## 4 Conclusions  
In this study, damage detection using heat and electrical resistance properties was conducted according to various parameters through the fabrication of different composites. The changes in the properties owing to the occurrence of damage were analyzed through heating and resistance experiments. The following conclusions were drawn. Regarding the differences in the properties of the cement paste owing to the presence of damage, the heat property decreased by up to 2.4 times, and the electrical resistance property improved by up to a factor of 3.0. Because the unit area of the composite was reduced by the damage, the electrical resistance increased, whereas the heat property deteriorated. Furthermore, unlike the mortar and concrete, the cement paste with 0.125 wt% MWCNT clearly exhibited differences in the heat and electrical resistance properties owing to such damage. This trend demonstrates that cement paste can be used for damage detection based on the heat and electrical resistance properties, even if it contains a low concentration of MWCNTs. The heat property of mortar deteriorated by up to 2.8 times, and the electrical resistance property improved by up to 2.7 times owing to the damage occurrence. The decrease in the mortar temperature owing to such damage was insignificant at 2.4 \({}^{\circ}\)C for the concentration of 0.125 wt%, although the temperature difference was high when the concentration exceeded 0.25 wt%. Therefore, it is estimated that damage to mortar can be detected based on the heat property at 0.25 wt% or higher concentrations of MWCNTs. The largest difference in the electrical resistance of mortar owing to the presence of damage was 37.0 k\(\Omega\), and this difference was high at every MWCNT concentration. Therefore, damage to mortar can be detected based on the electrical resistance property at a MWCNT concentration of 0.125 wt%. Figure 13: Field emission scanning electron microscopy (FE-SEM) images: (**a**) 0.5 wt% cement paste, (**b**) 0.5 wt% mortar, and (**c**) 0.5 wt% concrete. The heat property of concrete decreased by up to 2.8 \({}^{\circ}\)C, and the electrical resistance property improved by up to 40.3 k\(\Omega\) owing to the occurrence of damage. Because a temperature variation of below 3 \({}^{\circ}\)C was obtained at every MWCNT concentration in the concrete, the detection of damage in concrete using the heat property remains a challenging task. However, damage can be detected using the electrical resistance property, because, in this study, the electrical resistance of concrete increased by up to 40.3 k\(\Omega\). As the MWCNT concentration increased, the heat properties of the composites also improved, whereas the electrical resistance decreased. This is because many CNT networks were formed inside the composite as the conductive MWCNTs increased, which improved the heat property and deteriorated the electrical resistance. As the curing period of the composites increased, the heat properties deteriorated, whereas the electrical resistance property was enhanced. The largest deterioration in the heat property was 25.3 \({}^{\circ}\)C for the cement paste, and the improvement in the electrical resistance property was 24.8 k\(\Omega\) for concrete. In terms of the heat and electrical resistance properties of the composites according to the type of cement-based material, the cement paste exhibited the best properties, followed by mortar and concrete. Because the cement paste did not contain sand or fine aggregates that could interfere with the current flow, it formed a favorable environment for the formation of CNT networks. Subsequently, the heat and electrical resistance properties of the composites were enhanced. The internal microstructures of the composites were analyzed using FE-SEM. The results confirmed that MWCNTs were evenly distributed in all the composites of cement paste, mortar, and concrete mixed with MWCNTs.