Rheology of High-Volume Fly Ash Self-Compacting Recycled Aggregate Concrete

Effect of selected volumetric replacement (0%, 20%, 40%, and 60%) of cement with class-F fly ash in a binary binder and of three water-cementitious material ratios (0.40, 0.34, and 0.28) on rheology of self-compacting concrete (SCC) has been investigated using a coaxial concrete rheometer. The effects of the same parameters have also been studied on self-compacting recycled aggregate Concretes (SCRACs) made with 100% volumetric replacement of natural coarse aggregates with coarse recycled concrete aggregates. Data obtained from the flow-curve tests were used to calibrate selected rheological models, and it was noted that degree of shear-thinning in the SCCs and SCRACs was inversely proportional to fly ash dosage. Shear-thinning rheology transitioned to shear-thickening as the water-cementitious material ratio decreased from 0.40 to 0.28, and other mix characteristics remaining unchanged. Degree of shear thinning further decreased (in terms of increase in flow index of HB model and c/mu parameter of MB model) upon substitution of the natural coarse aggregates of SCCs with the coarse recycled aggregates in the SCRACs. Predictive efficacies of the selected rheological models are shown to be similar, and useful correlations between them have been proposed.

Automated summary

The study investigated the rheological properties of self-compacting concrete (SCC) and self-compacting recycled aggregate concrete (SCRAC) using a coaxial concrete rheometer. It found that the degree of shear thinning in both SCC and SCRAC was inversely proportional to the fly ash dosage, and shear-thinning transitioned to shear-thickening as the water-cementitious material ratio decreased. Furthermore, replacing natural coarse aggregates with coarse recycled aggregates in SCRAC further decreased the degree of shear thinning. The selected rheological models showed similar predictive efficacies and useful correlations were proposed between them.