Comparative pozzolanic activity and microstructure assessments of calcined copper heap leach residue fines with class-F fly ash and silica fume

Cement production requires thermo-mechanical processing of limestone for the activation of clinker phases and this energy intensive manufacturing process contributes to global CO 2 emissions. Supplementary cementitious materials (SCMs) are generally derived from industrial waste streams, and these can reduce clinker usage to enhance sustainability when appropriately activated. In this study, copper heap leach residue (CHLR) obtained from secondary copper refineries was calcined at 300, 600, 900˚C and used as a SCM to compare their pozzolanic activity with class-F fly ash (FA) and silica fume (SF). Raw CHLR fines possess 88.3% SiO 2 + Al 2 O 3 + Fe 2 O 3 , 31.31% amorphousness, and specific surface area of 725 m 2 /kg, making it a suitable candidate as a SCM. At 28 days, the CHLR600˚C consumed 864 mg Ca(OH) 2 /g of SCM, demonstrating significant pozzolanic reactivity and reduced 91% of initial electrical conductivity in a fixed lime test. In addition, CHLR600˚C mortar achieved 85% strength activity index (SAI) at 28 days and 185 J/g SCM hydration heat in R 3 test at 7 days for 20% cement and 25% lime replaced systems, respectively. In contrast, FA and SF yielded SAIs of 77% and 91%, respectively. The pozzolanic activity and hydration product development of these SCMs were supported by XRD and TEM-EDS microscopies.