Effects of delayed addition of polycarboxylate ether on one-part alkali-activated fly ash/slag pastes : Adsorption, reaction kinetics, and rheology

The admixture addition method is one of the vital factors influencing the fresh performance of ordinary Portland cement (OPC) through directly affecting the adsorption, hydration, and rheology. However, such an issue is less researched in the one-part alkali-activated materials (AAMs), which have great potentials in the industry due to their simple operation, similar to OPC. This study reports and discusses the effects of delayed polycarboxylate ether (PCE) addition at different contents on adsorption, reaction kinetics, and rheology of one-part AAMs. It is found that the delayed PCE addition had minimized the competitive adsorption phenomenon and reduced the consumption rate of PCE surfactants, which in turn facilitates easier adsorption of silicate species onto the GGBS grains. This had decreased the retardation effect of PCE, slightly improved the compressive strength, and lowered the viscosity and yield stress of the one-part AAMs. The mechanisms that govern such observations are further discussed. © 2022 Elsevier Ltd