Cyclic flexural behavior of hybrid SMA/steel fiber reinforced concrete analyzed by optical and acoustic techniques

Superelastic shape memory alloys (SMAs) are smart materials that can recover 6-8% elastic strains due to their phase transformation. SMAs also possess unique characteristics such as good energy dissipation, excellent re-centering capabilities and corrosion resistance. Recent studies have incorporated the use of superelastic SMA fibers in cementitious composites to achieve re-centering and crack-closing capabilities. Consequently, it is important to investigate the performance of fiber reinforced concrete (FRC) members under cyclic loading. This study investigates the use of hybrid steel/SMA fibers as reinforcement in concrete members subjected to cyclic flexural loading. Digital image correlation (DIC) was used to monitor the full field displacements and strains of the concrete beam specimens. Fiber density and statistical spatial point pattern functions were used to assess the fiber distribution. Two acoustic emission sensors were attached to each side of the concrete specimens to characterize crack development. A correlation between the crack width propagation and cumulative energy captured by the acoustic emission sensors was established. Results showed that the hybrid specimen with equal fiber volume ratios for steel and SMA fibers exhibit a lower mid-span deflection and smaller crack width.