Micro-scale characterisation of clay at elevated temperatures

Abstract

The main objective of this study is to use a suite of micro-scale tests to characterise the temperature effects on high plasticity clay. The unheated clay was examined using X-ray diffraction, field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometry to characterise the mineralogy, morphology and the elemental composition of natural soil. The clay was then cured under various temperatures ranging from 23 to 1000°C. The characteristics of heated clay were then evaluated using FESEM, cation-exchange capacity (CEC) tests, thermal gravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface area analyser. The results show minimal changes in soil fabric with increased temperature. However, specific surface area and CEC are shown to significantly decrease with temperatures beyond 100°C. TGA results can provide an insight into the drops of BET surface area and CEC. Depending on the range of temperature applied, the changes can be attributed to the temperature effects on the clay microstructure, loss of capillary and adsorbed water and organic matter, and the clay mineral's interaction with the displacement cation or nitrogen. The observed trends are used to discuss possible implications on the hydro-mechanical properties of soil such as the soil–water-retention curve, shear strength and volume change.