Characterization of pore water microdynamics and microstructure of clays: The effect of pore fluid chemistry and temperature

It is crucial to figure out the microdynamics of pore water and the microstructure of clays under various thermal and chemical environments when characterizing the physical properties of clays. In this study water microdynamics in clay was investigated via the nuclear magnetic resonance (NMR) technique. The NMR measurements were performed on three clays saturated with distilled water and three salt solutions from 25 to 75°C. The saline and thermal effect on soil-water interaction, water microdynamics and microstructure of clays has been investigated through relaxation times by invoking the DDL theory and the ionic hydration mechanism. Number of jumps (τS/τm) for water molecule is 82 for soils A or C and 520 for soil B when saturated with distilled water, implying the larger surface molecular affinity of soil B. Salt solutions increase the values of τS/τm in the sequence of K+>Ca2+>Na+. Effective activation energy of pore waterΔE= 2.33 kcal/mol, 1.49 kcal/mol and 1.19 kcal/mol for soils A, B and C when saturated with distilled water are obtained. The effect of salt solution on ΔE depends on cation exchange capacity (CEC) and specific surface area (SSA), the larger the CEC and SSA, the smaller the saline effect. In addition, it is found that the pore size distribution of the compacted clay is bimodal, and inter-aggregate pores are greatly influenced by pore fluid chemistry, due to clay aggregation. [Display omitted] •Salt solution suppresses the mobility of bound water.•Bound and ion-hydrated water contents increase effective activation energy of pore water.•Pore fluid chemistry promotes clay aggregation with increasing surface area.