Stockpiling Hydrated Lime-Soil Mixtures

The concept and feasibility of stockpiling and reusing hydrated lime-soil mixtures to stabilize particular areas on stabilization projects after the mixing contractor has departed were examined. In chemical stabilization of subgrades, situations often arise where additional areas need to be stabilized after the specialty contractor and mixing equipment have left the project. Field and laboratory investigations were performed to determine if a soil mixed with hydrated lime during routine lime subgrade stabilization could be mixed, stockpiled, and used later. In laboratory studies, hydrated lime-soil mixtures were stockpiled loosely in the laboratory. CBR specimens of the stockpile material were remolded and soaked at selected times. Values of CBR increased with increasing times. Those studies strongly indicated that hydrated soil-mixtures could be stockpiled and reused. Field trials were conducted on KY Route 1303 (Turkey Foot Road) in Kenton County, Kentucky. During stabilization of the mainline of that route a stockpile was constructed and cured. Subgrade areas of two intersections could not be stabilized by the specialty contractor because traffic had to be maintained during chemical stabilization of the mainline subgrade. About two or three months after the construction of the stockpiles, pavements at two intersections were removed and the top ten inches of the subgrades were constructed with hydrated lime-soil mixtures from the stockpile. In situ CBR tests were conducted on the treated subgrades of the two intersections after 8 and 28 days, and 20 months and 7 days and 20 months, respectively, after construction. The soaked laboratory CBR value of subgrade soils in this area is about 1.8 at the 85th percentile test value. At one intersection, the in situ CBR values of the treated subgrade after 7 and 28 days ranged from 7 to 18.3 and 11.7 to 18.1, respectively. Twenty months after construction, the in situ CBR ranged from 9.4 to 21.1. At the other intersection, the in situ value ranged from 4.5 to 10.2. However, 20 months after construction, the in situ CBR value ranged from 14.8 to 24.2. Bearing capacity analyses of the two flexible pavements of the two intersections, using a newly developed bearing capacity model based on limit equilibrium, yielded estimated factors of safety of 1.55 and 2.02, respectively. Factors of safety of this magnitude usually predict excellent long-term performances. After twenty months, pavements resting on the treated subgrades constructed of stockpile hydrated-lime soil have performed very well. It was recommended that other sites containing different types of soils should be evaluated to fully validate the stockpile concept.