Experimental investigation of actively confined concrete using shape memory alloys

This experimental study focuses on investigating the uniaxial compression behavior of concrete confined using an innovative active confinement technique. The thermally triggered recovery stress of prestrained Shape Memory Alloy (SMA) spirals is utilized to apply external active confining pressure to concrete cylinders. Thermo-mechanical tests are first conducted to determine the recovery stress and the prestrain losses of the spirals used. Next, the SMA spirals are utilized to confine concrete cylinders either solely or in conjunction with Glass Fiber Reinforced Polymer (GFRP) wraps. The confined cylinders are tested in compression and their behavior is compared with that of cylinders confined passively with GFRP only. The results of the study show that SMA spirals exhibit stable recovery stress under monotonic and cyclic loading. The amount of prestrain losses measured in the study is minimal and thus has no impact on the behavior of the confined cylinders. The compression test results indicate that the SMA spirals are effective in applying large and reliable active confining pressure on the tested concrete specimens. Additionally, the concrete cylinders confined with the SMA spirals show significantly higher ultimate strain and slightly higher strength compared to those of the GFRP passively confined cylinders.