Effect of hydrogel microcapsule on shrinkage and mechanical properties of cement mortars

Superabsorbent polymer (SAP) shows a good internal curing effect in cement-based materials, but its volume changes greatly after it releases water. This occurrence causes adverse effects on the properties of cement-based materials. Microcapsules were prepared with calcium alginate hydrogel as the shell and epoxy resin as the core material to mitigate these adverse effects. The effects of microcapsules on the shrinkage and mechanical properties of cement mortars were analysed by observing such parameters as the heat of hydration and relative humidity of the mortars, and such techniques as mercury intrusion porosimetry. The results showed that microcapsules can delay the hydration of cement and provide a superior early shrinkage reduction effect when compared with SAP. In addition, the presoaked microcapsules left pores that were smaller in diameter than those observed in the SAP mortars. As a result, the influence of microcapsules on the mortar's compressive strength was found to be less than that of SAP. Therefore, the compressive strength of the mortars containing microcapsules was essentially the same as that of the mortars containing SAP when the presoaked microcapsule content was 35 times that of the presoaked SAP content.