# New Methods for Assessing External Sulfate Attack on Cement-Based Specimens
## 5 Conclusions  
Two new test methods were introduced in this paper to study the ESA at the scale of cement paste specimens. First, sulfate ion penetration depth measurements were performed on cylindrical specimens after imposing drying conditions on their cut surfaces. Second, OF sensors were used to monitor the ESA-induced expansion of cement paste prisms. The results of the proposed drying method were compared with the sulfate ion penetration depths obtained by ICP-AES to determine the reliability of the proposed method. Two comparable and parallel paths were then observed in terms of penetration depths, especially considering the results obtained after 8 weeks of accelerated ESA. However, the ICP-AES curve maintained a higher amplitude than the drying method. This is attributed to the fact that ICP-AES is able to detect both chemical and physical sulfates, whereas drying only quantifies free sulfates. In future investigations, the white precipitate should be examined via SEM-EDX to identify all the phases that have formed there. It would also be beneficial to include other types of cement and different exposure conditions in future studies to obtain more information on the efficiency of this method compared with the traditional ICP-AES method. By using advanced techniques for analyzing images of sample surfaces and identifying sulfate profiles, artificial intelligence and image analysis methods can be used for the measurement of ESA profiles in the material. High-resolution images can be captured and analyzed using image analysis software. Artificial intelligence algorithms may be trained to recognize and extract key features associated with ESA, such as ettringite formation, gypsum deposits, and other indicators of sulfate attack. Furthermore, AI algorithms can learn to recognize patterns and characteristics specific to ESAs through the use of machine learning models. In this way, the system can automatically identify areas of the concrete surface that have been affected by sulfate attack before or after the appearance of the damage. This technique can then classify different levels of ESA severity and quantify the extent of damage in the material. In addition to providing valuable insights into the progression of sulfate attack, this type of quantitative information can also be used to assess the structural integrity of concrete. An optical fiber-based method was also developed to monitor the changes in length of cement paste samples as a result of ESA-induced expansion. The measurements were compared with those obtained using a conventional extensometer. After exposure to accelerated ESA, both techniques recorded almost the same expansion evolution and final average expansion (about 0.07%). This result confirms that ESA-induced expansion can be accurately monitored with OF sensors. Due to the deterioration of the optical fiber, the exposure lasted for only 78 days, which is a sufficient duration for some test methods, such as Swiss standard SN 505262-3 [46]. This suggests that future studies should continue this experimental work by testing other types of OF. In any case, the proposed method has great potential, for example as a means of automatically monitoring a large number of samples. Validation, conceptualization, methodology, and writing--review and editing, O.O.M., M.Q., M.J. and V.B.-B. ; writing--original draft preparation, investigation, and formal analysis, O.O.M. and M.Q. ; supervision, O.O.M., M.Q. and V.B.-B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data are contained within the article. The authors declare no conflicts of interest. * [PERSON] and [PERSON] (2023) [PERSON]; [PERSON] Deterioration Process of Cementitious Material Properties under Internal Sulphate Attack. _Appl. Sci._**2023**, _13_, 3982. [CrossRef]
* [PERSON] et al.