Mechanical properties, crack width control, and self-healing of lightweight high-strength engineered cementitious composites

High-strength engineered cementitious composites (ECC) with polyethylene fiber exhibits superior strength characteristics; however, its crack width is significantly larger, which compromises both its transmission performance and self-healing capability compared to conventional ECC with polyvinyl alcohol. To this end, this study prepared a lightweight high-strength ECC by synergistically utilizing fly ash cenospheres (FAC) and expanded vermiculite (EV) as lightweight fillers. The tensile and compressive properties of ECC with different contents of FAC and EV were examined experimentally, and its self-healing behavior was verified through wet-dry cycling tests. Additionally, the microstructure of the matrix was analyzed using scanning electron microscopy. The results indicated that, compared to reference ECC with only FAC (FE0), the incorporation of EV led to a maximum increase in density of 14%, while the compressive strength decreased by up to 9%. Despite this, the maximum density reached 1777 kg/m³, and the minimum compressive strength was 65.8 MPa, still placing it within the category of lightweight, high-strength ECC. The number of cracks increased from 21 in FE0 to 123 in FE75 (a combination of EV and FAC), while the crack width decreased from 75 μm to 20 μm. These narrow cracks contributed to the near-complete self-healing of cracks within the tensile specimens, except for those that led to ultimate failure.