Experimental Study of Geopolymer Binder Synthesized with Copper Mine Tailings and Low-Calcium Copper Slag

The use of waste materials in construction is gaining increasing interest due to the development of new technologies. This paper presents an experimental study on geopolymer binder produced with copper mine tailings (MT) and low-calcium slag (SG) for potential applications in road construction. The study systematically investigated the effects of water-to-solid ratio (w/s), SG content (0%, 25%, and 50%), sodium hydroxide (NaOH) concentration (5, 10 and 15 M), and the ratio of sodium silicate (SS) to sodium hydroxide (0.0, 0.5, 1.0, and 1.5) on the unconfined compressive strength (UCS) of synthesized geopolymer binder specimens. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were also performed to characterize the microstructure and phase composition of the geopolymer specimens. The results show that the inclusion of SG improves UCS and reduces the initial water content required for achieving a certain workability of the geopolymer paste. The geopolymer binder specimens prepared at 50% SG, 10-M NaOH, SS/NaOH=1.0, and cured at 60°C for seven days reached the highest UCS of 23.5 MPa. The geopolymer paste prepared at 50% SG, 15-M NaOH concentration, and SS/NaOH ratios of 0.5 and 1.0 showed flash setting, which led to poorer quality specimens and lower UCS. The SEM, EDS, and XRD analyses clearly showed the participation of iron dissolved from SG in the formation of geopolymer gels. This research helps promote the reuse of MT and SG through geopolymerization and contributes to the knowledge of geopolymer materials.