# Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age
## 3 Results
### Thermogravimetric Analysis  
TGA was conducted on the six mixes at two different time points: 8 (Ti1) and 80 (Ti2) weeks of immersion in the sulfate solution. The analysis included measurements on materials extracted at various depths within the 40 \(\times\) 40 \(\times\) 160 cm\({}^{3}\) specimens, specifically at 1 (surface), 2, 5, and 15 mm. According to some previous research [48; 49], when examining the DTG curve, the initial peak, observed between 30 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, signifies the decomposition of ettrinite, C-S-H, and free water. Furthermore, the presence of monosulfoaluminates (AFm) was indicated by a peak at around 190 \({}^{\circ}\)C. The dihydroxylation process of portlandite (Ca(OH)2) manifests as the third peak between 450 \({}^{\circ}\)C and 550 \({}^{\circ}\)C, while the decarbonation of calcite (CaCO3) was responsible for the peak observed between 650 \({}^{\circ}\)C and 820 \({}^{\circ}\)C.  
When investigating ESA, a careful analysis of portlandite consumption is imperative, as it provides valuable insights into the progression of this attack [16]. Additionally, AFm serves as a source of alumina during the sulfate attack, contributing to the formation of ettrinite [50]. The results related to portlandite content are presented in Figure 4.  
Upon a general examination of portlandite content, carried out using the TGA test, it can be shown that the progression of the attack at 80 weeks overtakes that observed at 8 weeks, aligning with expectations. A more detailed analysis comparing depths at 1 mm and 2 mm reveals a heightened aggression of the attack at the initial 1 mm, in direct contact with sulfate. This is notably reflected in the portlandite content at these respective depths. Furthermore, the reference mix P1 exhibits a significantly higher overall portlandite content compared to the blended mixes. This is attributed to the absence of the pozzolanic effect of SCM, which typically favors the formation of C-S-H [34; 51]. Figure 4: Portlandite content (%) of the six mix samples at 1 mm and 2 mm depths after being submerged in sulfate for 8 weeks (Ti1) and 80 weeks (Ti2). From the data presented in Figure 4, it becomes evident that the reference mix P1 exhibits weaker durability against sulfate attack. This conclusion is drawn from the higher portlandite loss observed in this mix, not only at different depths (1 and 2 mm) but also at different time points (Ti1 and Ti2). In the initial 8-week step, the portlandite content increased from 2.5% to 3.3% at depths of 1 and 2 mm, respectively. Subsequently, at Ti2, the portlandite content further increased from 0.85% at 1 mm to 2.2% at 2 mm. This consistent increase in portlandite content indicates a more pronounced degradation of the reference mix under sulfate attack conditions. However, when examining the blended mixes, their behavior in terms of portlandite loss appears to be quite similar. Considering the ternary mix T2, characterized by the best resistance based on the previously discussed results, its portlandite content, for instance, increased marginally from 0.63% at 1 mm depth to 0.8% at 2 mm depth at time Ti2, representing a minimal loss of 0.17%. This indicates a more robust performance of the blended mixes, particularly exemplified by mix T2, against sulfate attack conditions compared to the reference mix. Analyzing the first peak of the DTG curve (refer to Figure 5), it is evident that the content of ettrigite, C-S-H, and free water at all depths of the reference mix P1 is greater than in other mixes. Considering that all mixes underwent the same conditions and drying procedures and acknowledging that the C-S-H content is higher in the blended pastes [51], it can be concluded that the ettringite content in the reference mix is elevated, extending even to a depth of 15 mm. This indicates not only the poor resistance of P1 when it comes to ESA but also suggests that the attack has reached the core of the reference mix. In contrast, the attack remains superficial in the blended mixes even after 120 weeks.