Évaluation du potentiel de réactivité alcaline des granulats à béton produits dans les Basses-Terres du Saint-Laurent du Québec (Canada)

Abstract

Seventy-one samples of aggregates representative of the various sedimentary rock types exploited in the St. Lawrence Lowlands were submitted to standard and experimental laboratory tests to evaluate their potential alkali-reactivity in concrete. Among these, only the Trenton and Black River limestones with more than 6% insoluble residues produced excessive expansion in the concrete prism test, the most reliable method in assessing the alkali-reactivity potential of concrete aggregates. Expansion values of 0.1 and 0.15%, obtained respectively after 14 days in the accelerated mortar bar test (1 M NaOH at 80 °C) and 5 h of autoclave curing (0.17 MPa at 130 °C and 100% relative humidity), can only be used as acceptance limits, since nonexpansive aggregates (as per the concrete prism test) from the Black River, Chazy and Beekmantown Groups induced excessive expansion in these tests. Limiting the reactive alkali content of the concrete mix to 3 kg/m3 or using cements containing between 5 and 10% of condensed silica fume can reduce the risks of deleterious reactions associated with the siliceous limestone aggregates produced in the St. Lawrence Lowlands. Key words: concrete, aggregates, alkali–aggregate reaction, accelerated test methods, preventive measures, condensed silica fume.