Effects of kaolin-modified superabsorbent polymers on mortar properties

Abstract

This study investigates the impact of kaolin-modified superabsorbent polymers (SAPs) as internal curing agents on mortar properties. While SAPs have been known to mitigate the shrinkage of cement-based materials, their adverse effects on strength have limited their applicability. In this paper, the strength and shrinkage of mortars with varying SAP proportions were measured, along with an assessment of internal porosity and hydration conditions. Results indicate that kaolin-modified SAPs effectively reduce autogenous and drying shrinkages in mortars. Although modified SAPs influenced pore size distributions, resulting in reduced strength, higher content of kaolin composite strengthened the bond between SAPs and cement-based materials. This enhanced the spherical shape of SAPs and facilitated the release of internally stored water through capillary action, thereby increasing the contact area between cement slurry and water. Consequently, mortar hydration was promoted. Moreover, higher acrylamide content in modified SAPs improved alkali and Ca2+ resistance, increased the water absorption ratio, optimized the internal maintenance effect, and reduced the loss of flexural and compressive strength in mortars.