## 3 Results
### Thermogravimetric Analysis (TGA)  
Figure 7a,b presents the TGA results obtained by recording the mass loss when the cement composites in the MWNT0.3 and MWNT1.0 groups were subjected to progressive heating from 31 \({}^{\circ}\)C to 998 \({}^{\circ}\)C. Mass losses primarily occurred within two temperature ranges. The first range was between 31 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, where water molecules dehydrated from the calcium silicate hydrate gel [4; 13; 36; 38]. Therefore, the mass loss in the first range signified the amount of C-S-H produced by cement hydration in the composite [4; 13; 36; 38]. The second range was between 325 \({}^{\circ}\)C and 550 \({}^{\circ}\)C, where calcium hydroxide (also known as portlandite) decomposed, and the mass loss in this range represented the amount of CH produced as a result of cement hydration [4; 13; 36; 38]. Since CH can undergo a pozzolanic reaction with NS, and the reaction results in the formation of additional C-S-H, the reduction of the CH mass loss shown in the MWNT0.3 group and MWNT1.0 group of Table 4 signified an increased amount of C-S-H [4; 13; 36; 38].  
The mass losses computed from each composite in the first and second temperature ranges are presented in Table 4 and Figure 8. The mass loss in the first range increased with the increase in the NS content in the MWNT0.3 group, which indicated an increase in the amount of C-S-H due to the addition of NS. Meanwhile, a trend of the mass loss in the first range in the MWNT1.0 group was dissimilar to that obtained in the MWNT0.3 group. In the MWNT1.0 group, an increase in the mass loss with the increase in the NS content did not occur, which indicated that an increase in the C-S-H generation due to NS addition was not noticeable. When the amount of the incorporated-MWNT was relatively large, the structure of the cement composite was dense, and this hindered the contact between the CH and NS. This hindrance prevented the formation of additional C-S-H. This may have negatively affected the reinforcement effect of the NS on the mechanical properties due to the sluggish generation of C-S-H, which transports mechanical forces. This agrees with marginal changes of the porosity in the MWNT1.0 group and small changes or deterioration in the compressive and flexural strengths of the MWNT1.0 group shown in Figures 3a, 4a, and 5a, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline - & Tem. & **C0.3N0** & **C0.3N1** & **C0.3N3** & **C0.3N5** & **C1.0N0** & **C1.0N1** & **C1.0N3** & **C1.0N5** \\ \hline
1 st range & 31–200 \({}^{\circ}\)C & 8.9 & 8.7 & 9.6 & 9.4 & 8.5 & 8.4 & 8.6 & 8 \\
2 nd range & 325–550 \({}^{\circ}\)C & 4.4 & 4.2 & 4.1 & 3 & 3.7 & 3.1 & 3.7 & 3.1 \\ \hline \end{tabular}
\end{table}
Table 4: Mass loss results computed from two different ranges of TGA.  
Figure 7: The thermogravimetric analysis (TGA) assessed for (**a**) MWNT0.3 group and (**b**) MWNT1.0 group.  
In the second range, the decomposed portion in the MWNT0.3 and MWNT1.0 groups tended to decrease with the increase in the NS, which means that more CH underwent a pozzolanic reaction with NS [4; 13; 36; 38]. In addition, mass loss in the MWNT1.0 group was smaller than that in the MWNT0.3 group. In particular, the mass loss of C0.3N0 dropped by 31.8% as the NS content increased to 5%, whereas the mass loss of C1.0N0 only dropped by 16.7% as the NS content increased to 5%. This indicated that the cement composites of the MWNT1.0 group utilized a limited amount of CH, relatively less than that utilized in the MWNT0.3 group, though the amount of incorporated NS increased. This finding supports the aforementioned discussion of the dense microstructure due to incorporation of 1% MWNT, which hindered the pozzolanic reaction between CH and NS.