Sulfate Induced Heave in Oklahoma Soils due to Lime Stabilization

Sulfate-induced heave in lime-stabilized soils is a serious problem that can cause costly infrastructure damage if not addressed and occurs when lime is added to soil containing sulfate. Lime, a common soil stabilizer, is mixed with expansive soils to make them non-expansive. However, when a certain amount of sulfate is present naturally in the soil, in the form of gypsum (CaSO 4 ⋅2H 2 O), the addition of lime (CaO) and water (H 2 O) will form a highly expansive mineral, ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ⋅26H 2 O) and cause excessive swelling. When exposed to water, ettringite can expand up to 250% and the resulting lime/soil mixture becomes more expansive than the natural soil; affecting and often destroying infrastructure. The purpose of this research was to determine a threshold level of sulfate in Oklahoma soils, above which adverse reactions occur as a result of lime stabilization. The volume change behavior of three natural Oklahoma soil samples, with and without a lime additive, was analyzed with free swell tests and a parallel gypsum solubility study on manufactured soils was performed. The preliminary data shows that the level of sulfates at which adverse reactions occur with the addition of lime in Oklahoma soils lies between 200 ppm and 8500 ppm, and researchers are continuing work to narrow this range. The results of the gypsum solubility study with manufactured soils have led to a faster and more comprehensive method for measuring sulfate content in natural soils.