Link/Page Citation
Byline: Z.A.Siddiqi, R.Hameed, M.Saleem, Q.S.Khan and Jawad A.Qazi
ABSTRACT: In this research, effect of Styrene-Butadiene Rubber(SBR) latex on water absorption and compressive strength of concrete hasbeen studied. A locally available Sika-Latex is used as SBR Latex. Ithas been observed that SBR latex improves the internal structure of thelatex modified concrete resulting in considerable reduction in the waterabsorption value at 28 days of age. However, at early age, the effect ofSBR latex on water absorption is adverse. Same trend is noticed for thecompressive strength; at 7 days of age, SBR latex has negative effectwhile at 28 days, the addition of SBR latex in concrete results inenhancement of compressive strength. Based on the results of this study,latex modified concrete made using Sika-Latex may be recommended to beused in RC structures in Pakistan. However, for the mixes rich incement, the dosage of Sika-Latex needs to be adjusted to maintainrequired workability of concrete.
Key words: Concrete; SBR Latex; slump; compressive strength; waterabsorption.
INTRODUCTION
Concrete is the most widely used construction material all over theworld due to economy and easy availability of its constituents. Toenhance the durability of concrete structures, the internal structure ofconcrete must be improved to make it impervious. Due to the formation ofthree dimensional polymer network in the hardened cement based matrices,polymer cement concretes have high tensile strength, good ductilebehavior, and high impact resistance capability (Sakai and Sugita,1995). Consequently, the porosity is decreased and pore radius isrefined because of the void- filling effect of this network. In additionto this, improvement in the transition zone as a result of the adhesionof a polymer is also obtained (Silvaa et al. 2001; Ohama et al. 1991;Chandra and Flodin, 1987).
In the last two decades, many research studies have been carriedout on the use of different polymers suitable for admixing into freshconcrete to improve the mechanical properties, among them styrenebutadiene rubber (SBR) latex has been widely used in the past (Joao andMarcos, 2002; Ru W. et al., 2006; Zhengxian Y. et al., 2009; Baoshan H.et al., 2010). Latex is a polymer system formed by the emulsionpolymerization of monomers and it contains 50 (Percent) solids byweight. Styrene butadiene, polyvinyl acetate, acrylic and naturalrubbers are the best examples of polymers which are usually used inlatex. Since mechanical properties, hydration process in cement anddurability of concrete are highly dependent on the state ofmicro-structure, previous research studies have shown that the polymeras modifier is promising in improving micro-structure of concrete (Lewisand Lewis,1990; Ohama, 1997).
Styrene butadiene rubber (SBR) latex is a type of high-polymerdispersion emulsion composed of butadiene, styrene and water and it canbe successfully bonded to many materials. Due to its goodintermiscibility with vinyl pyridine latex for fabric dipping, its majorengineering application is in tire dip fabric industry. In civilengineering field, it is used to replace cement as binder to improvetensile, flexural and compressive strengths of concrete. SBR is whitethick liquid in appearance; it has good viscosity with 52.7 (Percent)water content (Baoshan H. et al., 2010).
In this present contribution, the effect of adding locallyavailable SBR latex known as Sika-Latex on water absorption andcompressive strength of normal strength concrete has been investigated.In cement based composites, water absorption is an important parameteras it is a measure of resistance against carbonation migration. Waterabsorption value indirectly provides information about the porosity ofconcrete. Compressive strength development of the concrete in thepresence of SBR latex was studied at 7 and 28 days of age. Similarly,water absorption of Latex Modified Concrete (LMC) was also investigatedat 7 and 28 days of age.
MATERIALS AND METHODS
Ordinary Portland cement conforming to British Standards (BS12:1991) was used for this study. Locally available Lawrencepur river sandand crushed stone (Marghallah Crush) were used as fine and coarseaggregates, respectively. The properties of fine and coarse aggregateswere determined as per ASTM specifications (ASTM C33-90) and are givenin Table 1.
Locally available polymer 'Sika-Latex' was investigatedin this study. Sika-Latex is a type of Styrene butadiene rubber (SBR)latex. The composition of the Sika-Latex used as polymer is given inTable 2.
Table 1: Properties of fine and coarse aggregates
Properties###Fine###Coarse aggregates
###Aggregate###(Marghallah
###(River send)###Crush)
Fineness Modulus###2.32###-
Specific Gravity###2.62###2.63
Loose Bulk Density (kg/m3)###1440###1312
Compacted Bulk Density
(kg/m3)###1713###1505
Water Absorption (Percent)###1.18###1.10
Two different types of admixtures were used to improve the freshand hardened properties of the latex modified concrete. First admixtureused is named as Glenium-51, which is a new generation admixture basedon modified polycarboxylic ether. Second type of admixture was PozzolithLD-10. It is a liquid admixture which acts on the cement particles inthe mix combining the effect of a powerful plasticizer anddeflocculating agent with controlled retardation (Qazi, 2008).
Table 2: Polymer Latex used in this study
Type###Styrene butadiene rubber
Form###White Liquid
Density###1 kg/L at 25degC
Solid Content###40 (Percent)
Chloride content 60 (Percent)
Mix Design: The control concrete mixture was comprised of Portlandcement, water, coarse (Marghallah crush) and fine aggregates(Lawrencepur sand). Two control concrete Mixes (Mix I and Mix II) withdifferent aggregate to cement ratios and w/c ratios were studied. Themix proportion of both control mixes is presented in Table 3.
Table 3: Composition of Control Concretes
Concrete Constituent###Quantity (kg/m)
###Mix I###Mix II
Cement###300###400
Fine Aggregate###600###600
Coarse Aggregate###1200###1200
Water###180###200
Latex Modified Concrete (LMC): In this research, latex modifiedconcrete compositions containing 5 (Percent) , 10 (Percent) and 20(Percent) SBR latex by weight of cement were prepared. Concretecylinders were cast using these latex modified concrete to performcompressive strength and water absorption tests. Since the SBR latexused in this study contained 60 (Percent) of water, the quantity ofwater required to be added in the concrete was accordingly adjusted tokeep the water cement ratio 0.6 for Mix I and 0.5 for Mix II.
Sample Preparation: All concrete mixtures (Control concrete andLatex modified concrete) were prepared using a mechanical mixer.Cylindrical specimens of 150 mm diameter and 300 mm height were cast.The specimens were cured in a curing room at 30oC temperature and 90(Percent) relative humidity. Both control and latex modified concreteswere tested at 7 and 28 days of age to get compressive strength andwater absorption values.
Compressive strength: The compressive strength of all concretecompositions was determined following American standard testingprocedure [ASTM C39]. The compressive strength tests were conducted on auniversal testing machine. For each concrete composition threecylindrical specimens were tested. In this paper, average value of threesamples has been reported.
Water absorption: For determination of water absorption of concretespecimen, wide variety of tests has been developed in the world. Inthese tests, usually weight gain of test specimen, volume of waterentering the test specimen, depth of water penetration from surface or acombination of two is measured. Standard testing procedures to determinewater absorption of hardened concrete have been developed in the world,for example, American standards [ASTM C 642] and British standards [BS1881-122].
In this study, American standard testing procedure [ASTM C 642] isfollowed to determine water absorption of latex modified concretes. Inthis test, concrete specimens are immersed in water for 48 hours andafter that water absorbed by the specimen is measured. ASTM C642 defineswater absorption as ratio of the water absorbed to dry weight of testspecimen. The expression to calculate water absorption is given inEquation 1.
Water Absorption B - A x 100
A
where, A = Dry weight of test specimen, B = Wet weight of testspecimen after immersion in water for 48hrs
RESULTS AND DISCUSSION
Slump Tests: Slump tests were performed on both control and latexmodified concretes and the results are presented in Fig.1. It is obviousin this figure that, the addition of SBR Latex increases slump value ofconcrete.
This shows that SBR latex has plasticizing effect due to whichworkability of concrete is increased. It was observed during the slumptest that Mix II containing 20 (Percent) SBR latex collapsed and it wasnot possible to measure slump. In some cases, higher value of slump isnot desirable as it will result in segregation. Consequently, mechanicalproperties of resulting concrete will be affected adversely.
Compressive Strength: The results of the compressive strength testperformed as per ASTM C39 for Mix I and Mix II containing differentpercentage of SBR are graphically represented in Fig.2 and Fig.3,respectively, along with values of control concrete. It is observed thatin case of LMC made using Mix I with aggregate to cement ratio 6.0,compressive strength is decreased with the addition of Sika- Latex at 7days of age. On the contrary, compressive strength of concrete isincreased at 28 days of age with the addition of Sika-Latex.
In case of LMC made using Mix-II, at 7 days of age, trend similarto LMC made using Mix-I is observed i.e., addition of Sika-Latex hasadverse effect on compressive strength. All three latex modifiedconcretes exhibited value of compressive strength lesser than controlmix at 7 days of age. On the contrary, at 28 days of age, compressivestrength of LMC made using Mix-II is observed to increase with increaseof dosage of Sika- Latex. This shows that addition of Sika-Latex haspositive effect on the compressive strength of Mix-II at 28 days of age.
Decrease and increase in the compressive strength at 7 and 28 days,respectively, is due to the formation of polymer film on the surfacethat retain the internal pressure for continuing cement hydration. Inaddition to this, polymers require time for the development of polymerstructure and formation of Portland cement matrix. This polymer filmmatures with age; this is the reason that at 28 days of age, increase incompressive strength is registered with the addition of Sika-Latex.However at 7 days, the development of polymer structure and cementhydration is in process of formation, consequently the effect ofSika-Latex addition on compressive strength is negative.
Water Absorption: Water absorption values of Mix I and Mix II withdifferent dosages of SBR Latex are shown in Fig.4 and Fig.5,respectively, along with values of control mixes. In comparison to MixI-Control, water absorption of LMC was more at 7 days of age. However,at 28 days of age, all three latex modified concretes (i.e., Mix I-5(Percent) SBR, Mix I-10 (Percent) SBR and Mix II-20 (Percent) SBR)showed water absorption values lesser than the value obtained withcontrol mix. The decrease in water absorption of latex modified concretecontaining 5 (Percent),10 (Percent) and 20 (Percent) Sika-Latex at 28days is due to the formation of polymer film which makes the concretewater tight.
In case of Mix II, the results showed the same trend as observedwith Mix-I; water absorption of concrete is increased at 7 days of agewith the addition of Sika-Latex but at 28 days of age, LMC with 5(Percent) , 10 (Percent) and 20 (Percent) Sika-Latex exhibited waterabsorption value lesser than the control mix.
The results about water absorption of control and LMCs clearlydepict that at an early age, addition of locally available Sika-Latexhas adverse effects. However, with increase of age, polymer film isformed which results in reduction of water absorption of concrete.
Conclusions: Based on the results and observations made in thisexperimental research study, the following conclusions are drawn:
1. By the addition of locally available SBR latex (Sika- Latex),the slump of the concrete is increased.
2. The presence of Sika-Latex is proved to be effective to reducethe ingress of water in concrete. However, for the mixes rich in cement,the dosage of Sika-Latex should be so adjusted that the workability ofconcrete should remain in controlled limits to avoid the highly flowableconcrete due to plasticizing effect of Sika-Latex.
3. Early age compressive strength of the concrete is reduced by theaddition of Sika-latex. However, the strength is increased at 28 days ofage. In comparison to control concrete, maximum increase at 28 days was72 (Percent) with the addition of 20 (Percent) Sika-Latex in concretemix having w/c ratio 0.6 and aggregate to cement ratio 6.0 while it was31 (Percent) with addition of 20 (Percent) Sika-Latex in concrete havingw/c ratio 0.5 and aggregate to cement ratio 4.5.
4. The Sika-Latex contributes significantly to the reduction ofwater absorption of concrete at 28 days of age. On the contrary, it isseen that Sika-Latex causes increase in the water absorption of concreteat early age.
Maximum decrease in the water absorption of LMC with 20 (Percent)Sika-latex, w/c ratio 0.6 and aggregate to cement ratio 6.0 was 30(Percent) compared to control mix. In case of LMC with 20 (Percent)Sika-Latex, w/c ratio 0.5 and aggregate to cement ratio 4.5, maximumreduction in water absorption was 45 (Percent) compared to control mix.
Acknowledgement: The financial support from University ofEngineering and Technology Lahore for this experimental study is highlyacknowledged.
REFERENCES
ASTM C33-90: Specifications for concrete aggregates (1990) ASTMStandard C39: Standard Test Method for Compressive Strength ofCylindrical Concrete Specimens ASTM C642 - 06: Standard Test Method forDensity, Absorption, and Voids in Hardened Concrete (2006) BS12 - 1991:Specifications for Portland cement (1991) BS 1881-122: Testing concrete.Method for determination of water absorption (2011) Baoshan H., W. Hao,S. Xiang and G. B. Edwin. Laboratory evaluation of permeability andstrength of polymer-modified pervious concrete. Construction andBuilding Materials, 24: 818-823 (2010)
Chandra S and P. Flodin. Interactions of polymer and organicadmixtures on Portland cement hydration. Cement and Concrete Res., 17:875-90 (1987)
Joao A. R. and V.C.A. Marcos. Mechanical properties ofpolymer-modified lightweight aggregate concrete. Cement and ConcreteRes., 32; 329-334 (2002)
Lewis W. J. and G. Lewis. The influence of polymer latex modifierson the properties of concrete. Composites, 21: 487-94 (1990)
Ohama Y. Recent progress in concrete-polymer composites. AdvancedCement Based Material,5: 31-40 (1997)
Ohama Y., K. Demura, K. Kobayashi, Y. Sato and M.Morikawa. Poresize distribution and oxygen diffusion resistance of polymer-modifiedmortars. Cement and Concrete Res., 21: 309-15 (1991)
Qazi J.A. Study on water absorption of concrete using SBR Latex,M.Sc Thesis, University of Eng. and Tech. Lahore (2008) Ru W., L.Xin-Gui and W. Pei-Ming. Influence of polymer on cement hydration inSBR-modified cement pastes. Cement and Concrete Res., 36;1744-1751(2006)
Sakai E. and J. Sugita. Composite mechanism of polymer modifiedcement. Cement and Concrete Res.,25: 127-35 (1995)
Silvaa D.A., V.M. Johnb, J.L.D. Ribeiroc and H.R.Roman. Pore sizedistribution of hydrated cement pastes modified with polymers. Cementand Concrete Res., 31; 1177-84 (2001)
Zhengxian Y., S. Xianming, T.C. Andrew and M.P.Marijean. Effect ofstyrene butadiene rubber latex on the chloride permeability andmicrostructure of portland cement mortar. Construction and BuildingMaterials, 23; 2283-2290 (2009).
Civil Engineering Department, University of Engineering andTechnology Lahore, Pakistan
Graduate Student, University of Engineering and Technology Lahore,Pakistan Corresponding Author, E-mail: [emailprotected], cell no.+92-322-3064000
COPYRIGHT 2013 Asianet-Pakistan
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.