Performance of multi-source solid wastes as road substrate filler: Mechanical tests, microscopic characterization and benefits evaluation

Recycling multi-source solid wastes (MSW) such as steel slag (SS1), silicon-manganese slag (SS2) and recycled concrete blocks (RCBs) as road substrate filler presents a promising alternative to natural crushed stone (NCS). Thus, this paper systematically investigated the road performance of cement and fly ash (FA)-bonded MSW (CFMSW) through unconfined compressive strength (UCS), splitting tensile strength (STS), triaxial and microscopic detection tests. Finally, field paving and environmental compatibility of CFMSW were evaluated. The results indicate that the UCS and STS of 4SS1-80 were superior, and the UCS at 7 days of the paving road sections were 5.04 MPa and 4.95 MPa, meeting the construction requirements for highways and grade Ⅰ or grade Ⅱ and below roads in China. Constitutive models for the MSW composition and cement dosage with peak stress and confining pressure were proposed with enhanced rigor. To compare the shear strength of CFMSW under different burial depths, the critical depth method was established. The alkaline medium progressively broke the covalent chemical bonds in the system and re-formed into Al-O-Al and Si-O-Si bonds. Therewith, the accumulation and growth of C-(A)-S-H and AFt gels contributed to the strength of 4SS1-80 reaching 12.84 MPa at 90 d. Environmental compatibility evaluation demonstrated that hazardous element concentrations in 4SS1-80 complied with regulations. Compared to cement-bonded NCS (CNCS), the CO₂ emission mass (EM-CO₂) of the mixture was reduced by 122.1 kg·m^-3. These significant advances endowed CFMSW with significant road-worthy prospects.