Multi-scale analysis of the mechanical improvement induced by lime addition on a pyroclastic soil

An extensive experimental work was developed on a lime treated pyroclastic soil coming from Central Italy, focusing on the link between the mechanical improvement induced by lime addition and the chemo-mineralogical evolution of the system. The shear strength behaviour of lime treated specimens was checked by means of conventional direct shear tests and compared with that of raw samples; lime addition induces an increase of shear strength and soil dilatancy, which is associated to a fragile-type behaviour. The chemo-physical evolution of the soil-lime-water system with time was investigated by XRD, TGA, FTIR, 29Si NMR analyses in order to deepen the knowledge of the modifications responsible for the mechanical improvements. The performed multi-scale analysis of the treated pyroclastic soil revealed the high reactivity of the system at micro level, with the occurrence of pozzolanic reactions since the very short time after the addition of lime. The availability of secondary phases is the main responsible for the observed mechanical improvement, showing the effectiveness of the treatment and the key role of zeolites in the chemo-physical evolution of the system.