Utilization of copper mine tailings as road base construction material through geopolymerization

This paper investigates the utilization of copper mine tailings (MT) as an alternative road base construction material through geopolymerization. Specifically, MT was mixed with different amounts of sodium hydroxide (NaOH) solution at various concentrations from 0 to 11 M, compacted, and then cured at 35°C. After 7 days' curing, unconfined compression tests were performed on the specimens to determine their unconfined compressive strength (UCS). Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analyses were also performed to study the microstructure and chemical composition of the specimens at different conditions. The study has systematically investigated the effect of two main factors, NaOH concentration and moisture content, on the behavior of geopolymerized MT. The results show that the maximum dry unit weight of the compacted MT is influenced by the NaOH concentration, with higher NaOH concentration leading to larger maximum dry unit weight. The behavior of the final geopolymerized MT depends strongly on the NaOH concentration and moisture content of the initial compacted MT. At a constant moisture content, the UCS of geopolymerized MT increases with higher NaOH concentration up to a certain level and then decreases. This behavior is simply related to the effect of NaOH content or Na:Al ratio on the geopolymerization. For specimens prepared at the same NaOH concentration, the highest UCS does not necessarily occur at the optimum water content or the maximum dry unit weight, emphasizing the contribution of geopolymerization to the UCS. Moreover, this study demonstrates that by selecting appropriate moisture content and NaOH concentration, the geopolymerized MT can meet the strength requirements for road base by different state DOTs and the Federal Highway Administration (FHWA) in the United States. However, before the field application of MTin road base construction, a comprehensive leachate study based on the new EPA standard should be performed to ensure that the MT is environmentally safe.