Pullout resistance of straight NiTi shape memory alloy fibers in cement mortar after cold drawing and heat treatment

In our study, we found cold drawing to be an effective method for enhancing the pullout resistance of NiTi shape memory alloy (SMA) fibers in concrete. The pullout resistance was observed to be dependent on the contact pressure and friction coefficient at the interface between the fibers and the mortar matrix. The drawing process increased the stiffness and yield stress of the fibers and consequently increased the contact pressure at the interface between the fibers and the mortar matrix. Moreover, heat treatment of the fibers after cold drawing was found to noticeably recover the fiber diameter, thereby significantly enhancing the pullout resistance. The enhancement of the interfacial bond strength by heat treatment verified the crack-closing capabilities of SMA-fiber-reinforced cement composites.