# New Methods for Assessing External Sulfate Attack on Cement-Based Specimens
## 1 Introduction
The assessment of carbonation and chloride diffusion is generally considered easier to conduct on existing structures compared with evaluating ESA for several reasons: Firstly, carbonation and chloride diffusion can be assessed nondestructively using methods such as concrete resistivity, half-cell potential measurements, and chloride ion penetration tests that do not require invasive measures that could damage the structure. In addition, carbonation and chloride diffusion are the two most common causes of concrete deterioration for which there are established test methods. ESA, on the other hand, is much less common, and its assessment often requires more specialized knowledge and techniques. Furthermore, carbonation and chloride diffusion on concrete are generally well understood and documented, making interpretation and action easier. Lastly, identifying carbonation- and chloride-induced corrosion on concrete surfaces is relatively straightforward with simple color indicators (phenolphthalein for carbonation and silver nitrate for chloride diffusion). However, identifying the specific mechanisms and manifestations of ESA may require additional expertise. To sum up, the assessment of ESA on structures is challenging for several reasons. ESA is complex and progressive in nature, making it difficult to detect and evaluate [23, 24, 25]. Laboratory analysis is often required to confirm the presence of sulfates. Furthermore, as discussed above, the effects of ESA vary depending on several factors including environmental conditions [26]. In addition, ESA can be difficult to distinguish from other types of degradation [13]. Expertise and continuous monitoring are then essential in cases of ESA [27]. Only a rigorous analysis can enable an accurate assessment of the damage caused by the ESA. According to survey results, repair recommendations and ongoing damage monitoring can be provided to ensure that structures are maintained in a safe and functional condition, thereby reducing the risk of structural failure. The inductively coupled plasma (ICP) test is considered one of the most reliable methods for measuring sulfate profiles in concrete [10,13,28,29]. However, this method can have some difficulties in application. In addition to its high cost, sample preparation is a complex process. Samples are often extracted from sulfates by dissolving them in a strong acid. It is important to note that this dissolution step can take a long time and may require additional steps to remove impurities. The method is also not highly sensitive, and needs a high concentration of sulfate ions, which poses another problem [30] because this concentration of sulfates can be quite low in attacked concrete. Furthermore, ICP is not capable of providing high-resolution sulfate profiles. Rather, it measures the concentration of sulfate in a small area of the sample. It may be necessary to make measurements at different depths, making the work quite tedious [10; 13]. To assess the progress of sulfate attack, an alternative to measuring the width of the penetration front of sulfate ions is to measure the effects of the attack, such as ESA-induced expansion. Invar wire (wire with low thermal expansion and dimensional stability) can be used to monitor the expansion of an RC structure [31]. Invar wire must be anchored to the concrete to function properly. A properly anchored and secured wire is necessary for accurate measurement. A second challenge is reading and interpreting the invar wire readings. Environmental factors such as moisture, temperature, and mechanical stress may affect the measurements. Additionally, invar wire is not a real-time expansion tracking tool. The process of reading and recording measurements at regular intervals often requires manual intervention. This can be time-consuming and resource-intensive, and limits the ability to detect specific concrete problems in a timely manner [31].