United States Department of Transportation
i
Factors Relating to Aggregate Durability in Portland Cement Concrete
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1983-02-01
[PDF-1.42 MB]
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Edition:Interim Report
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Abstract:Over the past several years a comprehensive study on the pore systems of limestones used as coarse aggregate in portland cement concrete (PCC) and their relationship to freeze-thaw aggregate failure was conducted. A simple test called the Iowa Pore Index Test was developed and used to identify those coarse aggregates that had freeze-thaw susceptible pore systems. Basically, it identified those aggregates that could take on a considerable amount of water but only at a slow rate. The assumption was that if an aggregate would take on a considerable amount of water at a slow rate, its pore system would impede the outward movement of water through a critically saturated particle during freezing, causing particle fracture. The test was quite successful when used to identify aggregates containing susceptible pore systems, if the aggregates were clean carbonates containing less than 2% or 3% insolubles. The correlation between service record, ASTM C666B and the pore index test was good, but not good enough. It became apparent over the past year that there were factors other than the pore system that could cause an aggregate to fail when used in PCC. The role that silica and clay play in aggregate durability was studied. This report presents the initial results of that study.
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