The Effects of Particle Packing and Inter-particle Force on Rheological Behaviors of Binary Cement Paste

This article aims to study the effects of particle packing and inter-particle force on the rheological behaviors of binary cement paste. Fly ash (FA), ground granulated blast furnace slag (GGBFS), and limestone powder (LP) were added by 10-40% of cement weight to prepare the binary binder. The particle packing of each binary binder was analyzed based on the close packing theory and bulk density test. Atomic force microscopy and direct shear method were used to investigate the Hamaker constant and friction coefficient of different binders. Fresh pastes of every binder were prepared with variable solid volume fractions (w/b is 0.50, 0.55, and 0.60), and the rheology was measured by a rotary rheometer. Eventually, two empirical models were proposed to predict the yield stress and plastic viscosity of paste based on the porosity, friction coefficient, and w/b obtained from the experiments, and the accuracy of these new models was verified by ANOVA and p-value approach. The results show that particle packing and inter-particle force play a collaborative role in determining the rheological behavior of paste. Increasing particle packing or reducing inter-particle force (i.e., decreasing porosity or friction coefficient) benefits the enhancement of paste rheology. Moreover, an increase in the Hamaker constant leads to higher friction coefficients for binders. Comparisons between the predicted and experimental results demonstrated that these empirical models accurately capture the rheological behaviors of fresh pastes.