# Flexural Behavior of Self-Prestressed RC Slabs with Fe-Based Shape Memory Alloy Rebar
## 1 Introduction  
Prestressed concrete is structural concrete in which internal stress is introduced using tendons in areas where tensile stress resulting from the external load is likely to occur. The internal stress can effectively control the occurrence of cracks by offsetting the tensile stress caused by the external load [1; 2]. Therefore, since prestressed concrete is recognized as being effective in resisting the load, the size of the cross-section and its self-weight can be reduced compared with a reinforced concrete (RC) member [3]. The prestressed method can be broadly divided into pre-tension and post-tension methods [4]. The pre-tension method is a method in which the tendons are tensioned before concrete is poured. In this method, the bonding force between the concrete and the tendon resists the recovery of elastic deformation of the tendon released after curing of the concrete and consequently acts as a compressive force on the cross-section. Because bulkheads are required in the process of introducing prestress with this method, this method is mostly used in precast concrete (PC) factories rather than on-site [5]. On the other hand, the post-tension method entails tensioning and anchoring the tendon after the concrete has been cured [6]. Unlike the pre-tension method, it can be easily applied in the field because separate support is not required. For this reason, the post-tension method is widely used in large-scale construction works such as long-span bridges [7]. Prestressed concrete manufactured by the post-tension method is classified into bonded prestressed concrete and unbonded prestressedconcrete [8]. In bonded prestressed concrete, the concrete and the tendon work integrally by grouting the ducts after tensioning and anchoring the tendon [9]. However, the grouting operation complicates the construction process and increases the construction period. Moreover, the prestressing force of the bonded prestressed concrete cannot be recovered, even if it decreases due to various causes such as concrete creep, drying shrinkage, and tendon relaxation over time [10]. On the other hand, in unbonded prestressed concrete, the sheath pipe is not grouted after tensioning the tendon [11]. Unlike bonded prestressed concrete, the tendons of unbonded prestressed concrete can be re-tensioned when the prestressing force is reduced. However, unbonded prestressed concrete has lower strength and lower durability due to increased crack widths compared with bonded prestressed concrete [12]. Technology to introduce prestress using shape memory alloy (SMA) can resolve the aforementioned disadvantages of conventional prestressed concrete [13]. SMA is a metal with special properties where even if plastic deformation occurs, it can be recovered by the shape recovery effect (SME), which is triggered by activation consisting of heating and cooling [14]. When the pre-tensioned SMA is activated under restraint, the alloy tries to return to its original shape by the SME, but because it is restrained, compressive stress, referred to as recovery stress, occurs inside the alloy [15]. Similarly, when a pre-tensioned SMA embedded in concrete is heated by electric resistance heating, the SME will be exerted on the SMA toward shrinking it to its original state by the SME. However, the recovery of the SMA deformation is restrained by the bond between the SMA and concrete, resulting in the generation of recovery stress acting as a compressive force on the concrete [16]. This prestress introduction principle is similar to that of the pre-tension method, in which the bonding force between the concrete and the tendon resists the recovery of elastic deformation of the tendon released and acts as a compressive force on the cross-section. In addition, this method has the advantage of being easily applied in the field like the conventional post-tension method because separate support is not required.