed to lowerpozzolanic reaction With time due to continued pozzolanicreaction blended cements are expected to exhibit highergain in compressive strength than OPC as observed in thiscase
3114 Compressive Strength Changes in Mortars Immersedin Sea Water Figure 28 shows the percent gain in com-pressive strength versus test cement in sea water
PPC had significant higher strength gain than OPC andPCDC in sea water (TCal 714 for PPC against OPC 985 forPPC against PCDC and 403 for OPC against PCDC[TCrit 430]) is could be attributed to the activation ofpozzolanic reaction and rehydration of residual cements dueto ingress of the sulphate chloride and sodium ions isimproves the compressive strength of the resultant mortarIn sea water deleterious products for example magnesiumsilicate hydrates calcium sulphates and ettringite areformed Brucite [Mg(OH)2] an expansive product isformed via the magnesium ion attack as shown in the fol-lowing equation
Mg2++ Ca(OH)2⟶ Mg(OH)2 + Ca2+ (7)
e buildup process of the magnesium and sodium saltsfor example sulphates through hydration dehydration andfinally rehydration is another expansive process that isdeleterious and likely in sea water are shown in the followingequations
OPC PPC PCDC
co
mpr
essiv
e str
engt
h ga
in
Test cement
SO1SO2
504540353025201510
50
Figure 26 Percent gain in compressive strength versus test cement
54
56
58
60
62
64
66
68
70
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 27 Percent gain in the compressive strength versus testcement in distilled water
10 Advances in Materials Science and Engineering
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
Na2SO4 + 10H2OharrNa2SO4 middot 10H2O
MgSO4 + H2OharrMgSO4 middot H2O harr5H2OMgSO4
middot 6H2OharrH2OMgSO4 middot 7H2O
(8)
A combination of the above products would be expectedto exhibit higher deleterious effects by sea water compared toseparate aggressive media of sulphates and chlorides ecomparatively low percent gain in strength for PCDC couldbe attributed to the high substitution level
4 Conclusion
From this study the following conclusions were made
(i) Despite the leaching andor intake of the selectedions analysed in this study PPC and PCDCexhibited comparative results suggesting thatPCDC could be used in similar manner to PPC ingeneral construction
(ii) Increased concentration of sulphate ions in thepresence of magnesium ions resulted in decreasedcompressive strength
Data Availability
e data used in the manuscript will be provided uponrequest
Conflicts of Interest
e authors declare that there are no conflicts of interest inthis paper
Acknowledgments
e authors wish to acknowledge the financial supportgranted by the Kenyatta University that facilitated this work
References
[1] P J Jackson and P C Hewlett ldquo2mdashportland cement clas-sification andmanufacturerdquo in Learsquos Chemistry of Cement and
Concrete pp 25ndash94 Butterworth-Heinemann Oxford UK4th edition 1998
[2] S Noor-ul-Amin ldquoUse of clay as a cement replacement inmortar and its chemical activation to reduce the cost andemission of greenhouse gasesrdquo Construction and BuildingMaterials vol 34 pp 381ndash384 2012
[3] M J Mwiti T J Karanja andW J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 article e00742 2018
[4] P Chindaprasirt S Rukzon and V Sirivivatnanon ldquoRe-sistance to chloride penetration of blended Portland cementmortar containing palm oil fuel ash rice husk ash and fly ashrdquoConstruction and Building Materials vol 22 no 5 pp 932ndash938 2008
[5] M J Washira M G Kanyago and T O J KaranjaldquoCementing material from rice husk-broken bricks-spentbleaching earth-dried calcium carbide residuerdquo Mediterra-nean Journal of Chemistry vol 2 no 2 pp 401ndash407 2012
[6] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018
[7] C Shi and R L Day ldquoChemical activation of blended cementsmade with lime and natural pozzolansrdquo Cement and ConcreteResearch vol 23 no 6 pp 1389ndash1396 1993
[8] C Shi and R L Day ldquoAcceleration of the reactivity of fly ashby chemical activationrdquo Cement and Concrete Researchvol 25 no 1 pp 15ndash21 1995
[9] F Sajedi andH A Razak ldquoe effect of chemical activators onearly strength of ordinary Portland cement-slag mortarsrdquoConstruction and Building Materials vol 24 no 10pp 1944ndash1951 2010
[10] G J Ochungrsquoo 7e Production of Rice Husk Ash BasedCementious Materials Kenyatta University Nairobi Kenya1993
[11] O E Gjoslashrv and Oslash Vennesland ldquoDiffusion of chloride ionsfrom seawater into concreterdquo Cement and Concrete Researchvol 9 no 2 pp 229ndash238 1979
[12] Kenya Bureau of Standards Kenya Standard Specification forPortland Pozzolana Cements KS 1775 Part 5 Kenya Bureau ofStandards Nairobi Kenya 1993
[13] O S B Al-Amoudi ldquoAttack on plain and blended cementsexposed to aggressive sulfate environmentsrdquo Cement andConcrete Composites vol 24 no 3-4 pp 305ndash316 2002
[14] W Kurdowski ldquoe protective layer and decalcification ofC-S-H in the mechanism of chloride corrosion of cementpasterdquo Cement and Concrete Research vol 34 no 9pp 1555ndash1559 2004
[15] A Seidell and W F Linke Solubilities of Inorganic and Or-ganic Compounds D Van Nostrand Company New YorkNY USA 3rd edition 1952
[16] F Adenot and M Buil ldquoModelling of the corrosion of thecement paste by deionized waterrdquo Cement and ConcreteResearch vol 22 no 2-3 pp 489ndash496 1992
[17] S Diamond ldquoLong-term status of calcium hydroxide satu-ration of pore solutions in hardened cementsrdquo Cement andConcrete Research vol 5 no 6 pp 607ndash616 1975
[18] G Herold ldquoCorrosion of cementious materials in acid wa-tersrdquo in Mechanisms of Chemical Degradation of Cement-Based Systems K L Scrivener and J F Young Edspp 98ndash105 E amp FN Spon An Imprint of Chapman and HallBoston USA 1995
[19] W G Hime and BMather ldquoldquoSulfate attackrdquo or is itrdquoCementand Concrete Research vol 29 no 5 pp 789ndash791 1999
0102030405060708090
100
OPC PPC PCDC
g
ain
in co
mpr
essiv
e str
engt
h
Test cement
Figure 28 Percent gain in compressive strength versus test cementin sea water
Advances in Materials Science and Engineering 11
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
[20] P W Brown ldquoAn evaluation of the sulfate resistance ofcements in a controlled environmentrdquo Cement and ConcreteResearch vol 11 no 5-6 pp 719ndash727 1981
[21] C F Ferraris J R Clifton P E Stutzman and E J GarboczildquoMechanisms of degradation of Portland cement-based sys-tems by sulphate attackrdquo in Mechanisms of Chemical Deg-radation of Cement-Based Systems K L Scrivener andJ F Young Eds pp 185ndash192 E amp FN Spon An Imprint ofChapman and Hall Boston MA USA 1995
[22] H F W Taylor Cement Chemistry Taylor and omasTelford Services Ltd London UK 1997
[23] C Arya N R Buenfeld and J B Newman ldquoFactors influ-encing chloride-binding in concreterdquo Cement and ConcreteResearch vol 20 no 2 pp 291ndash300 1990
[24] A Rasheeduzzafar S E Hussain and A S Al-Gahtani ldquoPoresolution composition and reinforcement corrosion charac-teristics of microsilica blended cement concreterdquo Cement andConcrete Research vol 21 no 6 pp 1035ndash1048 1991
[25] J K iongrsquoo7e Effects of Ions on Mortar Cubes Made withKenyan Cements and Sands University of Nairobi NairobiKenya 1987
[26] A Cheng R Huang J Wu and C Chen ldquoInfluence of GGBSon durability and corrosion behavior of reinforced concreterdquoMaterials Chemistry and Physics vol 93 no 2-3 pp 404ndash4112005
[27] E Ganjian and H S Pouya ldquoEffect of magnesium and sulfateions on durability of silica fume blended mixes exposed to theseawater tidal zonerdquo Cement and Concrete Research vol 35no 7 pp 1332ndash1343 2005
[28] K M A Hossain and M Lachemi ldquoCorrosion resistance andchloride diffusivity of volcanic ash blended cement mortarrdquoCement and Concrete Research vol 34 no 4 pp 695ndash7022004
[29] M D A omas and J D Matthews ldquoPerformance of pfaconcrete in a marine environmentmdash10-year resultsrdquo Cementand Concrete Composites vol 26 no 1 pp 5ndash20 2004
[30] O S B Al-Amoudi and M Maslehuddin ldquoe effect ofchloride and sulphate ions on reinforcement corrosionrdquoCement and Concrete Research vol 23 no 1 pp 139ndash1461993
[31] M Mather ldquoField and laboratory studies of the sulphateresistance of concreterdquo in Performance of ConcreteE G Swenson Ed pp 66ndash76 University of Toronto PressToronto Canada 1968
[32] H F W Taylor ldquoDiscussion sulfate attack mechanismsrdquoMaterials Science of Concrete vol 33-34 1999
[33] J Zuquan S Wei Z Yunsheng J Jinyang and L JianzhongldquoInteraction between of sulfate and chloride solution attack ofconcretes with and without fly ashrdquo Cement and ConcreteResearch vol 37 no 8 pp 1223ndash1232 2007
[34] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water re-sistance of concreterdquo Building and Environment vol 42 no 4pp 1770ndash1776 2007
12 Advances in Materials Science and Engineering
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom
CorrosionInternational Journal of
Hindawiwwwhindawicom Volume 2018
Advances in
Materials Science and EngineeringHindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Journal of
Chemistry
Analytical ChemistryInternational Journal of
Hindawiwwwhindawicom Volume 2018
ScienticaHindawiwwwhindawicom Volume 2018
Polymer ScienceInternational Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Advances in Condensed Matter Physics
Hindawiwwwhindawicom Volume 2018
International Journal of
BiomaterialsHindawiwwwhindawicom
Journal ofEngineeringVolume 2018
Applied ChemistryJournal of
Hindawiwwwhindawicom Volume 2018
NanotechnologyHindawiwwwhindawicom Volume 2018
Journal of
Hindawiwwwhindawicom Volume 2018
High Energy PhysicsAdvances in
Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom
The Scientific World Journal
Volume 2018
TribologyAdvances in
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
ChemistryAdvances in
Hindawiwwwhindawicom Volume 2018
Advances inPhysical Chemistry
Hindawiwwwhindawicom Volume 2018
BioMed Research InternationalMaterials
Journal of
Hindawiwwwhindawicom Volume 2018
Na
nom
ate
ria
ls
Hindawiwwwhindawicom Volume 2018
Journal ofNanomaterials
Submit your manuscripts atwwwhindawicom