A new accelerated mortar bar test to assess the potential deleterious effect of sulfide-bearing aggregate in concrete

Deterioration of concrete structures incorporating sulfide bearing aggregates has been reported in Trois-Rivières area, Québec, Canada. In this case, iron sulfide oxidation and internal sulfate attack were observed.The present study aims at developing a performance test that will reproduce, in the laboratory, the deterioration mechanisms observed on site. A two-phase accelerated mortar bar test was developed that consists 90 days of storage at 80 °C/80% RH, with two 3-h wetting cycles in a 6% bleach solution (Phase I) followed by up to 90 days of storage at 4 °C/100% RH (Phase II). Aggregates with oxidation potential presented an expansion over 0.15% during Phase I, while thaumasite formation potential is detected by rapid regain of expansion followed by destruction of the samples during Phase II. The control aggregates without sulfide mineral did not show any signs of deterioration in both phases of the testing program.