Reduction in Interaction between Coarse Aggregate and Mortar in ...

REDUCTION IN INTERACTION BETWEEN COARSE AGGREGATE ANDMORTAR IN SELF-COMPACTING CONCRETE AT FRESH STAGEBY SUPERPLASTICIZER WITH VISCOSITY AGENTMasahiro OUCHI, Jun-ya MORIZANEKochi University of Technology, JAPANABSTRACT: The purpose of this study is to clarify an effect of a new type of superplasticizer with viscosityagent on reduction in interaction between coarse aggregate and mortar in self-compacting concrete at freshstage. The interaction was defined as an increase in shear deform resistance of the fresh mortar due to normalstress generated by the approaching coarse aggregate particles when self-compacting concrete at fresh stagedeforms。The interaction was quantified by degree of reduction in the funnel speed of the fresh mortar due tomodel coarse aggregate mixed in the mortar in this study. The degree of the reduction in the funnel speed ofmortar employing the new type of superplasticizer was smaller and the effect on the reduction of the newtype of superplastcizer was verified. Also, a correlation between the increment of water to cement ratio andthe decrement of the interaction between fresh mortar and coarse aggregate particles by employing the newtype of superplasticizer was found.KEYWORDS: self-compacting concrete, viscosity agent, friction between solid particles1. INTRODUCTIONSelf-Compacting Concrete (SCC) has not become socommon as expected when it was developed. One ofthe reasons for it should be higher material cost dueto high unit cement content of the concrete (Fig. 1).RCCforDamNormalSCCAirCementWateror PowderFineCoarseaggregateaggregate0 20 40 60 80 100Volume(%)Fig. 1 Comparison of mix-proportioning of SCCwith conventional concrete by volumeRecently, a new type of superplasticizerwith viscosity agent was developed, by which theunit cement (powder) content can be reducedresulting in lower cost [1]. The authors haveassumed the mechanism for achieving lower cementcontent, which is equal to high aggregate content inself-compacting concrete, as a reduction ininteraction between the coarse aggregate particlesand the mortar.The authors defined the interactionbetween the coarse aggregate particles and themortar in self-compacting concrete as an increase inshear deform resistance of the fresh mortar due tonormal stress generated by the approaching coarseaggregate particles when self-compacting concrete atfresh stage deforms (Fig. 2) [2]. That is a commonphenomenon as the relationship between σ and τ in

Funnel speed of concrete R cFig. 4 Larger reduction in flowability due to10.80.60.4Fine aggregate content in mortar: 40%Interaction50%Smaller0.2Coarse aggregateLargercontent : fixed00 0.5 1 1.5 2Funnel speed of mortar R mlarger interaction by higher fine aggregatecontent in mortar [Ozawa & Nagamoto]Fig. 5 Reduction in funnel speed due toReduction in funnelspeed due to interactionR mR mbinteraction between mortar and glass beads asmodel coarse aggregateConcrete for the funnel test was obtainedby mixing glass beads as model coarse aggregate andmortar. The volumetric ratio of the coarse aggregatewas 20% of the concrete according to Ouchi et. al’sexperimental result suitable for quantifying thedegree of interaction in self-compacting concrete.The specific gravity of the glass beads was 2.55g/cm 3 , which was almost the same as commoncoarse aggregate. The diameter of the glass beadswas uniformly 10 mm.The funnel speed of fresh mortar R m wasdefned as 10/t, in which t was the duration ofmortar’s discharging through the funnel (Fig. 3). Thefunnel speed of fresh concrete (mortar and glassbeads as model coarse aggregate) was defined asR mb . The funnel for R m and R mb was common.If the interaction was zero, the value of R mbwas equal to that of R m . The degree of theinteraction between fresh mortar and coarseaggregate particles was defined as (1-R mb /R m ).Larger interaction resulted in larger (1-R mb /R m ) (Fig.5).3. EFFECT OF NEW TYPE OFSUPERPLASTICIZER WITH VISCOSITYAGENT ON REDUCING ITERACTIONBETWEEN MORTAR AND COARSEAGGREGATE PARTICLESThe degree of the interaction in fresh SCC mortarand coarse aggregate (1-R mb /R m ) was obtained forfour types of mix-proportioning (Table 1). The fineaggregate content in the mortar by volume (s/m) was45%, recommended value for SCC or 50%, a littlebit higher than recommended. The materials in useare shown in Table 2. The mixing and testingprocedures are shown in Fig. 6. and Fig. 7. Thetemperature was kept constant at 20 degreecentigrade.Table 1 Mix-proportioning of mortarSP s/m W/C Sp/C (%)SP10.35 1.200.45SP20.33 1.20SP10.40 0.700.45SP20.40 0.65SP10.35 1.200.50SP20.34 1.00

SP10.45 0.700.50SP20.40 1.00Table 2 Materials in useCement (C) Ordinary portland cement(3.15 g/cm 3 )Fine aggregate Crushed limestone sand (2.68(S)g/cm 3 , F.M.: 2.72)Model coarse Glass beads (2.55 g/cm 3 ,aggregate uniform diameter of 10 mm)New type of BASF Pozzolythsuperplasticizer Grenium 6550 (1.058 g/cm 3 )(SP1)Conventional BASF Pozzolythtype of Rhoebuild SP-8RV(1.095superplasticizer g/cm 3 )(SP2)C+SW+SPFor each mix-proportioning, both R m andR mb were obtained. Each mix-proportioning wasmixed and tested three times and the average valueand standard deviation (m ± σ) were obtained. Boththe dosage of superpasticizer and water to cementratio were adjusted so that R m may be almost thesame between the conventional and the new types ofsuperplasticizers. That is because the difference inthe degree of interaction can be compared betweenconventional and new types of superplasticizer byusing R mb clearly.The experimental results of R m and R mb areshown in Fig. 8. Also, the degree of the interaction(1 – R mb /R m ) was compared in Fig. 9 (left). In all thecases except of one, it is evident that the new type ofsuperplasticizer (SP1) reduced the degree of theinteraction compared with the conventional type ofsuperplasticizer (SP2).Mixing 30 secMixing 120 secFig. 6 Mixing procedure of mortarSP1Mixing of mortarSP220 min.Funnel test forR m & R mbFig. 8 R m and R mb with each type ofsuperplasticizer and mix-proportioning-LargerR mb with SP1 compared with almost same R mb(SP1: new type; SP2: conventional type)Fig. 7 Mixing procedure of mortar

However, there was a case in which thedecrement of the interaction was not zero in spite ofthe increment of water to cement ratio of zero. Thatmay be due to another effect of the new type ofsuperplasticizer in which the polymer itself canreduce the interaction. Further research on it isnecessary.superplasticizer was found. It can be a factor formechanism of the effect of the new type ofsuperplasticizer.Further investigation is necessary forclarifying the mechanism for reducing theinteraction.5. CONCLUSIONSThe purpose of this study is to clarify an effect of anew type of superplasticizer with viscosity agent onreduction in interaction between mortar and coarseaggregate particles in self-compacting concrete atfresh stage. The interaction was defined as anincrease in shear deform resistance of the freshmortar due to normal stress generated by theapproaching coarse aggregate particles whenself-compacting concrete at fresh stage deforms. Theinteraction was quantified by degree of reduction inthe funnel speed of the fresh mortar due to modelcoarse aggregate mixed in the mortar in this study.The following items were clarified in thisstudy:REFERENCES[1]http://www.pozzolith.basf.co.jp/ja/products/Documents/SDC.pdf[2] Ouchi, M., Edamatsu, Y., Ozawa, K. andOkamura, H.: "A simple evaluation method forinteraction between coarse aggregate and mortarparticles in self-compacting concrete," Transactionsof the Japan Concrete Institute, pp.1-6, Vol.21,February 2000.[3] Okamura, H., Ozawa, K. and Ouchi, M."Self-compacting concrete," fib Journal "StructuralConcrete," pp.3-17, March 2000.[4] Nagamoto, N., Ozawa, K.: Mixture properties ofself-compacting high performance concrete, HighPerformance Concrete: Design, Materials andAdvances in Concrete Technology, ACI Sp-172,pp.623-636, 1997.(1) The degree of the reduction in theinteraction between fresh mortar and coarseaggregate particles employing the new type ofsuperplasticizer was smaller. It is possible that theeffect on the reduction in friction between solidparticles by the new type of superplastcizer wasverified.(2) A correlation between the increment ofwater to cement ratio and the decrement of theinteraction between fresh mortar and coarseaggregate particles by employing the new type of