Micro porosity evolution in compacted swelling clays — A chemical approach

This paper presents a new approach to investigate the variation of microscopic porosity/pore water interactions in compacted swelling clays. The aim of the research has been to develop a theoretical formulation for the prediction of micro-porosity variations with suction and temperature in compacted smectite. The model developed is based on a geochemical formulation of interlayer hydration/dehydration of smectite.An established theoretical approach based on regular solid-solution theory is adopted to describe the water adsorption/desorption in the interlayer of smectite. The thermodynamic parameters of the model for the case of two bentonite clays, namely MX-80 and FEBEX are presented. Thermodynamic parameters of the hydration model including Margules parameter (Ws ) and logarithm of the equilibrium constant (log Keq ) at ambient temperature were found to be −2420 cal/mol and −1.42, for compacted MX-80 and −3330 cal/mol and −2.79, for compacted FEBEX, respectively.Micro/macro-porosity evolutions with dry density and relative humidity are presented. The results are compared with alternative approximations reported in the literature which show a close correlation. Variations of the micro and macro-porosity in compacted bentonite with hydration processes are also studied through the application of the model under restrained swelling and isothermal conditions. The results provide an insight into the evolution of pore water in compacted bentonite during saturation and quantify the distribution of water in micro and macro pores