Understanding the influence of cementitious blended mixtures on pyrrhotite oxidation and internal sulphate attack

The demand for aggregates and cement for construction has been rising faster than natural sources can sustain, enhancing the probability of using potentially problematic raw materials that may cause premature deterioration of concrete infrastructures (e.g., internal sulphate attack from oxidation of sulphide-bearing aggregates, ISA). Therefore, finding new protocols that allow the application of ISA reactive aggregates in concrete without reducing durability is imperative. This study aims to understand the effect of different exposure conditions (O₂, NaOCl, H₂O₂, CO₂, and temperature) in the Portland cement mortar phase assemblages through thermodynamic modelling, utilizing current performance-oriented methodologies and examining their benefits and obstacles. The results suggest that oxidation of FeS by air, H₂O₂, and NaOCl solutions results in different phase assemblages. While exposure to H₂O₂ solution displayed similar phase assemblages to “natural” oxidation by exposure to air, NaOCl solutions change the phase assemblage and lowered the potential of volume gain. Further studies are needed comparing additional experimental data to the modelling, which the authors are currently conducting.