Mitigating shrinkage of alkali-activated slag by polypropylene glycol with different molecular weights

Abstract

In this work, the influence of polypropylene glycol (PPG), as the shrinkage-reducing admixture (SRA), on the fresh and hardened properties of alkali-activated slag (AAS) paste is studied. The flowability, setting time, compressive strength, pore structure, and drying shrinkage performance of AAS with PPG of three different molecular weights (i.e., PPG400, PPG1000, and PPG2000) at two addition dosages (i.e., 0.5% and 1.0% by slag mass) are evaluated. The results show that PPG addition slightly affects the flowability and setting behaviors of AAS, but retards its strength development likely due to the inhibiting effect of polymer agglomerates in PPG on slag dissolution and reaction. The PPG400 shows a higher shrinkage mitigation efficiency in AAS systems than its counterparts with a higher molecular weight. Nevertheless, the beneficial shrinkage mitigation role of PPG addition is merely significant in the AAS dried under a relatively low relative humidity level. The mechanism by which PPG addition mitigates shrinkage of AAS is attributed to the combinational effects of surface tension reduction of pore solution and coarsening of pore structure.