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In this study, the pullout resistance of deformed shape memory alloy fibers embedded in a mortar matrix is investigated to develop self crack-closing capacity. Three types of deformed shape memory alloy fibers (dog bone–shaped, end-deformed, and crimped) and one type of smooth shape memory alloy fiber, fabricated from two different alloys, NiTi and NiTiNb, were embedded in a mortar matrix with a compressive strength of 55 MPa. The pullout resistance differed considerably depending on the geometry of the fiber and composition of the alloy. The pullout resistance was generally higher for deformed shape memory alloy fibers than for the smooth shape memory alloy fiber. Among the deformed shape memory alloy fibers, dog bone–shaped fibers showed the highest enhancement in bond strength after heat treatment. The pullout resistance was higher for the NiTiNb alloy than the NiTi alloy when the shape memory alloy fiber was deformed, whereas the relationship was reversed when the shape memory alloy fiber was smooth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]