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Solving the Prairie Concrete Problem

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Dr. Thorbergur ThorvaldsonIn 1908 there were reports from Winnipeg of destructive action on concrete from salts present in the ground water. Little was then known about the scientific design of concrete mixes, and the few cases of deterioration reported were usually ascribed to poor concrete. Ten years later, however, when expensive and well-designed structures became affected, engineers were alarmed. By 1918 in western Canada, the destructive action of alkali ground waters on concrete structures was generally recognized by engineers to be a problem of major importance.

In Saskatoon in 1919, a research team lead by the National Research Council conducted field exposure testing and analyses of the ground waters at the site of local problems. It was found that the concrete was being attacked by a high concentration of sulfates that reacted with the aluminate phase in the cement to produce ettringite and gypsum, causing the concrete to expand and deteriorate.

Concrete under Prairie SoilDr. Thorbergur Thorvaldson, professor of chemistry at the University of Saskatchewan, and his team, devised a steam curing technique that changed the crystalline structure of the concrete compounds, making them virtually immune to alkali damage. Chemically, this process transformed the aluminate into a less reactive phase and also removed the Ca(OH)2. Dr. Thorvaldson's life's work was the study of the properties and processes of cement and its compounds, his greatest achievement being the experimental demonstration of concepts which led directly to the development of a sulphate-resistant cement.

Today, the problem of sulfate in the soil reacting with the aluminate phase in cement is minimized by using cements with low aluminate content.