Long-Term Performance of Chemically Modified Subgrade Soils in Indiana

Chemical modification of soils with lime in Indiana is 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 or strength by pozzolanic and carbonation cementation processes of the treated soils have been expected but have not been quantified. Because of 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. Six roads that have been in service for 5 to 11 years were selected to conduct field tests. The selection was performed considering (a) location of road project in Indiana, (b) class of road, (c) year when chemical treatment was done, (d) type of chemical modifier used, (e) type of pavement, (f) availability of geotechnical information for postconstruction evaluation, and (g) traffic and safety control for field testing. The results from the field tests show that the long-term stiffness or strength of subgrades that were chemically treated 5 to 11 years ago is 4 to 11 times higher than that of natural sub-grades. This finding 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.