Triaxial compressive behavior of high-strength strain-hardening fiber-reinforced cementitious composites: Fiber hybridization effect and constitutive relations

High-strength ultra-high toughness cementitious composites (HS-UHTCC) are advanced materials characterized by a combination of high compressive strength and remarkable tensile ductility. In this study, the triaxial compressive behavior of HS-UHTCC reinforced with hybrid steel-polyethylene fibers was experimentally investigated under confining pressures up to 120 MPa. The results demonstrated that HS-UHTCC specimens predominantly exhibited oblique shear failure under triaxial loading. With increasing confining pressure, the deviatoric strength, axial/ lateral strain at peak load all increased. Peak stress increased by 244.54 % and 276.20 % as confining pressure increased up to 120 MPa for various fiber hybridizations. Notably, when the confining pressure exceeded 100 MPa, the material ceased to soften and instead exhibited ductile behavior. Among the classical failure criteria studied, both the Power-Law and Willam-Warnke criteria successfully captured the triaxial strength envelope of HS-UHTCC. Finally, a pressure-dependent constitutive model was proposed to characterize the pre-peak hardening, post-peak softening, and brittle-to-ductile transition of HS-UHTCC. • Triaxial compression tests on HS-UHTCC up to 120 MPa confining pressure were conducted. • The effect of steel–PE fiber hybridisation on HS-UHTCC triaxial behavior was analyzed. • The applicability of M–C, P–L, and W W criteria to HS-UHTCC was evaluated. • A pressure-dependent two-parameter constitutive model for HS-UHTCC was proposed.