A Comparative Study on Superabsorbent Polymer and Recycled Lightweight Aggregate as Internal Curing Agents for High-strength Concrete

High-strength concrete is more sensitive to changes in curing conditions and has a higher tendency to crack. To mitigate shrinkage and sensitivity to curing conditions, various methods, such as internal curing (IC) agents, have been proposed. Various types of materials, including pumice, ceramic aggregates, recycled concrete aggregates, perlite, and superabsorbent polymers (SAP), have been used for internal curing. Due to the difference in absorption content and rate of water absorption and desorption between SAP and recycled lightweight aggregate, their effect on the properties of high strength concrete can be different. This study explores the impact of IC using SAP on compressive strength, plastic shrinkage, and restrained shrinkage from drying in HSC, comparing it with IC using recycled lightweight aggregate (LWA).The utilization of pre-soaked SAP as an IC agent resulted in a minor enhancement in the workability of concrete. The use of LAW has reduced the workability of concrete. Because the shape of LAW particles is crushed, unlike SAP spherical particles. The results showed that pre-saturation with a superabsorbent polymer or recycled LWA slightly boosts compressive strength under drying conditions. The compressive strength of compounds with SAP and LAW in drying conditions was lower than that of the control mixture in standard curing conditions. This suggests that despite the favorable impact of IC with SAP and LAW on compressive strength, it does not fully address the decrease in concrete strength resulting from unfavorable curing. Regarding the effect of IC on shrinkage cracks, while IC with a recycled LWA proves more effective in reducing restrained shrinkage, IC with a superabsorbent polymer is more efficient in mitigating plastic shrinkage and minimizing concrete cracking risks.