Iron sulfide-bearing aggregates can undergo oxidation reactions that can cause an internal sulfide attack in concrete, leading to severe damage on concrete surfaces by the formation of rust, gypsum, ettringite, and pop-outs. Solving these issues is extremely important in the modern construction industry. Currently, several approaches such as screening, alternative mix design, and protection techniques are being investigated to achieve the desired goal, and this paper mainly focuses on the protection measures. Systematic performance-based evaluation methods are required for formulating guidelines to solve these issues. Nevertheless, appropriate test methods are not available in the state of the art standards. Therefore, this research made an effort to establish a complete set of test methods to evaluate the performance of concrete containing iron sulfide-bearing aggregates. These methods include evaluating expansion, quantitative evaluation of rusting, and quantitative determination of pop-out parameters. An accelerated mortar bar test was developed to assess the expansion by modifying the test method available in ASTM C1260 (accelerated mortar bar test for ASR). Accordingly, a storing temperature of 60^oC, 80% RH, and wetting and drying cycles of 7 cycles per two weeks (6% NaOCl or H₂O with oxygen added through the pump while submerging) were found to be very effective in accelerating the oxidation process in the laboratory (Fig. 1). The digital image processing method based on the 'Otsu technique' was used to evaluate the rusting quantitatively (Fig. 2). Moreover, the pop-out frequency (n) and the average chord length (l) were used to characterize the pop-out, and these parameters were evaluated based on the image-processing algorithm (Fig. 3).



The developed test methods were used to evaluate the effectiveness of different surface treatments, such as water repellent, crystalline waterproof system, and epoxy coating, in controlling the oxidation. The cast samples were oxidized and measured to obtain the expansion variation, as shown in Fig. 4. The samples treated with water repellent showed higher expansion, while the epoxy coating and crystalline waterproof system showed lower expansion than the control samples, as shown in Fig. 4. The microstructural examination was also carried out using SEM with EDS to understand the mechanisms that led to the significant expansion of the samples. Fig. 5 illustrates the SEM image of the damages that occurred in the controlled samples due to the presence of iron sulfide-bearing aggregates, where the micro-cracks and ettringite were detected. The efficacy of surface treatments in lowering the level of rusting caused by the presence of iron sulfide-bearing aggregates was also examined. The obtained results for rusting and expansion showed a similar trend, as shown in Fig. 4 and Fig. 6. Furthermore, pop-outs have been observed in the control samples and the samples treated with water repellent. Accordingly, the control sample's pop-out frequency and average chord length were found to be 280 pop-outs per m² and 0.01 m, respectively. Severe pop-outs have been observed in the samples that are treated with hydrophobic surface treatment compared to control samples, and the pop-out frequency and average chord length of these specimens were 520 pop-outs per m² and 0.015 m, respectively. The Epoxy and crystalline waterproof system were highly effective in reducing the oxidation rate of iron sulfide-bearing aggregates, as evidenced by the expansion, rusting, and pop-out evaluations. Further research is being conducted to propose a comprehensive set of guidelines to prevent the damages caused by the iron sulfide-bearing aggregates, which will be documented in the near future.