Identification, Quantification, and Stabilization of Sulfate-Bearing Soils in Texas

Over the last 15 years, the Texas Department of Transportation (TxDOT) has seen an increase in pavement failures during and immediately after construction on roads designed to last 20 years or more. The cause of many of these failures is sulfate-induced heave where an expansive mineral called ettringite is formed from a calcium-based stabilizer (lime or cement) reacting with clay and sulfate minerals (usually gypsum) in the soil. Traditionally, TxDOT has removed and replaced soils with more than 2000 ppm sulfates, which can be quite expensive. This project focused on four main objectives: 1. identifying sulfates prior to construction. 2. determining the highest sulfate concentration that can be treated with lime using normall construction techniques; 3. evaluating the effectiveness of alternate construction practices for calcium-based stabilizers aimed at reducing swell in high sulfate soils (these practices include extended mellowing, double lime application, and increased field moisture contents); and 4. identifying the maximum sulfate concentration that can safely be treated with calcium-based stabilizers and what alternative stabilizers can be used in subgrade soils with very high sulfate levels.