Reaction kinetics of sulfate-activated slag: effects of activator type, slag source, and triisopropanolamine on electrical conductivity

Electrical conductivity measurement using impedance spectroscopy is a promising technique for monitoring reaction processes in cementitious materials and understanding their reaction kinetics. In this study, alternating current electrochemical impedance spectroscopy (EIS), isothermal calorimetry, setting time measurements, compressive strength, zeta potential, and pore solution composition analysed via inductively coupled plasma optical emission spectroscopy (ICP-OES) were used to investigate the influence of calcium sulfate and sodium sulfate activators on the reaction mechanisms of two blast furnace slag (BFS) sources, with and without the addition of low concentrations of triisopropanolamine (TIPA). The results revealed that electrical conductivity trends varied significantly with both activator types and BFS reactivity. TIPA addition had a generally positive impact on strength development and demonstrated varying effects on conductivity depending on the BFS source and activator type. The findings confirmed that EIS is sufficiently sensitive to detect conductivity variations arising from different activator-BFS combinations and low dosage TIPA effects. However, the measured electrical conductivity was influenced not only by the ion concentrations in the pore solution but also by the reaction products, such as C-(A)-S-H and ettringite, as inferred from the combined trends of isothermal calorimetry, early strength and ICP-OES data, which are expected to progressively densify the microstructure and reduce pore network connectivity, thereby restricting ionic transport. This highlights the complex relationship between microstructure development and electrical properties in activated BFS systems.