Multi-scale analysis and time evolution of pozzolanic activity of lime treated clays

Abstract

A multi-scale investigation on the influence of clay mineralogy on the pozzolanic activity of lime treated clays has been presented. Two clays of different mineralogy have been considered for this study, namely kaolin and bentonite. The time dependent mineralogical and microstructural changes induced by lime addition have been monitored at increasing curing time by means of X-ray diffraction (XRD), thermogravimetric analysis, 29Si NMR spectroscopy, Scanning electron microscopy (SEM) and nitrogen adsorption/desorption measurements. Different lime contents of the treated samples have been considered in order to highlight the ongoing of pozzolanic reactions. The time scale of chemical reactions taking place after the addition of lime depends on clay mineralogy. In the short term, flocculation phenomena due to the cation exchange reactions control the microstructural features of lime treated kaolin. The low reactivity of kaolinite clay minerals to pozzolanic reactions was detected as a delay in precipitation of new hydrated phases. The chemo-physical evolution of lime treated bentonite depends on the combined effect of cation exchange and pozzolanic reactions which develop with a comparable time scale. The results of micro-scale investigations were directly linked to the experimental evidences at volume scale of the samples, allowing an interpretation of the mechanical improvement of the treated clays in the short and long term as a function of the chemo-physical evolution of the system.