Experimental studies to address volume change behaviors of chemically treated sulfate bearing soils

Sulfate-rich cohesive soils are found in several regions of the United States. When these soils are treated with calcium rich cement and lime stabilizers for soil improvements, the sulfates in soils will react with calcium from the stabilizers and free reactive alumina from clayey soils to form a crystalline mineral, ettringite. This mineral, upon growth and hydration, will undergo a large amount of heaving in soils. This heave, termed as sulfate induced heave in the literature, induce significant damage to buildings, pavements, runways and embankments built on cement and lime treated sulfate bearing soils. Rehabilitation costs of heave distressed structures are quite high and hence there is a significant research need to understand exact causes of this heaving. Such understanding would help in the development of more effective stabilizers for treating these soils.; This research is designed to understand ettringite formation and related heaving reactions among sulfates, calcium stabilizers and different soils under different environmental conditions. Four types of clayey soils: two artificial and two natural soils with different types of clay mineralogies, two cement and lime treatment levels, four sulfate levels, two moisture content levels, three levels of lateral confining pressures and three temperature conditions were investigated. Treated and untreated soil specimens were prepared, cured, and then tested under a variety of mineralogical, chemical and engineering swell, shrink, swell pressure and shear strength tests. Test results were analyzed to understand the possible causes of sulfate heave mechanisms.; Ettringite crystal growth has provided considerable contribution to overall sulfate heave. Different swell trends in present treated soils were attributed to different amounts of reactive alumina available for sulfate mineral reactions. Also, ettringite presence in present treated soils was confirmed by mineralogical studies and losses in soluble sulfates and free reactive alumina during curing reactions. The experimental data was used to establish the problematic sulfate levels for various swell strain and swell pressure conditions that are expected to induce distress to structures. Additionally, the correlations were developed to predict amount of vertical swell strains, swell pressure and volumetric shrinkage in sulfate rich soils subjected to both cement and lime treatments. These correlations were verified by comparing their predictions with the known heave test data of the present experimental program.