# New Methods for Assessing External Sulfate Attack on Cement-Based Specimens
## 3 Results
### Sulfate Profiles  
As part of this study, the penetration front of sulfate ions into cement pastes was investigated by visually inspecting the formation of white, fine, and powdery precipitates to determine the depth of the attacked zone. At each scheduled time (2, 4, 6, 8, 12, 16, and 24 weeks), a specimen was removed from the attacking solution, cut in half, and placed in a climatic chamber. Photos of the two cut surfaces were then taken. The visualizations are based on images analyzed using optical microscopy. The contrast of the images was enhanced to improve the visibility of the attacked zone (Figure 7). In each specimen, the width of the attacked zone was calculated as the average value of seven values measured at seven locations of the attacked zone. All the values obtained at the different measurement dates were then used to plot the time evolution of the attacking front (Figure 8). Figure 6: (**a**) ISO values of the displacement field predicted by the FE model; (**b**) visual appearances of the cement paste cylindrical samples after 24 weeks of exposure to ESA. In order to confirm that the white precipitation area in the attack zone was indeed precipitated sulfate, Raman tests were conducted on both affected and non-affected zones. The results of the tests confirmed that the precipitated product in the attack zone was indeed precipitated sulfate (Figure 9). Indeed, this figure shows two patterns for sulfate-affected and non-affected zones. The two patterns are quite similar, except for a peak around 980 cm\({}^{-1}\). This is identified as a characteristic peak associated with sulfate ions. It corresponds to the symmetric stretching vibration of the sulfur-oxygen bonds in the sulfate ions. Figure 8: Penetration depth of sulfate ions measured by the drying method for 24 weeks. Figure 7: (**a**) White precipitation obtained by drying method; (**b**) photo with enhanced contrasts. To challenge the proposed method, a comparison was made between the penetration depth measured by this drying method and the sulfate penetration results obtained using the inductively coupled plasma atomic emission spectroscopy (ICP-AES) method. This comparison was made between the profiles of sulfate penetration obtained by [PERSON] et al. in a previous research project using the ICP-AES technique [10]. In the present study, the exposure conditions related to the work of [PERSON] et al. were reproduced in order to ensure that the results obtained by the proposed investigation method and those obtained by ICP-AES are highly comparable. In the ICP method, a sample is prepared and subjected to acid to extract the sulfates. The resulting solution is then analyzed using ICP spectrometry, which involves the generation of high-temperature plasma to atomize and ionize the sample. The ionized atoms are then quantified based on their unique emission or absorption spectra, allowing for the precise measurement of sulfate concentrations in different layers of the sample. With the ICP-AES method, the total sulfur concentration ([SO\({}_{3}\)] weight percent in g/g of anhydrous cement) can be determined in cement paste samples, resulting in the quantification of the sulfate content. The specimens were ground from their exposed surfaces (bottom circular bases) to a depth of 12 mm. At each grinding step, the amount of powder corresponds to a 1 mm thick sample and contains an average particle size of 315 microns. The extracted powder contains sulfates that have been ionized by an acid attack. After the solution was prepared, it was analyzed using an ICP-AES instrument. Due to the laborious aspect of ICP analysis, only one ICP measurement was performed by measurement time and by considered depth. It should be noted that although the proposed technique (i.e., drying technique) allows a quantitative evaluation of the penetration depth of the attack by ESA, it is not able to measure the sulfate content that is associated with each penetration depth. On the contrary, the ICP-AES analysis can provide a detailed description of the penetration profile.