Assessment of Short-Term Curing Mechanisms of Lime-Stabilized Kaolinite and Montmorillonite Using Electrochemical Impedance Spectroscopy

The conventional design and quality-control practices of lime-stabilized soils rely primarily on the pH of the mix and empirical, arbitrary limits on strength, which provide limited insight into the early-age physicochemical mechanisms governing stabilization. This study aims to evaluate the capability of electrochemical impedance spectroscopy (EIS) to differentiate the effects of varying lime contents on two fundamentally distinct clayey soils containing kaolinite and montmorillonite by mechanistically investigating lime–clay interactions in pure kaolinite, pure montmorillonite, and controlled kaolinite–montmorillonite mixtures, thereby isolating mineral-specific responses that are normally difficult to discern directly. Cylindrical specimens with lime dosages ranging from 0% to 10% were prepared at their optimum moisture contents and tested using EIS immediately after compaction and after 2 and 24 h of curing. Complementary X-ray fluorescence (XRF), X-ray diffraction (XRD), and pH measurements link electrochemical behavior with chemical and mineralogical evolution. Kaolinite-rich systems exhibited rapid electrochemical stiffening, with maximum development at approximately 6% lime, above which effectiveness decreased. In contrast, montmorillonite-rich systems exhibited delayed but sustained impedance growth, reaching peak response only at the highest lime content (∼10%), due to higher cation exchange capacity and buffering capacity and slower reaction kinetics. Mixtures of different proportions of kaolinite and montmorillonite displayed intermediate impedance evolution governed by mineral proportions. Across all mixtures, electric impedance followed a characteristic temporal pattern comprising an initial decrease associated with increased ionic conductivity from lime dissolution, followed by a progressive increase as cementitious reaction products formed and pore connectivity decreased. Strong correlations among impedance evolution, Ca/(Si + Al) ratios, pH, and XRD-derived structural changes are an indication of EIS as a sensitive, nondestructive tool for identifying early-age stabilization mechanisms and optimal lime dosage.