## 3 Results and Discussion
### Thermogravimetric (TG) Analysis  
The TG and the differential thermogravimetry (DTG) curves of the 1-day and 28-day cured samples are presented in Figure 4. In the TG results, the loss of free water was not involved because free water was removed during the sample preparation through the process of solvent exchange and vacuum drying. The peak near 80 \({}^{\circ}\)C was mainly associated with dehydration of ettringite; the peak around 100-200 \({}^{\circ}\)C was linked to water loss from monosulfate and/or kuzelite. The peak around 200-300 \({}^{\circ}\)C was due to water loss of AH\({}_{3}\)[15; 44; 45]; gypsum is known to be decomposed around 120 \({}^{\circ}\)C in TG [39; 46]; [PERSON]'s salt is known to undergo 2 two steps of weight loss at different temperature ranges: (1) dehydration near 130 \({}^{\circ}\)C and (2) dehydroxylation at about 280 \({}^{\circ}\)C [41; 45; 47; 48]. Although [PERSON]'s salt also experiences a series of phase transformations (e.g., recrystallization) from 400 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C, no weight loss is involved in these transformations. In Figure 4a,b, when no gypsum was incorporated, the use of seawater or RO reject water considerably reduced the weight loss of monosulfate and/or kuzelite, whereas the weight loss of [PERSON]'s salt increased. This observation is fairly consistent with the results of XRD. As mentioned in the previous section, the formation of [PERSON]'s salt likely helped increase strength to some extent, which was particularly observed in the RO sample. In Figure 4c,d, when gypsum was incorporated, the DTG peaks of monosulfate and kuzelite were mostly removed in all samples, and large peaks of ettringite formed. As a result, all samples with gypsum showed similar curve profiles of weight loss, unlike the gypsum-free samples, and the quantities of ettringite were similar among all samples at 1 and 28 days. However, when seawater or RO reject water was used, a slightly higher degree of [PERSON]'s salt formation was observed. Note that the concentration of sulfate ions in the RO reject water was considerably lower than the sulfate amount due to gypsum addition in this study. Thus, the concentration of sulfate ions in the RO reject water was likely not high enough to noticeably increase the formation of ettringite in any sample. The DTG curves of ettringite in Figure 4b showed a slight increase when RO reject water was used. On the other hand, the DTG curves in Figure 4c,d indicate that ettringite production was significantly lower when RO reject water was used rather than other types of mixing water. Given that the presence of Mg\({}^{2+}\) has an inhibitory effect on the formation of ettringite [49; 50; 51], the reduced amount of ettringite may be partially due to the greatest concentration of Mg\({}^{2+}\) in the RO reject water. However, the dashed boxes in the TG curves in Figure 4 clarify that the weight loss of ettringite was not notably affected by changing mixing water; for instance, in Figure 4d, the difference in weight loss between CG and ROG up to ~120 \({}^{\circ}\)C was merely 0.6 wt%, and this mass difference corresponds to only 1.2 wt% of ettringite formation. Given that, in Figure 4d, the sample ROG showed ~12.7 wt% of weight loss up to ~120 \({}^{\circ}\)C, and this weight loss corresponds to ~27.7 wt% of ettringite formation, the 1.2 wt% of difference in ettringite formation was not significant. Thus, the strength differences among the samples were likely not significantly correlated with the influence of changing mixing water on ettringite formation, but rather more related to the formation of Friedel's salt in this study because earlier studies demonstrated that even a small increase in Friedel's salt notably decreased the porosities of the hardened pastes of cementitious binders [41; 42; 43].