Research on the Mechanical Properties, Hydration Mechanism and Engineering Applications of Road Base Materials Prepared from Harmless-Treated Barium Slag and Multiple Industrial Solid Wastes

Barium slag is classified as a hazardous waste due to its high content of soluble Ba2+. To achieve safe disposal and high-value utilization, this study developed a novel all-solid-waste road base material by synergistically combining harmlessly treated barium slag (HTBS) with steel slag, blast furnace slag, and flue-gas-desulfurization gypsum (SWB). The primary novelty of this work lies in the dual-immobilization mechanism of barium within a multi-solid-waste cementitious system. Our results showed that the mixture containing 16% binder achieved unconfined compressive strengths of 4.24 MPa (7 days) and 8.06 MPa (28 days), meeting the technical requirements for heavy-load road bases. Microstructural analyses revealed that the system evolved into a dense network composed of C–S–H gels and ettringite (AFt). Mechanistically, environmental safety is ensured by two pathways: (1) the chemical precipitation of stable BaSO4 and (2) the physical encapsulation of ions by the dense gel matrix. Leaching tests confirmed that Ba concentration remained far below the regulatory limit, ensuring environmental safety. This work provides a scalable, eco-friendly solution for the “waste-to-resource” conversion of hazardous barium slag in road engineering.