# Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age
## 3 Results
### Water Porosity  
A water porosity test was performed on all the mixes after 8 (Ti1) and 80 (Ti2) weeks of immersion in the sulfate solution in addition to 24 h after casting (Ti0). As illustrated in Figure 8, the initial porosity of the samples was notably high, approximately around 51% at time Ti0, consistent with select a W/B ratio of 0.55. A previous study conducted by [PERSON] et al. [57] demonstrated that increasing the W/B ratio leads to an increase in total porosity. The porosity then decreased by approximately 8% when cured in water (refer to Ti2 Ref) due to the ongoing hydration process. The significant initial porosity can be attributed to the fact that the samples were poured into the molds without vibration, as mentioned in Section 2.2. Additionally, it is evident that the porosity varies among the samples, and its evolution differs. This variability is attributed to differences in workability resulting from the substitution of clinker in the various mixes [58]. Figure 7: Raman specters of the sulfate solutions that are in contact with all the mixes after 80 weeks. Comparing water porosity results at 8 weeks between mixes exposed to sulfate (Ti1) and mixes cured in water (Ti1 Ref) reveals interesting trends. Notably, the reference mix, P1, showed slightly higher porosity in the water-cured environment (-49%) compared to its sulfate-exposed counterpart (-48%). A similar pattern was observed in other mixes, including S1, S2, T1, T2, and Q1, where slightly higher porosity values were seen underwater curing than with sulfate exposure. This is attributed to the formation of ettringite and gypsum due to sulfate exposure. The most significant increase in porosity occurred in S1, where the sulfate-exposed mix (-50%) surpassed the water-cured mix (-51%) by 1.2 percentage points. This aligns with the expansion rates and mass gain of mix S1, which exhibited the highest values among all mixes in the early stages of the attack. Similar findings have been documented by other studies, which have compared the porosity of mixes containing 100% CEMI with those incorporating supplementary cementitious materials [57]. However, examining water porosity results after 80 weeks of sulfate exposure (Ti2) and comparing them with mixes cured in water for the same duration (Ti2 Ref) reveals different trends when compared to Ti1 and Ti1 Ref. The reference mix (P1) demonstrated higher porosity in the sulfate-exposed environment (49.5%) compared to its water-exposed counterpart (-41%). This unexpected trend extended to other mixes, including S1, S2, T1, T2, and Q1, where sulfate-exposed mixes exhibited higher porosity values than their water-exposed counterparts. The most important increase in porosity was observed in P1, with the sulfate-exposed mix exceeding the water-cured mix by 8.2 percentage points. This is likely due to the formation of cracks due to ESA. These results are in accordance with all the previous findings of this study, including extensive mass and expansion gain, high formation of ettringite and gypsum, as well as visual deterioration of the reference mix. Moreover, the blended mixes exhibited similar behavior in the long-term exposure to sulfate, as previously demonstrated, with good values regarding porosity at this stage, with mix S2 leading. However, the difference between the blended mixes during the water porosity test is minor. The water porosity results are valuable for comparing two time-points. However, this parameter cannot be considered a major durability indicator concerning ESA. This is because there can be significant fluctuations in the porosity. These fluctuations may be attributed to various phenomena, including the pore-filling effect by the formation of ettringite and/or gypsum, cracks opening due to the crystallization pressure of the expensive products coming from ESA, subsequent sealing of these cracks, the creation of new cracks, and so forth.