Deterioration Caused By Sulfide-Bearing Aggregates: Performance Test Development

Bradley Maguire

doi:10.32920/ryerson.14657577.v1

Abstract

Recently in Quebec Canada, concrete structures suffered very rapid deterioration within 3 to 5 years of construction. The deterioration was caused by an iron sulfide, namely pyrrhotite, in the coarse aggregate that suffered oxidation inside concrete and promoted sulfate attack; indicated by the presence of ferric oxyhydroxides (“rust”), gypsum, ettringite, and thaumasite. The goal of the current work was to reproduce this reaction under accelerated laboratory conditions, in progression of a performance test. Conditions to promote pyrrhotite oxidation and internal sulfate attack were provided; exposure cycles were tested with heating and cooling, and saturation in oxidizing agents or lime solution. Oxidation was induced in concrete samples, however, other mechanisms contributed to deterioration. The bleach was found to promote NaCl and Friedel’s salt formation, furthermore, it seemed to mitigate expansion from sulfate attack. Sulfoaluminate decomposition was also found to cause secondary ettringite formation. More optimization to the test methods was recommended.

Highlights

In recent years, a rapid concrete deterioration has been observed in a few housing developments in the Trios-Rivières area in Quebec, Canada
To properly analyze the effects of the different testing regimes, the amount of time needed to saturate the samples, and the amount of time needed to dry the samples must be known. This information was used to estimate the degree of saturation of the samples at the different stages of testing of Phase I and Phase II,. This testing was done subsequent to Phase I and Phase II testing, as a method to investigate the moisture conditions inside of the concrete; it is presented here to aid in the analysis of Phase I and Phase II during analysis
Before this testing was conducted, the samples were conditioned in the same manner as in Phase II, followed by a drying period of 7-days in an oven at their respective testing temperatures

Summary

Introduction

A rapid concrete deterioration has been observed in a few housing developments in the Trios-Rivières area in Quebec, Canada. Figure 1.1.1: Pictures of damaged concrete foundations in Quebec, Canada. This problem has affected more than 900 residential owners, who face serious issues related to deterioration of their concrete foundations and slabs. In some cases the deterioration warranted immediate remedial actions This distressed concrete is the point of reference for all testing in this study, and will be referred to as “the foundations” from here forward. Damage and expansion caused by oxidation of iron sulfide minerals has been observed in other cases, but it occurred at a much slower rate and was not detrimental to the structure. There is currently very little information available on the exact reaction mechanism causing this severe damage

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Discussion

Conclusion