Use of Nondestructive Impedance Spectroscopy for the Assessment of Clay–Lime Reaction Kinetics: Influence of Clay Mineralogy, Lime Content, and Curing Conditions

This study describes the nondestructive testing and evaluation of different clay–lime composites by real-time impedance spectroscopy (IS) monitoring of lime hydration and cementation mechanisms. The experimental investigations were carried out on two different clays, white clay (with predominantly kaolinite mineralogy) and brown clay (with predominantly montmorillonite mineralogy), to determine the influence of clay mineralogy on the fate of lime stabilization processes in different soils. Additionally, the effects of key influencing parameters such as lime content, curing period, and curing temperature were assessed. The time-dependent electrical impedance behavior of different clay–lime systems was determined in terms of bulk resistance and interfacial capacitance, obtained by equivalent circuit modeling of the impedance spectra. The variations in the electrical impedance properties showed a strong correlation with unconfined compressive strength (UCS) of different clay–lime composites. Further, the microstructural improvement of various clay–lime composites was determined with the aid of scanning electron microscopy, mercury intrusion porosimetry, and thermogravimetric analysis to get an auxiliary interpretation of the electrical impedance spectroscopy (EIS) results. The time-dependent variations of the soil impedance evidently manifested the continuous chemical and morphological evolution of the different clay–lime systems during the curing process at different thermal conditions by the formation and deposition of cementitious calcium-silicate-hydrates (C-S-H) and calcium-aluminate-silicate-hydrates (C-A-S-H) compounds. Overall, the nondestructive impedance spectroscopy technique has been proven effective in describing the microstructural changes and related mechanical improvement of lime-treated soils. Although the use of this technique seems to be inefficient for a field quality control assessment, the analysis of the electrical parameters calculated from the impedance spectra measured gives a comprehensive idea of the evolution in the chemically stabilized soil material.