Activating robust fiber bridging via internal moisture regulation of cellulose fiber for ductile cementitious composite

The porous interfacial transition zone around chemically inert steel fiber restricts fiber bridging for stress transfer, limiting tensile ductility of cementitious composite. Herein, water-saturated cellulose fiber is incorporated into cementitious composite, aiming to densify interfacial transition zone for enhanced mechanical interlocking to elevate composite tensile toughness. The tensile performance and strain field evolution were evaluated, and the interfacial phase evolution was characterized by scanning electron microscopy and nanoindentation test. Driven by moisture gradients, cellulose fiber releases stored water to facilitate continuous cement hydration, promoting the nucleation and growth of abundant hydration products that fill and refine interfacial microdefects. The proportion of pores and unhydrated cement clinker at the interface decreases, and low-density hydration products cross-link and polymerize into high-density and ultra-high-density calcium silicate hydrate phases. This enhancement improves fiber bridging capacity, elevating the energy absorption of cementitious composite by 128.6%. The macroscopic failure pattern transforms from brittle strain localization to ductile distributed multiple-cracking propagation mode. This study presents a novel interface densification approach induced by internal curing to improve mechanical compatibility at fiber-matrix interface, facilitating the development of ductile cementitious composite for safe and durable construction.