Chemo-mineralogical evolution and microstructural modifications of a lime treated pyroclastic soil

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, 29Si Nuclear Magnetic Resonance, X-Ray 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.