Enhancing Self-Healing and Plastic Shrinkage Reduction in Superabsorbent Polymer (SAP) Concrete: Synergistic Effects of Micro-silica and Fly Ash

Concrete is susceptible to cracks that may arise from shrinkage under tensile stress, which reduces its mechanical strength and endangers the durability of structures. Superabsorbent polymers (SAP) have emerged as promising self-healing agents as they can reduce crack closure and help mitigate plastic shrinkage. However, incorporating SAP may increase porosity, reduce workability, and negatively influence the mechanical properties of cementitious composites. This study utilized micro-silica (MS) and fly ash (FA) to counteract the reduction in compressive strength and workability caused by SAP while enhancing the self-healing performance of mixtures incorporating these supplementary cementitious materials (SCMs). Thirteen mix proportions with varying SAP, MS, and FA replacements were analyzed to assess their effect on self-healing efficiency, mechanical performance, and shrinkage resistance. These specimens were preloaded to generate micro-cracks, and these pre-cracked specimens were exposed to a wet–dry cycle. The results demonstrate that the combination of SAP (0.2–0.4%) with FA (15–30%) accelerates crack closure and recovers workability up to 28%, while MS (3–5%) densifies the matrix, reducing permeability and recovering compressive strength up to 17%. Notably, a mixture of 0.4% SAP, 5% MS, and 15% FA achieves a maximum crack closure ratio of 97%, recovering the lost workability and restoring full compressive strength in the long term. This study represents a practical way to incorporate SAP for self-healing quality while maintaining workability and strength with the optimum proportions of MS and FA. The findings can contribute to developing long-lasting, self-healing concrete for real-world implications.