Multiscale interfacial mechanisms of polydopamine/graphene oxide functionalized polyethylene fibers for enhancing the strength–ductility synergy of ECC

Polyethylene (PE) fibers can impart excellent ductility to engineering cementitious composites (ECC), but their inherent chemical inertness and low surface energy limit the interfacial bonding between fibers and matrix. This study proposed a mild hierarchical surface functionalization strategy based on the synergistic effect of polydopamine (PDA) and graphene oxide (GO). By establishing a multiscale framework spanning macroscopic mechanical performance, microstructural evolution, and molecular-scale interactions, the effects of PE fiber modification on the mechanical response, microstructure, and interfacial properties of ECC were systematically evaluated. Multiscale analyses revealed that the PDA/GO hierarchical coating promoted local hydration reactions and interfacial transition zone (ITZ) densification, while dense hydrogen-bond networks and local Ca–O coordination enhanced interfacial interactions at the atomic scale. These coupled effects optimized fiber/matrix bonding and stabilized interfacial sliding, thereby enhancing pull-out energy dissipation and fiber-bridging efficiency, which in turn increased the ultimate tensile strength and strain of ECC by 49.64% and 19.72%, respectively, with more pronounced multiple cracking. This study provides a theoretical basis for the interface optimization design of high-performance fiber-reinforced cementitious composites.