Behaviour and mineralogy changes in lime-treated expansive soil at 50 °C

This paper presents a series of laboratory tests performed on the lime treatment of a highly expansive and extremely plastic clay soil and evaluates the effect of a high curing temperature of 50 °C on pozzolanic reaction progression, and consequently on soil behaviour. In the present study, a similar experimental protocol to that presented in Al-Mukhtar et al. [Al-Mukhtar M., Lasledj A., Alcover J-F. (2010). Behaviour and mineralogy changes in lime-treated expansive soil at 20 °C. Appl. Clay Sci.] concerning the behaviour of treated soil cured at room temperature was applied. The results indicate that a higher temperature accelerates the pozzolanic reaction, resulting in rapid soil strength development. There were significant increases in lime consumption during the first days at a curing temperature of 50 °C; all lime added up to 20% was quasi consumed during the first month. Consequently, the pH reduces slowly in the first day and then diminishes as lime content increases.The electrical conductivity of the lime–soil mixture decreased slowly in the first day, rapidly during the first week and practically stabilised after. The wave velocity of the treated soil increased with increasing amounts of lime and rapidly reached an asymptotic value within 7 days. However, the unconfined compressive strength of treated soil significantly increased during the first days and continued to increase at later stages with higher amounts of lime. In the treated Impersol with ≥ 6% lime, CAH was identified after 1 day and CSH after 7 days by X-ray diffraction. These new hydrates produced by the pozzolanic reaction continue to increase with curing time and lime added.

Research Highlights►Lime treatment of highly expansive and extremely plastic clay soil is monitored at high curing temperatures (50 °C). The kinetics of the lime–clay reactions increases, resulting in rapid soil strength development. Pozzolanic reaction and lime consumption accelerate and induces the formation of new phases: CAH and CSH.