Effects of fly ash and limestone powder on the paste rheological thresholds of self-compacting concrete

Self-compacting concrete (SCC) containing composite powders has many advantages, such as its abilities to reduce the heat of hydration, optimise the particle packing, and maintain the workability better than pure cement SCC. The rheology of the paste is important for understanding the flow behaviors of SCC. This study investigates the effects of fly ash (FA) and limestone powder (LP) on the rheological thresholds of SCC pastes. By introducing a powder fitting coefficient, intrinsic viscosity, and volume fractions, the original rheological model is improved. Both models are used to predict the paste yield stress threshold and paste plastic viscosity threshold of fresh SCC. After calibrating the fitting coefficient and intrinsic viscosity of the FA and LP, the modified model can accurately predict the self-compacting paste (SCP) zone, where SCC can be obtained by mixing paste with sand and gravel. The absolute and relative accuracies of the modified model are far greater than those of the original model, except for the case of C + 30%FA, for which the modified model is superior to the original model in terms of the location of the SCP zone. SCC experiments with different coarse aggregate contents, sand properties, and powder compositions are conducted to verify the modified model, and indicate that the powder fitting coefficient and intrinsic viscosity remain constant. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigates the effects of fly ash and limestone powder on the rheological thresholds of SCC pastes, and improves the original rheological model by introducing fitting coefficients and intrinsic viscosity to predict the paste yield stress and plastic viscosity thresholds. The modified model accurately predicts the SCP zone of SCC and shows greater accuracy compared to the original model in most cases.