Mechanical Behavior and Constitutive Model of Basalt-Fiber Textile-Reinforced Engineered Cementitious Composite Under Off-Axis Tension

Basalt-fiber textile-reinforced engineered cementitious composite (BTR-ECC) combines favorable durability, cost-effectiveness, and mechanics, making it a viable option for structural retrofitting. Although axial behavior is well-documented, off-axis loading zones often constitute structural weak points. To address this gap, this study experimentally and theoretically examines the mechanical responses and failure mechanisms of BTR-ECC at off-axis tensile angles of 0°, 15°, 30°, and 45°. The results demonstrate that: (1) The tensile stress–strain curves exhibit a distinct trilinear characteristic (linear elastic, strain-hardening, and fracture), featuring densely distributed microcracks confined to 30–50 μm. Dominant failure modes include textile rupture, interfacial debonding and pull-out, and PVA fiber bridging. (2) With increasing angles, tensile strength at 0°, 15°, 30°, and 45° surpasses plain ECC by 84.8%, 73.6%, 52.9%, and 54.0%, respectively, confirming effective synergistic load transfer between the basalt-fiber textile and the matrix. Despite progressive strength degradation, the strain energy density remains relatively stable across all orientations, indicating robust energy dissipation capacity. (3) A phenomenological constitutive model based on the tangent modulus approach is established to describe the off-axis tensile response. The model shows good agreement with the experimental data and may serve as a reference for the analysis of BTR-ECC structures within the calibrated range of the four tested angles.