Microstructure and shear strength evolution of a lime-treated clay for use in road construction

The results of a comprehensive experimental programme are presented for assessing the long-term microstructural modifications and evaluating the effects of microstructural rearrangement on the stress-strain behaviour of a lime-treated high-plasticity clay for road embankments. The stress-strain behaviour at different lime content and curing time was investigated by means of direct shear tests; microstructural analyses were carried out combining Scanning Electron Microscope observations and Mercury Intrusion Porosimetry tests. The results show that the stress-strain behaviour of treated clay is strongly dilatant with a high peak of strength, which increases with time and lime content. Furthermore, a hyperbolic function may be used for predicting the increase in strength at the end of the stabilisation process. Microstructural analysis shows that the treatment induces a redistribution of the porosity between macro- and micropores and an increase in matric suction, associated to a low reduction of water content and to aggregates shrinkage. This behaviour is affected by lime content and curing time since it results from the formation of the pozzolanic compounds on the surface of clay aggregates that induces both a bonding between hardened clay aggregates and an increase of their interlocking degree, with a consequent increase in the shear strength.