Effect of superabsorbent polymer (SAP) on the early hydration and macro-properties of cement paste: A novel perspective based on water migration

The water absorption-release characteristic of SAP will change the water distribution of cement paste, thereby affecting the hydration kinetics. In this study, the effect of SAP on the early hydration and macroscopic properties of cement paste was investigated in situ from the perspective of water migration. The results showed that within the first 24 hours, the water absorption of SAP significantly effected cement hydration kinetics, reducing non-surface water content, shortening the induction period, and lowering peak heat release, which in turn decreased setting time and fluidity. The entrained extra water could offset the effect of SAP on hydration during this period. From 24 hours to 7 days, the water released from SAP compensated non-surface water, enhancing continuous hydration. Compared to pure cement paste, more hydration products refined the pore structure, increasing gel and small capillary pores, which reduced autogenous shrinkage and improved compressive strength. At this stage, the increase in the amount of extra water alone did not amplify the effect of SAP on cement hydration. It was only when both the amount of SAP and the extra water it absorbed increased simultaneously that a promoting effect on cement hydration was observed. Overall, this study provides new insights into how SAP influences cement hydration through water migration.