Alkali-aggregate reactivity in Québec (Canada)

Abstract

In the province of Québec, due to the particular geology and the historic use of high-alkali cements, a large number of concrete structures are affected by alkali-silica reactivity (ASR). Consequently, tremendous effort was made in this province during the last 20 years on (1) the determination in the laboratory (testing methods) as well as in the field (inspection of structures) of the potential alkali-aggregate reactivity (AAR) of concrete aggregates, (2) the prevention of AAR in new structures, and (3) the management of existing structures affected by this problem. For new structures, the most popular measure used in Québec in the presence of potentially reactive aggregates consists of limiting the alkali contribution by the cement to 3 kg/m3 of concrete (Na2Oeq). Also, blended silica fume cements were used on many occasions against ASR; ternary cements containing fly ash and silica fume, which proved in the laboratory to be effective against ASR, are presently available. As concerns the existing structures affected by ASR, many of them were repaired using various techniques ranging from the simple application of a penetrating sealer to the application of post-constraints or slot cutting.Key words: aggregate, alkali-aggregate reaction, cement, concrete, diagnosis, management, preventive measures, prognosis, Québec, testing.