Synergistic interaction of polycarboxylate superplasticisers and shrinkage-reducing agent in cementitious materials from mixing consequence perspective

The issue of shrinkage can have a significant impact on the long-term performance of concrete, which can be mitigated by incorporating a shrinkage reducing agent (SRA). However, when commonly using polycarboxylate superplasticizer (PCE), the compatibility between these two admixtures becomes an uncontrollable factor that affects their synergistic effect. Therefore, this study aims to investigate the combined performance of synthesized PCE and SRA in cementitious materials under different mixing sequences: simultaneous addition, prior addition, and delayed addition. After characterizing the admixtures, we examined their effects on workability, rheology, drying shrinkage, and compressive strength. Additionally, surface tension analysis, hydration heat analysis, pore structure examination, and microstructure analysis were conducted to explore the underlying mechanisms. The results demonstrated that the separate addition of PCE and SRA effectively mitigated the adsorption competition between these two admixtures, thereby enhancing workability, reducing cement particle agglomeration, and decreasing yield stress and plastic viscosity. Pre-addition of PCE resulted in its preferential absorption, leading to a prolonged induction period of cement hydration and an accelerated phase with increased nucleation and growth of calcium silicate hydrate. Delayed introduction of PCE facilitated further reduction in surface tension within cement pores, while SRA minimized peak hydration heat flow and consequent shrinkage of the cementitious material.