Title: Pyrrhotite Epidemic in Eastern Connecticut: Diagnosis and Prevention
Author(s): Dipayan Jana
Publication: Materials Journal
Appears on pages(s): 61-70
Keywords: cracking; durability; oxidation; petrography; pyrrhotite; sulfate attack
Extensive cracking in thousands of residential concrete foundations in eastern Connecticut is found to be due to two-stage expansions associated with oxidation of pyrrhotite in crushed gneiss coarse aggregate of concrete used from a local quarry that sits on a hydrothermal vein of significant pyrrhotite crystallization, followed by internal sulfate attack in concrete from the sulfates released by pyrrhotite oxidation. Microstructural, chemical, and mineralogical evidences of pyrrhotite oxidation and the resultant internal sulfate attack in concrete are presented from a case study. A five-step laboratory testing protocol is suggested for assessment of aggregates from the area to prevent pyrrhotite-related deterioration for future construction.