The addition of chemicals into the subgrade has been widely used during construction to improve the soil properties. The chemicals, often Lime Kiln Dust (LKD) and Portland cement, are added to the soil to improve its workability, compactability and engineering properties. Many DOTs have been using chemical modification for more than 20 years. In fact, 90% of the current subgrade is treated. Despite the wide experience-based in treating subgrade soils, several problems still exist. The INDOT (Indiana Department of Transportation) design manual states that subgrade clays with low plasticity (PI< 10) must be treated with cement and that high plasticity clays (Density < 95 pcf, or PI ≥ 25) in the subgrade must be replaced with suitable soils. Uniform granular soils do not stabilize with lime products or with low dosage of cement. Current knowledge does not provide information about stabilization of these soils. This research explores LKD, combinations of LKD and Portland cement to treat high and low plasticity clayey soils (problem soils, e.g. expansive and organic soils are not considered in the research) and treatment with Portland cement of uniform granular soils. A comprehensive laboratory testing program has been undertaken to investigate the potential for the treatment and to report the changes in mineralogy and engineering properties of the treated soils with time. Unconfined compression tests performed over time, as well as XRD tests, show that treatment is possible and that it remains over time since the strength of the treated soil improves with time and its mineralogy does not change.

Report Number



high/low plasticity soil, LKD, cement, modification

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version