Effect of Particle Contact and High-Range Water-Reducing Admixture Adsorption on Rheology of Cement Paste
Jiang Zhu, Jiaping Liu, Kamal H. Khayat, Xin Shu, and Zhen Li
Appears on pages(s):
energy dissipation; particle contact; particle flocculation; surface coverage; viscosity; yield stress
This paper investigates the effect of the dosage rate of polycarboxylate ether (PCE) high-range water-reducing admixture and the water-powder ratio (w/p) on the rheological properties of cement paste added with 10% limestone powder. Qualitative approaches describing particle flocculation and energy dissipation mechanisms that can influence rheological properties are proposed by taking into account the degree of contact between the powder particles and the surface coverage of the powder particles by the PCE polymer. Test results show that the variations of the yield stress and viscosity of the cement pastes with changes in the w/p and PCE dosage are essentially affected by the coupled effect of the particle contact and surface coverage. Particle contacts can be enhanced by reducing the w/p. With the decrease of the w/p, the surface coverage of the powder particles decreases for a given PCE dosage, while it increases with the increase of the PCE dosage, indicating a reduction in colloidal interactions. Particle flocculation can be weakened as a combined result of the decrease in colloidal interactions and the enhancement of particle contacts. This can reduce the energy dissipated to break the internal particle network to initiate the flow of the cement paste and yield stress. Moreover, the energy dissipation inside the interstitial fluid between the powder particles can decrease with the increase of the surface coverage of the powder particles by the PCE. This can reduce the energy dissipation needed to maintain the flow of cement paste, despite the enhancement of the particle contacts. Residual viscosity is shown to decrease with the reduction of energy dissipation.