## 3 Experimental Results
### Heat Test and Thermal Imaging Analysis Results
Damage detection was feasible for cement paste and mortar, which exhibited high temperature differences exceeding 10 \({}^{\circ}\)C under damage conditions. However, in the case of concrete, damage detection was challenging because the temperature difference owing to such damage was less than 3 \({}^{\circ}\)C.  
Figure 6 shows the temperature variation of the composites after 28 curing days according to the parameters. When the MWCNT concentration was 0.125 wt%, the temperatures of the cement paste were 19.6 \({}^{\circ}\)C for CP-0.125-28D-X and 8.2 \({}^{\circ}\)C for CP-0.125-28D-O. The temperatures of the mortar were 3.7 \({}^{\circ}\)C for M-0.125-28D-X and 1.3 \({}^{\circ}\)C for M-0.125-28D-O. The temperatures of the concrete were 0.8 \({}^{\circ}\)C for Co-0.125-28D-X and 0.4 \({}^{\circ}\)C for Co-0.125-28D-O (Figure 6a). Compared to the temperature variation after 7 curing days, the temperatures decreased by up to 17.5 \({}^{\circ}\)C for cement paste, 0.1 \({}^{\circ}\)C for mortar, and 2.1 \({}^{\circ}\)C for concrete. Damage detection was possible for cement paste because the temperature gradients decreased by 11.4 \({}^{\circ}\)C owing to the damage, but it was impossible for mortar and concrete because the temperature gradients decreased by only 2.4 \({}^{\circ}\)C and 0.4 \({}^{\circ}\)C, respectively, owing to the effect of moisture. These results are identical to those obtained for 7 curing days. Figure 6b shows the temperature variation of the composites with 0.25 wt% MWCNT. The temperatures of the composites without damage were 30.6 \({}^{\circ}\)C for CP-0.25-28D-X, 9.0 \({}^{\circ}\)C for M-0.25-28D-X, and 3.1 \({}^{\circ}\)C for Co-0.25-28D-X. The temperatures of the composites with damage were 21.8 \({}^{\circ}\)C for CP-0.25-28D-O, 2.5 \({}^{\circ}\)C for M-0.25-28D-O, and 0.8 \({}^{\circ}\)C for Co-0.25-28D-O. The temperature decrease owing to the damage was the largest, with 8.8 \({}^{\circ}\)C for cement paste, 6.5 \({}^{\circ}\)C for mortar, and 2.3 \({}^{\circ}\)C for concrete. In the case of concrete, damage could not be easily detected using the heat property because the temperature difference was lower than that obtained for cement paste and mortar. Figure 6c shows the temperature variation of the composites with 0.5 wt% MWCNT, with an applied voltage of 60 V. The temperatures of the cement paste were 42.5 \({}^{\circ}\)C for CP-0.5-28D-X and 31.2 \({}^{\circ}\)C for CP-0.5-28D-O. When compared with 7 curing days, the temperature decreased by up to 25.3 \({}^{\circ}\)C. The cement paste was significantly affected by moisture because 100 g of water was used during the fabrication as compared to that in mortar and concrete. The temperatures of the mortar were 16.8 \({}^{\circ}\)C for M-0.5-28D-X and 6.7 \({}^{\circ}\)C for M-0.5-28D-O and were thus 2.5-times lower than that of the cement paste. The temperature difference of the mortar owing to the damage was 10.1 \({}^{\circ}\)C, whereas the temperature difference was 3.3 \({}^{\circ}\)C lower than that for 7 curing days. The temperature of the concrete was 6.5 \({}^{\circ}\)C for Co-0.5-28D-X and 5.8 \({}^{\circ}\)C for Co-0.5-28D-O. The temperature difference owing to the occurrence of damage was 0.7 \({}^{\circ}\)C, which was the lowest among the 0.5 wt% composites. This is because the concrete contained aggregates that had a larger diameter than those of the cement paste and mortar, which caused the resistance to increase. Figure 6: Temperature variations by voltage supply at 28 curing days: (**a**) 0.125 wt%, (**b**) 0.25 wt%, and (**c**) 0.5 wt%. The temperature gradients of the composites according to these parameters are summarized in Table 3. Among the composites cured after 7 d, the highest temperature obtained was 67.8 \({}^{\circ}\)C for CP-0.5-7D-X. Likewise, among the composites cured after 28 d, CP-0.5-28D-X exhibited the highest temperature of 42.5 \({}^{\circ}\)C. The cement paste showed the best heat properties among the cement-based materials, followed by mortar and concrete.