Optimization of strength and ductility of Class C fly ash stabilized soft subgrade soils

Self-cementing Class C fly ashes are being increasingly used for stabilizing soft subgrade for road construction. Fly ash stabilized soils are usually very brittle in nature, which does not follow the philosophy of flexible pavement structure. This paper discusses how the strength and ductility of Class C fly ash stabilized soft soils varies with the molding water contents during stabilization. Unconfined compression tests were conducted on a series of specimens prepared with stabilized soils to determine the strength and strain at failure. Soft soils were mixed with Class C fly ash at different molding water contents and at different doses to prepare test specimens. One set of test specimens were molded just after mixing, where as, a second set of test specimens were molded 2 hrs after mixing to mimic the field delay during construction. All test specimens were allowed to cure in a wet room for seven days and subjected to test. Test results show that strength is highest at a particular molding water content and decreases with increasing or decreasing water content, where as, ductility increases with increasing molding water content and increases rapidly at the wet side of the optimum water content. An "acceptable region" is developed and a specified range of water content is recommended to optimize the strength and ductility of the fly ash stabilized layer.