Effect of Superabsorbent Polymer on the Rheological Behavior and Structural Evolution of Alkali-Activated Slag

Abstract

Utilizing superabsorbent polymers (SAP) in alkali activated slag (AAS) can promote internal curing and remarkably alleviate the shrinkage of AAS. This promising additive has attracted considerable attention for its potential to enhance the performance of AAS. In this research, rheological tests, Vicat tests, and isothermal calorimetry tests were conducted to investigate the effect of SAP particle size and content on the fresh performance of AAS. For AAS containing the theoretically required amount of SAP to compensate for self-desiccation, an insignificant effect is observed on the setting time, while the rheological characteristics vary substantially. With an increase of SAP from 0% to 0.6%, AAS exhibits higher yield stress and plastic viscosity, depending on their particle size. The addition of SAP generally reduces the initial structural build-up rate, while after resting for more than 30 min, the structural build-up rate of AAS with SAP is faster than that of the reference paste without SAP. At the same SAP concentrations, AAS pastes containing larger-sized SAP exhibit higher early viscous behavior compared to those with smaller-sized SAP, while after a longer resting period, they demonstrate a more rapid structural evolution. The second hydration peaks of AAS with SAP are delayed and reduced, despite achieving more thorough hydration at 7 days. Notably, the addition of more than 0.2% SAP results in a prolonged setting time, particularly with smaller particle size, due to the varying absorptions and release rates. This study provides a theoretical support for the practical applications of SAP in AAS, specifically in terms of rheological considerations.