Promotion mechanisms of calcium carbide residue on the early-age hydration of sodium carbonate-activated GBFS materials

Sodium carbonate-activated GBFS materials (SCSM) present compelling sustainability advantages, including low-carbon footprint and economic viability. However, its long setting time and low early strength limit its practical application. In this study, calcium carbide residue (CCR) was added to modify SCSM. Effects of CCR on the reaction kinetics, phase assemblage, and microstructure of SCSM were investigated, and promotion mechanisms of CCR on the early hydration of SCSM were discussed. Results showed that the OH⁻ released by CCR promoted the depolymerization of GBFS and improved the early exothermic rate. Meanwhile, the Ca²⁺ provided by CCR and GBFS reacted with CO₃²⁻ to form calcium carbonate, and promoted the formation of C-(A)-S-H with [SiO₄]^4- and [AlO₄]^5- released by GBFS. In addition, CCR provided additional nucleation sites to promote the hydration reaction. Through combined chemical and physical effects, CCR significantly shortened the induction period from 24 h to 0.8 h, drastically reduced the setting time from 688 min to 171 min. It increased the 1 d compressive and flexural strength from negligible values to 11.24 MPa and 4.31 MPa, respectively. Therefore, CCR as a high-quality modified material provides a scalable paradigm for developing high-performance and low-carbon SCSM.