New Unreacted-Core Model to Predict Pyrrhotite Oxidation in Concrete Dams

Abstract

Pyrites and pyrrhotites are the most abundant minerals of the iron sulfide group in nature and may be found in the aggregates used to produce concrete. In the presence of water and oxygen, such compounds generate expansive reactions that may have severe structural damages. This is especially critical in concrete dams, given the large volume of material used and the restrictions in movement imposed by the surroundings. In these cases, the definition of adequate rehabilitation programs depends on the prediction of the expansive reaction evolution and the future behavior of the structure. Although models that describe solid particle–gas reactions may be used with this purpose, none were specifically developed to simulate this phenomenon in dams. This paper introduces a new kinetic model based on the unreacted-core model for pyrrhotite oxidation. The comparison of the results obtained with this new model and with the direct application of the unreacted-core model show significant differences. Following an extensive parametric study, a simplified constitutive equation is proposed to estimate the pyrrhotite oxidation kinetics in concrete dams. The estimations performed with this constitutive equation agree with the experimental data obtained in the tests of different particle sizes.