Synergy between sodium lactate and basic oxygen furnace slag in supersulfated cement: hydration and properties

Supersulfated cement (SSC), a low carbon dioxide binder utilising 80–90% ground granulated blast-furnace slag (GGBS), faces a critical challenge in balancing mechanical performance and carbon dioxide footprint reduction when incorporating basic oxygen furnace slag (BOFS) – a steelmaking byproduct with underutilised potential. However, adding more than 10% BOFS to SSC causes a significant reduction in strength, which limits both its broader application and its potential for further reducing carbon dioxide emissions. This study explores the synergistic effect of sodium lactate in BOFS-modified SSC (BSC) to address this limitation. The results show that even a small addition of 0.5% sodium lactate significantly improves the 7-day and 28-day strength of BSC. Hydration heat tests reveal that the combined use of BOFS and sodium lactate significantly inhibits early hydration, leading to a more porous initial microstructure. This porosity facilitates the dissolution of slag during the later stages of hydration. Furthermore, the chelating properties of lactate ions promote the dissolution of ions from both GGBS and BOFS, increasing the formation of ettringite and enhancing the hydration of SSC. These findings demonstrate that the simultaneous use of sodium lactate and BOFS offers a significant improvement in both the performance and environmental benefits of SSC, making it a more viable option for sustainable cement production.