The Effect of Pyrite Content in Aggregates on Concrete Deformation and Failure Prediction

Iron ore mining requires the surrounding rock to be excavated, and the beneficiation process generates tailings. When used as construction aggregates, these materials can cause concrete to crack due to the presence of pyrite. Currently, there are no established technical methods to prevent damage caused by pyrite, which limits the resource recovery of such solid waste. In this study, we selected the surrounding rock and tailings to serve as coarse or fine aggregates for C50 concrete based on standard engineering mix proportions. We found that surface-exposed pyrite on aggregates oxidizes first to form ettringite, triggering expansion, with the expansion rate positively correlated with the surface-exposed pyrite content. The deformation process was quantitatively characterized using the Arrhenius equation and by analyzing the acceleration effect of temperature on expansion, yielding an apparent activation energy of 8.28-9.47 kJ/mol. Using a 0.04% expansion value as the failure criterion, the results indicate that at an annual average temperature of 20 °C, C50 concrete with surface-exposed pyrite introduced by concrete aggregates exceeding 20 kg/m³ will fail within its service life.