Prestressing and Self-Healing of Fiber-Reinforced and Ultra-High-Performance Concrete Using Shape Memory Alloys

A large number of existing studies show that fiber-reinforced concrete (FRC) and ultra-high-performance concrete (UHPC) have improved crack resistance relative to conventional concrete, but there is limited research on further advancing the structural performance of FRC and UHPC through prestressing and self-healing. This study addresses this knowledge gap by introducing shape memory alloy (SMA) bars as reinforcement. Existing studies on using SMA bars for prestressing or healing are focused on conventional concrete. Thus, this study experimentally evaluates SMA bars in FRC and UHPC. Small-scale flexural specimens are fabricated for this purpose. Three mix designs are considered, corresponding to mortar, FRC, and UHPC. The prestrained and embedded SMA bars are employed in two different ways. The first method is to activate the SMA to prestress the concrete, thereby delaying cracking. The second is to activate the SMA after cracks develop, thereby closing and “healing” the cracks. Additionally, different heating methods are considered. Heating with electricity is compared to heating by electromagnetic induction to study their efficiency and safety. The experimental results validate the use of SMA for prestressing the different types of concrete. The concept of healing is also validated for all three types of concrete. Reductions in crack width as high as 80%, 90%, and 84% are measured in the mortar, FRC, and UHPC specimens, respectively.