Alkali-aggregate reactivity in Newfoundland, Canada

Abstract

Alkali-aggregate reactivity is a chemical reaction that occurs in some concrete structures. This reaction causes expansion and cracking of concrete. It may not be the main cause of premature deterioration; however, it is often the catalyst for other forms of deterioration. Since 1989, field work and laboratory testing for alkali-reactivity has been undertaken on selected aggregate, rock, and concrete core samples throughout Newfoundland. The field work and laboratory tests consisted of an assessment of the bedrock and aggregate sites to determine their quality and quantity for use as construction material; an examination of existing concrete structures to assess their durability with regard to alkali-aggregate reactivity. The site investigation of the concrete structures consisted of noting their date of construction, the rock and aggregate types used, the types of cracking, and the degree and type of deterioration of each structure. Results from laboratory testing, petrographic examination, and visual observation show that certain sedimentary, igneous, and metamorphic rock types may be potentially alkali-reactive, but the reaction may not always be deleterious to the concrete structure.Key words: alkali-aggregate reaction, concrete structures, laboratory tests, petrographic examination, rock types.