Low-carbon cementitious materials for cement-stabilized macadam from synergistically calcined high-calcium solid waste and coal gangue: Insights into hydration, life cycle assessment, and mechanical properties

• A new coal gangue-based cementitious material (CGCM) was developed. • The optimal calcination formulation for CGCM was identified. • Cradle-to-gate life cycle assessment shows 60–77% CO 2 e reduction compared to cement. • 50% of OPC was replaced with CGCM to produce cement-stabilized macadam (CSM). • CGCM significantly improved the fatigue resistance of the CSM. Coal gangue exhibits pozzolanic activity after calcination, making it a potential option for preparing low-carbon cement substitute materials. However, its inherently low calcium content results in insufficient cementitious capacity, which presents a key constraint on its large-scale application in low-strength structures such as cement-stabilized macadam. In this work, a CG-based cementitious material (CGCM) was developed by co-calcining CG with carbide slag and desulfurized gypsum. Using paste compressive strength as the key indicator, the calcination parameters and mix design were optimized via the response surface methodology. After that, the hydration mechanism of CGCM mixed with cement was studied and its life cycle assessment was carried out. Subsequently, to evaluate the feasibility of using CGCM in the preparation of cement-stabilized macadam (CSM), CSM specimens with varying cementitious material contents were prepared by replacing 50% cement with CGCM and calcined CG, respectively. Based on the loading conditions of CSM in practical engineering, uniaxial compression tests and cyclic loading and unloading tests were conducted to analyze the short-term mechanical properties and fatigue resistance of the CSM specimens. The test results indicate that the 7-day compressive strength of CSM specimens with 11% cementitious material content exceeds the 5 MPa performance requirement specified in technical specifications, and the 28-day strength of the specimen with CGCM is 34.1% higher than that of the specimen with conventional calcined CG. Meanwhile, CGCM-based CSM showed enhanced fatigue resistance under cyclic loading. After 60 stress-controlled cycles, the CGCM-CSM system demonstrated lower strength degradation than the calcined CG system under different stress levels (0.8 UCS and 0.6 UCS), with reductions in strength loss of 3.3–4.0% and 0.5–2.6%, respectively.