## 4 Results and Discussion
### Hydration Product Analysis of RCPB
#### 4.3.2 TG and DTG  
Since C-S-H and C-A-S-H gels have low crystallinity and amorphous structures, it is challenging to detect these gels by XRD, so TG analysis was added to further detect the amount of C-S-H and C-A-S-H generated, and TG and DTG analysis was used to further determine the relative amount of amorphous phases in the filler. The TG and DTG analysis was performed to determine the differences in the substances formed in different concentrations. Two different weight loss scenarios can be most easily recognized as negative peaks in the DTG curves, with the intervals of highest weight loss being 60-200 \({}^{\circ}\)C and 650-800 \({}^{\circ}\)C [37].  
From the TG and DTG analysis of the tested samples (Figure 7), the weight loss curves of all the samples showed similar profiles, which were mainly categorized into three weight loss temperature intervals:  
(1) Within the temperature interval of 60 \({}^{\circ}\)C to 200 \({}^{\circ}\)C the material exhibited significant mass loss peaks, with calculated weight losses of 7.97 wt%, 7.37 wt%, 8.24 wt%, and 9.20 wt% for the respective samples, primarily attributed to the evaporation of free and bound water in hydration products [38]. Specifically, gypsum dihydrate (CaSO\({}_{4}\) 2H\({}_{2}\)O) undergoes weight loss between 70 and 130 \({}^{\circ}\)C as it transforms into hemihydrate gypsum (CaSO\({}_{4}\)-0.5H\({}_{2}\)O), while the latter loses structural moisture at 190-230 \({}^{\circ}\)C. The weight loss of C-S-H and C-A-S-H gels occurs in the range of 105-200 \({}^{\circ}\)C, slightly higher than that of gypsum dihydrate but lower than hemihydrate gypsum, corresponding to the release of bound and free water in these gels. Concurrently, AFt demonstrates weight loss between 110 and 150 \({}^{\circ}\)C due to the escape of crystalline water. Notably, higher concentrations correlate with greater mass loss, exemplified by the 69% concentration sample showing a 9.3% mass loss. This is hypothesized to result from increased AFt content in high-concentration hydration products, aligning with prior observations from UCS tests where reduced late-stage strength enhancement in high-concentration specimens implied a dominant role of hydration product composition in overall mechanical performance, thereby validating the interplay between hydration chemistry and material strength.  
(2) CH decomposes to CaO between 400 \({}^{\circ}\)C and 550 \({}^{\circ}\)C, and the following reactions usually occur:  
\[\text{Ca(OH)}_{2}\rightarrow\text{CaO}+\text{H}_{2}\text{O} \tag{5}\]  
In Figure 7, it can be seen that the DTG graphs of the four groups of materials almost overlap, and all four groups lost about 3% of their mass, which proves that the concentration is less for CH content and proves that the degree of hydration is high.  
(3) In the range of 650 \({}^{\circ}\)C to 800 \({}^{\circ}\)C, which is the region of carbonate decarbonization, there is a significant fluctuation in the DTG images of the materials [39], with the TG curves showing a mass loss of about 3.27 wt%, 3.69 wt%, 2.67 wt%, and 2.52 wt%. This is attributed to the high-temperature decomposition of calcite:  
\[\text{CaCO}_{3}\rightarrow\text{CaO}+\text{CO}_{2} \tag{6}\]