Alkali-reaction in concrete structures — Mechanism, pathology and prevention

Alkali-reaction, also commonly referred to as alkali-aggregate reaction, refers to the chemical reaction that causes disorders due to an imbalance between the minerals in the aggregates and the highly alkaline interstitial solution in the concrete. Although this reaction is predominant, it is not the only internal swelling reaction in concrete.

This reaction is now found in most parts of the world. It was probably R.J. Holden who first observed the presence of chemical reactions in concrete, between cements and certain aggregates, in the United States in 1935. Kammer and Carlson also noted the existence of disorders, but it was Stanton who first specified (in 1940) the nature of the reagents involved in the deterioration observed on pavements in California. In France, we had to wait until the late 1970s to certify the presence of alkali-reaction within a few dams [1][2] , and 1987 to discover that several bridges were affected by this disease [3] . The structures most affected are those in contact with water or located in damp environments; civil engineering structures and certain damp parts of buildings are therefore the most vulnerable.

After explaining the reaction mechanism and reviewing the latest knowledge on the subject, we'll look at the pathology of alkali-affected structures and the resulting management problems, then conclude with the prevention policy applied in France since the early 1990s, which is proving effective in hindsight.