# Flexural Behavior of Self-Prestressed RC Slabs with Fe-Based Shape Memory Alloy Rebar
## 2 Materials and Methods
### Materials  
The concrete used in constructing the specimens was ready-mixed concrete, and the mixture design of the concrete is shown in Table 2. The design compressive strength, the water-to-cement ratio, and the cement type of the mixture with a 25-mm maximum aggregate size were 40 MPa, 30.7%, and type 1 ordinary Portland cement, respectively. Simultaneous with the concrete pouring, 5 cylinders with a size of \(\Phi\) 100 mm \(\times\) 200 mm were produced to measure the compressive strength of the concrete. The cylinders were demolded and cured under the same conditions as the specimens, and a compressive strength test was performed in accordance with the ASTM standard [28] on the testing date. Through the analysis of the test results, the average compressive strength of the concrete was determined to be 46.2 MPa. The chemical composition ratio of the Fe-SMA rebar used in this study was Fe-17 Mn-55i-5 Cr-0.3C-4 Ni-1 Ti (mass %). A vacuum induction melting apparatus was used to manufacture the Fe-SMA plate. The Fe-SMA rebar was prepared as follows. (1) The elements of the alloy were put into a vacuum induction melting device and manufactured into an ingot of 1000 kg. (2) A homogenization treatment of the ingot was given for 6 h at 1250 \({}^{\circ}\)C. (3) The Fe-SMA plate was manufactured by forging into a plate with a thickness \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Slump** & **Air Content** & **W/B** & **S/a** & \multicolumn{3}{c}{**Weight Per Unit Volume (kg/m\({}^{3}\))**} \\ \cline{4-9}
**(cm)** & **(\%)** & **(\%)** & **(\%)** & **W** & **C** & **S** & **G** & **AD** \\ \hline
12 & 4.5 & 30.7 & 47 & 192 & 625 & 684 & 780 & 4.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test variables. Figure 1: Details of the test specimens: (**a**) SL-2N and SL-2A, (**b**) SL-3N, SL-3A, and SL-3R, (**c**) SL-4N and SL-4A, and (**d**) SL-5N and SL-5A. of 10 mm by a hydraulic press. Finally, (4) the Fe-SMA rebar was manufactured by cutting a 10-mm thick Fe-SMA plate to a width of 100 mm with a water jet. A direct tensile test was performed to investigate the mechanical properties of the Fe-SMA rebar. For the direct tensile test, the Fe-SMA rebar was machined into a tensile specimen having a thickness of 2.5 mm, a width of 10 mm, and a length of 200 mm. [PERSON] et al. [29] reported that the corrosion resistance of Fe-SMA rapidly decreased when its pre-strain exceeded 0.04. Referring to their research results, the pre-strain of the specimen to evaluate the mechanical properties of the Fe-SMA rebar was set to 0.04. First, the specimen was tensioned with a displacement control of 0.25 mm/min up to a pre-strain of 0.04 by a universal testing machine (UTM) with a capacity of 100 kN. Afterward, the load applied to the specimen was reduced at the same speed until it became zero. A residual strain of 0.032 occurred in the specimen that had undergone a pre-strain of 0.04. The direct tensile test for evaluating the mechanical properties of the pre-strained specimen was performed with a displacement control of 0.5 mm/min using the same equipment. A strain gauge was attached to measure the strain of the specimen during the test, and the measured data were collected at a time interval of 1 s through a data acquisition system (DAQ). Figure 2 shows the stress-strain relationship of the Fe-SMA obtained by the direct tensile test. The modulus of elasticity of the Fe-SMA was 127.3 GPa, and its ultimate strength and elongation were 1035 MPa and 16.8%, respectively. Figures 3 and 4 show the test set-up for evaluating the recovery stress of Fe-SMA and the strain-temperature-stress relationship of the Fe-SMA rebar in three dimensions, respectively. The X, Y, and Z axes in Figure 4 represent the strain, temperature, and stress of the Fe-SMA specimen, respectively. The specimen used in this test was the same as the specimen used in the direct tensile test. [PERSON] et al.