# New Methods for Assessing External Sulfate Attack on Cement-Based Specimens
## 3 Results
### Sulfate Profiles
An example of the penetration profiles measured during the study of [PERSON] et al. is shown in Figure 10. More detailed information regarding the procedure for obtaining sulfate profiles by ICP-AES can be found in [10]. Figure 9: Sulfate signal in the affected zone of the sample. It is important to note that sulfate ions are transferred to the cement matrix during the process of ESA, and calcium ions are leached to the outer solution during the process. It is a two-mode process, one involving diffusion, which is considered to be the dominant phenomenon, and the other involving the physicochemical fixation of sulfate ions in the cement matrix [10]. Sulfate ions penetrate materials more slowly when the concentration difference between the inside and outside of the material is reduced. This case shows an accumulation of sulfate ions on the surface of the samples. This means that sulfates detected through the drying procedure correspond to those remaining in the interstitial porous solution that crystallized under applied evaporation conditions (T = 20 \({}^{\circ}\)C and RH = 50%). The sulfate profiles measured by ICP-AES are presented in Figure 10. These profiles were considered in order to obtain the values of the penetration front depth to be compared with those obtained by the drying method. In Figure 10, the black dashed line illustrates the initial content of sulfate in sound cement paste (of the order of 2% in g/g of anhydrous cement). Considering this initial presence of sulfate, the depth value deducted for each exposure period is the highest depth value of the corresponding profile (in the X axis) for which the concentration of SO\({}_{3}\) is bigger than the initial value. It must be underlined that, in the ICP-AES method, sulfate concentrations were calculated from the total sulfur concentration ([SO\({}_{3}\)] % in g/g of anhydrous cement). As a consequence, the sulfate content measured by ICP-AES is more similar to the solid phase content, which includes the total sulfates present in the matrix (free sulfates and combined sulfates). Figure 11 illustrates the comparison between the results obtained by the ICP-AES and drying methods. By comparing the penetration depths obtained by drying and ICP-AES, it is apparent that both techniques permit us to describe the evolution of the penetration front of sulfate. According to ICP-AES, the highest depth recorded by the method was 6.5 mm, whereas the highest depth recorded by drying was 5 mm. Compared with the results obtained by the drying method, which revealed only free sulfate contributions, the ICP-AES results were higher due to the significant sulfate content in the solid phase, which was physically and chemically combined. This contributed to the higher depths obtained by ICP-AES compared with those obtained by the drying method. Despite the differences in results between the two methods, we note a similar trend in the curves, particularly after 8 weeks of exposure to the sulfate solution. This suggests that there is a relationship between the results of the two techniques and that a coefficient should be proposed to switch between them. It can be concluded that the drying method is suitable for expert cases because of its ease of use compared with the ICP technique. Figure 10: Sulfate profiles measured by ICP-AES for different exposure durations to ESA (from [45]). Some parameters, such as type of binder, w/c, and curing period, may influence the definition of the white precipitation zone. The type of binder used in a material can influence the definition of a white precipitation zone due to its chemical composition, reactivity, and interactions with other elements present in the material. Different binders, such as Portland cement, slag, or fly ash, have distinct hydration behaviors and produce varying reaction products. The lower the portlandite content, the less this white precipitation zone appears.