## 3 Results and Discussions
### Structural and Microstructural Properties
#### 3.4.2 TG/DTG Analysis  
Thermogravimetric analysis is widely used to monitor the hydration process and identify and determine the content of reaction products, such as silicates, gels, other hydrates and carbonates. The TG/DTG of two different pastes (0.75M-4% and 2.22M-4%) as a function of the curing time are presented in Figure 11. The high mass loss below 120 \({}^{\circ}\)C was assigned to the complete release of physically bound water within the gel structure [77]. All pastes presented a shift toward high temperatures in the DTG peaks in this region as the curing progressed from 1 to 28 days (as represented in Figure 11). This suggested the formation of gels with more tightly bonded water as the reaction products developed [76]. The continuous mass loss after 120 \({}^{\circ}\)C until 600 \({}^{\circ}\)C was attributed to the decomposition of hydrated gels, such as C-S-H and C-(A)-S-H [78], and the dehydroxylation of residual Ca(OH)\({}_{2}\)[77]. Notably, further mass loss can be observed at 600-800 \({}^{\circ}\)C, which was caused by the decomposition of calcium carbonate CaCO\({}_{3}\)[76, 77]. No other abrupt mass loss was observed until 1000 \({}^{\circ}\)C; all formulations had a slight and continuous mass loss. Figure 9: XRD patterns of pastes at 28 days (dotted red circle: broad hump indicating amorphous phase structure). Figure 11a presents the TG/DTG curves of the 0.75M-4% sample, representing the same behavior as the 0.75M-6% sample. It is possible to identify a more defined mass loss around 400 \({}^{\circ}\)C, probably due to the residual Ca(OH)2 that was not totally consumed during the reaction. This was in line with the Ca(OH)2 that was also identified in the XRD analysis for those formulations, as discussed in the previous section (Section 3.4.1--Figure 9). Alternatively, Figure 11b presents the TG/DTG curves of the 2.22M-4% sample as a representative curve for the remaining formulations. It is possible to observe the significant mass loss below 120 \({}^{\circ}\)C, the continuous mass loss above 120 \({}^{\circ}\)C, the calcite decomposition around 600 \({}^{\circ}\)C, and the constant and slight mass loss until 1000 \({}^{\circ}\)C.  
Figure 12 presents the mass losses of all pastes as the curing progressed for two different temperature ranges (120-600 \({}^{\circ}\)C and 600-1000 \({}^{\circ}\)C). The curves showed an apparent increase in mass loss over the curing time for all formulations. Those two temperature ranges correspond to the decomposition of the main reaction products, namely, C-S-H/C-A-S-H gels and CaCO\({}_{3}\), respectively. The results confirmed the findings of previous studies [42; 43; 44]. Moreover, the high content of reaction products primarily in the TGA 120-600 \({}^{\circ}\)C range correlated well with the strength development (Figure 13). Figure 10: Comparison of the XRD patterns of 0.75M-4% (blue) and 2.22M-4% (yellow) at 1 and 28 days (dotted red circle: broad hump indicating amorphous phase structure). As the quantity and density of the gels increased, the mass loss also increased (Figure 12), which was revealed macroscopically as the enhancement in compressive strength [31]. Nevertheless, there was no correlation between mass loss and compressive strength. For instance, all formulations contained mass loss between 6.5-7.5% at 28 days but presented completely different mechanical behavior (Figure 13). It is essential to say that not all hydrates decomposed from 120-600 \({}^{\circ}\)C contributed to the strength development. In addition, other external factors are related to compressive strength, such as workability, casting/molding capacity, water content and internal porosity. The variation in the activation parameters affected the hydration process. Figure 14 presents the TGA mass loss at 28 days and the initial heat release found via calorimetry (Section 3.2) against the silica modulus and Na\({}_{2}\)O concentration (4% and 6%).