Effects of Hydrogel on Early Hydration and Microscopic Properties of Cementitious Materials

The incorporation of hydrogel into cementitious systems is a promising approach to mitigating issues related to shrinkage and cracking, and to improving the self-healing of conventional portland cement. However, the mechanism by which hydrogels affect cement hydration remains unclear. Therefore, this study analyzed the effects of hydrogel on the hydration, microstructure, physical, electrochemical, and mechanical properties of cement. Hydrogel was prepared via the physical freeze–thaw method using polyvinyl alcohol (PVA), nanocrystalline cellulose (NCC), and polyethylene glycol (PEG). Our findings show that the hydrogel forms a three-dimensional network structure. In this structure, the NCC gel film creates a large skeleton, PVA forms a small skeleton, and PEG enhances the complexity of the network. Although hydrogel inhibits the early hydration rate of cement, it promotes the generation of hydration products at later stages. Notably, the addition of hydrogel does not result in new hydration products. When the hydrogel dosage was 3.0%, the initial setting time increased by 146 min, and the final setting time increased by 135 min. The Ca ( OH ) 2 formation of cementitious material increased by 0.406% compared with that of cement slurry. Hydrogels offer new conductive paths for cementitious materials. The porosity of harmful pores and very harmful pores increases from 0.16% and 0.34% to 0.58% and 0.69%, respectively. Hydrogel significantly alters hydration properties. The insights gained from this study provide a better understanding of the role of hydrogel in cement hydration and pave the way for the development of advanced cementitious materials with low shrinkage cracking.