Use of mercury intrusion porosimetry for microstructural investigation of reconstituted clays at high water contents

• A bimodal distribution of pore sizes was formed in all reconstituted clay samples.
• The peak associated with larger diameters represented inter-aggregate pores.
• The peak associated with smaller diameters corresponded to intra-aggregate pores.
• The intra-aggregate pore volume remained constant with changes in moisture content.
• MIP method underestimated the void ratio of saturated clays with w > 50%.

The use of mercury intrusion porosimetry to investigate the fabric of different porous media is becoming more common. In this study, the effects of variations in moisture content on the pore size distribution of two clays was studied for specimens over a large range of liquidity indices from 0 to 3 (gravimetric moisture content range of 23 to 98%) prepared by freeze-drying. This analysis was also performed on air-dried specimens, to study fabric changes and particle rearrangements due to air-drying. The mercury intrusion porosimetry (MIP) results confirmed the existence of two major groups of pores within the material, i.e. intra- and inter-cluster pores. It was found that the addition of water to air-dried clay increased the volume of inter-cluster pores, leaving intra-cluster pores almost constant. Any further increase in the moisture content of the wet material was also attributed to changes in the inter-cluster pore volume. Amongst the inter-cluster pores, smaller diameter pores were more sensitive to changes in moisture content. In addition, limitations associated with using MIP analysis on saturated clays with a high moisture content are discussed. It is shown that due to an inability to detect all of the large pores, MIP underestimates the void ratio of specimens with a moisture content higher than 50%, regardless of the liquidity index.