KSCE Journal of Civil Engineering (2012) 16(5):803-808DOI 10.1007/s12205-012-1373-3

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www.springer.com/12205

Structural Engineering

Effects of Polymer-Binder Ratio and Slag Content on Strength Properties ofAutoclaved Polymer-Modified Concrete

Byeong Cheol Lho*, Myung Ki. Joo**, Kyu Hyung Choi***, and Jong Yun Choi****

Received November 2, 2010/Revised April 23, 2011/Accepted November 1, 2011

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Abstract

The effects of polymer-binder ratio and slag content on the strength properties of autoclaved SBR-modified concrete using groundgranulated blast-furnace slag and styrene-butadiene rubber latex are examined. As results, the compressive and tensile strength of theautoclaved SBR-modified concrete using slag are higher at a slag content of 40%, and are increasing according to polymer-binderratio. In particular, the autoclaved SBR-modified concrete with a slag content of 40% is about three times higher tensile strength thanunmodified concrete. Such a high strength development is due to the improved bond between cement hydrates and aggregatesbecause of the incorporation of SBR latex. From the point of deteriorated physical properties and changed infrared spectra, theapplication of autoclaving under saturated Ca(OH)2 solution immersion causes no degradation for SBR polymer films.Keywords: autoclave curing, polymer-modified concrete, polymer-binder ratio, slag content, Styrene-Butadiene Rubber (SBR) latex

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1. Introduction

Ground Granulated Blast-Furnace Slag (GGBFS) has widelybeen used as an admixture for the purpose of improving long-term strength and durability, and reducing heat of hydration andalkali-aggregate reaction (Saraswati and Basu, 2006; Yamamotoet al., 2007; Bahador, and Jong, 2007; Kumar et al., 2008;Yuksel et al., 2006). In general, autoclave curing or autoclavingis applied to precast concrete products for the development of thestrength equivalent to 28 d under ambient temperature within 24h, substantially less shrinkage and reduced efflorescence (Sharaand Chaturvedi, 1997; Menzel, 1934; Honda et al., 1995).

The application of autoclaving is anticipated to cause degrada-tion of the polymer films due to exposure to high temperature andpressure. However the strength development of the autoclavedpolymer-modified concretes may depend largely on the type ofpolymer and mineral admixture (Joo et al., 1999). The autoclavedSBR-modified concretes using GGBFS are expected to excellentproperties, such as high strengths, adhesion, water resistance anddurability.

In this paper, the effect of the autoclave curing conditions,polymer-binder ratio and slag content on the strength propertiesof the autoclaved polymer-modified concrete using groundgranulated blast-furnace slag with SBR latex are examined tohave better strength and durability.

2. Materials

2.1 CementOrdinary Portland cement as specified in KS (Korean Standard)

L 5201 (Portland cement) was used as a cement. The Propertiesof the cement are given in Table 1.

2.2 Mineral and Polymeric AdmixturesGGBFS was used as a mineral admixture. The properties of

the slag are listed in Table 2.Styrene-Butadiene Rubber (SBR) latex was employed as a

polymeric admixture. The properties of the SBR latex are listedin Table 3. Before mixing, a silicone emulsion–type antifoamerwas added to the SBR latex in a ratio of 0.7%, which is theratio of the silicone solids to the total solids of the SBR latex.

*Member, Professor, Dept. of Civil Engineering, Sangji University, Wonju 220-702, Korea (E-mail: bclho@sangji.ac.kr)**Member, Research Professor, Dept. of Civil Engineering, Sangji University, Wonju 220-702, Korea (Corresponding Author, E-mail: joomyk@sangji.

ac.kr)***Member, Ph.D. Student, Dept. of Civil Engineering, Sangji University, Wonju 220-702, Korea (E-mail: choikyuhyung@nate.com)

****Ph.D. Student, Dept. of Civil Engineering, Sangji University, Wonju 220-702, Korea (E-mail: indi721@nate.com)

Table 1. Physical Properties and Chemical Compositions of Cement

Density(g/cm3)

Blaine SpecificSurface(cm2/g)

Setting Time(h-min)

Compressive Strengthof Mortar (MPa)

Initial Set Final Set 3d 7d 28d3.16 3290 2-22 3-31 29.5 44.1 61.5

Chemical Compositions (%)MgO SiO2 Al2O3 SO3 CaO FeO K2O ig. loss1.4 22.7 4.8 2.0 63.8 2.3 0.8 1.9

Byeong Cheol Lho, Myung Ki. Joo, Kyu Hyung Choi, and Jong Yun Choi

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2.3 Fine and Coarse AggregatesRiver sand (maximum size = 2.5 mm) was used as a fine

aggregate and river gravel (maximum size = 20 mm) used as acoarse aggregate. The physical properties of the aggregates aregiven in Table 4.

3. Testing Procedures

3.1. Durability Test of Polymer Films under AutoclavingPolymer films 200×200×1 mm were cast with SBR latex on

glass plates, dried at 30oC for 1 d, and at 20 oC and 60%(RH) for

5 d. The polymer films immersed in a saturated Ca(OH)2 solu-tion were exposed to autoclaving at a maximum temperature of180 oC under a pressure of 1.01 MPa for 7 h. The temperaturerise rate until 180oC was 60 oC/h. Dumbbell No.2 specimens wereprepared from the polymer films before and after autoclaving,and tested for tensile strengths and elongation at a crossheadspeed of 50 mm for tensile strength and elongation according toKS M 6518 (Physical test methods for vulcanized rubber). Thesamples extracted by toluene from the polymer films before andafter autoclaving were determined in the wave number range of4000 to 400 cm-1 by infrared spectroscopy.

3.2 Preparation of SpecimensAccording to KS F 2403 (Method of making and curing

concrete specimens), polymer-modified concretes were mixedwith polymer-binder ratios (P/B) of 0, 5, 10, 15 and 20%. Theirslump values were adjusted to be constant at 10.0±1.0 cm bychanging water-binder ratios. Cylindrical specimens (Ø100×200mm) for compressive and splitting tensile strengths were molded,and pre-cured at 20oC and 80%(RH) for 2 d, and then subjectedto an autoclave curing at a maximum temperature of 180oC undera pressure of 1.01 MPa for 7 h. Before mixing of the polymer-modified concrete, the binders were prepared by blending cementand mineral admixture (GGBFS) by use of a small ball mill for4h. The cement to mineral admixture (GGBFS) ratios (by mass)of the binders were 100:0, 70:30, 60:40 and 50:50, correspondingto slag contents (SL) of 0, 30, 40 and 50%. The mix proportions ofautoclaved SBR-modified concrete using slag are given in Table 5.

3.3 Determination of Pore Size DistributionThe samples 3×3×3 mm which had been taken from cured

Table 2. Properties of GGBFS

Density(g/cm3)

Blaine SpecificSurface (cm2/ g)

Percent Flow(%)

Activity Index (%)7 d 28 d 91 d

2.91 10,070 87 128 115 106 Chemical Compositions (%)

MgO SiO2 Al2O3 SO3 CaO FeO K2O ig. loss Cl- Basicity5.58 33.5 13.8 0.12 45.4 1.3 0.3 < 0.05 0.003 1.89

Table 3. Properties of SBR LatexType of Polymer

DispersionDensity

(20oC, g/cm3)pH

(20 oC)Viscosity

(20 oC, mPa·s)Total Solids

(%)SBR 1.00 9.4 64 44.8

Table 4. Properties of Aggregates

Type ofAggregate

MaximumSize

(mm)

FinenessModulus

BulkDensity(kg/l)

Density(g/cm3)

WaterAbsorption

(%)River Sand 2.5 2.60 1.60 2.54 2.29

River Gravel 20 6.68 1.62 2.53 1.95

Table 5. Mix Proportions of Autoclaved SBR-Modified Concrete Using GGBFS

Slag Content(%)

Slump(cm)

Air Content(%)

Polymer- Binder

Ratio (%)Water-Binder

Ratio (%)Sand-

AggregateRatio (%)

Unit WaterContent

(%)

Mix Proportions by Mass (kg/m3)

Ce-ment Slag Poly-mer Sand Gr-avel

0

10.0 3.0 0 60.0 40 180

300 0

0 706 10559.5 2.8 5 53.0 40 159 15 714 10679.5 2.3 10 49.0 40 147 30 716 107010.0 2.0 15 42.0 40 126 45 726 108410.5 1.9 20 38.0 40 114 60 723 1081

30

10.5 3.1 0 58.0 40 174

210 90

0 709 105910.5 2.7 5 53.0 40 159 15 713 106510.0 2.2 10 49.0 40 147 30 715 10689.5 2.0 15 42.0 40 126 45 723 108010.0 1.8 20 38.0 40 114 60 722 1079

40

10.0 2.9 0 57.0 40 171

180 120

0 713 106510.5 2.5 5 52.0 40 156 15 717 107110.0 2.0 10 48.0 40 144 30 719 107410.5 1.8 15 41.0 40 123 45 727 108610.5 1.8 20 37.0 40 111 60 724 1082

50

10.0 2.8 0 57.0 40 171

150 150

0 713 10669.5 2.2 5 52.0 40 156 15 719 107510.5 1.9 10 48.0 40 144 30 719 10759.5 1.8 15 41.0 40 123 45 726 108510.0 1.7 20 37.0 40 111 60 727 1087

Effects of Polymer-Binder Ratio and Slag Content on Strength Properties of Autoclaved Polymer-Modified Concrete

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cylindrical specimen were cleaned with acetone, and then treatedby D-dry method. The pore size distribution of the treatedsamples was determined in the pore radius range of 3.75 to 7500nm by mercury intrusion proximity. The total pore volume of thesamples was calculated using the pore size distribution data.

3.4 Compressive and Tensile Strength TestsThe cylindrical specimens were tested for compressive strength

according to KS F 2405 (Method of test for compressive strengthof concrete). During the compressive strength test, compressivestrain was measured by wire type strain gages (gage length : 60mm) to estimate the modulus of elasticity.

The cylindrical specimens were also tested for splitting tensilestrengths according to KS F 2423 (Method of test for splittingtensile strength of concrete).

4. Test Results and Discussion

4.1 Durability of SBR Polymer FilmsTable 6 and Fig. 1 show the physical properties and infrared

spectra of SBR polymer film before and after autoclaving in asaturated Ca(OH)2 solution, respectively. The durability of SBRpolymer film is evaluated from the points of the deterioratedphysical properties and changed infrared spectra, in comparisonwith the physical properties and infrared spectra of SBR polymerfilm before and after autoclaving under the saturated Ca(OH)2

solution immersion, the reductions in the tensile strength and

elongation of SBR polymer film are about 25%, and a change inthe infrared spectra is not recognized.

4.2 Pore Size DistributionFigures 2 and 3 show the pore size distributions of autoclaved

SBR-modified concrete with slag contents of 0, 30, 40 and 50%at polymer-binder ratios of 0 and 20%, respectively. Fig. 4 givesthe relationship between the slag content and total pore volumeof the autoclaved SBR-modified concrete with slag contents of0, 30, 40 and 50% at polymer-binder ratios of 0 and 20%.Regardless of the slag content, the incorporation of SBR latexinto the autoclaved unmodified concrete causes a decrease in thetotal pore volume, but leads to a lesser effect on the pore sizedistribution. However, the largest peaks of the pore volume in thepore size distributions of the autoclaved SBR-modified andunmodified concretes tend to move from the larger pore radii tothe smaller pore radii. Such movements of the largest peaks tothe smaller pore radii mean that the smaller pores are increased,and are found to be a factor of contribution for an improvementin the strength. The total volume of the autoclaved SBR-modified and unmodified concrete is hardly affected by theGGBFS content.

Fig. 1. Infrared Spectra of SBR Polymer Films before and afterAutoclave Curing in Saturated Ca(OH)2 Solution

Fig. 2. Pore Size Distribution of Autoclaved Unmodified Concrete with GGBFS

Table 6. Physical Properties of SBR Polymer Films before andafter Autoclave Curing in Saturated Ca(OH)2 Solutions

BeforeAutoclave

Curing

Appearance Transparent filmTensile Strength (MPa) 6.67

Elongation (%) 922

After AutoclaveCuring in SaturatedCa(OH)2 Solution

Appearance Whitened film with some shallow depressions

Tensile Strength (MPa) 7.57Tensile Strength

Change (%) +13

Elongation (%) 798Elongation Change (%) -13

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4.3 Compressive StrengthFigures 5 and 6 illustrate the relationship between the slag

content and compressive strength of autoclaved SBR-modifiedconcrete using GGBFS with polymer-binder ratios of 0, 5, 10, 15and 20%, and the relationship between the polymer-binder ratioand compressive strength of the autoclaved SBR-modified con-crete with GGBFS contents of 0, 30, 40 and 50%, respectively.Regardless of the polymer-binder ratio, the compressive strengthof the autoclaved SBR-modified concrete using GGBFS increaseswith increasing GGBFS content, and reaches a maximum atGGBFS contents of 30 to 40%. The compressive strength tendsto increase with increasing polymer-binder ratio irrespective ofthe GGBFS content.

From the above results, such a high compressive strength de-velopment is attributed to the formations of the denser micro-structures by the 11Å tobermorite produced as the result of theaccelerated pozzolanic reaction between the GGBFS and portlandcement, and the marked water-reducing effect and improvedbonds between cement hydrates and aggregates due to theincorporation of SBR latex. In particular, Photo 1 demonstratesthe improved bonds between the cement hydrates and aggregates.In the autoclaved unmodified concrete, adhesive failure occurs atthe interfaces between the cement hydrates and aggregates, andthe traces (* is put in Fig. 7) on which coarse aggregates were

fallen out as seen in Fig. 7. By contrast, in the autoclaved SBR-modified concrete, adhesive failure does not occur at the inter-faces between the cement hydrates and aggregates, and manycoarse aggregates were failed, that is, the cohesive failure of thecoarse aggregates is observed as seen in Fig. 7. To make clear themechanism of such improved bonds, the microstructures of thetransition zone are currently investigated by the authors. Asmentioned above, the high strength development is explained onterms of the movements of the highest peaks of the pore volume

Fig. 3. Pore Size Distribution of Autoclaved SBR-modified Concrete with GGBFS

Fig. 4. GGBFS Content versus Total Pore Volume of AutoclavedSBR-modified Concrete

Fig. 5. GGBFS Content versus Compressive Strength of Auto-claved SBR-Modified Concrete

Fig. 6. Polymer-binder Ratio versus Compressive Strength of Auto-claved SBR-modified Concrete

Effects of Polymer-Binder Ratio and Slag Content on Strength Properties of Autoclaved Polymer-Modified Concrete

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from the larger pore radii to the smaller pore radii and a decreasein the total pore volume at both high GGBFS content andpolymer-binder ratio.

Figures 8 and 9 show the relationship between the GGBFScontent and modulus of elasticity of autoclaved SBR-modifiedconcrete using GGBFS with polymer-binder ratios of 0, 5, 10, 15and 20%, and the relationship between the polymer-binder ratioand modulus of elasticity of the autoclaved SBR-modified con-crete with GGBFS contents of 0, 30, 40 and 50%, respectively.The modulus of elasticity of the autoclaved SBR-modified con-crete using GGBFS tends to increase with increasing GGBFScontent and polymer-binder ratio, and to reach maximums atGGBFS content of 40%, and a polymer-binder ratio of 15%,

respectively. Although the modulus of elasticity of the SBRpolymer films formed in the autoclaved SBR-modified concretewas lower than that of the cement hydrates, it is considered thatthe modulus of elasticity of the autoclaved SBR-modified concreteis increased until a polymer-binder ratio of 15% by the samereasons as those for the above-mentioned compressive strengthdevelopment.

4.4 Tensile StrengthFigures 10 and 11 show the relationship between the GGBFS

content and tensile strength of autoclaved SBR-modified concreteusing GGBFS with polymer-binder ratios of 0, 5, 10, 15 and20%, and the relationship between the polymer-binder ratio andtensile strength of the autoclaved SBR-modified concrete withGGBFS contents of 0, 30, 40 and 50%, respectively. Regardlessof the polymer-binder ratio, the tensile strength of the autoclavedSBR-modified concrete using GGBFS increases with increasingGGBFS content, and reaches maximum at a GGBFS content of40%. Irrespective of the GGBFS content, the tensile strength isgreatly increased with an increase in the polymer-binder ratio.Especially, the tensile strength of the autoclaved SBR-modifiedconcrete with a GGBFS content of 40% and a polymer-binder

Fig. 7. Cross Sections of Specimens after Strength Test: (a) Un-modified Concrete, (b) SBR-modified Concrete using GGBFS

Fig. 8. GGBFS Content versus Modulus of Elasticity of AutoclavedSBR-modified Concrete

Fig. 9. Polymer-binder Ratio versus Modulus of Elasticity of Auto-claved SBR-modified Concrete

Fig. 10. GGBFS Content versus Tensile Strength of AutoclavedSBR-modified Concrete

Byeong Cheol Lho, Myung Ki. Joo, Kyu Hyung Choi, and Jong Yun Choi

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ratio of 20% is about three times higher than that of unmodifiedconcretes with a slag content of 0%. This is due to the addition ofthe tensile strength of the polymer films formed in the autoclavedSBR-modified concrete using GGBFS to cement hydrates andthe improved bonds between the cement hydrates and aggregates,developed by the polymer films as seen in Fig. 12.

The compressive and tensile strengths of autoclaved SBR-modified concrete using GGBFS are improved by an increase inthe polymer-binder ratio. This tendency is marked in the tensilestrength of the autoclaved SBR-modified concrete. In addition,the autoclaved SBR-modified concrete using GGBFS with higherpolymer-binder ratio provide higher compressive and tensilestrengths than combined wet/dry-cured [2 d-20oC -80%(RH)moist-plus 5 d-20oC -water-plus 21 d-20oC -60% (RH)-dry-cured]SBR-modified concretes (Ohama and Kan, 1982).

5. Conclusions

There is no degradation for SBR polymer films due to theapplication of autoclaving under saturated Ca(OH)2 solution, andthe total pore volume of autoclaved SBR-modified concretestends to slightly decrease by the incorporation of slag and SBRlatex. The autoclaved polymer-modified concrete has highercompressive and tensile strengths than normal polymer concrete

due to the use of GGBFS, and the elastic modulus also tends toincrease with higher slag content and polymer-binder ratio, andthey reach a maximum values at 40% of slag content and 15% ofpolymer-binder ratio.

Acknowledgements

This study was supported by Sangji University, and the authorsare grateful to Sangji University.

References

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Fig. 11. Polymer-binder Ratio versus Tensile Strength of Autoclav-ed SBR-modified Concrete

Fig. 12. Microstructures of Autoclaved SBR-modified Concreteusing GGBFS