Reaction kinetics of Na2CO3-activated blast furnace slag with organic ligands: insights from electrical conductivity measurements

Electrical conductivity measurement using impedance spectroscopy could be a valuable technique for monitoring the various reaction processes of cementitious materials and predicting their long-term durability. In this study, alternating current impedance spectroscopy was employed to investigate the influence of two ligands, 2,3-dihydroxynaphthalene and 3,4-dihydroxybenzoic acid with a 0.1 wt% dosage, on the hardening process of four types of blast furnace slag (BFS) activated with sodium carbonate solution. The objectives of the study were to investigate whether impedance spectroscopy could be used for estimating the reactivity of BFS and monitoring the reaction kinetics of this type of binder as well as evaluating the correlation between electrical conductivity and reaction heat, pore solution chemistry, setting time, flowability and compressive strength. The results demonstrated that both ligands accelerated the hardening process and increased compressive strength, which was confirmed by the various techniques used. The measured electrical conductivities varied among BFS pastes due to differences in their pore solution composition and microstructure and correlated with compressive strength evolution. The results demonstrated that impedance spectroscopy is sensitive enough to detect differences in conductivity due to differences in the reactivity of BFS and the effect of low a dosage of ligands in the binder. However, because of the overall complexity of reactions in this type of binder, responses in electrical conductivity do not show systematic trends.