Rheological study of cement paste with metakaolin and/or limestone filler using Mixture Design of Experiments

Abstract

Several cement pastes with different amounts of metakaolin (MK) and/or limestone filler (LF) were prepared. The water/cementitious materials ratio was maintained constant at 0.3, with addition of 0.5%wt/wt of poly-carboxylate ether (PCE) superplasticizer admixture. The following parameters of the fresh cement pastes were evaluated: the slump and spread, the Marsh funnel time, the plastic viscosity, yield stress, viscoelastic properties and thixotropy. After the curing of 7day old pastes, compressive strength tests were performed according to the Brazilian standard using 50×100mm cylinder specimens. We conclude that LF alone is not able to avoid segregation or bleeding, and there is no difference between cement pastes mixed with LF and pure OPC pastes, in terms of rheology. On the other hand, if one needs low slump and low spread, the use of MK is recommended because this material creates a strong, thixotropic interconnected net inside of the paste, increasing the yield stress and the thixotropy of the cement paste. By adding 5–10%wt/wt MK, the average increase of compressive strength is approximately 45% at 7days, compared to the control (only OPC, water and PCE). The maximum recommended amount of LF or MK substitution in our case was 10%wt.