# Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age
## 3 Results
### Mass Changes and Visual Inspection  
The mass of all samples was regularly measured over 120 weeks. The mass evolution over time is illustrated in Figure 2 for the six different mixes. Each reported value is the average of three measurements from three different samples. Figure 2 indicates that all samples experienced a mass increase throughout the entire attack period. This phenomenon is expected, as ESA leads to a mass gain, as shown by previous studies [41; 42; 43]. However, the rate of mass gain varied among the mixes. Binary (S1 and S2), ternary (T1 and T2), and quaternary (Q1) blended pastes exhibited similar rates of mass gain, distinct from the reference mix (P1) composed of 100% clinker. Blended pastes demonstrated a significant mass gain in the initial 35 weeks, stabilizing thereafter with a slight increase up to week 120. In contrast, the mass gain kinetics of the reference mix (P1) were different from the other formulations, showing a rather regular mass gain during the 62 weeks and a beginning of stabilization afterward. Mass measurements for P1 were terminated at week 82 due to the samples' full deterioration caused by ESA. The initial 12 weeks witnessed substantial mass gain for all mixes, attributable to various factors. The samples, immersed in sulfate at an early age (24 h after casting), experienced both the hydration of cementitious pastes, leading to the formation of hydrated products, and water absorption [42; 44]. Additionally, this gain can be associated with the chemical reaction between hydrated cementitious materials and sulfate, resulting in the formation of ettrinigite and gypsum within micro-pores and cracks, contributing to the observed mass gain [16; 40; 45]. Following this period, marking the completion of the hydration of cementitious materials (lasting 90 days, notably longer for blended pastes  
Figure 2: Mass of the six mixes during the ESA over time. compared to 28 days for P1, as discussed by [PERSON] et al. (2018)), the blended mixes continued to experience mass gain but at reduced rates before almost stabilizing (having however minor gain), as discussed earlier. At this stage, with hydration nearly complete and the samples saturated, the observed mass gain could be attributed to the formation of gypsum and ettrinigite resulting from the chemical reaction between the hydrated products and sulfate. It is important to note that 90 days after the fabrication (upon completion of hydration), a significant reduction in porosity and capillary water absorption in the blended pastes is observed, according to previous studies ([PERSON] et al., 2018). This decrease in porosity contributes to stabilizing the mass gain. The above-explained results highlight that the reference mix (P1) exhibited the least favorable behavior in terms of mass gain and overall durability, as evidenced by its degradation after 90 weeks of exposure. In contrast, the other mixes, which incorporate SCM to partially substitute the clinker, demonstrated a more robust performance, maintaining their structural integrity even after 120 weeks of sulfate exposure. Upon comparing the mass gains of the blended pastes, it becomes evident that the ternary mix (T2), composed of CEM I, blast furnace slag, and metakoolin, exhibited the lowest mass gain from the initiation of the sulfate attack. In contrast, the mix containing CEM I and fly ash (S1) displayed the highest mass gain among the blended mixes. This, coupled with the mass gain rates of the other blended mixes, could imply that the inclusion of blast furnace slag and metakoolin, within specified replacement percentages, enhanced the overall performance of the mixes. In terms of visual inspection, the reference mix P1 exhibited the highest visual aging rate, as depicted in Figure 3. After 60 weeks of exposure, P1 underwent a significant color change compared to the minor changes observed in the other mixes, which exhibited similar behavior in terms of color alteration and crack development.