Alkali-aggregate reactivity in Nova Scotia

Alkali-silica reactivity, a reaction between alkalies usually contained in the cement paste and siliceous aggregates, was positively identified in Nova Scotia in 1962. Powerhouse structures on the Mersey River constructed in 1928-1929 showed intolerable expansion by 1938, and this expansion continues to the present day. Extensive research conducted in the 1960s and 1980s has shown that widespread meta-sediments in Nova Scotia are the principal rock types responsible for the reaction. The rate and extent of reactivity is somewhat dependent on the degree to which the rock has been re-crystallized as a result of contact with intrusive granites. Supplementary cementing materials are effective in reducing or eliminating the excessive expansions caused by the reaction. Class F fly ash has been in general use in Nova Scotia since 1986 and used specifically for reducing alkali-aggregate reactivity since 1990.Key words: alkali-aggregate reaction, expansion, fly ash, meta-sediments, mortar bar test, pozzolans, prism test, quarries, supplementary cementing materials.