# Flexural Behavior of Self-Prestressed RC Slabs with Fe-Based Shape Memory Alloy Rebar
## 1 Introduction
Concrete to which prestress is introduced in this way can have excellent mechanical performance because the SMA and concrete work integrally, similar to conventional bonded prestressed concrete. Moreover, unlike bonded prestressed concrete, the prestressing force of prestressed concrete using SMAs can be recovered through its reactivation, even if it is reduced by various causes. To date, more than 300 types of SMAs have been reported [17]. Among them, Ni-Ti-based SMA (Nitinol), developed by [PERSON] et al. [18] in 1963, is currently the most widely used because it shows excellent superelasticity and an SME [19]. However, Nitinol has a relatively narrow temperature history. Moreover, because it contains high-priced nickel and titanium in large proportions, Nitinol is not used as a construction material [20]. On the other hand, Fe-based shape memory alloy (Fe-SMA) has a lower manufacturing cost compared with Nitinol because iron is the main constituent material, and many researchers are studying it for use as a construction material. [PERSON] et al. [21] conducted an experimental study to use Fe-SMA strips as a strengthening material in conjunction with use of the NSM method. They evaluated the flexural performance of RC beams with Fe-SMA strips as reinforcement in the NSM method through a four-point loading test. They reported that the specimen with activated Fe-SMA exhibited a higher initial stiffness than the specimen with non-activated Fe-SMA through analysis of the test results. In addition, they argued that the cause was the action on the cross-section of the compressive force due to the activation of Fe-SMA. [PERSON] et al. [22] evaluated the mechanical properties, recovery properties, and relaxation of Fe-SMA in order to secure basic data for using Fe-SMA strips as strengthening materials for RC members. The alloy composition ratio of the Fe-SMA strip used in the study was Fe-17 Mn-5 Si-10 Cr-4 Ni-1(V,C) (mass %), and the specimen was 100 mm wide and 1.5 mm thick. They reported that when Fe-SMA was heated to 160 \({}^{\circ}\)C, a recovery stress of 300-350 MPa was generated, which was reduced by about 10% by relaxation after 1000 h. [PERSON] et al. [23] performed an analytical study to predict the flexural performance of RC members strengthened with Fe-SMAby the NSM method. They presented a finite element analysis model of an RC member strengthened with Fe-SMA by the NSM method using a commercial structural analysis program. They compared the experimental results published by [PERSON] et al. [21] with the results predicted by the FE model in order to secure the reliability of the finite element analysis results. They also confirmed through a parametric analysis that the ductility of the RC beams strengthened with Fe-SMA increased as the concrete strength increased, and the initial stiffness of the RC beams increased by more than 60% when the Fe-SMA was activated. As such, few studies on the use of Fe-SMA rebars in new structures have been reported. Most of the research to introduce a prestress force to a structure using Fe-SMA has been focused on using Fe-SMA for the repair and strengthening of aging structures [24; 25; 26]. In previous studies, a cementitious matrix or anchoring device was used to attach Fe-SMA rebars, plates, or strips to RC members. However, it is difficult to accurately evaluate the effect of Fe-SMA on the RC member because the behavior of the strengthening RC member is affected by the anchoring device and the bonding strength between the RC member and the cement matrix. In addition, previous studies evaluated the reactivation potential of Fe-SMA through material tests [27], and there are few studies testing the reactivation possibility of Fe-SMA used in the RC member. Therefore, this study conducts flexural tests on one-way RC slabs using Fe-SMA rebars as a tensile reinforcement and evaluates the effect of the prestressing force by Fe-SMA rebar on their flexural behavior. In addition, the possibility of reactivation of Fe-SMA was experimentally evaluated.