## 3 Results  
### pH Variations  
The results of pH variation as a function of time are shown in Figure 2.  
The curves demonstrate a significant increase in the pH of the solutions after submerging the cement paste powders in the four different environments. In the case of EXP0 (tap water only), the pH rose from 7.6 to a range of 8-9 after 1 day of contact between the water and the specimens, stabilizing with negligible fluctuations over the subsequent 24 days of exposure. This increase was due to the alkalinity of the submerged pastes [41]. For the other exposures (EXP1, EXP2, and EXP3), the pH increase was even more pronounced, ranging from 6.9-7.2 to 12.5-14, and was directly related to the leaching of calcium and hydroxyl ions into the solutions [38; 39; 40], as previously mentioned in Section 2.4.1. The chemical reaction between sulfate and cementitious materials resulted in the generation of hydroxyl  
Figure 2: pH variation of the four different mixes after being exposed to the four different environments at different exposure times.  
ions, which subsequently elevated the pH of the surrounding solution. Sulfates replace two moles of hydroxyl during their interaction with concrete, thereby causing an increase in the pH. Additionally, chloride ions affect pH levels. The presence of chloride ions can facilitate the release of calcium from cementitious materials, leading to its dissolution into the adjacent solution. This phenomenon further contributes to pH changes. Understanding the interplay between sulfate and chloride ions and their impacts on pH variations is crucial for a comprehensive grasp of the intricate deterioration processes occurring within cementitious materials.  
In the case of EXP1 (chloride-only exposure), the pH was the lowest compared to EXP2 and EXP3, because chloride does not influence pH in the way sulfate does, due to the kinetics of the chemical reactions. On the other hand, EXP2 (sulfate-only exposure) exhibited the highest pH among the different exposures. The decomposition of calcium hydroxide and calcium-silicate-hydrate compounds can significantly elevate the pH of the surrounding solution [42; 43]. This observation suggests that hydroxyl and calcium leaching is the most significant when cementitious materials are exposed to sulfate alone, and the coupling of chloride and sulfate attenuates the attack since the pH of EXP3 always ranged between the values of the pH of EXP1 and EXP2, even though both chloride and sulfate increase pH levels. Notably, the differences in pH between the various mixes were not considerable.  
When comparing the various mixtures, it was evident that the incorporation of SCM caused a comparatively lower increase in pH compared to Mix1, composed entirely of CEM I. SCM plays a role in reducing the presence of calcium hydroxide, often referred to as portlandite [44]. This reduction results in the decreased leaching of calcium and hydroxyl ions into the solution, consequently leading to a less pronounced rise in the pH of the surrounding environment.  
Overall, these pH variations provide valuable insights into the chemical reactions and leaching processes occurring in cementitious materials when exposed to different environments.  
Furthermore, it is worth noting that in the presence of sulfate (EXP2 and EXP3), a change in color and the formation of a thin white film were observed on the surface of the submerged powders after 11 days of exposure (as shown in Figure 3). These visible changes indicate the occurrence of chemical reactions within the cementitious materials. The formation of a white film is likely associated with the precipitation of compounds resulting from the reaction between sulfate ions and the cementitious matrix. According to other studies, it is more common for gypsum to build up on the surface of the material [45; 46]. All of the present solids have been filtered and analyzed together.  
Figure 3: Tested powders originating from Mix1 after 11 days of exposure to (**a**) water (EXP0) and (**b**) sulfate (EXP2).