Ettringite induced heaving in stabilized high sulfate soils

Abstract

Stabilization of expansive soils using lime and cement additives have been used by practitioners over the years. However, recent heaving and premature pavement failures in lime and cement-treated subgrades containing sulfates led to questioning the use of calcium-based stabilization methods for these soils. Annually, millions of dollars are spent to repair pavements distressed by this Ettringite induced heaving. Based on the past studies, researchers and practitioners have proposed various methods to treat sulfate soils. Applicability of these methods is mostly limited to soils with sulfate levels below 8000 ppm. Soils with sulfate content above 8000 ppm are termed as “high sulfate” soils, and chemical treatment of such soils is currently not considered. A research study was designed to aid in understanding the heaving phenomenon in soils with sulfate contents above 8000 ppm and to develop practical techniques to stabilize such soils. High sulfate soils were sampled and treated with lime at varying mellowing periods and treated soils were then subjected to the engineering and chemical tests. Tests results were analyzed to understand the effectiveness of mellowing period on the heaving phenomenon of these soils. Treated soils at higher mellowing periods showed reduced sulfate-induced heaving when sulfate levels are lower than 30,000 ppm. Sulfate levels in excess of 30,000 ppm did not result in effective treatment of soils. It was also observed that compaction void ratios and soil clay mineralogy have a significant impact on the swell behavior of chemically treated high sulfate soils. An innovative method comprising of aerial technologies is used to monitor the pavement heaving. This keynote paper provides a comprehensive review of stabilization of high sulfate soils and methods studied to mitigate sulfate heaving.