Safety and environmental assessment of high-content coal gangue in road base applications

This study investigates the utilisation of coal gangue (CG) as a primary raw material for road base construction. An optimised cementitious binder was developed with a mass ratio of CG : RM (Red mud) : KZ (Slag) : cement = 40% : 38.5% : 16.5% : 5%, utilising a 0.3 water–binder ratio and a 2.5% dosage of water-reducing agent. This binder achieved a 28-day compressive strength of 17.5 MPa. The optimal aggregate gradation for the road base was determined to be 17.3 (20–30 mm): 34.7 (10–20 mm) : 24.5 (5–10 mm, CG) : 23.5 (0–5 mm), with a 12% binder content and 7.30% water consumption. The resulting base specimens yielded unconfined compressive strengths (UCS) of 2.1 MPa at 7 days and 4.3 MPa at 28 days, satisfying the requirements of the ‘Highway Pavement Base Construction Technical Rules’ (JTG/T F20, Chinese transportation industry standard). While the 28-day water stability coefficient was recorded at 39.96%, the material exhibited excellent frost resistance; after five freeze–thaw cycles, the mass loss rate was only 1.472%, with a residual UCS of 3.2 MPa (despite a strength loss of 75.58% relative to the binder phase). Furthermore, various risk assessment methods were employed to analyse characteristic heavy metals (HMs) within base specimens crushed to different particle sizes. By applying a leaching kinetics model to evaluate HM migration, an environmental safety control system for CG-based road bases was established to ensure sustainable engineering application.