Manufacture of all-solid-waste cementitious materials using steel slag and phosphogypsum: Hydration characteristics and salt-alkali synergistic mechanism

This study investigated the synergistic activation of steel slag powder (SSP) and phosphogypsum (PG) on ground granulated blast furnace slag (GGBS) and developed a novel all-solid-waste supersulfated cementitious materials (ASCMs). The activation mechanism was examined through compressive strength, isothermal calorimetry (IC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), pH values, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The environmental impact was assessed using the toxicity characteristic leaching procedure (TCLP) and life cycle assessment (LCA). The results showed that ASCM achieved a compressive strength of 59.2 MPa at 28 days due to the synergistic activation of SSP and PG. The weak alkaline environment created by SSP dissolution facilitated the release of [Al(OH)₆]^{3 -} from GGBS. The abundant SO₄^2- supplied by PG then reacted with [Al(OH)₆]^3- to form ettringite. The rapid consumption of [Al(OH)₆]^3- further promoted GGBS dissolution, releasing [SiO₄]^4- and OH^-, thereby increasing the pore solution alkalinity and enhancing calcium-aluminum-silicate-hydrate (C-(A)-S-H) formation. This process resulted in the development of an interwoven skeletal structure composed of C-(A)-S-H and ettringite, contributing to the densification of the microstructure. The TCLP results revealed that the leaching concentrations of heavy metal ions in the designed ASCMs were significantly lower than those in PG. LCA analysis showed the designed ASCMs lowered carbon emissions and energy consumption by 81.5 % and 62.6 %, respectively, compared to conventional blended cement. These findings highlight the potential of the designed ASCMs for sustainable solid waste utilization and low-carbon cement production.