Quantification of Water Content during Freeze–Thaw Cycles: A Nuclear Magnetic Resonance Based Method

Abstract

In analyzing the phase transition and water migration processes in multiphase porous systems, it is helpful to properly evaluate the unfrozen capillary water content and adsorptive water content, respectively. In this study, an innovative procedure was developed to determine the total, adsorptive, and capillary water contents in frozen soils based on the nuclear magnetic resonance (NMR) technique. We found a threshold value of the proton spin–spin relaxation time, T2, that separates the unfrozen pore water into two distinct regimes: the adsorptive regime for small T2 values and the capillary regime for large T2 values. We showed that the relationship between adsorptive (or capillary) water content and temperature is hysteretic for all three tested soils experiencing a freeze–thaw cycle. The hysteresis behavior of capillary or adsorptive water content during a freeze–thaw cycle is attributable to capillary effect, metastable nucleation, pore blocking, and variation of microstructure. In all the tested soils, the adsorptive water content was significantly larger than the capillary water content and was supported by the experimental evidence inferred from previous pore water potential measurements of various soils.