Influence of Thermally Activated Crimped NiTi SMA Fibers on the Pure Shear Performance of Z-Shaped Mortar Specimens

Concrete and cementitious composites exhibit brittle failure under shear stress, limiting their resilience in seismic and high-load applications; this study investigates whether crimped NiTi shape memory alloy (SMA) fibers can enhance pure shear strength and ductility of mortar specimens, with particular focus on the effect of thermal activation. Z-shaped mortar specimens were prepared with SMA fiber volume fractions of 0%, 1.0%, and 1.25%, tested under both non-heated and heated conditions using a Universal Testing Machine, with deformation monitored via LVDTs and Digital Image Correlation. SMA fiber reinforcement increased peak shear strength by 13% and 14.5% for 1.0% and 1.25% fiber volumes, respectively, under ambient conditions, reaching up to 22% enhancement after thermal activation due to recovery-stress-induced prestressing; the 1.0% fiber volume achieved the highest ductility index of 4.05 compared to 1.03 for plain mortar, while SMA fibers had negligible influence on initial shear modulus but substantially improved post-cracking response and crack bridging. These findings demonstrate that crimped SMA fibers effectively improve shear resilience of cementitious composites, with 1.0% fiber content offering the optimal balance between strength and ductility, though activation protocols require careful calibration to minimize thermal degradation of the matrix.