# New Methods for Assessing External Sulfate Attack on Cement-Based Specimens
## 4 Discussion  
### Discussion Regarding the Drying Method  
Based on the results of the described study, the proposed method for assessing the depth of the affected zone due to ESA appeared to be quite effective. As a result of the aggressive evaporation conditions imposed in the procedure (T = 20 \({}^{\circ}\)C and RH = 50%), sodium sulfate crystallized inside the material, creating a sort of white precipitate on the surface exposed by the cut of the specimen. It should be noted that even though the quantitative results obtained by the drying method differed from those obtained by ICP-AES, the same trends and slopes were observed for both methods, particularly after 8 weeks of exposure. The observed differences are explained by the fact that ICP-AES takes into account all of the total sulfur concentration (free and combined sulfates) while sulfate content examined by the drying method represents the number of free sulfates remaining in the interstitial solution. By using the proposed method, time can be saved and measurements can be taken without prior thorough preparation. Moreover, the results are easily obtained and interpreted within a few minutes owing to the use of a simple steel ruler. As an alternative, the quantitative determination of the affected depth using ICP-AES requires many hours of meticulous preparation while respecting and following very specific procedures. Also, it should be noted that the quantitative identification of the penetration front of sulfate ions by the drying method appears to be applicable in situ to assess the depth of the sulfate front in a real RC structure. An evaluation of this type can be carried out by coring a sample and then allowing the curved lateral surface to dry by air. However, the drying method is not as accurate as ICP-AES. Also, due to the dark texture of the binders usually used in sulfate-resisting cements (like CEM III and CEM V), it could be difficult to detect visible white precipitates in the drying surface. As a final note, the primary concern with the drying method is that it detects only free sulfates that are present in the cement matrix's interstitial solution. Several aspects should be considered in future works to complete and improve the technique presented in this section. For example, the images obtained after drying could be processed and analyzed using a specific image analysis software. In the presented work, image contrast processing was performed in a very simple way using basic software, and depth measurement was performed manually, whereas software could have provided a depth measurement based on contrast analysis. In addition, a colored indicator that reacts with sulfate ions can help detect whitish precipitates. Lastly, it is possible to optimize the treatment conditions (RH and temperature) in order to enhance their effects and to obtain a more visible contrast between the cement paste and the attacked area. Using simple assessment techniques to determine the extent of ESA has several advantages over more complex chemical methods. It is worth noting that simple assessment techniques are generally less expensive and easier to implement, allowing preliminary results to be obtained quickly. Furthermore, these simple assessment techniques can be used in the field to facilitate the inspection of structures and to provide real-time assessment. In this way, areas affected by ESA can be quickly identified, and appropriate preventive or corrective action can be taken. However, even though the proposed simple assessment technique can provide preliminary and indicative results regarding sulfate penetration in concrete structures, it is not as accurate as more complex chemical methods. Therefore, it may be necessary to use more advanced chemical techniques to accurately assess the progress of the ESA attack.