Influence of Coarse Cement Particle Content on Intrinsic Self-Healing of Mortar

This study investigated the effect of coarse cement on the self-healing ability of mortar. Coarse cement, prepared via negative-pressure screening, was substituted (0–40%) in mortar mixes with water/cement (w/c) ratios of 0.45–0.55. The specimens were cured for 28 days, cracked, and allowed to self-heal for another 28 days. Self-healing was evaluated based on compressive strength recovery and ultrasonic pulse velocity. At a 0.50 w/c ratio, 10% coarse cement substitution achieved 87.7% strength recovery (21.2 MPa increase), outperforming the control group (74.1%, 13.0 MPa). Reducing the w/c ratio to 0.45 further enhanced recovery to 89.4% (21.5 MPa). While coarse particles alone reduced the initial strength, combining their addition (e.g., 10%) with a lower w/c ratio (0.45) improved self-healing without significant strength loss. Based on the Krstulović–Dabić model and a micro-geometric model incorporating hydration units, this study analyzed the intrinsic self-healing mechanism of cement-based materials through computational results. Theoretical calculations demonstrated that during cement hydration, coarser particles can form a microcapsule-like structure where hydration products encapsulate unhydrated cement. The findings suggest that optimizing coarse particle content and the w/c ratio can balance self-healing enhancement and mechanical performance, offering a viable strategy for energy saving and emission reduction by reducing the carbon emissions per unit of service life and the grinding process in cement production.