Performance of hydrated lime-activated Saudi Natural Pozzolan as a partial cement replacement in copper tailings cemented paste backfill

Abstract This study evaluates the effect of chemically treated (CT) Saudi Natural Pozzolan (SNP) as a partial replacement for Ordinary Portland Cement (OPC) in copper-tailings Cemented Paste Backfill (CPB). The short- and long-term performance of CPB incorporating chemically treated SNP (CT-SNP) was evaluated through a comprehensive experimental program that included physical, mechanical, and microstructural characterization over 7 to 91 days of curing. CPB mixtures containing 5, 10, 15, and 20 wt.% CT-SNP in the binder were assessed using bulk density, ultrasonic pulse velocity (UPV), unconfined compressive strength (UCS), indirect tensile strength (ITS), elastic modulus (E), and selected microstructural analyses (XRD, TGA, and FTIR). The results showed that bulk density was highest at a 10% replacement level. Across most curing ages, the mixture containing 5% CT-SNP exhibited the best overall mechanical performance. However, the mixture containing 10% CT-SNP slightly exceeded it in UCS at 91 days. Microstructural observations were consistent with the formation of hydration products associated with C-(A)-S–H development. Therefore, CT-SNP represents a viable and sustainable option for CPB applications, as the treatment process not only enhances its pozzolanic performance but also remains an environmentally friendly procedure.