The effect of curing conditions on the unconfined compression strength of lime-treated expansive soils

Unconfined compressive strength (UCS) is one of the main design parameters for flexible pavement and earthwork construction. During the design phase of lime-treated expansive subgrade, compacted specimens of different lime–soil mixtures are prepared and tested for UCS after being cured under controlled temperature and a high-humidity environment. During the field application of lime treatment, the curing conditions are far from been controlled especially in arid and semi-arid climates. This study aims at investigating the effect of different curing environments on the UCS of lime-treated expansive clays. Specifically, the study aims to assess the contribution of suction and cementation to the gain in UCS. Tests were conducted on expansive clays originated from two areas in Kingdom of Saudi Arabia (KSA). Remoulded specimens of lime-treated expansive clays with lime contents of 2%, 4%, and 6% (of dry weight basis) were cured under different curing environments; namely, normal curing (NC) (i.e. controlled temperature and high humidity environment), in-laboratory curing (ILC), and out-laboratory curing (OC) conditions. Curing periods considered were 7, 14, and 28 days. The main characteristics of ILC and OC environments evaluated based on continuous logging of climatic data (i.e. temperature and relative humidity) indicated low relative humidity which is a main characteristic of semi-arid and arid climates. For all curing environments, there is an observed increase in UCS with curing period, with maximum UCS values observed for OC-cured specimens. Furthermore, the soil water characteristic curves of lime-treated specimens under different curing periods and lime content were evaluated to assess suction in specimens at the end of selected curing periods. Test results indicated that the gain in UCS for specimens cured under NC conditions is mainly attributed to an increase in cementation bonds. On the other hand, both ILC and OC environments promote the development of suction stresses that is a significant contributor to the gain in UCS as compared to cementation bonds.