From waste to hyper-ductility: Micromechanical and techno-ecological assessment of ECC incorporating high-volume ultrafine marble powder

Engineered Cementitious Composites (ECC) offer exceptional ductility but suffer from high ecological and economic costs due to heavy cementitious binder requirements, while waste marble powder poses severe environmental disposal hazards. This study aims to evaluate the micromechanical, structural, and eco-economic impacts of utilizing ultrafine marble powder (UF-MP) as a partial to complete replacement for fly ash in PVA-ECC, hypothesizing that UF-MP can re-engineer the matrix toughness to enhance ductility while lowering embodied energy. To test this, ECC mixtures containing 2% PVA fibers were formulated with UF-MP substituting fly ash at 0%, 10%, 25%, 40%, and 100% by weight. Performance was rigorously assessed through flowability, compressive and four-point bending tests, fracture toughness evaluation, single-crack tension, SEM, TGA, and life-cycle sustainability of ECC mixtures. The results demonstrated that a 10% substitution (ECC-10) yielded the highest compressive (42.23 MPa) and flexural (12.16 MPa) strengths via micro-filling and nucleation effects. However, higher substitutions progressively reduced matrix toughness while exponentially increasing the complementary fiber-bridging energy. Consequently, the fully substituted ECC-100 exhibited a remarkable 71.37% increase in mid-span deflection (4.37 mm) accompanied by highly dense micro-cracking. SEM and TGA confirmed that high UF-MP volumes dilute rigid hydration products, transforming the fiber-matrix interface from a brittle chemical bond to a steady frictional slip. Furthermore, eco-efficiency analysis revealed a 27.2% reduction in embodied energy alongside lowered material costs. Ultimately, UF-MP successfully re-engineers the interfacial transition zone, trading absolute strength for high ductility, providing a framework where ECC-10 optimizes load-bearing capacity and ECC-100 maximizes sustainable, high deformability.