Chemical modification of soils with lime, especially with LKD (Lime Kiln Dust), in the State of Indiana has been widely used to improve the workability and compactability of weak subgrade soils. Although the modification process is primarily aimed at construction expediency, additional effects such as long-term improvement of stiffness and/or strength by pozzolanic and carbonation cementation processes of the treated soils have been expected, but have not been quantified. Due to a lack of confidence in the long-term performance of the chemically modified soils, their enhanced stiffness has not been taken into account in pavement design, leading to a conservative design of the asphalt or concrete pavement layers. FWD (Falling Weight Deflectometer) and DCP (Dynamic Cone Penetrometer) tests are performed to evaluate the durability and long-term performance of lime treated subgrades soils. Six roads that have been in service for 5 to 11 years have been selected to conduct field tests. The selection has been done considering: (1) location of road project in the State of Indiana; (2) class of road; (3) year when lime treatment was done; (4) type of lime used; (5) type of pavement; (6) availability of geotechnical information for post-construction evaluation; and (7) traffic and safety control for field testing. Based on the results from the field tests, it has been found that the effects of treatment remained after 5 to 11 years, no leaching of the lime was detected, and the long-term stiffness or/and strength of lime-treated subgrades was 4 to 11 times higher than natural subgrades. This suggests that the enhanced stiffness of the chemically modified subgrade could be accounted for in pavement design, which would lead to a reduction of the thickness of asphalt or concrete pavement layers.
Abstract