ROLE OF CARBONATION AND RESIDUAL LIME CONTENT ON LONG TERM STRENGTH BEHAVIOR OF LIME TREATED SUBGRADE SOILS

Abstract

Lime stabilization of subgrade soils is an established practice to improve the engineering properties of poor-quality soils encountered in pavement construction. However, long term exposure to environmental conditions can cause diffusion of carbon dioxide (CO₂) into the stabilized matrix and can lead to carbonation of available lime which in turn can adversely affect the long-term strength gain in these treated layers. Limited studies are available on the role of residual lime on long term strength gain in lime stabilized mixes as there are no available techniques to quantify residual lime content after stabilization. The research proposes applying a thermogravimetric technique to quantify the residual amount of lime available in lime treated matrix at any given time. Manufactured soils with varying clay contents were treated with lime and used to identify the carbonation profile of the matrix. Mixes subjected to carbonation for up to 240 days were used to investigate the impact of changes in residual lime content on long term strength behavior. Observations of the study clearly show a reduction in long-term strength with carbonation of the matrix. Possible changes in Ca/Si ratio leading to transformation of calcium silicate hydrate phases to silicate gel and the precipitation of calcium carbonate phase can cause strength deterioration in mixes during carbonation. Residual lime content in the stabilized matrix was found to increase slightly during curing periods.