Synergistic utilization of white mud and coal gasification slag in low-carbon cement

Abstract

This study investigates the synergistic use of two typical industrial solid wastes, coal gasification slag (CGS) and white mud (WM), common to coal chemical companies, as supplementary cementitious materials (SCMs) at high substitution levels. Studies demonstrate that CGS and WM (alkali/carbonate-rich) enhance cement hydration by consuming calcium hydroxide and promoting carboaluminate phases like hemicarboaluminate (Hc) and monocarboaluminate (Mc). In contrast to cement systems containing only CGS, the introduction of WM enhances early strength development and stabilises calcite, preventing its conversion to monosulphide-type sulphoaluminate (Ms) in the later stages of hydration. However, over-addition (>5 %) can lead to excessive alkalinity in the system, which inhibits the stable existence of the Hc/Mc phase and is detrimental to the development of long-term compressive strength. The optimum replacement level of CGS and WM was determined to be 35 % CGS and 5 % WM with a 28 days compressive strength of 36.5 MPa. The incorporation of WM optimised the pore structure and improved the densification of the microstructure. These findings underscore the potential of coal-derived wastes as sustainable SCMs, particularly for eco-friendly construction. Additionally, the CGS-WM system demonstrates heavy metal immobilization capacity, further amplifying its environmental advantages.