(This is a sample cover image for this issue. The actual cover is not yet available at this time.) This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Transcript
(This is a sample cover image for this issue. The actual cover is not yet available at this time.)
This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies areencouraged to visit:
Applying a polyurea coating to high-performance organic cementitious materials
H.A. Toutanji a,⇑, H. Choi a, D. Wong a, J.A. Gilbert b, D.J. Alldredge b
a Dept. of Civil and Environmental Engineering, University of Alabama in Huntsville, Huntsville 35899, USAb Dept. of Mechanical and Aerospace Engineering, University of Alabama in Huntsville, Huntsville 35899, USA
h i g h l i g h t s
" A low modulus polyurea coating was sprayed under field conditions." Lightweight concrete and high-performance cementitious composite materials were used." Flexure tests were conducted on plates constructed with three different mixes." The addition of PVA fibers and the polyurea coating increased the flexural strength." The polyurea coating allows the plates to sustain higher strains.
a r t i c l e i n f o
Article history:Received 2 May 2012Received in revised form 3 September 2012Accepted 22 September 2012
Polyurea is a polymeric material that can be used to provide environmental protection and structuralenhancement. In this study, a low modulus polyurea coating, having high elongation and energy absorp-tion capacities and a fast gel time, was sprayed under field conditions onto the surfaces of cementitiousmaterials. Compression tests were conducted to establish the wet–dry performance of uncoated and cir-cumferentially coated cylinders fabricated from a high-performance matrix constructed with Poly(vinylbutyral) (PVB) as the only aggregate. Results showed that the coating increased the compressive strengthof specimens exposed to both fresh and sea water environments. Similar results were obtained when alightweight matrix containing sand was subjected to the same sea water environment. Flexure tests wereconducted on uncoated and fully encapsulated plates kept under normal operating conditions to estab-lish the stress–strain behavior of these two matrices, as well as a PVB matrix with Poly(vinyl alcohol)(PVA) fibers added as reinforcement. Results showed that the addition of the fibers and the coatingincreased the ultimate flexural strength, decreased the stiffness, allowed the structure to sustain higherstrains prior to failure, and increased the fracture toughness. Comparisons are made between the perfor-mance of lightweight and high-performance concretes.
� 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Cementitious-matrix composites are often plagued in applica-tions such as piers, docks, and bridge decks by the extensive crack-ing that occurs under load. While such structures can be designedto be relatively mechanically insensitive to matrix cracking per se,the cracking can introduce extensive and unwanted internal con-tamination by the environment resulting in direct corrosion, stresscorrosion cracking, etc. of the reinforcing fibers and internal micro-structure. As a result, steps have been taken to reduce corrosive at-tack and chemical wear.
One approach to moisture proofing and preventing corrosive at-tacks on concrete structures is to coat them with polyurea [1]. Thecoatings have been shown to reduce water absorption and improve
chemical wear and frost resistance [2,3]. The material lends itselfto construction because of its flexibility, excellent elongation char-acteristics, rapid-cure rate, and wide service temperature range(�50 �C to �150 �C) [4]. Because of its many unique physical andchemical properties, polyurea is widely used for moisture andchemical proof protection of pipelines, bridges, tanks, and roofs [5].
Polyurea also offers unique advantages for structural enhance-ment due to its excellent flexibility and elongation characteristics[6,7]. The polymer adheres well to concrete, metal and to woodand it has been applied to light-frame rafter to top plate connec-tions for strengthening the building envelope in costal construc-tion [8].
Polyurea is also used for truck bed liners and for explosive blastresistant walls. Thin interlayers of polyurea have been shown to in-crease blast resistance of carbon fiber foam composites [9].Researchers have demonstrated that the impact performance ofsandwich composites can be improved by strategically positioning
0950-0618/$ - see front matter � 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2012.09.041
a thin interlayer of polyurea relative to the impact source [10]. TheU.S. Army uses polyurea to coat and harden field buildings againstexplosive blast because polyurea strain hardens under load [11];and, polyurea is likely used to retrofit Government offices. Signifi-cantly, the addition of polyurea to cement-based materials led tovarious structural responses due to nonlinear material behaviorand dispersive wave propagation, making it possible to containspall and reduce fragmentation [12,13].
As mentioned below, researchers recently employed an ap-proach, originally developed by material scientists to produce novelnanocomposites, to fabricate cementitious materials with enhancedproperties [14,15]. The application of a polyurea coating to the sur-faces of these high performance cementitious materials offers thepotential to further improve their performance. Thus, the goals ofthe present study are to see what effects a polyurea coating hason structural integrity when it is used to coat cylinders and platesmade with such materials and to discover how this performancecompares with that of a lightweight concrete of equal density.
The study may help designers fabricate concrete structures hav-ing special requirements, work crews to repair or retrofit existingstructures, and builders to produce new structures that involvemass concrete and/or skin applications. The results may be espe-cially helpful in costal construction where structures are exposedto sea water from storm surge or high winds from hurricanes.The facts are that fifty percent of the US population lives within50 miles of the coast in trillions of dollars of insured property[16]. It is evident that significant problems exist in coastal build-ings and there is a need for new water resistant building materialsand techniques that can reinforce new and existing structureswhile providing safety for building occupants.
2. Polyurea
Polyurea is a high strength polymer with scalable and predict-able material characteristics that can be sprayed onto a substrateto make it waterproof or chemically resistant. The material has be-come widespread in the coating industry because of its quick-cureproperties and great tolerance to extreme temperatures.
Polyurea has a variable gel time (the period of time that it takesthe resin to change from a liquid to a non-flowing gel); tensilestrengths in commercially available materials vary from 13.8 to34.5 MPa with inversely related elongation rates. It can be appliedunder field conditions by using a brush, a high temperature pumpapplicator, or a low temperature low pressure dispenser.
From a chemical standpoint, polyurea is similar to polyureathanein its chemical makeup. The main components of polyurethane aredi- or polyisocyanate molecules (cyanate functional group –NCO)and polyols (hydroxyl functional group –OH). Through an exother-mic reaction process, the two components form extended chainsand networks bonded by urethane groups –O(CO)(NH)–.
As for its mechanical properties, polyurea displays a nearly elas-tic response to volumetric deformations; while above the glasstransition temperature, Tg, its shearing response at moderate pres-sure and strain rate is soft and viscoelastic, so that its laterallyunconfined deformation is nearly incompressible [17].
In the present study, specimens were coated at room tempera-ture by spraying them with a white polyurea called Dyna-Pur 8817which was manufactured by Creative Material Technologies, Ltd.According to the manufacturer, in this specially designed aliphaticcompound, carbon atoms are joined together to produce extensiveintermolecular hydrogen bonding which results in ‘‘tough’’mechanical properties: an elongation of greater than 100%, an elas-tic modulus of 483 MPa, and a tensile strength of 43 MPa.
The polyurea was sprayed onto test specimens at a pressure of414 kPa with a ‘‘Voyager’’ cold spray system also manufactured by
Creative Material Technologies, Ltd. The coating was deposited atroom temperature and sprayed to a thickness of approximately0.76 mm. The coating thickness was adjusted by controlling thepressure, offset distance, and exposure time. The compound hada gel time of about 30 s and a full curing time of 30–60 mindepending on humidity and temperature.
3. High performance cementitious materials
In civil infrastructure and building construction, cement-basedmaterials have been extensively used as the most common andimportant material but many studies have shown disadvantages.Traditional cement-based concrete consists of two parts: a cementpaste matrix and the aggregate. The properties of these constitu-ents and the interactions that take place between them determinethe behavior of the material [18].
Prior research has shown that the interfacial transition zone(ITZ) is the weakest region in a concrete structure. It is character-ized by the prevalence of calcium hydroxide and higher porosityand interactions that take place there drive many important mac-roscopic properties, such as strength, permeability, and durability[19–21].
Researchers studying the microstructure of the ITZ and thehydration progression into it have confirmed a wall effect [21–29]. They noted that ions have a tendency to flow slightly fasternear the wall because of the decreased permeability in this zone[30]. As a result, the space around the aggregates is less effectivelyfilled by hydration products. At the same time, there is greater ten-dency for calcium hydroxide [CH (Ca(OH)2)] and ettringite to de-velop in this space.
As a result, methods have been studied to improve the aggregate/matrix bonding in the ITZ by reducing the size of the aggregates[31,32], using basalt and quartzite as aggregates [33], and replacingthe cement with ultrafine additions of constituents, such as silicafume and metakaolin [34–37]. However, these methods are limitedin scope since they are siliceous and do not significantly alter thenature of the interaction between the matrix and the aggregate.
A viable alternative is to adjust phenomena associated withatomic and molecular interactions that strongly influence macro-scopic material properties [38]. Materials having the potential toform strong interactions at the molecular level, for example, havebeen developed and utilized to produce novel nanocompositeswith enhanced properties [39–43]. This approach was applied toproduce high-performance cementitious composites whenresearchers employed Poly(vinyl butyral) powder as a non-sili-ceous organic aggregate [14].
Steel and glass fibers are typically added to reinforce the matrixbecause of their high tensile strength. However, the bond strengthbetween these traditional materials and the matrix is often limited.As a result, in addition to the interactions that take place withinthe ITZ, fiber/matrix debonding may occur due to mechanismssuch as shear type deformation and fiber sliding [44]. This problemcan be solved to some degree by adding Poly(vinyl alcohol) fibersto reinforce the cementitious matrix [15].
The concretes studied herein contain Poly(vinyl butyral) andPoly(vinyl alcohol), also known as PVB and PVA, respectively. Priorresearch has shown that the use of these materials in cementitiouscomposites results in improved ductility, impact resistance, andfracture toughness [15].
PVB is a resin material which is usually used in applications thatrequire strong binding, optical clarity, surface adhesion, toughness,and flexibility [45,46]. As illustrated in Fig. 1, the compound is pro-duced by the well-known reaction between aldehydes and alcohols.
Butvar� B-79 is one of a number of commercially availablePVB products. As illustrated in Fig. 2, it is sold as a white and
H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179 1171
Author's personal copy
free-flowing powder; and, based on properties associated withButvar dispersions, the particle size ranges between 0.25 and1.5 lm [47]. It has a unique combination of properties for coatingor adhesive applications and its addition to a system can improveadhesion, toughness, and flexibility [48]. Table 1 shows the proper-ties of Butvar� Resin B-79.
Mowital M-B75H is another type of Poly(vinyl butyral). It is athermoplastic material that is soluble in a large number of organicsolvents and can be cross-linked with other compounds [49]. Ta-ble 2 shows the properties of Mowital M-B75H.
Poly(viny alcohol) is a synthetic material formed from the poly-merization of vinyl acetate, followed by partial hydrolysis of theacetate in the presence of an alkaline catalyst [50]. The chemicalstructure of PVA is shown in Fig. 3.
The compound is a white powder with a specific gravity in therange of 1.2–1.3 and a glass transition temperature of approxi-mately 80 �C. The powder can be formed and extruded into PVAfibers [51].
PVA fibers typically have a tensile strength between 1600 and2500 MPa. PVA fibers also have alkaline resistance, a high tenacity,and a high modulus [52]. Because of the high strength and alkalineresistance, PVA fibers are considered to be one of the most suitable
Fig. 1. Chemical reaction for forming PVB [46].
Fig. 2. Butvar B-79.
Table 1Properties of Butvar Resin B-79 (white, free-flowing powder) [46].
Non-volatile content wt.% >97.5Polyvinyl alcohol contentsa wt.% 18–21Polyvinyl acetate contentb wt.% 0–4Viscosityc mPa s 60–100Glass transition temperature �C 73Water absorption wt.% 4–6Bulk density g/l 200
a Hydroxyl groups, in terms of polyvinyl alcohol.b Acetyl groups, in terms of polyvinyl acetate.c 10% Solution in ethanol.
Fig. 3. Chemical structure of PVA.
1172 H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179
Author's personal copy
polymeric fibers used in the reinforcement of concrete [53]. Theyfirmly bond to the surrounding cementitious matrix which causesthe fibers to fail by rupture rather than pull out. This hydrophilicnature of PVA fiber tends to limit the multiple cracking effectand results in lower strain hardening for the composite [53–55].Table 3 lists the properties of Kuraray PVA fiber (RECS7) used inthe present study [56].
4. Experimental test program
4.1. Mix proportions
Compression and bending specimens (cylinders and plates,respectively) were fabricated from two different high-performanceconcrete mixes, and a lightweight concrete mix, having the mixproportions described in Table 4. The PVB mix contains Poly(vinylbutyral) as the only aggregate while the PVA fiber mix includesPoly(vinyl alcohol) fibers added for reinforcement. The lightweightconcrete mix has the same density (1500 kg/m3) as the othermixes. It was constructed using sand as the aggregate for compar-ative purposes. The mixes have comparable slumps which rage be-tween 25 and 35 mm.
Referring to the constituents listed in Table 4, the cement was aSAKRETE
�Portland Cement Type I-II which conformed to ASTM
C150 [57]. Metakaolin [58], conforming to ASTM C618 [59], wasadded at approximately ten percent by mass to take advantage ofthe ‘‘filler’’ effect and narrow the interfacial transaction zone(ITZ). This reduces the amount of bleeding and helps yield a morehomogenous material [32]. The Sika� ViscoCrete� 2100 high rangewater reducing admixture conformed to ASTM C494 [60] and actsas a superplasticizer to reduce the amount of water.
The PVB added to each mix consisted of a combination of ButvarB-79 and Mowital B75H. These constituents were selected andblended based on their particle sizes, densities, and tensilestrengths (40–47 MPa) to provide a unique combination of aggre-gates [14,15]. Butvar B-79 is manufactured by Solutia Inc.; Mowitalis produced by Kuraray Specialties Europe (KSE).
As mentioned earlier, the PVA fibers used were manufactured byKuraray Co. Ltd of Japan and are classified by the manufacturer asRECS7. They were added to the PVA Fiber mix at a fiber volume frac-tion, Vf, equal to 0.6% as reinforcement. Their high tensile strength(1.6 GPa) helps bridge cracks which may form in the matrix.
Both PVB and PVA contain hydroxyl groups that have the poten-tial to form a hydrogen bond between molecules, or within differ-ent parts of a single molecule. This unique feature providesremarkable changes in the surface bond strength, not only betweenthe aggregate and the matrix, but also between the fiber reinforce-ment and the matrix. Additionally the ether oxygen functionalgroups act as a weak base and could potentially interact with Lewisacids and electropositive materials such as CSH [14].
Interaction may also occur between the high performancecementitious matrix and the aliphatic polyurea used to coat it.The reactions between Butvar and isocynates, for example, areshown in Fig. 4 [46].
4.2. Compression tests
Table 5 summarizes the game plan developed for wet–dry test-ing. A total of 30 cylinders (7.62 cm diameter by 15.24 cm long)were prepared; 18 from the PVB mix and 12 from the lightweightconcrete mix (see Table 4).
As can be seen from Table 5, the game plan called for coatingone half of the cylinders (15 of them) around their circumferenceswith polyurea. Of the nine PVB cylinders of each type (uncoatedand coated), three remained unexposed while the remaining sixwere subjected to wet/dry conditions; three cylinders of each typewere exposed to sea water while the remaining three were ex-posed to fresh water.
Of the six lightweight cylinders of each type, three remainedunexposed while the remaining three were exposed to sea water.No exposure to fresh water was done for the lightweight concretecylinders primarily because the research effort was geared towardcostal construction. Photographs of typical uncoated specimens areshown in Fig. 5 while Fig. 6 shows a photograph taken during thecoating process.
Fig. 7a shows a photograph of the exterior of the wet–dry envi-ronmental chamber that was built to perform the wet/dry studywhile Fig. 7b shows a schematic of its interior. The device utilizestwo electronically timed pumps and an industrial dryer to allowspecimens to be subjected to an aqueous solution, with alternatingwet and dry cycles (hot air at 35 �C averages and 90% humidity).
The test method involved a cyclic regime developed based onprior research [61,62] to simulate site conditions. To establishwhat would happen to a structure located on the sea coast, forexample, the concentration of the saline solution was made 35ppt (35 g of salt per 1000 g of water), which corresponded to aver-age ocean salinity.
Specimens were subjected to a total of 100 cycles. The durationof the wet cycle was 4 h and that of the dry cycle, 8 h; thus, spec-imens were exposed to two cycles per day for a total of 50 days.
All specimens were tested to determine the ultimate strength inaccordance with ASTM C39/C39M-11a [63]. Table 6 includes theresults obtained for the compressive strength while Figs. 8 and 9illustrate how the compressive strength varies with different coat-ing and curing conditions for PVB and lightweight concretes,respectively. Each of the vertical range bars shown on the plotsin Figs. 8 and 9 correspond to the standard deviation.
Referring to Fig. 8, the addition of the polyurea coating to thehigh-performance concrete led to a slight decrease in the compres-sive strength of cylinders cured at room temperature. However, the
Table 3Properties of Kuraray PVA fiber (RECS7) [56].
Properties Diameter Thickness Cut length Young’s modulus Density Specific gravityUnits (mm) dtex (mm) (kN/mm2) (g/cm3) –
RECS7 0.027 7 6 39 1.19–1.31 1.3
Table 4Mix proportions for PVB, PVA fiber, and lightweight concretes (kg/m3).
H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179 1173
Author's personal copy
process did improve the strength of the PVB concrete when it wassubjected to a wet/dry environment, especially in the case of freshwater.
Referring to Fig. 9, similar to the trend seen in Fig 8, the additionof the polyurea coating to the lightweight concrete led to a slightdecrease in the compressive strength of cylinders cured at roomtemperature. Although no tests were conducted using fresh water,the coating process resulted in an increase in strength when thelightweight concrete was subjected to sea water.
It should be noted that the sample sets used to generate thesefigures were small. Moreover, the standard deviations were rela-tively large in some cases, especially when the lightweight con-crete was subjected to sea water.
In general, maintaining constant environmental conditionsleads to increased strength because of better cement hydration.The trends seen in Figs. 8 and 9 suggest that the application of apolyurea coating helped in this regard when the specimens weresubjected to wet–dry cycling.
It should also be noted that the curing and coating conditionsinfluenced the manner in which different concretes failed. This isevident in Fig. 10. In the case of the lightweight concrete, for exam-ple, failure took place when cracks developed at the end of the cyl-inder. When the PVB cylinders were tested, the polyurea coatingcontained the concrete until the coating ruptured.
Fig. 4. Reactions between Butvar and isocynates [46].
Table 5Game plan for testing concrete cylinders under wet–dry conditions.
1174 H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179
Author's personal copy
4.3. Flexure tests
Table 7 summarizes the game plan developed to evaluate theflexural strength and toughness of uncoated and fully encapsulated
plates. Eighteen plates were fabricated from the mixtures listed inTable 4. One half of the plates (nine total; three from each mix)were coated with polyurea.
Six, relatively large cementitious panels (three for each mix)were fabricated to produce the plates. Molds were constructedby nailing 1.27 cm thick pine rails to plywood that was coveredwith PVC plastic film. The final dimensions of each mold were61 cm � 30.5 cm � 1.27 cm.
The mix was placed in each mold and placed on a vibration ta-ble to help fill the mold evenly. After placing the panels, the moldswere loosely covered with plastic and allowed to cure for 3 days.After 3 days, the panels were carefully removed and placed inwater to finish curing. The panels were water cured for 25 days,for a total cure cycle of 28 days. The panels were removed and al-lowed to dry before cutting. Each plate was cut using a table sawinto the final dimensions. Fig. 11 shows the eighteen, 61 cmlong � 10.2 cm wide � 1.27 cm thick, plates cut from the panels.
Flexure tests were conducted in accordance with ASTM C78/C78-10 [64]. As illustrated in the photos shown in Fig. 12, eachspecimen was tested to failure over a 45.7 cm span with supportsplaced at 15.24 cm apart.
Strain was measured in the central span using strain gages. Twogages were initially used on the uncoated samples to check for con-sistency. This number was reduced to one on the coated samplesafter tests revealed that the readings from the gage pairs werenearly equal.
A load cell was used to measure the applied force which wasused to compute the bending moment by multiplying half the loadby the distance between the outer and inner supports. Stresseswere computed based on the standard flexure formula and thedimensions of the cross section at the gage location.
Fig. 13 shows six, stress versus strain curves generated for thesix different specimen categories found by averaging the resultsobtained for the three specimens in each. For comparison and clar-ity purposes, Fig. 14 shows the same curves plotted for strains upto 1000 le. Each of the vertical range bars shown on the plots inFig. 14 correspond to the standard deviation computed for thestresses measured in three different specimens at the strain levelwhere the bar is located.
Table 8 lists the average maximum flexural strength and the elas-tic modulus for each category. The strain energy density, found bycomputing the total area under the stress versus strain curve, isshown for the uncoated samples. The latter, referred to as the tough-ness, indicates how much energy a material can absorb before rup-turing. Fig. 15 illustrates how the flexural strength of each mix varieswith different coating conditions. Each of the vertical range barsshown on the plots in Fig. 15 correspond to the standard deviation.
The stress–strain results for all of the uncoated and coated sam-ples were fairly consistent when the materials remained in theelastic range. The peak stresses determined for the coated samplesagreed fairly well but strain results varied dramatically at highstrain levels. Consequently, the curves drawn past the point atwhich the coated specimens begin to strain harden represent onlybehavioral trends drawn to the point at which maximum load wassustained. In these regions, the underlying substrate is sustainingprogressively more damage at a critical location which, in mostcases, is not located where strain is actually being measured. Ascracks develop in tension beneath the polyurea coating in the crit-ical section, the centroid begins to shift toward the compressiveside of the beam. The moment of inertia decreases as stress is pro-gressively transferred to the coating where bonding, thickness, andstrength considerations come into play as the coating reaches itsbreaking strength. In general, the addition of PVA fibers createdmore dispersion in the data as compared to that collected for platesplaced with the lightweight concrete and PVB alone because of therandom orientation and distribution of the free fibers [38,65].
Fig. 8. Wet/dry behavior of uncoated and polyurea coated samples for PVBconcrete.
Fig. 9. Wet/dry behavior of uncoated and polyurea coated samples for lightweightconcrete.
Fig. 10. Failure modes for cylinders cured (a) at room temperature and (b)underwater.
H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179 1175
Author's personal copy
Table 7Game plan for testing unreinforced plates under normal operating conditions.
Coated condition Uncoated Coated with Polyurea
Curing condition/type of concrete PVB PVB fiber Lightweight PVB PVB fiber Lightweight Total
Room temperature 3 3 3 3 3 3 18
Fig. 11. Plate specimens: (a) uncoated and (b) coated.
Fig. 12. Flexure tests were conducted on (a) uncoated and (b) coated plates.
Fig. 13. Stress versus strain curves for uncoated and coated specimens (full range).Fig. 14. Stress versus strain curves for uncoated and coated specimens (limitedrange). See legend in Fig. 13.
1176 H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179
Author's personal copy
Referring to the curves in Figs. 13 and 14, the stress–strain re-sponses of the uncoated plates were all fairly linear to failure.The plate that contained PVB showed a slight hint of strain harden-ing while the one with the PVA fibers showed slightly more. Theaddition of the polyurea coating allowed the plates to sustain dra-matically higher strains especially when PVA was added. Strainhardening is prevalent in the plots corresponding to the coatedspecimens, much more so in the PVA specimens.
Referring to Table 8, the addition of PVA fibers to the PVB mixincreases the flexural strength, lowers the elastic modulus, and in-creases the toughness. In general, the addition of the polyureacoating increases the maximum flexural strength and decreasesthe global stiffness.
5. Lightweight versus PVB concrete
Fig. 16 shows a comparison between the compressive and flex-ural strengths for the lightweight and PVB mixes. Each of the ver-tical range bars shown on the plots correspond to the standarddeviation.
Although the compressive strength of the lightweight mix ishigher than that of the PVB mix, the flexural strength is lower. Thistrend was seen elsewhere where it was observed that the additionof PVB to a baseline mix led to an increase in the tensile-to-compressive strength ratio [65]. The further addition of PVAincreased this ratio even further which accounts for the higherflexural strength seen here when PVA fibers are added.
The lower modulus and higher flexural strength of PVB con-cretes make them more attractive for applications in which loadreversals take place. The lower modulus leads to a greater stresstransfer from the matrix to the reinforcement and the higher ten-sile-to-compressive strength ratio increases the potential to storeand release energy. Thus, PVB concretes show great potential forapplications ranging from the construction of seismic structuresto energy harvesting devices.
The greater toughness of PVB concretes also makes them moreattractive for creating impact resistant structures in applicationsranging from blast resistant walls to rocket casings. Finally, the
cross linking which takes place between the polyurea and the con-stituents used to produce high-performance concretes (i.e., PVB andPVA) helps to make structures fabricated with them more efficient.
It is important to mention that although various comparisonswere made between lightweight and PVB concretes, it is evidentfrom Table 4 that the cement content of the latter are much higherand that the water/cement ratio is smaller. Both of these parame-ters, as well as the size and shape of the aggregates, strongly influ-ence the properties of concrete; and, in this case, the differencesare both in favor of the PVB concretes.
6. Discussion
The results of the tests depend drastically on the scale of thespecimens and structural elements tested. For example, in termsof compressive or flexural strength, the improvements obtaineddue to the coating will tend to be negligible in larger specimens.These factors should be taken into consideration during the designprocess, specifically while evaluating the feasibility of the solution.
As mentioned previously, it is fundamental to guarantee that ex-cess water in cementitious materials is allowed to be released aswater vapor through its skin. Although the water vapor permeabilityof the Dyna-Pur 8817 polyurea used in this study was not measured,a value of 10 mg/m2/day was reported for a similar product [66].
In general, the key constituents in high performance concretecost far more than those in typical normal weight concrete. Thereis also a sizable cost associated with applying a polyurea coating tothe substrates made from them.
Based on a study done in 2010, typical normal weight concretemixes used for civil engineering structures cost about $103/m3
[67]; albeit, this price is for large construction projects. For smallbatch sizes batches similar to those used in the present study,the cost for procuring the cement and aggregates used for normalweight concrete is estimated to be twice as much as the figurequoted above, or about $206/m3.
By comparison, cost estimates for the PVB and PVA Fiber mixesused in the present study are shown in Tables 9 and 10, respec-tively. The estimates were prepared based on the mix proportionslisted in Table 4.
It is evident that for small batch sizes, the cost of high performanceconcrete is about ten times that of normal weight concrete. However,for specialized applications where impact resistance is of paramountimportance, the additional performance may justify the cost.
As far as the polyurea coating is concerned, the installed cost fordepositing a 0.75 mm thick coating like the one used in the presentstudy is estimated to be on the order of $100/m2. But this cost
Table 8Data compiled based on averaging results for three specimens.
Fig. 15. Flexural strengths for uncoated and coated plates.
Fig. 16. Compressive versus flexural strengths for the lightweight and PVB mixes.
H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179 1177
Author's personal copy
could be easily offset by safety considerations in some applicationsand/or reductions in insurance premiums in others. Additionally,the polyurea family is a specialty market now. The applied costscould decrease toward the $40/m2–$60/m2 range when and if thistechnology is commercialized.
Despite the fact that polyurea coatings enhance the structuralperformance of PVB concretes, additional research is needed tofully explore this potential in specific applications. In cases wherea structure would likely be subjected to fire, for example, it wouldbe important to evaluate the fire behavior of PVB concrete, PVA fi-bers, and the polyurea coating relative to that of conventional con-crete and aggregates. In environmentally sensitive applications, itwould be beneficial to know whether there was leaching of delete-rious substances from the PVB concretes or the polyurea coating.And, in cases where long term performance was important, assess-ing the durability of the polyurea coating and concrete constitu-ents would be essential.
7. Conclusions
In this study, a low modulus polyurea coating was sprayed un-der field conditions onto the surface of a lightweight concrete andtwo high-performance cementitious composite materials: one con-taining Poly(vinyl butyral) (PVB) as the only aggregate, the otherwith Poly(vinyl alcohol) (PVA) fibers added for reinforcement.Compression tests were conducted to establish the wet–dry perfor-mance of uncoated and circumferentially coated cylinders madefrom the PVB and lightweight concretes; and, flexure tests wereconducted on plates constructed with all three mixes to measurethe flexural strength and toughness of uncoated and coated sam-ples. As a result, the following conclusions were reached:
Regarding wet/dry behavior:– The circumferential polyurea coating improved the strength of
the PVB concrete cylinders when they were subjected to awet/dry environment, especially in the case of fresh water. Anincrease in strength was seen when the lightweight concretecylinders were coated and exposed to sea water.
Regarding flexure:– The stress–strain plots of uncoated plates made from the mate-
rials were all fairly linear to failure.
– The addition of PVA fibers to the PVB mix increased the flexuralstrength, decreased the stiffness, and increased the toughness.
Regarding coating flexure specimens with polyurea:– The addition of the polyurea coating allowed the plates to sus-
tain higher strains especially when PVA was added. The strainhardening was prevalent in the stress–strain plots; much moreso when PVA fibers were added.
– The addition of the coating increased the flexural strength,decreased the stiffness, and increased the toughness.
Regarding lightweight versus high-performance concretes:– Although the compressive strength of the lightweight concrete
was greater than that of the PVB concrete, the flexural strengthwas not. This trend was attributed to the higher tensile-to-com-pressive strength ratio associated with high-performanceconcretes.
Acknowledgements
The authors would like to thank the US Department of Com-merce for supporting this research under NOAA SBIR ContractNo. WC133R-09-CN-0108. They would also like to thank Dr. KirkBiszick, Mr. Ravi Bomu, and Mr. Shigeyuki Ueno for their help withspecimen preparation, running the tests, and acquiring data; and,John Becker for designing and producing the polyurea used to coatthe specimens. Any opinions, findings, conclusions or recommen-dations expressed in this publication are those of the authors anddo not necessarily reflect the views of the Department ofCommerce.
References
[1] Delucchi M, Barbucci A, Cerisola G. Crack-bridging ability and liquid waterpermeability of protective coatings for concrete. Progr Org Coat1998;33:76–82.
[2] Eliezer A. Polyurea – the new generation of lining and coating. Adv Mater Res2010;95:85–6.
[3] Awad WH, Wilkie CA. Investigation of the thermal degradation of polyurea: theeffect of ammonium polyphosphate and expandable graphite. Polymer2010;51(11):2277–85.
[4] Broekaert M. Coating solution for concrete applications, Concrete. ABI/InformTrade Industry 2007;41:20.
[5] Polyurea.com. Markets and applications for spray polyurea. 2012. <http://www.polyurea.com/spps/ahpg.cfm?>spgid=18; [last date of access: August 29,2012].
[6] Morrison S. Tough at the top: Heavy duty protective coating. 2006. <http://www.specialchem4coatings.com/resources/articles/article.aspx?>id=4023&q=polyurea [last date of access: August 29, 2012].
[7] Futura Tech Company, Truth and mith of polyurea. 2011. http://www.futura-tech.com/news/200512041620_2.pdf [last date of access: August 29, 2012].
[8] Alldredge DJ, Gilbert JA, Toutanji HA, Lavin T, Balasubramanyam MS. Upliftcapacity of polyurea-coated light-frame rafter to top plate connections. J MaterCivil Eng 2012;24(9):1–10.
[9] Bahei-El-Din YA, Dvorak GJ. Behavior of sandwich plates reinforced withpolyurethane/polyurea interlayers under blast loads. J Sandwich Struct Mater2007;9:261–81.
[10] Gardner N, Wang E, Kumar P, Shukla A. Blast mitigation in a sandwichcomposite using graded core and polyurea interlayer. Exp Mech2012;52(2):119–34.
[11] Roland CM, Twigg JN, Vu Y, Mott PH. High strain rate mechanical behavior ofpolyurea. Polymer 2007;48:574–8.
[12] Carey NL, Myers JJ. Impact testing of polyurea coated reinforced concrete andhybrid panels, FRPRCS-9, Sydney, Australia, 2009. <http://transportation.mst.edu/media/research/transportation/documents/C14_2009_Myers.pdf>[last date of access: August 29, 2012].
[13] Tekalur SA, Shukla A, Shivakumar K. Blast resistance of polyurea based layeredcomposite materials. Compos Struct 2008;84:271–81.
[14] Lavin T, Toutanji HA, Xu B, Ooi TK, Biszick KR, Gilbert JA. Matrix design forstrategically tuned absolutely resilient structures (STARS). Proc. of SEM XIinternational congress on experimental and applied mechanics, Orlando,Florida, June 2–5, 2008. Paper no. 71. 12 pages.
Constituent Quantity (kg/m3) Unit cost ($/kg) Price ($/m3)
Cement 832.96 $0.13/kg $108/m3
Metakaolin 79.30 $1.65/kg $131/m3
B-79 (Butvar-PVB) 182.39 $5.50/kg $1003/m3
B-75 (Butvar-PVB) 118.95 $5.50/kg $654/m3
Water 364.78 $0.005/gal $0/m3
Sika 26.68 $3.72/kg $99/m3
Total cost $1995/m3
Table 10Cost estimate for PVA fiber concrete ($/m3).
Constituent Quantity (kg/m3) Unit cost ($/kg) Price ($/m3)
Cement 832.96 $0.13/kg $108/m3
Metakaolin 79.30 $1.65/kg $131/m3
B-79 (Butvar-PVB) 182.39 $5.50/kg $1003/m3
B-75 (Butvar-PVB) 118.95 $5.50/kg $654/m3
Water 364.78 $0.005/gal $0/m3
Sika 26.68 $3.72/kg $99/m3
PVA fiber (RECS7) 7.93 $27.43/kg $218/m3
Total cost $2213/m3
1178 H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179
Author's personal copy
[16] Insurance Institute for Business and Home Safety. Hurricane Ike, nature’s forcevs. structural strength. 2009. <http://www.disastersafety.org/research/article?>articleId=4449; [last date of access: August 29, 2012]. p. 7
[17] McGee J, Nemat-Nasser S. An experimentally-based viscoelastic constitutivemodel for polyurea, including pressure and temperature effects. Philos Mag2006;86(36):21.
[18] Lo TY, Cui HZ. Effect of porous lightweight aggregate on strength of concrete.Mater Lett 2004;58:916–9.
[19] Prokopski G, Halbiniak J. Interfacial transition zone in cementitious materials.Cem Concr Res 2000;30:579–83.
[20] Breton D, Carles-Gibergues A, Ballivy G, Grandet J. Contribution to theformation mechanism of the transition zone between rock and cementpaste. Cem Concr Res 1993;23:333–46.
[21] Ollivier JP, Maso JC, Bourdette B. Interfacial transition zone in concrete. AdvCem Mater 1995;2:30–8.
[22] Sun Z, Garboczi EJ, Shah SP. Modeling the elastic properties of concretecomposites: experiment, differential effective medium theory, and numericalsimulation. Cem Concr Compos 2007;29(1):22–38.
[23] Leemann A, Münch B, Gasser P, Holzer L. Influence of compaction on theinterfacial transition zone and the permeability of concrete. Cem Concr Res2003;36(8):1425–33.
[24] Elsharief A, Cohen MD, Olek J. Influence of aggregate size, water cement ratioand age on the microstructure of the interfacial transition zone. Cem Concr Res2003;33(11):1837–49.
[25] Nadeau JC. Water–cement ratio gradients in mortars and correspondingeffective elastic properties. Cem Concr Res 2002;32(3):481–90.
[26] Belaïd F, Arliguie G, François R. Porous structure of the ITZ around galvanizedand ordinary steel reinforcements. Cem Concr Res 2001;31(11):1561–6.
[27] Diamond S, Huang JD. The ITZ in concrete-a different view based on imageanalysis and SEM observations. Cem Concr Compos 2001;23(2–3):179–88.
[28] Harutyunyan VS, Abovyan ES, Monteiro PJM, Mkrtchyan VP, Balyan MK.Microstrain distribution in calcium hydroxide present in the interfacialtransition zone. Cem Concr Res 2000;30(5):709–13.
[29] Scrivener KL, Nemati KM. The percolation of pore space in the cement paste/aggregate interfacial zone of concrete. Cem Concr Res 1996;26(1):35–40.
[30] Richard JS. Purifying proteins for proteomics: a laboratory manual. Cold SpringHarbor (New York): CSHL Press; 2004. p. 73.
[31] Akçaolu T, Tokyay M, Çelik T. Effect of coarse aggregate size on interfacialcracking under uniaxial compression. Mater Lett 2002;57(4):828–33.
[32] Akçaolu T, Tokyay M, Çelik T. Effect of coarse aggregate size and matrix qualityon ITZ and failure behavior of concrete under uniaxial compression. Cem ConcrCompos 2004;26(6):633–8.
[33] Tasong WA, Lynsdale CJ, Cripps JC. Aggregate-cement paste interface. Part I.Influence of aggregate geochemistry. Cem Concr Res 1999;29(7):1019–25.
[34] Wild S, Khatib JM, Jones A. Relative strength, pozzolanic activity and cementhydration in superplasticised metakaolin concrete. Cem Concr Res1996;26(10):1537–44.
[35] Bentz DP. Influence of silica fume on diffusivity in cement-based materials. II.Multi-scale modeling of concrete diffusivity. Cem Concr Res2000;30(7):1121–9.
[36] Asbridge AH, Chadbourn GA, Page CL. Effects of metakaolin and the interfacialtransition zone on the diffusion of chloride ions through cement mortars. CemConcr Res 2001;31(11):1567–72.
[37] Poon C, Lam L, Kou SC, Wong Y, Wong R. Rate of pozzolanic reaction ofMetakaolin in high-performance cement pastes. Cem Concr Res2001;31(9):1301–6.
[38] Chong KP. Nanoscience and engineering in mechanics and materials. J PhysChem Solids 2004;65(8–9):1501–6.
[39] Peng Z, Kong L, Li S. Thermal properties and morphology of a poly(vinylalcohol)/silica nanocomposite prepared with a self-assembled monolayertechnique. J Appl Polym Sci 2005;96(4):1436–42.
[40] Piscevic D, Tarlov MJ, Knoll W. Surface plasmon microscopy of biotin-streptavidin binding reactions on UV-photopatterned alkanethiol self-assembled monolayers. Supramol Sci 1995;2:99–106.
[41] Yang G, Gong J, Yang R, Guo H, Wang Y, Liu B, et al. Modification of electrodesurface through electrospinning followed by self-assembly multilayer film ofpolyoxometalate and its photochromic. Electrochem Commun 2006;8(5):790–6.
[42] Peng Z, Kong LX, Li SD, Spiridonov P. Polyvinyl alcohol/silica nanocomposite:its morphology and thermal degradation kinetics. J Nanosci Nanotechnol2006;12:340–93.
[43] Peng Z, Kong LX, Li SD. Non-isothermal crystallisation kinetics of self-assembledpolyvinylalcohol/silica nano-composite. Polymer 2005;46:1949–52.
[44] Friedrich K, Fakirov S, Zhang Z. Polymer composites: from nano-to-macro-scale. New York: Springer Inc.; 2005. p. 129–30.
[45] Xu J, Li Y, Ge D. Experimental investigation on constitutive behavior of PVBunder impact loading. J Impact Eng 2011;38(2–3):106–14.
[46] Solutia, Inc., Butvar polyvinyl butyral resin, properties and uses, Publicationno. 2008084E Technical Brochure, Solutia Inc., St. Louis, Missouri, 2008.<http://butvar.com/pdfs/en/Butvar_Properties_and_Uses.pdf>; [last date ofaccess: August 29, 2012]. p. 1–30.
[49] KSE Specialties Europe, Mowital: Polyvinyl butyral of superior quality:specialized in specialties brochure, Kuraray Specialties Europe (KSE)Gesellschaft mit beschränkter Haftung (GmbH), Frankfurt am Main,Germany, 2003. <http://www.kuraray-am.com/pvoh-pvb/mowital.php>; [lastdate of access: August 29, 2012]. p. 1–36.
[51] Feldman D, Barbalata A. Synthetic polymers: technology, properties,applications. London: Chapman and Hall; 1996. p. 101.
[52] Hoshiro H, Ogawa A, Hitomi Y. Super ductile PVA-fiber reinforced cementboard. In: 11th Int. inorganic-bonded fiber composites conference Madrid,Spain. November 5–7; 2008.
[53] Wang S, Li VC. Polyvinyl alcohol fiber reinforced engineered cementitiouscomposites: material design and performances. Department of Civil andEnvironmental Engineering. University of Michigan. p. 1–8. doi 10.1.1.67.4523.
[54] Davidson JS, et al. PVA fiber reinforced shotcrete for rehabilitation andpreventative maintenance of aging culverts, Final Report submitted to theAlabama Department of Transportation, Department of Civil EngineeringAuburn University. <www.eng.auburn.edu/files/centers/hrc/930-657.pdf>;[last date of access: August 29, 2012]. p. 1–67; 2008,
[55] Redon C, Li VC, Cynthia Wu. Measuring and modifying interface properties ofPVA fibers in ECC matrix. J Mater Civil Eng 2001;13(6):399–406.
[56] Kurray. Worldwide, PVA fiber & industrial materials: Kurray PVA fiber forcement, mortar and concrete. <http://www.kuraray-am.com/pvaf/fibers.php>;[last date of access: August 29, 2012].
[57] ASTM C150/C150M-11, Standard specification for Portland cement. AmericanSociety for Testing and Materials; 2011. <http://www.astm.org>; [last date ofaccess: August 29, 2012].
[58] Metakaolin description: PowerPozz™ high reactivity Metakaolin (HRM):Engineered mineral admixture for use with Portland cement bulletin,Advanced Cement Technologies Limited Liability Company (LLC), Blaine,Washington, 1–4, 2010, <http://www.bigfreshcontrol.com/documents/act_documents/MetakaolinDescription.pdf>.
[59] ASTM C618-08a, Standard specification for coal fly ash and raw or calcinednatural pozzolan for use in concrete. American Society for Testing andMaterials; 2008. <http://www.astm.org>; [last date of access: August 29,2012].
[60] ASTM C494/C494-11, Standard specification for chemical admixtures forconcrete. American Society for Testing and Materials; 2011. <http://www.astm.org>; [last date of access: August 29, 2012].
[61] Toutanji H, Gomez W. Durability of concrete beams externally bonded withFRP sheets in aggressive environments. Cem Concr Compos J1997;19a(4):351–8.
[62] Toutanji H. Durability characteristics of concrete columns confined withadvanced composite materials. J Compos Struct 1999;44(2–3):155–61.
[63] ASTM C39/C39M-11a. Test method for compressive strength of cylindricalconcrete specimens. American Society for Testing and Materials; 2011.<http://www.astm.org>; [last date of access: August 29, 2012].
[64] ASTM C78/C78M-10. Standard test method for flexural strength of concrete(using simple beam with third-point loading. American Society for Testing andMaterials; 2010. <http://www.astm.org>; [last date of access: August 29,2012].
[65] Pinkston M. Quantative evaluation of polymer enhanced cementitiousmaterials, MS Thesis. Department of Mechanical and Aerospace Engineering,University of Alabama in Huntsville; 2011. [p. 105–11].
[66] Broekaert M, Van Buyten T. A polyurea waterproofing membrane, the idealsurface preparation for Huntsman’s innovative green roof VYDRO� substratefoam, PDA Europe 2010 Annual Conference; 2010. <http://www.pda-europe.org/documents/08_Huntsman_MBroekaert.pdf>; [last date of access:August 29, 2012].
[67] King T. The average cost of a cubic yard of concrete, Ehow.com article, Bellevue,Washington; 2012. <http://www.ehow.com/about_5869747_average-cost-cubic-yard-concrete.html>; [last date of access: August 29, 2012]. [p. 1–2].
H.A. Toutanji et al. / Construction and Building Materials 38 (2013) 1170–1179 1179
