醋酸乙烯酯共聚物乳胶粉在水泥砂浆中的作用

Action of redispersible vinyl acetate and versatate copolymer powder in cement mortarRu Wang a ,b ,⇑,Pei-Ming Wang aaKey Laboratory of Advanced Civil Engineering Materials of Ministry of Education,School of Materials Science and Engineering,Tongji University,4800Caoan Road,Shanghai 201804,China bDepartment of Civil Engineering and Engineering Mechanics,Columbia University,New York,NY 10027,USAa r t i c l e i n f o Article history:Received 4February 2011Received in revised form 21April 2011Accepted 22April 2011Available online 8May 2011Keywords:Redispersible VA/VeoVa powder Cement mortarPhysical and mechanical properties Shrinkage rateWater capillary adsorption Anti-penetration capacitya b s t r a c tRedispersible polymer powder of vinyl acetate and versatate copolymer (VA/VeoVa)is applied to modify cement mortar.The effect of VA/VeoVa powder on physical and mechanical properties of cement mortar is investigated.VA/VeoVa powder exhibits excellent water-reduction and water-retention effects in cement mortar and improves mortar properties effectively.Due to the air-entrainment effect of VA/VeoVa powder,the air content of fresh mortar is increased and the bulk density is decreased.VA/VeoVa powder makes the compressive strength decrease,but not so significant the effect on the flexural strength is,which results in the ratio of compressive strength to flexural strength goes down sharply with the increase of VA/VeoVa powder,indicating the toughness of cement mortar is improved markedly.Fur-thermore,VA/VeoVa powder reduces the shrinkage rate and improves the hydrophobicity and water impermeability of cement mortar.Ó2011Elsevier Ltd.All rights reserved.1.IntroductionPolymer-modified mortars are good repair materials for excellent properties.Polymers can improve the flowability of fresh mortar,mechanical properties [1],anti-penetrability [2],freezing–thawing resistance [3],anti-corrosion [4],and so on of hardened mortar.Former research shows that polymers change the micro-structure,have physical and chemical interaction with cementi-tious phase,effect the flowability,hydration,setting,hardening,pore structure,and thus physical and mechanical properties of hardened mortar [5–8].In fact,different polymers have different influences on cement mortar.For example,styrene–butadiene rubber (SBR)latex im-proves the flexural strength,tensile bond strength,waterproofing property,carbonation resistance and anti-shrinkage of cement mortar [9–11].Styrene–acrylic ester copolymer (SAE)latex de-creases the elastic modulus and increases the toughness of cement mortar to a larger extent [12,13].Ethylene–vinyl acetate copoly-mer (EVA),the most widely used polymer in mortar,improves the tensile bond strength,flexural strength,and toughness of ce-ment mortar [14,15].Whereas vinyl acetate and versatate copolymer (VA/VeoVa)is a special copolymer that introduces the versatate group with three long a -alkyl molecule side chains into the copolymer.The three long a -alkyl molecule side chains make the copolymer have many superior properties.The ester group of vinyl versatate is stable for the hindering effect of long side chains,resulting in good alkali resistance;the long side chains of vinyl versatate protect neighbor-ing ester group of vinyl acetate too,making the copolymer have good alkali resistance.VA/VeoVa powder is a potential modifier for brittle cement mortar.In Ref.[16],lower degeneration of VA/VeoVa in an alkaline environment rather than other copolymers that contain vinyl acetate group was found.The former researches [17,18]show that with antifoamer together the VA/VeoVa powder increases the strengths of cement mortar.After that,little research on the application of VA/VeoVa powder in cement mortar is pub-lished.This paper focuses on evaluating the action of single VA/VeoVa powder in cement mortar,trying to compare the properties with other polymer powders and dispersions modified mortars those are tested using the same method.2.Experimental 2.1.MaterialsPortland cement type P ÁII 52.5R,according to Chinese standard GB 175,and standard sand,according to ISO 679,were used for preparing the specimens.The chemical composition and physical properties of the cement are listed in Table 10950-0618/$-see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.conbuildmat.2011.04.060⇑Corresponding author at:Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education,School of Materials Science and Engineering,Tongji University,4800Caoan Road,Shanghai 201804,China.Tel.:+862169582140.E-mail address:ruwang@ (R.Wang).and Table2,respectively.The redispersible VA/VeoVa powder(density:0.5g/cm3; average particle size:80l m;minimumfilm formation temperature:6°C)was used in the experiment.2.2.Specimen preparationThe mortar specimens were prepared with VA/VeoVa powder to cement ratio by mass(m p/m c)of0,1%,2%,3%,4%,5%,6%,7%,8%,9%,10%,12%,15%,and20%,con-stantflow of(170±5)mm,and sand to cement ratio by mass of3.The specimens with the dimension of40mmÂ40mmÂ160mm were prepared according to ISO679.The specimens were unmolded after24h.Mixed cure method,1day im-mersed in20°C water followed by1day in air of20°C and RH50%for specimens tested at the age of3days and6days immersed in20°C water followed by21days in air of20°C and RH50%for the specimens tested at the age of28days,was used.2.3.Test methods2.3.1.FlowTheflow table value of fresh mortars was measured according to GB/T2419-2005.A cone-shaped metal ring isfilled with fresh cement mortar on a shock table, and after lifting the ring the mix is subjected to25drops of the table within25s. Thefinal diameter is the so-calledflow table value.The water to cement ratio (m w/m c)of VA/VeoVa powder-modified mortars was determined byfixing theflow table value at a constant of(170±5)mm,as listed in Table3.2.3.2.Water-retention rateThe water-retention rate of fresh mortar was tested according to DIN18555-7. During test,the fresh mortar with settled volume was put on afilter-film allowing waterfilter through,fixed on absorbentfilter papers.Then the water absorbed by thefilter papers(lost water of fresh mortar)was measured after5min.The water-retention rate was calculated based on that.2.3.3.Air entrainment testThe air content of fresh mortars was measured using an air entrainment meter made according to DIN18555/-557,from which the air content can be read directly.2.3.4.Bulk density of fresh mortarsThe bulk density of fresh mortars was tested according to JGJ70-90.One liter container was used during test.After the fresh mortar was cased into the container, it should be vibrated for10s before the mass was measured.pressive andflexural strengthsThe compressive andflexural strengths were determined according to ISO679.2.3.6.Shrinkage rateThe shrinkage rate of mortars was determined according to JGJ70-90.The initial length of mortar was tested right after the specimen was unmolded.The shrinkage rate was calculated according to the length of mortar at different curing ages and the initial length.2.3.7.Water capillary adsorptionThe water capillary adsorption was measured according to DIN52617.Before test,the mortar specimens were dried at70°C for2days.The four around surfaces were sealed with EP resin before the upside of the specimens was dipped into water.The water capillary adsorption was calculated based on the adsorbed water at different times.2.3.8.Anti-penetration capacityThe anti-penetration capacity was measured according to DL/T5126-2001. Conic specimens with upside and underside surface diameters of70mm and 80mm,height of30mm were prepared.The curing is the same as that described in2.2.Before test,the around surface of specimens was sealed with olefin and the underside surface was contacted with water.During test,the water pressure was increased step by step to1.5MPa within8h to observe whether the water pen-etrates through the mortar specimens.If water penetrates through three of six spec-imens under one pressure,then the pressure was determined as the pressure that the mortar survives.3.Results and discussion3.1.Water-reduction effectThe m w/m c of VA/VeoVa powder-modified mortars decreases significantly with the increase of m p/m c when theflow wasfixed at a constant of(170±5)mm(see Table3).So it is apparent that the VA/VeoVa powder has water-reduction effect in cement mor-tar.Water-reduction rate is an important factor to evaluate water-reduction effect,which can be calculated according to the following equation:[13].R¼1Àm w2Áq2Ám1m w1Áq1Ám2;ð1Þwhere R is the water-reduction rate,m w2,q2and m2is water mass, bulk density and mass of fresh VA/VeoVa powder-modified mortars, respectively;m w1,q1and m1is water mass,bulk density and mass of fresh control mortar,respectively.The water-reduction rate of VA/VeoVa powder-modified mor-tars calculated according to Eq.(1)is displayed in Fig.1.A small amount of VA/VeoVa powder addition of1%makes the water-reduction rate rise to about6%.Then the water-reduction rate rises gradually with the increase of m p/m c.When the m p/m c is15%the water-reduction rate increases to about35%.With the m p/m c increasing from15%to20%,no significant change of water-reduc-tion rate was observed.The experimental results explain that VA/ VeoVa powder has good water-reduction effect in mortar,enhanc-ing theflowability of fresh mortar,which is attributed to the dis-persion and air entrainment functions of VA/VeoVa powder.3.2.Water-retention effectGood water-retention property is helpful for the construction and properties of mortar.Water-retention rate is a quantitative in-dex to evaluate the water-retention effect of mortar.Fig.2presents the water-retention rate of VA/VeoVa powder-modified mortars.Table1Chemical composition of PII52.5R Portland cement.Component SiO2CaO Al2O3Fe2O3MgO SO3K2O TiO2BaOContent(%)21.365.1 5.1 2.9 1.1 1.80.70.20.3Table2Physical properties of PII52.5R Portland cement.Specific gravity at20°C(g/cm3)Blaine’s specific area(m2/kg)Setting time(min)Flexural strength(MPa)Compressive strength(MPa)Initial Final3days7days28days3days7days28days3.20385.5125190 6.97.88.439.049.060.6Table3Water to cement ratio(m w/m c)of VA/VeoVa powder-modified mortars with a constantflow of(170±5)mm.m p/m c(%)012345678910121520 m w/m c0.4890.4720.4580.4440.4350.4260.4180.4100.4040.3990.3940.3920.3900.388R.Wang,P.-M.Wang/Construction and Building Materials25(2011)4210–42144211The water-retention rate augments apparently with the increase of m p/m c.It reaches98%with the m p/m c increasing up to6%,and then keeps augmenting stably,indicating the water-retention property of the modified mortar is very good.The good water-retention property may be attributed to following reasons:first,the water-reduction effect of VA/VeoVa powder reduces the unit water usage; second,the VA/VeoVa powder induces water to distribute well in cement mortar;third,the VA/VeoVa powder has blocking effect on the water in cement mortar and makes it more difficult to separate from the system.3.3.Air contentThe relationship between the air content of fresh mortars and the m p/m c is illustrated in Fig.3.A small amount of VA/VeoVa pow-der addition of1%makes the air content of fresh mortar rise from 6%to8.6%.Then a linear increment of air content appears with theincrease of m p/m c up to15%.The air content change indicates that the VA/VeoVa powder has air-entrainment effect in cement mor-tar,making the density of fresh mortar decrease(see Fig.4).The bulk density of fresh mortars reduces gradually with the increase of m p/m c up to15%.It is easy tofind that the bulk density of fresh mortar is closely related to its air content.pressive strengthThe compressive strengths of VA/VeoVa powder-modified mor-tars with curing ages of3days and28days are displayed in Fig.5.The compressive strength of cement mortars depresses with the addition of VA/VeoVa powder.When the m p/m c increases from 0%to3%,the compressive strength falls from30MPa to14MPa for the mortars cured for3days,from72MPa to34MPa for the mortars cured for28days.The compressive strength declines slightly with the m p/m c increasing from3%to5%,and does not decrease any more when the m p/m c is higher than5%.The decrease tendency of compressive strength with the increasing m p/m c of VA/VeoVa powder-modified mortars is similar with that of SBR latex-or PAE latex-modified mortars.But the decrease is faster than that for SBR latex-modified mortars,which4212R.Wang,P.-M.Wang/Construction and Building Materials25(2011)4210–4214decreases to30MPa when the SBR latex/cement-ratio increases to 8%,and then keeps at around this value with the m p/m c range from 8%to20%[10],and slower than that for PAE latex-modified mor-tars,which decreases to20MPa when the PAE latex/cement-ratio increases to5%,and then keeps at around this value with the m p/ m c range from5%to20%[19].The compressive strength of VA/Veo-Va powder-modified mortars is lower than that of SAE latex-mod-ified mortar when the m p/m c is lower than15%[13].3.5.Flexural strengthFig.6presents theflexural strengths of VA/VeoVa powder-mod-ified mortars with curing ages of3days and28days.The change of flexural strength with the m p/m c is similar with that of compres-sive strength except for a smaller changing magnitude.When the m p/m c increases from0%to3%,theflexural strength decreases from7.2MPa to4.8MPa for the mortar tested at the age of3days and from12.5MPa to9.3MPa for the mortar tested at the age of28days.Then theflexural strength of mortars cured for3days de-creases slowly until the m p/m c of8%,followed by an almost con-stantflexural strength value at the m p/m c range from8%to20%. Whereas no significant change offlexural strength of mortars cured for28days appears when the m p/m c is in the range from 3%to8%.When the m p/m c increases from8%to20%,theflexural strength of VA/VeoVa powder-modified mortar rises to almost equal to that of control mortar.That is probably due to the VA/Veo-Va content is high enough to form a continuous network structure in the mortar and also improve the interface structure between the cement hydrates and the aggregates.When the m p/m c is higher than5%,theflexural strength of VA/ VeoVa powder-modified mortar,higher than9MPa,is higher than that of SBR latex-,SAE latex-or PAE latex-modified mortar,8MPa [10],7MPa[13]and7MPa[19],respectively.3.6.ToughnessThe ratio of compressive strength toflexural strength(r C/r F)of mortar is an important factor to judge its toughness.Lower r C/r F indicates better toughness.Several Chinese standards have the rule that the r C/r F of some mortar must be lower than3[20–22]. The r C/r F calculated based on above compressive andflexural strengths is illustrated in Fig.7.The r C/r F of VA/VeoVa powder-modified mortars cured for3days and28days goes down sharply with the increase of m p/m c,indicating the toughness of mortars is improved significantly.Both the rate and magnitude of decrease are larger for the mortars cured for28days than that cured for 3days.When the m p/m c is above5%,the r C/r F for all the modified mortars is below3.To compare with Refs.[10,13,14,19],with low polymer addi-tion,the VA/VeoVa powder is more effective for the improvement of the toughness of cement mortar than SBR latex that makes the r C/r F decrease to4.5when the m p/m c is20%,SAE latex that makes the r C/r F decrease to below3when the m p/m c is higher than15%, redispersible EVA powder that makes the r C/r F decrease to below 3when the m p/m c is higher than10%,and PAE latex that makes the r C/r F decrease to below3when the m p/m c is higher than7%.3.7.Shrinkage propertyThe shrinkage rate of VA/VeoVa powder-modified mortars with different curing ages is presented in Fig.8.An amount of VA/VeoVa powder below6%makes the shrinkage rate enlarge slightly.When the m p/m c reaches7%,the shrinkage rate reduces sharply and then keeps around this value until the m p/m c of20%,lower than that of control mortar.A slight expansion was found for the VA/VeoVa powder-modified mortars at the curing age of3days with the m p/m c higher than7%.The shrinkage reducing effect of the VA/Veo-Va powder in the mortar when the m p/m c is higher than7%is prob-ably due to the polymerfilm formed in the mortar prevents the water escape from the system.3.8.Water capillary adsorptionThe water capillary adsorption of VA/VeoVa powder-modified mortars within48h was measured,as shown in Fig.9.The water capillary adsorption decreases gradually with the increase ofR.Wang,P.-M.Wang/Construction and Building Materials25(2011)4210–42144213m p/m c.When the m p/m c is below7%,the decrease of water capil-lary adsorption with the m p/m c is more evident,indicating at this range a little increase of m p/m c leads to an apparent decrease of water capillary adsorption.However,when the m p/m c is higher than7%,the effect of the increase of m p/m c on the water capillary adsorption is not so marked and the water capillary adsorption va-lue is low.The water capillary adsorption of VA/VeoVa powder-modified mortars with the m p/m c of7%at24h is about0.7kg/m2,which is better than that of redispersible EVA powder-modified mortar 0.8kg/m2[15],similar to that of SAE latex-modified mortar 0.7kg/m2[13],but not so good as that of SBR latex-modified mor-tar0.7kg/m2with SBR latex to cement ratio of5%[23].3.9.Anti-penetration capacityThe experimental results show that the water does not pene-trate through the specimens for all the mortars when the water pressure was increased step by step to1.5MPa within8h.After test,the mortar specimens were broken to observe the penetration depth of water into the specimens,as listed in Table4.It is found that the water penetration depth decreases from12mm to2mm with the increase of the m p/m c from0%to15%.When the m p/m c is20%,no water penetrating into the mortar specimens was ob-served.It can be drawn that the VA/VeoVa powder enhances the anti-penetration capacity of mortar remarkably.4.ConclusionsVA/VeoVa powder has good water-reduction and water-reten-tion effects in cement mortar.The water-reduction rate augments gradually with the increase of m p/m c,reaching about35%when the m p/m c is15%.The water-retention rate rises significantly to about 98%with the increase of m p/m c up to7%.VA/VeoVa powder has air-entrainment effect,making the air content of fresh mortar increase and the bulk density decrease.VA/VeoVa powder depresses the compressive strength of ce-ment mortar,but not so significant the effect on theflexural strength is.That makes the ratio of compressive strength toflex-ural strength goes down to below3when the m p/m c is above5%. The toughness of cement mortar is improved significantly.VA/VeoVa powder has shrinkage rate reducing effect in cement mortar when the m p/m c is higher than7%.VA/VeoVa powder improves the hydrophobicity and water impermeability of cement mortar.The water capillary adsorption decreases with the increase of m p/m c and to about0.7kg/m2at 24h when the m p/m c increases to7%;the water penetration depth decreases from12mm to2mm with the increase of m p/m c from0%to15%when the pressure was increased step by step to 1.5MPa.AcknowledgmentsThe authors acknowledge thefinancial support of the National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science&Technology of China(2006 BAJ05B03)and the Specialized Research Fund for the Doctoral Pro-gram of Higher Education(20060247023).References[1]Flavio LM,Vanderley MJ.Bond strength and transversal deformation aging oncement-polymer adhesive mortar.Constr Build Mater2009;23:1022–7.[2]Zhong SY,Chen ZY.Properties of latex blends and its modified cement mortars.Cem Concr Res2002;32:1515–24.[3]Mirza J,Mirza MS,Lapointe boratory andfield performance of polymer-modified cement-based repair mortars in cold climates.Constr Build Mater 2002;16:365–74.[4]Xiong JP,Shen AQ,Qiu YB.A study on road performance and modificationmechanism of polymer cement mortar.Highway2007(5):144–8.[5]Nestle N,Kühn A,Friedemann K,Horch C,et al.Water balance and porestructure development in cementitious materials in internal curing with modified superabsorbent polymer studied by NMR.Micropor Mesopor Mater 2009;125:51–7.[6]Afridi MUK,Ohama Y,Demura K,Iqbal MZ.Development of polymerfilms bythe coalescence of polymer particles in powdered and aqueous polymer-modified mortars.Cem Concr Res2003;33:1715–21.[7]Beeldens A,Monteny J,Vincke W,et al.Resistance to sulphuric acid corrosionof polymer-modified mortars.Cem Concr Compos2001;23:47–56.[8]Kong XM,Li QH.Properties and microstructure of polymer modified mortarbased on different acrylate latexes.J Chin Ceram Soc2009;37(1):107–14. [9]Wang PM,Xu Q,Stark J.Mechanical properties of styrene–butadiene emulsionmodified cement mortar used for repair of bridge surface.J Build Mater 2001;4(1):1–6.[10]Wang R,Wang PM,Li XG.Physical and mechanical properties of styrene–butadiene rubber emulsion modified cement mortars.Cem Concr Res 2005;35:900–6.[11]Wang R,Wang PM.Physical properties of SBR latex-modified mortar underdifferent curing methods.J Chin Ceram Soc2009;37(12):2118–23.[12]Wong WG,Fang P,Pan JK.Dynamic properties impact toughness andabrasiveness of polymer-modified pastes by using nondestructive tests.Cem Concr Res2003;33:1371–4.[13]Wang R,Wang PM.Function of styrene-acrylic ester copolymer latex incement mortar.Mater Struct2010;43:443–51.[14]Wang PM,Zhang GF,Zhang YM.Influence of polymer powders on mechanicalproperties of cement mortar.New Build Mater2005(1):32–6.[15]Zhang GF,Wang PM,Wu JG.Influence of polymer powder on the bulk densityand capillary water adsorption of cement mortar.New Build Mater 2004:29–31.[16]Gomes CEM,Ferreira OP,Fernandes MR.Influence of vinyl acetate–versaticvinylester copolymer on the microstructural characteristics of cement pastes.Mater Res2005;8:51–6.[17]Afridi MUK,Chaudhary ZU,Ohama Y,Demura K,Iqbal MZ.Strength and elasticproperties of powdered and aqueous polymer-modified mortars.Cem Concr Res1994;24:1199–213.[18]Afridi MUK,Ohama Y,Iqbal MZ,Demura K.Water retention and adhesion ofpowdered and aqueous polymer-modified mortars.Cem Concr Compos 1995;17:113–8.[19]Wang R,Wang PM.Application of polyacrylic ester latex to cement mortar.JChin Ceram Soc2008;36(7):946–9.[20]JC/T984-2005Polymer modified cement mortars for waterproof.[21]JG158-2004External thermal insulating rendering systems made of mortarwith mineral binder and using expanded polystyrene granule as aggregate.[22]JG149-2003External thermal insulation composite systems based onexpanded polystyrene.[23]Li J.Difference between SBR emulsion and PAE emulsion in modifying cementmortar.MSc thesis.Tongji University;2005.Table4Penetration depth of water into VA/VeoVa powder-modified mortars at8h with thewater pressure increasing to1.5MPa.m p/m c(%)0135810121520Penetration depth(mm)12755643204214R.Wang,P.-M.Wang/Construction and Building Materials25(2011)4210–4214。