Effect of pre-wetted coal gangue powder on the properties of cementitious materials

Coal gangue, a solid waste byproduct generated during coal mining, poses serious environmental challenges in China, with an estimated stockpile exceeding 7 billion tons, leading to land occupation and pollution. Traditional activation techniques—including thermal, chemical, and mechanical methods—for utilizing coal gangue powder (CGP) as a supplementary cementitious material (SCM) are often energy-intensive and economically unfeasible, limiting their practical application. In this study, a pre-wetting strategy was adopted to improve the reactivity and performance of CGP in cementitious systems, with a focus on shrinkage reduction and strength development. Pre-wetted CGP was incorporated at 5 %, 10 %, and 15 % replacement levels for cement, and comprehensive testing was conducted, including isothermal calorimetry, nanoindentation, chemical/autogenous/drying shrinkage measurements, compressive strength testing, and internal relative humidity monitoring. The results demonstrate that pre-wetted CGP at a 15 % replacement level effectively mitigated shrinkage, reducing chemical shrinkage by 36.5 %, autogenous shrinkage by 46.5 %, and drying shrinkage by 31.94 % compared to dry CGP. Furthermore, a 6.16 % increase in 28-day compressive strength was observed. These enhancements are primarily attributed to internal curing provided by the absorbed water within CGP, which promoted sustained hydration, as evidenced by a 24.1 % increase in the main hydration peak. In addition, pore structure refinement and a 33.71 % reduction in capillary pore pressure were achieved, contributing to improved microstructural compactness and mechanical performance. This study highlights pre-wetted CGP as a promising, low-energy, and scalable approach for coal gangue valorization. Further research should investigate long-term durability, performance in concrete-scale applications, and industrial feasibility to support standardization of the pre-wetting method. • A method of preparing cement paste with pre-wetted coal gangue powder (CGP) was proposed. • Pre-wetted CGP reduced chemical, autogenous, and drying shrinkage by 36.5%, 46.5%, and 31.9%. • Adding 10% pre-wetted CGP improved 28-day strength by 6.1% and refined the pore structure. • Pre-wetted CGP offers a sustainable strategy for recycling coal gangue in cement materials.