Effect of electrostatic repulsion induced by superplasticizers on the flow behaviour of fly ash pastes

Abstract

Effect of superplasticizers on fly ash pastes was evaluated by consistency tests (for lower water content pastes) and mini-slump tests (for higher water content pastes). Results indicate that only the polycarboxylate superplasticizers (PCEs) largely improved the flowability of fly ash pastes. Zeta potential measurements were conducted to explain the influence of electrostatic repulsion on flow behaviours of pastes with different superplasticizers. In fly ash pastes, Lignosulfonates (LS) and Polynaphthalene superplasticisers (PNS) depressed the zeta potential to more negative values, while the PCEs increased the zeta potential to less negative values. The more negative zeta potential represents higher electrostatic repulsion between particles. However, the workability results revealed that PCEs had better dispersing ability than PNS and LS. It was deduced that the steric hindrance may be the dominating mechanism for the better dispersing noticed with fly ash pastes, while the electrostatic repulsion may have no impact on dispersing of these pastes.