## 3 Results
### Thermogravimetric Analysis  
A TGA was conducted on the four mixes after 1, 2, 5, 11, 18, and 25 days of exposure following their removal from the solutions and subsequent drying at 55 \(\pm\) 5 \({}^{\circ}\)C for 24 h (see Figure 4). In accordance with previous research findings [47, 48], it was assumed that the first peak or major mass loss observed between 30 \({}^{\circ}\)C and 200 \({}^{\circ}\)C is related to the decomposition of ettringite, calcium silicate hydrate (C-S-H), and free water elimination. Additionally, the presence of monosulfouluminates (AFms) is indicated by a peak at 190 \({}^{\circ}\)C. A third peak, occurring between 450 \({}^{\circ}\)C and 550 \({}^{\circ}\)C, corresponds to the dihydroxylation process of portlandite or calcium hydroxide (Ca(OH)\({}_{2}\)), while a peak between 650 \({}^{\circ}\)C and 820 \({}^{\circ}\)C is attributed to the decarbonization of calcite (CaCO\({}_{3}\)). The thermogravimetric derivative (DTG) was obtained to quickly identify the peaks. In this study, portlandite losses were quantified and are presented in Table 3. Moreover, careful observation was made regarding the AFm peaks (as represented in Figure 4). This approach is crucial because, in addition to the reasons discussed in Section 3.1, portlandite and AFm, in the presence of sulfate ions, are known to participate in the formation of expansive products [49, 50]. Figure 4: TGA and DTG of the four mixes after 25 days of exposure to (**a**) water, (**b**) chloride, (**c**) sulfate, and (**d**) sulfate–chloride. As shown in Table 3, Mix2 experienced a loss of portlandite when immersed in water, chloride, sulfate, or a combination of chloride and sulfate solutions. On the other hand, Mix1 experienced the loss of portlandite only when in contact with sulfate and the combination of sulfate and chloride. This loss can be attributed to the consumption of portlandite by chloride and sulfate ions, particularly evident in EXP1, EXP2, and EXP3. The loss of portlandite in Mix2 at EXP0, and its absence in Mix3 and Mix4 in all four exposure conditions, even though the pastes were at an early age (the hydration process of cementitious materials was still ongoing), might contribute to the pozzolanic effect of SCM, which leads to calcium hydroxide consumption [51]. While comparing the loss of portlandite content under different exposure conditions, it was noted that the highest loss occurred when the mixes (Mix1 and Mix2 in this case) were exposed solely to sulfate (EXP2). This finding indicates that the coupling of the two ions (chloride and sulfate) in EXP3 mitigated the attack and resulted in a lesser reduction in portlandite content. As shown in Figure 4, the disappearance of AFm in the pastes subjected to only sulfate ions suggests that the sulfate attack led to the consumption or transformation of AFm compounds. AFm is recognized as relatively less stable and is generated through the hydration of C\({}_{3}\)A and C\({}_{4}\)AF [52]. Subsequently, when the aluminate reacts with gypsum, the formation of AFt occurs [53]. However, interestingly, when both chloride and sulfate ions were present together (EXP3), AFm was still present after 25 days of exposure when compared to exposure to sulfate ions alone (EXP2). This indicates that the coupling of chloride and sulfate ions in the solution has a protective effect and mitigates the deterioration of cementitious materials. It is important to note that while an increase was observed in the mass loss associated with the first DTG peak (at T \(<\) 200 \({}^{\circ}\)C), as illustrated in Figure 4, which represents the quantities of free water, C-S-H, and ettrinigite in the presence of sulfate (EXP2 and EXP3), the results were not consistently conclusive. This ambiguity arises from the simultaneous presence of free water, the decomposition of C-S-H, and the formation of ettrinigite.