Strength and Durability Behaviors of Stabilized Copper Heap Leach Residue as Road Base Materials

Copper heap leach residue (CHLR) is an unwanted material left as a stockpile in mine tailings after extraction of copper from the ore. This study examines the effectiveness of approximately 5 million metric tons of annual CHLR production as a sustainable and alternative road base or subbase material for the construction and maintenance of the 880,000 km Australian road network. Five different mixes of CHLR stabilized with optimized content of binders such as 3% ordinary portland cement (OPC), 4% and 5% of blended blast furnace slag, and hydrated lime (HL); further, 7.5% and 10% of blended fly ash (FA) and HL were examined against the control counterpart of crushed rock base stabilized with 2% OPC. Tests were conducted to assess unconfined compressive strengths (UCS), resilient modulus (Mr), permanent deformation against cyclic loading, and durability against the cycle of wet–dry exposure. The test data highlighted that the stabilized CHLR containing 5% combined BFS and HL (BFSHL) outperformed all other CHLR mixes and achieved the highest UCS of 4.67 MPa at 28 days, followed by 3% OPC with a UCS of 3.58 MPa. However, all CHLR mixes exhibited a greater UCS than the required UCS of 1 MPa for road base construction. Similar outcomes were observed in the modulus of resilience and permanent deformation test, exhibiting the highest resilience of 2,300–2,800 MPa by 3% OPC and 5% BFSHL stabilized CHLR, outperforming the control counterpart, indicating excellent resistance under repeated loading. Fly ash and hydraulic lime (FAHL) mixed stabilized CHLR, while compliant with the minimum Mr requirement, underperformed significantly in stiffness and deformation resistance. The study also found that the mass of all CHLR-containing mixes was substantially lower than the standard threshold of 14%, lowering below 4% when stabilized with BFSHL and OPC and 5.5% when FAHL was used as stabilizing binder. A similar trend was followed by the mixes in terms of change in volume and ‍noticeable improvement observed in shape and strength retention, remaining above 60% for all CHLR mixes. Backscattered images revealed a compact and densified microstructure of OPC and BFSHL stabilized CHLR mixes with a higher degree of bonding between the particles and hydration of binder materials, while porous and loosely packed particles were observed in FAHL stabilized mixes.