Comprehensive performance of ECC incorporating coal gangue as aggregate and supplementary cementitious material

Engineered cementitious composites (ECC) are conventionally manufactured using quartz sand and a high cement dosage, causing substantial resource consumption, high carbon emissions, and significant drying shrinkage. In this study, quartz sand was replaced by coal gangue aggregate (CGA). The effects of the replacement ratio, nano-SiO 2 aggregate modification, and pre-wetted coal gangue powder on the compressive, tensile, and flexural properties, sag resistance, tensile bond strength, and drying shrinkage were investigated. The nano-SiO 2 modification and tensile bond mechanisms were elucidated through microstructural characterization. Mechanical properties decreased with increasing CGA replacement ratio, whereas all specimens achieved an ultimate tensile strength above 3 MPa and an ultimate tensile strain exceeding 4%. CGA significantly improved sag resistance and tensile bond strength, with 100% replacement showing optimal performance. Nano-SiO 2 densified the interfacial transition zone (ITZ) and refined pore structure via the synergistic effects of the filling, nucleation, and pozzolanic reactions, thereby optimizing 7 d crack distribution. Nevertheless, it reduced the sag resistance, tensile bond strength, and 28 d ductility, while increasing the drying shrinkage. The 5% dosage achieved the best modification effect. Pre-wetted coal gangue powder markedly reduced the mechanical and sag-resistance performance, and decreased the early-age (<90 d) drying shrinkage but increased the long-term shrinkage. Overall, a 50% CGA replacement achieved an optimal balance without additional modification, providing a feasible approach for green and sustainable ECC design.