Pore solution compositions and redox potentials of ground granulated blast furnace slag-containing cement pastes

The pore solutions of hardened ground granulated blast furnace slag (GGBFS)-containing cements differ from the pore solutions of other cements with effects on reinforcement corrosion, application of electrochemical methods and immobilisation of radioactive waste. In the present study, the pore solutions of seven different GGBFS-containing cements (alkali-activated slag, alkali-activated slag/fly ash blends, hybrid alkaline cement (HAC), CEM III/C and CEM III/B) were extracted and their elemental and sulfate concentration, pH, redox potential and conductivity were determined; a Portland cement (CEM I) pore solution was analysed analogously. The silicon and aluminium concentrations of the alkali-activated cements increased with fly ash fraction, reaching values up to 5 mM and 10 mM, respectively, and thus were considerably higher than those of the standard cements. The redox potentials of the pore solutions of the GGBFS-containing cements were in the range from −100 mV to –500 mV vs Ag/AgCl, that is considerably lower than that of the Portland cement (8–20 mV vs Ag/AgCl), with the value depending on the GGBFS fraction and whether the cements were alkali-activated or not. These results indicate that the effects of reduced sulfur species from GGBFS in cements are more pronounced in alkali-activated materials, including HAC, and increase with GGBFS fraction.