## 3 Results and Discussion
### Electrical and Self-Sensing Properties  
The development curves of tensile stress, strain and FCR with duration presented in Figure 6 were compared to investigate the effect of steel fiber content and steel bar on the electrical and tensile properties of PE-SHCC mixtures with 1.0% MWCNTs. In Figure 6,  
Figure 5: Typical cracking procedures of PE-SHCC tensile specimens without steel bar: (**a**) PE-SHCC specimen without steel fibers; (**b**) PE-SHCC specimen with 0.5% steel fibers; (**c**) PE-SHCC specimen with 1.0% steel fibers. the FCR value for the PE-SHCC specimens with the steel bar is expressed as a percentage different from that of PE-SHCC specimens without the steel bar. As noted in a previous study on the electrical and self-sensing properties of PE-SHCC in repeated compression by the authors [26], Figure 6 shows that the addition of steel fibers also improves the piezoresistive response of PE-SHCC dumbbell-shaped specimens in direct tension. As the tensile strains in PE-SHCC-SF00-0 and PE-SHCC-SF05-0 specimens increase, FCR contained a lot of noise and was scattered. The trend between tensile strain and FCR was not clear while PE-SHCC-SF10-0 specimens showed a clear trend that FCR increases as tensile strain increases. This tensile-piezoresistive response of SHCCs was reported in several studies [24; 25]. The reason to increase in FCR under uniaxial loading is that the arrangement of conductive fillers such as steel fibers and MWCNTs slightly changes, resulting in less contact between the conductive fillers and a little increase in FCR of cement-based composites [32]. As the reinforcing ratio of steel bar in the tensile specimen increases, the FCR of PE-SHCC tensile specimens shows more stable variation with tensile strain. Comparison of FCR value in the PE-SHCC specimens with and without steel bar indicates that the FCR value of plain PE-SHCC specimens without steel bar is higher than that of PE-SHCC with steel bar during tensile loading. This is because for PE-SHCC with steel bar, the electrical  
Figure 6: Typical tensile stress, strain and fractional changes in resistivity (FCR) variation with time: (a) PE-SHCC-SF00 tensile specimens; (b) PE-SHCC-SF05 tensile specimens; (c) PE-SHCC-SF10 tensile specimens. current penetrates largely into steel bar. Since the electrical current penetrating into PE-SHCC matrix is relatively small, the FCR obtained from the surface resistance variation in the PE-SHCC matrix were not changed significantly although the tensile strain increased. Figure 7a,b show the typical FCR- tensile strain of plain PE-SHCC specimens with different contents of steel fibers and reinforced PE-SHCC specimens with 1.0% steel fibers, respectively. As illustrated in Figure 7a, the scatter in the FCR of PE-SHCC-SF00-0 and -SF05-0 specimens is quite large, while the PE-SHCC specimen with 1.0% steel fibers (PE-SHCC-SF10) shows a good linear regression between FCR and tensile strain. From these results, it can be concluded that PE-SHCC-SF00-0 and -SF05-0 mixtures may not be used as a cement-based sensor for accurate condition monitoring of civil infrastructures. Figure 7a indicates that the addition of steel fibers improves the conductive and self-sensing properties of cement-based composites, PE-SHCC mixture. Figure 7b presents the FCR-tensile strain relationship of PE-SHCC-SF10 mixture with and without steel bar and includes the tensile strain range at initial cracking for each specimen. As shown in Figure 7b, the FCR-tensile strain responses showed a stiff slope prior to initial crack. After initial crack, the curves softened and showed a constant value despite the increase in tensile strain. It is concluded from these results that steel reinforcing bar placed at the center of PE-SHCC tensile specimens improves self-sensing performance prior to initial crack but impaired the self-sensing ability after initial crack.