Beyond tensile performance: Efficiency-oriented hybrid fiber design for sustainable Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC)

Engineered/Strain-hardening cementitious composites (ECC/SHCC) exhibit excellent tensile ductility but face an inherent trade-off between mechanical performance, embodied carbon, and material cost. This study investigated the tensile performance of ECC with a high-volume fly ash matrix and 0.5–2.0% multi-scale fibers, aiming to introduce a new concept for sustainable ECC/SHCC design. Polyvinyl alcohol and polypropylene fibers with different lengths, diameters, and volume fractions were incorporated into ECC mixtures with comparable matrix compositions. The cracking strength, ultimate tensile strength, tensile strain capacity, work-to-fracture were evaluated to ensure fundamental fiber descriptors. The sustainability of different fiber systems was evaluated by coupling embodied carbon and fiber cost with tensile performance. Results show that the tensile performance of ECC can be interpreted within a reduced two-descriptor space: the specific bonding surface area s sf and fiber length L . For a fixed L , cracking-related properties exhibit an approximately linear dependence on s sf , while L does not change the governing descriptor but modulates the sensitivity of cracking strength to variations in s sf . In contrast, in the post-cracking regime, the hierarchical role of L becomes increasingly pronounced. From a sustainability and efficiency perspective, all performance-normalized embodied carbon and cost indices decrease with increasing s sf , regardless of fiber type. This intrinsic conflict between performance maximization and sustainability efficiency reveals the existence of a balanced design frontier in the ( s sf , L ) design space, where a sufficiently large fiber length combined with an intermediate s sf provides a more rational and robust design strategy, enabling high tensile performance without incurring a disproportionate carbon or cost penalty.