Research on factors influencing the repair performance of the SMA crack self repairing concrete beams

To overcome the problem of bearing capacity degradation caused by cracks in traditional concrete structures, this paper explores the crack self-repairing technology of concrete beams based on Shape Memory Alloy (SMA). This paper designs specimens with different reinforcement rates of SMA wires (0–0.59%), pre-stretching degrees (4%, 6%, 8%, 10%, 12%), configuration forms and excitation modes as key parameters. Through the test process of loading–repair–reloading–rerepair, the influences of various parameters on the crack repairing effect and mechanical properties of SMA self-repairing concrete beams, as well as their degradation laws, were quantified. The results indicate that the crack repairing rate of SMA self-repairing concrete beams can reach 82.99–97.75%. After the secondary loading, the secondary cracks repair rate can still be maintained between 70.59% and 94.12%. Increasing the reinforcement ratio of SMA wires (multiple strands with fine diameters) and the pre-stretching degree (≤ 8%) can significantly enhance the ultimate bearing capacity and crack repairing rate under the loading–repair cycle, and resist the degradation of repair performance. Beams without longitudinal reinforcement achieve better crack repairing effects, but have lower load-bearing capacity and higher degradation rates. Additionally, employing a constant high current excitation mode can significantly shorten repair time without affecting the crack repairing effectiveness. The research provides referenceable parameters for the design of SMA self-repairing concrete specimens.