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This paper reviews the problem of alkali-silica surface popouts on slabs in the north central United States and adjacent southern Canada. Based on the review, it is concluded that the popouts occur as a result of reaction of alkalies in the concrete with siliceous shale in the concrete sand. The reaction is caused by increased alkali concentration at the slab surface, which results when soluble alkalies are left behind by evaporating mixing water. The soluble alkalies in the cement, fly ash, aggregates, admixtures, and mixing water contribute to alkalies in solution. Weather conditions and placing and finishing methods are primarily responsible for concentration of water-soluble alkalies at the slab surface where the popouts occur.
The correlation between water-soluble alkalies and total alkalies is determined for a plant which produces cement that has several levels of alkali. The results indicate good correlation, but the benefit of reduction of total alkalies on resultant level of water-soluble alkalies does not appear significant compared to other factors which cause greatly increased alkali concentration at the slab surface.
Cements from other sources are also compared for correlation. The results indicate the portion of the total alkalies which is water-soluble varies widely from one cement plant to another and within the production from some plants.
water-soluble alkalies, alkalies, alkali-silica reaction, popouts, siliceous shale, slabs, slab defects, finishing problems
Minnesota Territory Manager, Davenport Cement Company, St. Paul, MN