<p>This study presents a multi-technique investigation into the microstructural evolution of slag-modified Calcium Aluminate Cement (CAC)-based materials. A central focus is placed on Electrochemical Impedance Spectroscopy (EIS) to non-destructively monitor the underlying mechanisms governing strength development, with XRD-Rietveld and MIP providing phase evolution and porosity data for validation. The results of the Nyquist plots qualitatively revealed a transition from simple to complex charge transfer mechanisms, justifying the use of a deconstructed equivalent circuit model. This quantitative analysis allowed for the extraction of bulk resistance (<i>R</i>_<i>b</i>), which reflects pore solution changes, and the novel separation of charge transfer resistance into two components: continuous capillary pore resistance (<i>R</i>_<i>CCP</i>) and discontinuous path resistance (<i>R</i>_<i>CP</i>). The integrated results show that the superior later-age strength of slag, which is physically linked to C-(A)-S-H gel formation and pore refinement, is dynamically and quantitatively captured by the sharp increase in <i>R</i>_<i>CP</i>. While R_CP showed a composition-dependent correlation with strength, the analysis confirms that R_CP serves as a universal indicator of microstructural integrity. This work establishes a robust framework, demonstrating how detailed EIS analysis, from qualitative Nyquist plots to deconstructed parameters, can provide powerful insights into the performance of complex cementitious materials.</p>