Sodium aluminate activated BOF steel slag: Impact of Al(OH)4− on reaction mechanism

The limited hydraulic reactivity of Basic Oxygen Furnace (BOF) slag, caused by its low-aluminum and high-iron composition, restricts its high-value applications. This study employs sodium aluminate (NaAlO 2 , NA) as an activator, with a focus on the mechanistic role of Al(OH) 4 − in modulating the hydration pathways of belite in BOF slag. Systematic investigations of phase evolution, microstructural development, pore solution chemistry, and mechanical properties reveal that NA significantly enhances the early reactivity of belite and brownmillerite and promotes the formation of Si(Fe)-rich hydrogarnet and C(N)-A-S-H gels, enabling synergistic hydration between belite and brownmillerite at early ages. The NA-activated pastes develop a denser microstructure, exhibiting quadrupled early strength compared to the non-activated system. Crucially, the system demonstrates superior environmental performance, with heavy metal leaching concentrations consistently below regulatory thresholds. These findings elucidate the activation mechanisms of NA and propose a viable strategy for advanced BOF slag utilization.