Effect of internal curing by superabsorbent polymers on the densification and microstructural development of cementitious materials exposed to different environmental conditions

Superabsorbent polymers (SAPs) are among the internal curing agents used in cementitious materials. This study aims to evaluate the influence of wider SAP dosages under different exposure environments on the microstructural densification of cementitious materials and the development of strength and durability based on this. With SAP incorporation, hydrate crystallization most easily occurs in the wet/dry condition through hydration with externally supplied water and by internal SAP curing, which leads to the formation of the densest microstructures. Microstructure densification further progresses as the SAP dosages increase. Despite the internal curing effect of SAPs, the ultrasonic pulse velocity and the compressive strength of S0.5 specimens compared with those of the REF specimens decrease due to SAP void presence. However, these mechanical properties of the S1.0 specimens are all recovered at later ages when exposed to the wet/dry condition, forming densest microstructures. As the SAP dosages increase, the sealing effect of SAPs improves the water permeability characteristics at early ages. The lowest water permeability coefficient is observed in the S1.0 specimen exposed to the wet/dry condition as the further hydration effect of SAPs is exerted with increasing ages. In conclusion, utilizing the appropriate amount of SAPs and environmental conditions can effectively densify the internal pore structures, thereby securing the mechanical and durable properties of concrete structures.