# Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age
## 3 Results  
### Expansion  
Expansion measurements were periodically recorded over the full 120-week duration of the study. The expansion evolution of the samples over time is presented in Figure 1. The provided values are derived from three measurements conducted on distinct samples.  
Figure 1 clearly shows that the expansion behavior of the reference mix P1 differs significantly from that of the binary, ternary, and quaternary blended pastes, particularly after week 54. The expansion rate of P1 can be divided into five phases. These phases closely resemble those documented in the current literature [6]. In the initial phase, spanning the first 4 weeks, there is a substantial expansion, reaching 0.08%. The second phase involves a slower but continuous expansion, reaching 0.12% after 54 weeks of sulfate exposure. The third phase extends from week 54 to 72, characterized by a rapid and pronounced expansion, peaking at 0.29%. The fourth phase, between weeks 72 and 84, is characterized by stability,  
remaining around 0.3%. The fifth phase occurs after that period, reaching an expansion of 0.95% by week 90, at which point the samples were completely degraded. The behavior of the blended pastes (S1, S2, T1, T2, and Q1) exhibited two major phases globally (with three fluctuations in general). The first phase, similar to the reference mix P1, occurred during the initial 4 weeks, where the expansion was around 0.05%. Subsequently, insignificant changes were recorded until week 120, when the expansion reached 0.145%. Throughout this phase, three minor fluctuations were observed. The first fluctuation extended from week 4 to week 54, during which the expansion increased slowly. The second phase persisted until week 70, remaining almost stable before experiencing a subsequent increase at a higher rate.  
Based on the description of the expansion rates provided earlier, a common pattern emerged between the expansion rates of the reference mix and the blended ones. After each increase in the expansion rates, a period of stability is observed, followed by a subsequent increase. This pattern is likely attributed to the formation of ettrigite and/or gypsum in the pores, leading to internal stresses and causing cracking [20; 40] (resulting in an increase in expansion). Subsequently, these products begin to fill the formed cracks (resulting in the stability of the expansion) until they recreate internal stresses and induce new cracks (leading to an increase in expansion). This phenomenon gains further confirmation when examining the continuous mass gain of the samples (refer to Section 3.2).  
Figure 1: Longitudinal expansion of the six mixes over time during the ESA: (**a**) Results of the measurements over the total duration of the test; (**b**) Zoom of the results over the first 64 weeks; (**c**) Zoom of the results from week 70 to week 120.  
When comparing the mixes among themselves, the reference mix exhibits the least favorable behavior in terms of expansion and overall durability against ESA. While the other mixes maintained satisfactory expansion rates for 120 weeks, the reference mix P1 expanded by 0.95% after only 90 weeks and deteriorated thereafter. Regarding the blended pastes, as depicted in Figure 1 and considering the scale and low expansion rates, it is evident that they exhibit almost similar behavior. Upon closer examination, mix T2 (composed of CEM I, blast furnace slag, and metakaolin) stood out with the lowest expansion rates. These findings could suggest that the combination of blast furnace slag and a low quantity of metakaolin contributes to the enhanced durability of the overall mix (as previously shown in a study considering 10 to 15% of metakaolin replacement of cement [29]). This is particularly evident when comparing the behavior of other blended mixes that lack this specific combination of slag and metakaolin.