## 4 Conclusions  
The influence of steel fiber content and a steel reinforcing bar on the synthetic PE fiber reinforced strain-hardening cement composite (PE-SHCC) with 1.0 wt % MWCNTs was investigated experimentally in the study. The following conclusion can be drawn from test results.  
Electrical polarization during resistivity measurement led to the measured resistivity of PE-SHCC mixtures to decrease slightly with time. The reinforcement of the steel fibers and steel reinforcing bar into PE-SHCC mixture decreased significantly average resistivity measured during the first 30 min without tensile loading. The incorporation of 0.5 and 1.0 vol.% steel fibers caused lower resistivity, approximately 0.70 and 0.34 of PE-SHCC  
Figure 7: Typical FCR and tensile strain relationships of PE-SHCC dumbbell-shaped specimens in direct tension: (**a**) PE-SHCC tensile specimens without steel bar for 0, 0.5 and 1.0% steel fibers; (**b**) PE-SHCC tensile specimens with 1.0% steel fibers for specimens with a 4 mm and 7 mm steel bar.  
without steel fiber, respectively. These results indicate that the addition of steel fibers and the placement of steel bar are effective to enhance the conductivity of cement composite reinforced with synthetic fibers.  
All the PE-SHCC mixtures with different contents of steel fibers showed multiple cracking and strain-hardening behaviors in direct tension. As steel fiber volume fraction within 1.0 vol.% increased, the initial cracking and tensile strengths of PE-SHCC specimens increased while strain capacity was decreased.  
The FCR values in the plain PE-SHCC specimens increased as the tensile stress and strain increased until tensile strength. After the peak point, FCR increased abruptly. Multiple cracking and strain-hardening behaviors after initial crack led to less contact between conductive materials such as MWCNTs and steel fibers and a steady increase in electrical resistivity of the plain PE-SHCC specimens. The incorporation of the steel fibers and steel bar reduced effectively the error margins and noise in the FCR variation. The self-sensing ability for tensile strain measurements was achieved in synthetic PE fibers reinforced SHCC mixture with 1.0 vol.% steel fibers, even with 1 wt % liquid-type MWCNTs. It can be concluded that the steel fiber content of 1.0 vol.% is optimal for the self-sensing performance of the PE-SHCC mixture with 1.0 wt % MWCNTs.  
The higher GF in the plain PE-SHCC specimens with 1.0 wt % MWCNTs under direct tension was obtained from adding 1.0 vol.% steel fibers. At the initial loading stage, prior to the initial crack, the self-sensing ability of the PE-SHCC-SF10 specimens was improved by the presence of the embedded steel bar while the PE-SHCC-SF10 specimens with the steel bar were less sensitive as the tensile strain increased after initial crack.  
Conceptualization, H.-D.Y., S.-Y.S. and M.-S.L.; methodology, S.-W.K., W.-S.P. and D.-H.K.; investigation, S.-W.K., W.-S.P. and D.-H.K.; data curation, S.-W.K. and D.-H.K.; writing--original draft preparation, H.-D.Y. and D.-H.K.; writing--review and editing, S.-Y.S. and M.-S.L.; visualization, S.-W.K. and W.-S.P.; supervision, H.-D.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Research Foundation (NRF) of Korea, grant number 2018R1A4A1025953.  
Not applicable.  
The authors declare no conflict of interest.