Empirical Models to Predict Concrete Expansion Caused by Sulfate Attack

Abstract

The development of empirical models to predict concrete expansion produced by sulfate attack is described. Data collected by the U.S. Bureau of Reclamation over more than 40 years of nonaccelerated testing form the basis for the model. In the nonaccelerated test program, concrete cylinders were continuously submerged at room temperature in 2.1% sodium sulfate solution, which corresponds to severe field exposure conditions. Expansion measurements were made periodically. Over 8,000 expansion measurements were collected for 114 specimens cast from 51 different mixtures. Analysis of the data showed the significance of water-to-cement ratio (w/c) and C3A content of the cement, with the data revealing distinct behavior for mixtures containing cements with low C3A content (less than 8%) and high C3A content (greater than 10%). As a result, two models are proposed to predict expansion by sulfate attack as a function of w/c, duration of exposure, and C3A content. The random effects method was used to capture unobserved heterogeneity in the data set, and the results from a simple regression and a regression including the random effects method are compared.