Microstructural evolution of saturated normally consolidated kaolinite clay under thermal cycles

Abstract

This study aims to quantify the microstructural evolution of saturated clay during one thermal cycle. For this purpose, five saturated normally consolidated kaolinite clay triaxial specimens were consolidated under the same conditions. One specimen was subjected to a mechanical consolidation only; while the other four specimens were subjected to different thermal paths: freezing (F), freezing-thawing (FT), freezing-thawing-heating (FTH), and freezing-thawing-heating-cooling (FTHC). After completing the mechanical and thermal stages, thin disks were cut from the bottom of each specimen. The microstructures of these disks were preserved using flash freezing and freeze-drying. The evolutions of the microstructure of the specimens during the thermal cycle was assessed using mercury intrusion porosimetry, gas adsorption methods, and processing of scanning electron microscopy (SEM) images. The results show that (1) freezing increased the modal throat size and the specific surface area (SSA); (2) freezing-thawing decreased both modal throat and pore sizes, while the SSA recovered to its initial value; (3) freezing-thawing-heating reduced the pore and throat sizes and SSA even further; and (4) freezing-thawing-heating-cooling caused permanent reduction in SSA and throat and pore size distributions. Finally, the shape of the pores became more circular after temperature changes, while the number of pores increased during the thermal cycle with the highest number corresponding to the end of heating (i.e., the third stage in the thermal cycle).