The understanding of environmental influenced on the properties of polymer mortar composites is still far from complete. This preliminary investigation is to provide some informative data to this unsettle topic. When cured in hot humid environment, it has been observed that the specified compressive strength is obtained as early as 1 day age but the modulus of elasticity is significantly less than the specified values. The flexural strength of polymer mortar composites has been expressed as a function of compressive strength. However, the compressive strength of polymer mortar composites cannot be used as a measure of the modulus of elasticity

Makhtar, Ahmad Mahir

English

Universiti Teknologi Malaysia Institutional Repository

25Jamal Kej. Awam Jil. 9 BiI. 21996ENGINEERING PROPERTIES OF POLYMER MORTARCOMPOSITES IN HOT HUMID ENVIRONMENTbyAhmad Mahir MakhlarFaculty of Civil EngineeringUniversiti Teknologi MalaysiaABSTRACTThe understanding of environmental influenced on the properties of polymermortar composites is still far from complete. This preliminary investigation isto provide some informative data to this unsettle topic. When cured in hothumid environment, it has been observed that the specified compressivestrength is obtained as early as 1 day age but the modulus of elasticity issignificantly less than the specified values. The flexural strength of polymermortar composites has been expressed as a function of compressive strength.However, the compressive strength of polymer mortar composites cannot beused as a measure of the modulus of elasticity.INTRODUCTIONAs the design principles of both reinforced and prestressed concrete wererefined. more elegant and complex structures were built with subsequentenhanced aesthetics. Unfortunately, this also led to serviceability problemswith some of these structures. Blame is often attributed to the quality of theconcrete and its inability to resist aggressive environmental attack. As aresult, there have been a revival of interest in the understanding of normalconcrete of high quality and also the development of new materials includingpolymer mortar and concrete composites.The polymer behaviour is well recognised that these materials are influencedby the environmental conditions during the curing phase and in service. whichmay range from subzero to refractory temperatures and from a very dry to fullsaturation. While normal concrete is slightly affected by these conditions, thepolymer materials are significantly affected and may be completely inhibited[1]. Nevertheless polymer mortar and concrete composites may be formulatedto provide a very wide range of properties including from brittle to ductile,impermeable to porous and skid resistant to water shedding.26The polymer materials used in the repair works in the construction industryare generally epoxy resins. They are commonly used which can be categorisedas cosmetic repair or structural repair [2]. Epoxy resins are produced bycombining modified or unmodified resins with a variety of curing agents whichare often referred to as hardeners. The selection of these resins and hardenersare greatly depend on the requirements of the final applications. Someimportant considerations in the selection include product viscosity. adequatepot life, good chemical and water resistance, impermeable to water and oil,high strength and good adhesion. Often no single product will meet all of thedesired requirements and the manufacturers are constantly forced to prioritisedthe requirements to make intelligent choice.Malaysia is a hot humid climate country which encounters heavy rainfall withan average amount mean relative humidity of about 85% on the lowlands. Itstemperature is uniform throughout the year with annual average temperaturesvaries within I 1.66 of 26.27°C (3]. Nevertheless it's monthly highestmaximum and monthly lowest minimum temperatures ranging from 35°C to20°C respectively.The present investigation is therefore aimed to evaluate the mechanicalproperties of three types of polymer mortar composites which were cured in ahot humid condition until the age for testing. The evaluation was made bymeasuring the compressive strength, flexural strength and modulus ofelasticity at different curing period. Statistical ex.pressions are also presentedin an attempt to estimate the long term engineering properties.EXPERIMENTAL PROGRAMMEMaterials and Specimen PreparationThree types of epoxy resin mortars, which are commercially available in theMalaysian market, were used in this investigation. These materials weresupplied in a prepacked container which consist of the liquid resin, hardenerand the filler if required, Mixing was carried out following the proportion andprocedure specified by the manufacturer. Specimens were cured in an ambientlaboratory condition of 27°C and 80% rho Table 1 shows the mechanicalproperties of all the three types of polymer mortar composites specified by themanufacturer which were determined at 20°C. It also includes the code ofidentification of the polymer mortar composites.Compressille StrengthThe compressive strength test was carried out using 40 mm cubes inaccordance with BS 6319: Part 2 [4]. A 3000 kN Tonipact machine was usedin all tests at a loading rate of 1.2 kN/s. Three specimens were tested at eachcuring age of 0.75, 3, 7,14 and 21 days.27Flexural StrengthThe flexural strength test was conducted with a central point loading systemusing specimens of 25 x 25 x 100 mm prisms in accordance with BS 6319:Part 3 [4]. Three specimens were used in determining the flexural strength ateach curing age of 0.75, 3. 7,14 and 21 days.Table 1: Engineering properties and code of identification of polymermortar compositesELS50.0021.0015.00EPM70.0030.0016.00EPP80,0065.0010.00Modulus of ElasticityThe modulus of elasticity was measured using 40 x 40 x t 60 mm prisms inaccordance with BS 6319: Part 6 [4]. Measurements were made at 3. 7, 14and 21 days.PRESENTATION OF RESULTS AND DISCUSSIONThe results of properties investigated in this work are shown in Figure I,Figure 2 and Figure 3. Each data point used to obtain lhe empirical expressionis the average of three measurements. The curves shown in these Figureswere obtained statistically using the least square method. They were intendedto show the engineering properties trends of different types of polymer mortarcomposites cured in hot humid environment.Compressive strengthCompressive strength is an important strucutural parameter used forcompliance in most codes and standards, in designing concrete structures.Frequently, this compressive strength is also used as an indication of thedevelopment of other properties such as modulus of rupture and modulus ofelasticity. These relationships are also presented and discussed in this paper.Figure 1 shows the development of compressive strength of all the three typesof polymer mortars investigated. In comparison with the specified strength(Table 1), all the three types of polymer mortar composites attain the specifiedstrength, which was determined at 20°C, as early as I day age. Thisobservation indicates that the rate of strength development of polymer mortarcomposites is higher when cured in hot humid environment. In addition, thesematerials are specified to achieve their full cure from 2 to 7 days depending ontemperature. It can also be seen that compressive strength of polymer mortarcomposites is governed by the curing length and type of polymer used. J28The ELS polymer mortar composite shows a small increase in strength from 1day to 21 day age, while EPM and EPP polymer mortar composites show asubstantial increase in strength of 47% and 30% respectively.Flexural strengthFigure 2 presents the flexural strength of all the three types of polymer mortarcomposites investigated. Regardless of the polymer type, the flexural strengthdevelopment trends are similar in all the three types of polymer mortarcomposites. Nevertheless the flexural strength value for EPP polymer mortaris 20% lower than that of the specified value which was determined at 20uC.However, the flexural strength values for ELS and EPM polymer mortars are43% and 82% higher respectively. These results confirm the established factthat flexural strength of polymer mortar composites is governed by the type ofpolymer and the curing condition.Modulus of elasticityThe modulus of elasticity of all the three types of polymer mortar compositesdetennined at various curing ages are shown in Figure 3. The increase in themodulus of elasticity for EPM and EPP polymer mortar composites shows asimilar trend. However, the modulus of elasticity of ELS polymer mortarcomposite shows a higher rate of increase. The results also indicate that themodulus of elasticity at 7 day age of all the three types of polymer mortarcomposites are 50 - 60% lower than those specified values which weredetermined at 20°C. This reveals the fact that modulus of elasticity of polymermortar composites depends on the exposure condition, Similar observationhas also been reported for hardened concrete in hot humid climate [3],STATISTICAL EXPRESSIONS FOR ENGINEERING PROPERTIESIn practice, statistical expressions are useful in estimating the long termengineering properties. In this investigation, the compressive strength andflexural strength of polymer mortar composites are expressed as follows:Compressive strength/<., = a Ln ( t) + bFlexural strengthIh' = c Ln (t) + dwhereI"Ib'a,b,c,dCompressive strength (MPa)Flexural strength (MPa)Empirical constants29Table 2: Values of constants and coefficient of determination forengineering propertiesEngineering Mix Emoirical constants R'DraDerties lVoe a b c dCompressive ELS 2.7088 54.827 - - 0.9599strength EPM 9.9545 80.176 - - 0.9715EPP 7.1946 87.255 - - 0.7508Aexural ELS - - 3.0291 28.207 0.6932strength EPM - - 2.5863 51.574 0.8707EPP - - 3.1872 45.860 0.9948Table 2 gives the values of constants a, b. c and d together with the coefficientof determination (R2). The high values of R2 indicate that engineeringproperties of polymer mortar composites can be expressed as a function ofnatural logarithm of curing period. This natural logarithm function has alsobeen used to express the engineering properties of polymer modified concretecomposites [5]. It can De seen that these constants are influenced by the typeof polymer mortar composites. These observations agree with the well.established fact that properties of polymer mortar and concrete composites aredependent on the polymer type. of which can be formulated for a wide range ofspecific applications.RELATION BETWEEN FLEXURAL STRENGTH,MODULUS OF ELASTICITY AND COMPRESSIVE STRENGTHFigure 4 and Figure 5 show the relationships between flexural strength andmodulus of elasticity with compressive strength respectively. Regardless ofthe type of polymer mortar composite. it can be seen that in hot humidenvironment, a linear relationship between flexural strength and compressivestrength is established which can be expressed as fbI = 0.55 fell' (Figure 4).This tends to suggest that these polymer mortar composite materials arepractically suitable to be used as repair material in either beam or columnrepair works. Although improve in flexural strength is beneficial in designinga concrete structure. this consideration still needs to be examined further whenmaking the selection for repair material.Unlike the concrete. of which the modulus of elasticity can be expressed as afunction of compressive strength [6], the scatter points in Figure 5 indicate thatthe compressive strength cannot be used as a measure of modulus of elasticityof polymer mortar composites. The results show that some polymer mortarcomposites with high compressive strength deform more than some of thelower strength polymer mortar composites.30This fact is very significant to engineers when selecting the appropriate repairmaterial. For example. if these materials are used in column repair work andthe load is applied parallel to the bond line of repair, this load will betransferred to the higher modulus material, i.e. concrete, which may causefailure [7].CONCLUSIONSThis investigation has examined the influence of curing condition on theengineering properties of polymer mortar composites. By examining theeffects on commercially available products, it is possible to highlight theimportance of considering more than a single parameter in the selection ofrepair materials. The understanding that high compressive strength material,such as concrete. exhibits high modulus of elasticity is no more applicable topolymer mortar composite when tested in hot humid environment. Inoptimizing the use of polymer mortar composite as repair material, it has to bedesigned not only for its final application but also for its service environmentalcondition.ACKNOWLEDGEMENTSThis work is part of the IRPA-RM6 research project which has been carriedout at the Concrete Laboratory, Faculty of Civil Engineering. UniversitiTeknologi Malaysia. The author wishes to express his appreciation to theMinistry of Science, Technology and Environment Malaysia for providing theresearch grant. The author also wishes to acknowledge the considerable workby many students which has contributed to the data included in this study.REFERENCES[I] Plum, D R, The behaviour of polymer materials in concrete repair andfactors influencing selection, The Structural Engineer. V.68, n. 17, Sept.1990, pp 337 -345.[2] Plum. D R, Environmental effects on polymer modified materials,International Conference on Highrise Building, Nanjing, China, March1989, pp 726 -731.[3] Mustafa, M A and Yusof. K M, Mechanical properties of hardenedconcrete in hot-humid climate, Cement and Concrete Research. V, 21, n. 4,1991,pp601-613.31[4] British Standard Institution, BS 6319 - Testing of resin compositions foruse in construction, London, 1983 - 1984.[5} Cabrera, J G and Makhtar, A M, The influence of type of hydraulic cementon the properties of polymer modified concrete, 3rd Southern AfricanConference on Polymers in Concrete, South Africa, (to be published), July1997.[6) Neville, A M and Brooks, J J, Cnncrete Technology, Longman, England,1990, pp 212.[7] Warner, J, Selecting repair materials, Concrete Construction, Oct. 1984, pp865-871.'"~ 10032I9060"ooofeu =' 7.J9461.J1(I) .•. 1I7.255I{l '" O.7_~Ollf .• = 'J.'J545lJl(I)'" ~U.176RJ =0.9115.ELS A13j'~11DEI'I'".f~ '"2.7fll\IILfl(IJ'" .'14,827I{l = n.'!.'i'J'J20Figure J COlllpn.:ssivc strength devel0plllent or polymer lIlorl:lrsFigure 2 Flcxur:1J strength development of polymer Illortars'"~ 10,~ to"of", = 2.5863Ln(l)-+ 51.514R' =0.1:\707~•.a'> ",EPM OEI'!''";•"f ••= 3.1snUI(J) .•.45,M,I{I = n.'J'NX•/ •• = J,O!')I LII(l) .••2l\.2U71('=lIHJ.l2,J". •"ls "• ,~.'" 0•,~, ,., 0,~.l:L'> •••EI'M 0 EI'l'0I'" "2U 2.'1 1,\~c.I (d"plFigure 3 Modulus of clasticilY of polymer mortars at various curing ages33110lOllso""."1(17"l6() f ••= O.J-I5Jj •• •III = 0.84511 • • •(;'"•• •~1."J"0;~ '"" '"Figure 4 Relation between flexural strength and comprcs~ivc strengthof polymer mortarsH.l "s"•S '".~3•j:;ooooo00oooWI! 120CuonprcMlY<: Strcuglh. t.•(l\-Jl'u)'\jFigure 5 Relation between modulus of elasticity and compressive strengthof polymer mortars

Engineering properties of polymer mortar composites in hot humid environment

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Engineering properties of polymer mortar composites in hot humid environment

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