Crack-Width Threshold-Guided Design of Self-Healing Polyethylene Fiber-Reinforced Engineered Cementitious Composites (ECCs)

Polyethylene (PE) fibers enable engineered cementitious composites (ECCs) to achieve tensile strain-hardening and multiple-cracking behavior through fiber bridging; however, the relatively large crack widths that can develop in PE fiber-reinforced high-strength ECC (HS-ECC) may limit its autogenous self-healing capability. This study therefore establishes a direct link between PE fiber-mediated crack control, matrix micromechanical tailoring, and autogenous self-healing. The critical crack-width thresholds for reliable self-healing were first determined using water sorptivity tests combined with wet–dry cyclic exposure. The results showed that transport properties could be restored to nearly their original levels when crack widths were below approximately 50 μm in tap water and 60 μm in seawater. Based on these thresholds, waste fly ash ceramsite (FAC) was subsequently incorporated to tailor the matrix fracture characteristics and promote saturated multiple cracking under PE fiber bridging. Replacing 20% of quartz sand with FAC increased the tensile strain capacity from 2.75% to 7.14% and the crack number from 17 to 61, while reducing the average crack width from 110 μm to approximately 49 μm. The refined crack pattern enabled reliable autogenous self-healing under wet–dry cycling, with seawater exhibiting particularly favorable healing behavior. These findings provide a micromechanics-based strategy for designing sustainable PE fiber-reinforced HS-ECC with enhanced ductility, crack control, and intrinsic self-healing capability.