## 4 Conclusions  
CNT is a novel construction material because of its enhancement of the concrete property. Furthermore, electrical and thermal conductivity were highly improved with the cement composites \begin{table}
\begin{tabular}{c c c} \hline \hline
**Specimen** & **Time to Reach the Highest Temperature (min)** & **Peak Temperature (\({}^{\circ}\)C)** \\ \hline MC00 & 63.0 & 38.8 \\ MC01 & 61.0 & 42.5 \\ MC02 & 63.7 & 46.3 \\ MC03 & 51.0 & 54.6 \\ MC04 & 47.2 & 64.5 \\ MC05 & 44.9 & 74.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Experiment results for thermal conductivity. Figure 9: Thermal Gravimetric Analysis (TGA) results for PC00, PC02 and PC05 before and after thermal conductivity test. because CNTs have high conductivity. In this study, various experiments were conducted to investigate the mechanical properties and hydration reaction of CNT-cement composites with various CNT contents and low water-to-binder ratio (0.28). Thermal conductivity by CNT addition was simply estimated by designing a thermal conductivity test with two stainless-steel electrodes to develop multi-functional cement composites in the near future. From the test results, thermal conductivity capacity increased as CNT contents become higher in the mixtures. Figure 8 shows that peak temperature for MC00 and MC05 were 38.8 \({}^{\circ}\)C and 74.9 \({}^{\circ}\)C during the test, so large amount of CNT addition directly influences on the thermal property on cement composites. As the amount of CNT increased in the mixtures, the compressive strengths decreased initially owing to the water absorption of CNT. However, the strengths of specimens with large amount of CNTs rapidly increased as much as MC00 after 28 days. This was because of the internal curing effects of water contents in and around the CNT particles that released water. Thus, the compressive strength for MC04, which showed the lowest strength, was 94.0 percent of MC00. CNT addition did not significantly influence cement hydration reaction, as shown by isothermal calorimetry. The largest and smallest cumulative heats (PC00 and PC05) were 54.4 cal/g and 50.5 cal/g, respectively, less than 10 percent difference. Cement hydrates were formed around the CNT particles inside the pores of hardened cement composites in SEM images, and it can be considered that CNT played a role in connecting cement hydrates. Thus, strength development can be achieved later. Weight losses for PC00, PC02, and PC05 were measured to find out the different types of hydration products; however, it was concluded that CNT did not have a considerable effect on the change in hydration products. After the thermal conductivity test, significant phase changes were not observed by the mass change data for all mixtures. It appears that nano-materials do have an influence on concrete properties at the early age, but over time, the strength development is improved. Moreover, hydration reaction and microstructures of CNT-cement composites were similar to normal cement composites. Although CNT did not dramatically improve the strength of composites, it can be considered that CNT is a multifunctional material from thermal conductivity test. Thermal conductivity capacity for CNT-cement composite increased as more CNT was added in the mixtures. The optimum mix proportions of CNT contents and water-to-binder ratio shows potential for improving the concrete property in the construction field. In particular, the thermal conductivity can be applied to bridges and roadways to avoid black ice that can cause traffic accidents by melting surface ice. Pre-fabricated CNT-cement blocks with electrodes can be embedded before concrete pouring as heat resources during roadway construction or pre-cast CNT-concrete bridge-decks can be adopted on-site. [PERSON] and [PERSON] conceived, designed and conducted experimental program; [PERSON] contributed materials and analysis tools; [PERSON] and [PERSON] wrote the paper; [PERSON] and [PERSON] analysed the data and designed the project.