Reduction of Sulfate Swell in Expansive Clay Subgrades in the Dallas District (3929-1)

There are three purposes for stabilizing the natural soil in place beneath pavements: (1) to provide a working table for construction equipment during wet weather, (2) to reduce the roughness due to an expansive clay subgrade; and (3) to provide a permanent layer in the pavement structure that is stiffer than the natural soil. No stabilized layer only 0.2 m (8 in) thick will reduce expansive clay roughness very much. This report shows that there are non calcium stabilizers that will serve successfully as a working table (purpose No.1) but the study did not and could not determine the permanence of the treatment (Purpose No.3). That determination must await the results of monitored pavement test sections.|Lime has been a commonly used and successfully applied stabilizing agent. However, lime reacts with sulfate-rich clay soils to create expansive minerals, which cause the pavement surface to buckle and to become undesirable rough. This report gives the details of a successful effort to find non-calcium stabilizers, which can replace lime in providing a construction-working table in sulfate-rich soils. It also gives the ranges of electrical conductivity below which lime stabilization will cause no lime-sulfate reaction problems and above which non-calcium stabilizers should be considered. The electrical conductivity test is a simple and inexpensive test that can be run in the field or in the lab to identify those lengths of roadway where non-calcium stabilizers should be considered The details of the test equipment and procedure are provided in an appendix to the report|The objective of this research was to find, if possible, non-calcium stabilizers which impart the following properties to the treated soil:¿· Increase the strength and stiffness of the soil above that of the natural soil so as to form a working table for construction traffic,¿· Reduce the swelling of the treated soil below that of the natural soil and eliminate the lime-sulfate interaction, if possible,¿· Decrease the permeability of the treated soil below that of the natural soil so as to reduce the amount of water that will penetrate into the natural subgrade from the surface, and¿· Decrease the suction of the treated soil below that of the natural soil so the treated layer will not attract water from below.|The results of the study point towards the use of two commercial stabilizers that can be used in lieu of lime in lime-sulfate heave areas. These stabilizers have been shown to be superior to lime in terms of strength, stiffness, permeability, and swell resistance potential.