Advances in Concrete Construction, Vol. 11, No. 1 (2021) 73-80
DOI: https://doi.org/10.12989/acc.2021.11.1.073 73
Copyright © 2021 Techno-Press, Ltd. http://www.techno-press.org/?journal=acc&subpage=7 ISSN: 2287-5301 (Print), 2287-531X (Online)
1. Introduction
Global production of cement, with more than 4 billion
tons, accounts for the third largest source of anthropogenic
source of carbon dioxide with fossil fuels and land-use
changes being first and second respectively. Global CO2
emission from the production of cement was estimated at
1.45±0.20 Gt for the year 2016 (Andrew 2017). India with
cement production of 300,000 tons in 2016, is the second
largest producer of cement in the world (U.S. Geological
Survey 2019). Cement production also contributes to
greenhouse effects and acid rain with emission of SO2
(Sulphur dioxide), NOx (Nitrous oxide) (Valipour 2014),
consumption of subsequent amount of natural resources and
massive energy (Rashad 2011, 2013). Cement industry,
hence is faced tremendous challenges to address these
issues. Consequently, many researchers worked on partial
replacement of cement by utilization of by-products such as
fly ash, slag, silica fume, rice husk ash etc., which were
termed as supplementary cementitious materials (SCM).
Corresponding author, Associate Professor
E-mail: [email protected] aPh.D. Scholar
E-mail: [email protected] bAssociate Professor
E-mail: [email protected]
Another school of thought worked on developing alternate
binders which will contribute to lesser emission of CO2 and
consume lesser energy without compromising the quality
and efficiency. Geopolymers as alternate binders, shows
encouraging or even better properties than cement (Provis
2014).
Geopolymers are alkali aluminosilicate binders formed
by alkali silicate activation of aluminosilicate materials
(Davidovits 1994). Any material containing silica and
aluminum can be a source of geopolymer primer.
Researchers have studied different precursors like kaolinite
clays (Raheir et al. 1996, 1997, Barbosa et al. 2000),
metakaolin (Wang et al. 2005, Lee et al.2005, Praven et al.
2019), fly ash (Fernadez and Palomo 2005, Suresh et al.
2011), GGBS (Goriparthi 2007, Khater 2014), silica fume
(Khater 2013, Brew and MacKenzie, 2007), rice husk ash
(RHA) (Rattanasak et al. 2010, Kim et al. 2014, Singhal
and Jindal 2017).These precursors were normally activated
by hydroxides and silicates of sodium (Rattanasak and
Chindaprasirt 2009) and potassium (He et al. 2003, Shaikh
and Haque 2018). The production cost, viscous and
corrosive nature of these activators are the main hindrances
in adopting geopolymer widely and hence a search for a
new efficient activator is needed. Also, a limited research
are presently reported for RHA based geopolymer.
Rice is being cultivated on more than 165 million
hectares worldwide and with more than 756 million MT of
production in 2017. Asia accounts for more than 90% of
this production with India second at more than 168 MT of
Correlation study on microstructure and mechanical properties of rice husk ash-Sodium aluminate geopolymer pastes
N. Shyamananda Singh1a, Suresh Thokchom2 and Rama Debbarma1b
1Department of Civil Engineering, National Institute of Technology Agartala, Tripura, India 2Department of Civil Engineering, Manipur Institute of Technology, Imphal, Manipur, India
(Received September 12, 2019, Revised December 3, 2020, Accepted December 18, 2020)
Abstract. Rice Husk Ash (RHA) geopolymer paste activated by sodium aluminate were characterized by X-ray diffractogram
(XRD), scanning electron microscope (SEM), energy dispersion X-Ray analysis (EDAX)and fourier transform infrared
spectroscopy (FTIR). Five series of RHA geopolymer specimens were prepared by varying the Si/Al ratio as 1.5, 2.0, 2.5, 3.0
and 3.5. The paper focuses on the correlation of microstructure with hardened state parameters like bulk density, apparent
porosity, sorptivity, water absorption and compressive strength. XRD analysis peaks indicates quartz, cristobalite and gibbsite
for raw RHA and new peaks corresponding to Zeolite A in geopolymer specimens. In general, SEM micrographs show
interconnected pores and loosely packed geopolymer matrix except for specimens made with Si/Al of 2.0 which exhibited
comparatively better matrix. Incorporation of Al from sodium aluminate were confirmed with the stretching and bending
vibration of Si-O-Si and O-Si-O observations from the FTIR analysis of geopolymer specimen. The dense microstructure of
SA2.0 correlate into better performance in terms of 28 days maximum compressive strength of 16.96 MPa and minimum for
porosity, absorption and sorptivity among the specimens. However, due to the higher water demand to make the paste workable,
the value of porosity, absorption and sorptivity were reportedly higher as compared with other geopolymer systems. Correlation
regression equations were proposed to validate the interrelation between physical parameters and mechanical strength. RHA
geopolymer shows comparatively lower compressive strength as compared to Fly ash geopolymer.
Keywords: rice husk ash; sodium aluminate; XRD; SEM EDAX; FTIR
N. Shyamananda Singh, Suresh Thokchom and Rama Debbarma
Table 1 Physical properties of RHA
RHA
Natural Humidity (%) 3
Theoretical Density (g/cm3) 2.2
Colour Grey
Table 2 Chemical composition of RHA
Chemical Component (Weight %)
SiO2 92.19
Al2O3 0.09
Fe2O3 0.10
TiO2 0.71
MgO 0.41
K2O 0.05
Na2O 1.64
SO3 0.41
CaO 0.09
P2O5 0.01
LOI 4.14
production (FAO 2018). Rice husk being by-products of
milling process, accounts for around 20% of the rice
production (Jain et al. 1996). The silica content of ash
obtained from rice husk burned at 550°-700° is transformed
into amorphous stage (Boateng and Skeete1990). The
amorphous stage of RHA mainly consist of SiO2 (Mehta
and Pitt 1976). A strong network of Si-Al in three
dimension is one of the criteria for a strong geopolymer.
Sodium aluminate as alternative activator were proposed
and studied for fly ash based geopolymer by Phair and
Deventer (2002). Sturm et al. (2016) and Hajimohammadi
and van Deventer (2016) reported geopolymer based on the
“one -part” formulation of RHA and sodium aluminate.
This paper aims to validate the use of RHA and sodium
aluminate in the conventional “two part” geopolymer as
these were known for their versatility. Further, the paper
reports on the microstructure of the RHA geopolymer
specimens and correlates the observed microstructures with
the physical and mechanical parameters.
2. Experimental
2.1 Raw materials
The main raw material used in the study was RHA
collected from Kolkata, India. RHA samples were burned at
a temperature of (650-700)°C, collected and stored in air
tight containers. The physical characteristics for RHA is
tabulated in Table 1.
The X-Ray Fluorescence (XRF) results of RHA shown
in Table 2 indicate the bulk component as SiO2 at 92.19%
by weight. It also has traces of other oxides as well.
The SEM microstructure of the raw RHA shows rough,
flaky extended features with maximum percentage of Si and
trace amount of Al as evident from EDAX analysis in Fig.
1.
Sodium aluminate powder used as activator for RHA
Table 3 Series composition of RHA geopolymer samples
Specimen
Name Si/Al
RHA
(%wt)
Sodium Aluminate
(%wt)
Water
(%wt)
SA 1.5 1.5 40.65 18.70 40.65
SA 2.0 2.0 42.64 14.71 42.64
SA 2.5 2.5 43.94 12.13 43.94
SA 3.0 3.0 44.84 10.31 44.84
SA 3.5 3.5 45.51 8.972 45.51
was sourced from Sigma -Aldrich. The chemical
composition of sodium aluminate includes 54.62% of Al2O3
and 40.5% of Na2O and traces (≤ 0.05%) of Fe2O3.
2.2 Sample preparation
Based on the molar ratio of SiO2/Al2O3, five series of
geopolymer pastes with different sample designations were
prepared as shown in Table 3. Sodium aluminate was mixed
with required amount of distilled water and kept for 24
hours at room temperature. A constant Water/Binder ratio of
1:1 were maintained as RHA has low workability. 50 mm
cubes were used as per ASTM C109. After pouring into the
mould, the specimens were kept undisturbed for 1 hour. The
moulds were then placed into an electric oven maintained at
80°C for 24 hours. After cooling and demolding, samples
were organized systematically for relevant studies. The
nomenclature of the samples are such that the alphabets
denotes silicon and aluminum whereas the number denotes
the ratio of Si/Al. In all the series of the specimens, the ratio
of Na/Al was maintained constant at 1.
2.3 Testing procedure
2.3.1 Mechanical test The direct compressive strength of hardened
geopolymer specimens was determined at the ages of 7 and
28 days in a 3000kN capacity Servo-Hydraulic Computer
Controlled Compression Testing Machine. In each case,
three identical specimens were tested in accordance to
ASTM C-109-02 and average values were reported.
2.3.2 Bulk density and apparent porosity The bulk density and apparent porosity were determined
for 28 days old specimens. The specimens were dried in a
ventilated oven for 24 hours at a temperature of
80°C.Weight of the dried specimens were measured and
recorded as Wd. Specimens were then soaked in water for
24 hours. After removal from water, specimens were
suspended by a thin wire inside water and its weight
recorded as Wi.
The specimens were then wiped dry and its weight
measured in saturated surface dry condition as Ws. The bulk
density and apparent porosity of the specimens were then
determined using the relationships given below
Dry density (kg/m3) = Wd
WS−Wix 1000 (1)
Apparent porosity (%) = (ws −wd)
(ws − wi)x100 (2)
74
Correlation study on microstructure and mechanical properties of rice husk ash-Sodium aluminate geopolymer pastes
Fig. 1 SEM and EDAX of raw RHA sample
Where,
𝑊𝑑=Weight of the specimens after drying for 24 hours
in a ventilated oven.
𝑊𝑠=Weight of the specimens in saturated surface dry
condition.
𝑊𝑖=Weight of the specimens suspended by a thin wire
inside water.
2.3.3 Water absorption and water sorptivity The procedure followed for determination of water
absorption of geopolymer specimens was in accordance to
ASTM C-642. 28 days old specimens were dried at 80°C
for 24 hours, weighed and kept immersed in water for 24
hours. The specimens were then removed from water, wiped
clean and immediately weighed in saturated surface dry
(SSD) condition to find increase in weight.
The Sorptivity test determines the rate of capillary rise
absorption by the geopolymer paste cube. The specimens
were initially painted with water proof enamel paint on all
sides except the bottom and top surfaces, so as to allow
capillary uptake of water only from bottom. The slope of
the linear portion of the curve between cumulative mass
gained per exposed surface area and square root of time
taken was reported as the sorptivity of the geopolymer
paste.
2.3.4 X-ray diffraction (XRD) analysis X-ray diffraction analysis was made using D8 Advance
(Bruker) XRD machine with Cu-Kα radiation with the
following conditions: 40 kV, 30 mA. Fragments collected
from the compressive strength tests were powdered and
used for XRD in the scan angle (2θ) range of 2ᵒ to 45ᵒ.
Scanning was performed in continuous mode with step size
of (2θ) of 0.02 and scan step time of 1 sec. The slow
Fig. 2 Compressive strength after 7 and 28 days
scanning rate was used to improve resolution of peaks. The
reflection positions and d-spacing were calculated by
automated programs.
2.3.5 Scanning electron microscope RHA raw materials as well as the geopolymer paste
were microscopically examined by FEI Quanta 250.
Quantification of the elements present in the geopolymer
paste were performed by Energy Dispersion X-Ray
Analysis (EDAX) at an accelerating voltage of 20 kV.
2.3.6 Fourier transform infrared spectroscopy FTIR experiments were performed on powdered
samples with a Perkin Elmer, Simultaneous Thermal
Analyser STA 8000 device. Spectra were recorded in the
range 4000-400 cm-1 with a resolution of 4 cm-1 and 16
scans per spectrum.
3. Results and discussion
3.1 Compressive strength
A similar trend of increasing compressive strength of
geopolymer paste were observed for SA1.5 and SA 2.0 for
both the samples tested after 7 days and 28 days as shown
in Fig 2. With respect to SA2.5 to SA3.0, a sharp decline in
compressive strength values were observed for the
corresponding test days. The percentage increase in
compressive strength between SA1.5 and SA2.0 were
12.64% for 7 days and 15.84% for 28 days. Linear
increment of compressive strength was observed for Si/Al
1.5-2.0. Similar results were also reported in earlier studies
by Sturm et al. (2016) and Hajimohammaddi et al. (2016).
For SA 2.5, SA3.0 and SA3.5, with Si/Al ratio higher than
2.0, there were sharp decrease in the compressive strength.
This observation may be due to the formation of lesser
crystalline phase in the geopolymer matrix as evident from
the XRD in Fig.5. The maximum compressive strength was
observed for SA2.0 with average value of 16.96 MPa. The
increment in the compressive strength may be attributed to
the formation of a strong geopolymer network with more
active role of released aluminium from sodium aluminate
75
N. Shyamananda Singh, Suresh Thokchom and Rama Debbarma
Fig. 3 Bulk density and apparent porosity
and hence gaining strength in the later stages of
geopolymerisation.
It was observed that RHA geopolymer paste achieve
relatively lower strength for the samples tested after 7 days
as compared with those tested after 28 days. In all the
series, an average strength increase of approximately 15%
occur from 7 days to 28 days. Slow release of silica from
RHA and extended time taken for silica and alumina to
form a stable nuclei causes the initial low strength of the
geopolymer paste. Similar research outcomes were also
highlighted by Hajimohammaddi et al. (2016) and Jiminez
et al. (2006).
3.2 Bulk density and apparent porosity
The values of bulk density and apparent porosity for
geopolymer pastes are presented in Fig. 3. Bulk density
increases with increase in Si/Al ratio up to 2. Further
increase of Si/Al beyond 2 resulted in decrease of bulk
density for RHA geopolymer pastes. However, apparent
porosity exhibits a reverse trend. With increasing Si/Al
ratio, apparent porosity values dropped in paste specimens.
For SA1.5 specimens with Si/Al ratio of 1.5, the bulk
density and apparent porosity values were 1.18 g/cc and
36.71% respectively. When the Si/Al is increased to 2, the
corresponding bulk density was 1.37 g/cc, which showed a
marked increase. In addition, apparent porosity in this
specimen reduced to 32.71%, which is far lesser than that of
SA1.5 specimen. The increase in bulk density of
geopolymer composites with Si/Al=2 can be attributed to
better dissolution of rice husk ash and subsequent formation
of more geopolymer gel. Moreover, the same reason should
be the cause of decrease in apparent porosity with
increasing Si/Al up to 2. When Si/Al was increased beyond
2, the unreacted RHA and partially formed geopolymer gel
tends to decrease the bulk density and thereby increasing
the apparent porosity.
3.3 Water sorptivity and water absorption
Water absorption and sorptivity tests were conducted on
the geopolymer specimens after 28 days from casting. The
effect of Si/Al ratio on water absorption and sorptivity for
RHA geopolymer paste specimens are shown in Fig. 4.
SA2.0 samples shows minimum water absorption at 32.29%
Fig. 4 Water absorption of geopolymer specimen
while maximum value of 48.63% was recorded for SA3.5
samples. The variation of the water absorption values with
compressive strength follows a trend such that specimen
with maximum compressive strength (16.96 MPa) yields
least water absorption (32.29%). This also validates the
observation that higher compressive strength indicate
denser microstructure with lesser voids in the matrix.
Sorptivity of RHA geopolymer tends to decrease with
increasing Si/Al ratio in general. A clear decrease in
sorptivity was visible when Si/Al ratio increased from 1.5 to
2.0. However, sorptivity values showed increasing trend
beyond Si/Al of 2.0 though not remarkably significant. The
sharp decrease of sorptivity for SA2.0 specimen may be
attributed to its better gel formation and improved matrix
among the RHA geopolymer specimens. Sorptivity values
for RHA specimens were found to be 20.14×10-3, 18.83×10-
3, 18.84×10-3, 19.50×10-3, and 19.61×10-3g/mm2/min0.5 for
SA1.5, SA2.0, SA2.5, SA3.0 and SA3.5 respectively. The
lower sorptivity for SA2.0 specimen could enhance its
durability properties in acids and sulphates.
3.4 X-ray diffraction analysis (XRD)
Fig. 5 presents a combined XRD for the geopolymer
specimens for comparison. The XRD pattern of raw RHA
shows peaks corresponding to d- spacing values around
4.08Å (21.71°), 3.35 Å (26.51°), 3.03 Å (29.37°) and 2.03
Å (44.56°). Previous studies by Kordatos et al. (2008),
Shinohara et al. (2004) and Hajimohammaddi et al. (2016),
the peak with d spacing value of 3.35 Å (26.51°)
corresponds to quartz (PDF 01-070-7344) while d spacing
values of 4.08Å, 3.03Å were assigned for cristobalite (PDF
00-039-1425) and 2.03 Å were associated with gibbsite
(PDF 00-033-0018). The characteristic peak of quartz at
around 3.35 Å (26.51°) remains same in the in raw RHA
and in all the geopolymer specimen. For SA1.5 specimen,
new peaks appear at d- spacing values of 4.33 Å (20.48°),
3.67 Å (24.22°), 2.93Å (30.43°), 2.59Å (34.50°) and 2.12Å
(42.60°) indicating the reaction between raw RHA and
sodium aluminate leading to the formation of Zeolite X
(PDF 00-012-0246). This is further evident from the FTIR
analysis with the formation of new bond. SA2.0 specimen
with the highest 28 days compressive strength of 16.96 MPa
shows maximum number of new peaks as compared to
other geopolymer specimens. New peaks were observed at
76
Correlation study on microstructure and mechanical properties of rice husk ash-Sodium aluminate geopolymer pastes
Fig. 5 XRD diffractogram of RHA and geopolymers
specimen
4.83Å (18.35°), 4.36Å (20.33°), 3.67Å (24.22°), 2.61Å
(34.21°), 2.45Å (36.58°) and 2.38Å (37.74°) for SA2.0
specimens which corresponds to Zeolite X.
The optimal amount of silica for the geopolymerisation
might be the reason for SA2.0 specimen (Si/Al=2) resulting
in maximum number of new peaks and highest compressive
strength among the RHA geopolymer specimens. The
maximum compressive strength may be due to the increased
interaction between the zeolite and the amorphous phase
(Jaarsveld et al. 1998). As the ratio of Si/Al is increased
beyond 2, the crystalline phase might have surpassed the
tolerance limit of the matrix causing reduction of
compressive strength. This lead to drastically lowering of
the compressive strength from 16.96 MPa for SA2.0
specimen to only 8.60 MPa for SA2.5 as observed in Fig.2.
The difference in the d- spacing of new peaks and its peak
intensities in all the geopolymer specimen studied might be
due to the difference in the kinetics of the
geopolymerisation as reported by Hajimohammaddi et al.
(2016).
3.5 Scanning electron microscopy with EDAX
The physico-mechanical properties of geopolymer
Fig. 6 SEM micrographs of RHA specimens (a) SA1.5 (b) 2.0 (c) SA2.5 (d) SA3.0 (e) SA3.5
77
N. Shyamananda Singh, Suresh Thokchom and Rama Debbarma
Table 4 Elemental weight composition % by EDAX
Specimen Si Al Na O Ca Mg P K Si/Al Na/Al
SA1.5 20.3 16.15 16.97 41.05 0.88 1.11 2.05 1.49 1.257 1.051
SA2.0 25.5 12.14 13.49 40.82 2.78 1.12 2.18 1.97 2.1 1.111
SA2.5 30.63 9.94 8.95 44.05 1.75 0.95 2.14 1.59 3.081 0.9
SA3.0 33.23 8.11 9.5 42.4 1.16 1.62 2.15 1.83 4.097 1.171
SA3.5 27.29 7.76 11.36 44.13 2.6 1.34 3.42 2.1 3.517 1.464
specimen would depend on the microstructure of the
specimen. The observed properties can be correlated with
the changes in the microstructure. Fig. 6(a) shows SEM
micrographs for SA1.5 where interconnected pores and
loosely packed geopolymer matrix abound. Significant
improvement in the microstructure were observed for SA
2.0 samples shown in Fig 6(b). RHA geopolymer specimens
SA2.5, SA 3.0 and SA3.5 (Si/Al ˃2) presents an unstable
matrix with comparatively larger pores and even unreacted
RHA were observed in the SEM micrographs of Fig. 6 (c),
(d) and (e). The comparatively better microstructural
homogeneity matrix for SA2.0 correlates to improved
physico- mechanical properties. It resulted in maximum
compressive strength and minimum porosity, water
absorption and sorptivity for SA2.0 among the specimens.
The relatively higher value of porosity, absorption and
sorptivity of RHA geopolymers as compared with other
geopolymer system may be attributed to the higher water
demand to make the paste workable. The larger surface area
of raw RHA increases the water requirement for preparation
of geopolymer to maintain the required level of reactivity.
Physico- mechanical parameters may be further improved
by adopting optimal water/binders ratio and also by making
mortar specimens with appropriate amount of fillers.
The elemental weight percentage composition of the
geopolymer specimens as determined by EDAX is tabulated
in Table 4. It was observed that the samples except SA 3.5
indicate Na/Al ~1, comparable with the original batch
composition. Si/Al ratio of SA2.0 was found nearly equal to
that of original batch composition. However, other
geopolymer specimens shows Si/Al ratio different from the
initially adopted values. As Si/Al ratio is increased from 2
to 3.5, the quantity of unreacted RHA in the specimen were
found to increase as seen in SEM micrographs in Fig. 6(d)
and (e). Hence, the elemental Si/Al tabulated in Table4 is
slightly higher than the actual value taken during
preparation. The higher quantity of unreacted silica in RHA
is reportedly due to the rapid release of aluminum from
sodium aluminate (Hajimohammaddi et al. 2010). The
unreacted RHA caused defects in density which increased
the potential failure planes of the specimens under
compressive loading. Similar findings were also reported by
Duxson et al. (2005), where higher Si/Al ratios leads to
negative effect on the mechanical strength of the specimen.
3.6 Fourier Transform Infrared Spectroscopy (FTIR)
The FTIR spectra for original RHA and prepared
geopolymer specimens in the wavenumber region of 4000-
400 are shown in Fig. 7. Raw RHA shows broad peak at
1062 cm-1 and minor peaks at 2894 cm-1, 1685 cm-1, 793
Fig. 7 IR spectra of original RHA and geopolymer specimen
Fig. 8 Correlation between compressive strength and
apparent porosity
cm-1, 621 cm-1 and 562 cm-1. The strong intense peak at
1062 cm-1 is assigned to the Si-O-Si asymmetric vibration
(Yousuf et al. 2009). Minor peak at 2894 cm-1corresponds
to C-H stretching bands as the raw rice husk were burned at
temperature of around 700°C to get RHA (Sharma et al.
2010). Peak at 1685 cm-1 corresponds to the deformation
vibration of chemically bonded water molecules due to the
presence of Gypsum (Suyanta et al. 2011). The band at 793
cm-1 was assigned for Si-O-Si symmetric stretching
vibration. A small band at 621 cm-1 was indicative of the
presence of cristobalite. The presence of cristobalite and
gypsum in the raw RHA was also inferred from XRD in
Fig. 5. Peak at 562 cm-1 are mainly due to stretching and
bending vibration of Si-O-Si and O-Si-O (Mozgawa et al.
2011).
All the RHA geopolymer specimens have peaks at
around 562 cm-1 confirming the formation of Zeolite X with
the stretching and bending vibration of Si-O-Si and O-Si-O
(Naskar et al. 2011). Si-O symmetric stretching vibrations
were observed in the range of 1005-1021 cm-1. As Si/Al
ratio is increased from 1.5 to 3.5, the Si-O peaks were
observed to have shifted to higher wavenumber. The band at
793 cm-1 and 621 cm-1 were characteristics peaks for Si-O-
Al bending vibration in tetrahedral and 6-coordinated Al
(Jakobsoon et al. 2002). The disappearance of these bands
would further authenticate the continuous replacement of Al
for Si in the framework.
78
Correlation study on microstructure and mechanical properties of rice husk ash-Sodium aluminate geopolymer pastes
Fig. 9 Correlation between compressive strength and water
absorption
3.7 Correlation of physical properties with compressive strength
A correlation between compressive strength and
physical parameters (apparent porosity and water
absorption) was studied and highlighted in Fig. 8 and Fig. 9
respectively. Both the parameters exhibit a decreasing trend
with increase in compressive strength. Polynomial
regression analysis were performed to establish the
correlation of the parameters with compressive strength.
The good correlation values of R2=97.84% and R2=97.42%
indicate that denser microstructure with lower voids in the
matrix leads to higher compressive strength and lower
porosity and water absorption among the specimens.
However, besides porosity, the permeability properties
of the specimens may depend on other factors like
tortuosity, specific surface, pore size distribution and
connectivity of pores (Lafhaj et al. 2006).
4. Conclusions
Through a series of tests, RHA geopolymer paste
activated with sodium aluminate were investigated. The
effects of microstructure of the geopolymers on the physico
mechanical properties were studied. Based on the present
study the following conclusions were highlighted:
1. Sodium Aluminate can be used as a viable source of
aluminum for the establishment of a strong geopolymer
network in the traditional two- system geopolymer. The
fast release rate of Al from sodium aluminate provides a
rapid formation of better homogenous geopolymer gel.
2. The porosity, water absorption and sorptivity of RHA
geopolymers were relatively higher than those of other
geopolymer system. This may be attributed to the higher
water demand to make the paste workable. The larger
surface area of raw RHA increases the water
requirement to maintain the required level of reactivity.
The physico- mechanical parameters can be further
improved by adopting optimal water/binders ratio.
3. XRD analysis indicates quartz, cristobalite and
gibbsite for raw RHA and new peaks corresponding to
Zeolite X in geopolymer specimens. The maximum
compressive strength for SA2 specimen may be due to
the increased interaction between the zeolite and the
amorphous phase as is evident from the formation of
many new peaks. As the ratio of Si/Al is increased
beyond 2, the crystalline phase of the geopolymer
matrix decreases and hence reduces the compressive
strength.
4. SEM micrographs shows interconnected pores and
loosely packed geopolymer matrix for specimen SA1.5,
SA2.5, SA3.0 and SA3.5. Comparatively large pores,
unstable matrix and even unreacted RHA were seen in
the SEM micrographs of SA3.0 and SA3.5. Better
microstructural homogeneity for SA2.0 correlates to
improved physico- mechanical parameters.
5. FTIR spectra for original RHA shows peaks
corresponding to wavenumber of Si-O-Si asymmetric
vibration, C-H stretching band, Si-O-Si symmetric
stretching and vibration validating the presence of
quartz, cristobalite and gibbsite. Formation of Zeolite X
with the stretching and bending vibration of Si-O-Si and
O-Si-O were also observed from the FTIR analysis of
geopolymer specimen.
6. Polynomial regression analysis between compressive
strength and physical parameters namely porosity and
water absorption established equations with high
correlation values of R2=97.84% and R2=97.42%
respectively.
7. The comparatively low compressive strength might
restrict RHA geopolymer from various practical
applications. However, the deficiency in strength could
be overcome by blending with other source materials.
References Al-khalaf, M.N. and Yousift, H.A. (1984), “Use of rice husk ash in
concrete”, Int. J. Cement Compos. Light Weight Concrete, 6(4),
241-248.
Andrew, R.M. (2019), “Global CO2 emissions from cement
production, 1928–2018”, Earth Syst. Sci. Data, 11(4), 1675-
1710. https://doi.org/10.5194/essd-11-1675-2019.
Barbosa, V.F.F., Mackenzie, K.J.D. and Thaumaturgo, C. (2000),
“2000, Valeria. F.F. Barbosa”, Int. J. Inorg. Mater., 2, 309-317.
https://doi.org/10.1016/S1466-6049(00)00041-6.
Boateng, A.A. and Skeete, D.A. (1990), “Incineration of rice h u l
l for use as a cementitious material: the guyana experience”,
Cement Concrete Res., 20, 795-802. https://doi.org/10.1016/0008-8846(90)90013-N.
Brew, D.R.M. and MacKenzie, K.J.D. (2007), “Geopolymer
synthesis using silica fume and sodium aluminate”, J. Mater.
Sci., 42(11), 3990-3993. https://doi.org/10.1007/s10853-006-0376-1.
Davidovits, J. (1994), “Global warming impact on the cement and
aggregates industries”, World Resour. Rev., 6(2), 263-278.
Duxson, P., Provis, J.L., Lukey, G.C., Mallicoat, S.W., Kriven,
W.M. and Van Deventer, J.S.J. (2005), “Understanding the
relationship between geopolymer composition, microstructure
and mechanical properties”, Coll. Surf. A: Physicochem. Eng.
Aspect., 269(1-3), 47-58.
https://doi.org/10.1016/j.colsurfa.2005.06.060.
FAO Statistical Yearbook (2018), World Food and Agriculture,
Food and Agriculture Organization of the United Nations,
Rome.
79
N. Shyamananda Singh, Suresh Thokchom and Rama Debbarma
Fernández-Jiménez, A. and Palomo, A. (2005), “Composition and
microstructure of alkali activated fly ash binder: Effect of the
activator”, Cement Concrete Res., 35(10), 1984-1992.
https://doi.org/10.1016/j.cemconres.2005.03.003.
Goriparthi, M.R. (2017), “Effect of fly ash and GGBS
combination on mechanical and durability properties of GPC”,
Adv. Concrete Constr., 5(4), 313-330.
https://doi.org/10.12989/acc.2017.5.4.313.
Hajimohammadi, A. and van Deventer, J.S.J. (2016), “Solid
reactant-based geopolymers from rice hull ash and sodium
aluminate”, Waste Biomass Valoriz., 1-10.
https://doi.org/10.1007/s12649-016-9735-6.
Hajimohammadi, A., Provis, J.L. and Van Deventer, J.S.J. (2010),
“Effect of alumina release rate on the mechanism of geopolymer
gel formation”, Chem. Mater., 22(3), 5199-5208.
https://doi.org/10.1021/cm101151n.
He, P., Jia, D. and Wang, S. (2013), “Microstructure and integrity
of leucite ceramic derived from potassium-based geopolymer
precursor”, J. Eur. Ceram. Soc., 33(4), 689-698.
https://doi.org/10.1016/j.jeurceramsoc.2012.10.019.
Jaarsveld, J.G.S.V.A.N., Deventer, J.S.J.V.A.N. and Lorenzen, L.
(1998), “Factors affecting the immobilization of metals in
geopolymerized flyash”, Metal. Mater. Tran. B, 29(B), 283-291.
Jain, A.K., Sharma, S.K. and Singh, D. (1996), “Reaction kinetics
of paddy husk thermal decomposition”, IECEC 96. Proceedings
of the 31st Intersociety Energy Conversion Engineering
Conference, Washington, DC, USA.
Jakobsson, S. (2002), “Spectroscopic techniques determination of
Si/Al Ratios in Semicrystalline Aluminosilicates by FT-IR
Spectroscopy”, Appl. Spectroscopy, 56(6), 797-799.
Khater, H.M. (2013), “Effect of silica fume on the characterization
of the geopolymer materials”, Int. J. Adv. Struct. Eng., 5(1), 12.
https://doi.org/10.1186/2008-6695-5-12.
Khater, H.M. (2014), “Studying the effect of thermal and acid
exposure on alkali-activated slag geopolymer”, Adv. Cement
Res., 26(1), 1-9. https://doi.org/10.1680/adcr.11.00052.
Kim, Y.Y., Lee, B., Saraswathy, V. and Kwon, S. (2014),
“Strength and durability performance of alkali-activated rice
husk ash geopolymer mortar”, Scientif. World J., 2014, 1-10.
http://dx.doi.org/10.1155/2014/209584.
Kordatos, K., Gavela, S., Ntziouni, A., Pistiolas, K.N. and Kyritsi,
A. (2008), “Synthesis of highly siliceous ZSM-5 zeolite using
silica from rice husk ash”, Microporous Mesoporous Mater.,
115, 189-196. https://doi.org/10.1016/j.micromeso.2007.12.032.
Kuncaka, A. (2011), “Utilization of rice husk as raw material in
synthesis of mesoporous silicates mcm-41”, Indo. J. Chem.,
11(3), 279-284.
Lafhaj, Z., Goueygou, M., Djerbi, A. and Kaczmarek, M. (2006),
“Correlation between porosity, permeability and ultrasonic
parameters of mortar with variable water/cement ratio and
watercontent”, Cement Concrete Res., 36(4), 625-633.
https://doi.org/10.1016/j.cemconres.2005.11.009.
Lee, S.T., Moon, H.Y., Hooton, R.D. and Kim, J.P. (2005),
“Effect of solution concentrations and replacement levels of
metakaolin on the resistance of mortars exposed to magnesium
sulfate solutions”, Cement Concrete Res,, 35(7), 1314-1323.
https://doi.org/10.1016/j.cemconres.2004.10.035.
Mehata, P.K. and Pitt, N. (1976), “Energy and industrial materials
from crop residues”, Resour. Recovery Conserv., 2, 23-38.
Mozgawa, W., Król, M., Barczyk, K. and Science, M. (2011),
“FT-IR studies of zeolites from different structural groups”,
Chemik, 65(7), 671-674.
Naskar, M.K., Kundu, D. and Chatterjee, M. (2011), “Coral-like
hydroxy sodalite particles from rice husk ash as silica source”,
Mater. Lett., 65(23-24), 3408-3410.
https://doi.org/10.1016/j.matlet.2011.07.084.
Phair, J.W. and Van Deventer, J.S.J. (2002), “Characterization of
fly-ash-based geopolymeric binders activated with sodium
aluminate”, Indus. Eng. Chem. Res., 41(17), 4242-4251.
https://doi.org/10.1021/ie010937o.
Praven, Mehta, A. and Saloni. (2019), “Effect of ultra-fine slag on
mechanical and permeability properties of Metakaolin-based
sustainable geopolymer concrete”, Adva. Concrete Constr.,
7(4), 231-239. https://doi.org/10.12989/acc.2019.7.4.231.
Provis, J.L. and Van Deventer, J.S.J. (2014), “Alkali activated
materials, State-of-the-art report”, RILEM TC 224-AAM,
Springer, Dordrecht, 1-9.
Rashad, A.M. and Zeedan, S.R. (2011), “The effect of activator
concentration on the residual strength of alkali-activated fly ash
pastes subjected to thermal load”, Constr. Build. Mater., 25(7),
3098-3107. https://doi.org/10.1016/j.conbuildmat.2010.12.044.
Rashad, A.M., Bai, Y., Basheer, P.A.M., Milestone, N.B. and
Collier, N.C. (2013), “Hydration and properties of sodium
sulfate activated slag”, Cement Concrete Compos., 37(1), 20-29.
https://doi.org/10.1016/j.cemconcomp.2012.12.010.
Rattanasak, U. and Chindaprasirt, P. (2009), “Influence of NaOH
solution on the synthesis of fly ash geopolymer”, Mineral. Eng.,
22(12), 1073-1078. https://doi.org/10.1016/j.mineng.2009.03.022.
Rattanasak, U., Chindaprasirt, P. and Suwanvitaya, P. (2010),
“Development of high volume rice husk ash alumino silicate
composites”, J. Mineral. Metal. Mater., 17(5), 654-659.
https://doi.org/10.1007/s12613-010-0370-0.
Shaikh, F. and Haque, S. (2018), “Effect of nano silica and fine
silica sand on compressive strength of sodium and potassium
activators synthesised fly ash geopolymer at elevated
temperatures”, Fire Mater., 42(3), 324-335.
https://doi.org/10.1002/fam.2496.
Sharma, P., Kaur, R., Baskar, C. and Chung, W. (2010), “Removal
of methylene blue from aqueous waste using rice husk and rice
husk ash”, Desalination, 259, 249-257.
https://doi.org/10.1016/j.desal.2010.03.044.
Singhal, D. and Jindal, B.B. (2017), “Experimental study on
geopolymer concrete prepared using high-silica RHA
incorporating alccofine”, Adv. Concrete Constr., 5(4), 345-358.
https://doi.org/10.12989/acc.2017.5.4.345.
Sturm, P., Gluth, G.J.G., Brouwers, H.J.H. and Khne, H.C. (2016),
“Synthesizing one-part geopolymers from rice husk ash”,
Constr. Build. Mater., 124, 961-966.
https://doi.org/10.1016/j.conbuildmat.2016.08.017.
Thokchom, S., Ghosh, P. and Ghosh, S. (2011), “Durability of fly
ash geopolymer mortars in nitric acid-effect of alkali (Na 2 o)
content”, J. Civil Eng. Manage., 17(3), 393-399.
https://doi.org/10.3846/13923730.2011.594225.
U.S. Geological Survey (2019), Mineral Commodity Summaries
2019, U.S. Geological Survey.
Valipour, M., Yekkalar, M., Shekarchi, M. and Panahi, S. (2013),
“Environmental assessment of green concrete containing natural
zeolite on the global warming index in marine environments”, J.
Clean. Prod., 1-6. https://doi.org/10.1016/j.jclepro.2013.07.055.
Wang, H., Li, H. and Yan, F. (2005), “Synthesis and mechanical
properties of metakaolinite-based geopolymer”, Coll. Surf. A:
Physicochem. Eng. Aspect., 268(1-3), 1-6.
https://doi.org/10.1016/j.colsurfa.2005.01.016.
Yusof, A.M., Nizam, N.A. and Abd Rashid, N.A. (2010),
“Hydrothermal conversion of rice husk ash to faujasite-types
and NaA-type of zeolites”, J. Porous. Mater., 17, 39-47.
https://doi.org/10.1007/s10934-009-9262-y.
CC
80