A feasible evaluation protocol to determine the most reactive sulfide-bearing aggregate for use in concrete

•The iron sulfides (pyrite and pyrrhotite) oxidation in aggregates was investigated.•Sulfides spatial distribution for different aggregate particle size was evaluated.•To promote the sulfide oxidation a leaching process was carried out.•Sulfur from each sulfide in aggregate was determined according to the particle size.•Total sulfur before and after oxidation was determined according to the particle size. Internal sulfate attack is one of the most harmful deterioration mechanisms to concrete. A testing procedure was developed to evaluate how reactive is a sulfide-bearing aggregate to use in concrete. The aggregates were produced from iron sulfide rocks that have at least 1.5% of sulfur. Particle sizes between 0.15- and 4.80-mm had the sulfur quantities from sulfide (pyrite and pyrrhotite) determined by direct combustion test. The exposed surface of each sulfide was calculated using a scanning electron microscope (SEM) connected to an automated image analysis system - Mineral Liberation Analyzer (MLA). Samples also were immersed in an H2O2 solution and the released sulfate (from the sulfide oxidation) was quantified. The results showed that the larger the sulfide exposed surface and the smaller the particle size are, the more effective is its oxidation and consequently more reactive the aggregate.