Microstructural evolution of saturated normally consolidated kaolinite clay under thermal cycles

• Published in: Engineering geology 2023-06, Vol.318, p.107101, Article 107101
• Main Authors: Zeinali, Seyed Morteza, Abdelaziz, Sherif L.
• Format: Article
• Language: English
• Subjects: adsorption; clay; electron microscopy; freeze drying; freeze-thaw cycles; kaolinite; mercury; Mercury intrusion porosiemtry; microstructure; Microstructure analysis; porosimetry; porosity; SEM; Specific surface area; surface area; temperature; Thermal behavior of soils; throat
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2023.107101

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). •With the temperature changing, the circularity and number of the pores increases.•Macroscale parameters such as void ratio, do not showcase the microstructural conditions.•Water flow is the main source of microstructural change.•A full thermal cycle of freezing, thawing, heating, and cooling causes permeant microstructural changes.•Heating imposes the highest degree of microstructural alteration.