An extensive experimental multi-scale analysis was developed on a pyroclastic soil, coming from Central Italy, to investigate the link between the mineralogical and microstructural evolution of the system and the mechanical improvements induced by lime treatment. Chemo-mineralogical and microstructural evolution of the hydrated lime-soil system was monitored by means of Thermo-Gravimetric Analysis, Si-29 Nuclear Magnetic Resonance, XRay Diffraction, Mercury Intrusion Porosimetry and Scanning Electron Microscopy. Rietvield analysis of X-Ray Diffraction results allowed a quantitative evaluation of amorphous phase and mineralogical components over time. Compressibility properties were measured by means of oedometer tests on raw and treated specimens. Amorphous phase plays a fundamental role in the development of pozzolanic reactions and in the formation of new cementitious compounds, whereas the contribution of zeolites, abundant in the raw soil, and other minerals is negligible. Formation of new phases induces microstructural modifications of the system, mainly detected within 28 days of curing. Chemo-mineralogical evolution of the system and the microstructural modifications affect the macroscopic behaviour of lime treated samples towards a structured behaviour, with a decrease of compressibility and an increase of yield stress.

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.