Understanding the Mechanism and Kinetics of Pyrrhotite-induced Damage in Concrete

This research will deliver fundamental knowledge necessary to rapidly and reliably distinguish durable from deleterious aggregates for concrete. Specifically, it will focus on mechanisms and kinetics of pyrrhotite-induced damage in concrete, a situation that has devastated some residential communities in the northern United States. Challenges in identifying and procuring high quality and durable construction aggregate are on the rise, as good quality virgin aggregates are being depleted. Sustainable management of natural resources requires a well-thought-out philosophy of using the remaining supplies. This project will lead to identifying optimal protocols for detection and quantification of pyrrhotite reactivity in concrete. By enabling science-driven selection of the aggregates, the costs of remediating premature deterioration and concrete degradation can be reduced. As such, societal and economic benefits are high and translate into new knowledge and technology to design sustainable built environment. The outcomes of this project will ensure safety, serviceability and continued use of concrete buildings and structures, along with protecting health and financial livelihood of their owners and occupants.

The pyrrhotite damage in concrete is a result of deleterious expansions taking place when pyrrhotite (an abundant sulfide mineral in aggregates) oxidizes in contact with moisture and atmospheric oxygen, forming expansive iron hydroxides and sulfuric acid inside concrete. The latter subsequently leads to secondary damages, including acid attack, sulfate attack, and rebar corrosion. To date, pyrrhotite oxidation has been analyzed only in the context of acid mine drainage (low pH). The novelty of this research is in thorough investigation of pyrrhotite oxidation in concrete environment. Specifically, the effects of pH, temperature, RH, and oxygen level on the magnitude and rate of reaction and damage evolution in concrete will be quantified. Selective dissolution of Fe-oxide phases will be conducted and geochemical calculations executed to calculate volumetric changes resulting from pyrrhotite reactivity. Integrated oxygen transport and thermodynamic models will be created for rapid and reliable assessment and prediction of damage. While developed for pyrrhotite-related degradation, this transformative approach will be applicable to a wide array of aggregate-induced damages in concrete.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.