Effect of copper mine tailings and copper slag on the hydration, microstructure, and mechanical property in Portland cement

• The incorporation of CMT and CS as alternative SCM are evaluated. • The modified R3 reactivity test shows low reactivity of CMT and CS. • Quantitative TGA results reveal the filler effect of CMT and CS. • LS demonstrates an enhanced filler effect compared to CMT and CS. • A lower replacement level of CMT and CS has comparable performance to PC control. There has been a growing interest in exploring copper mine tailings (CMT) and copper slag (CS) as alternative supplementary cementitious materials (SCMs). However, limited studies systematically compare CMT and CS with traditional SCMs in terms of hydration products and microstructural characteristics. And conflicting findings exist regarding their impact on mechanical performance and hydration mechanisms in Portland cement. To address these gaps, this study evaluates the reactivity and performance of CMT and CS in comparison with fly ash, blast furnace slag, and limestone powder (LS). The modified R 3 reactivity test results indicate that CMT is inert, while CS exhibits lower reactivity. Compressive strength, water absorption, pore volume, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to evaluate cementitious paste. The results show that at low replacement levels, their mechanical performance remains comparable to that of reference mixtures. SEM micrographs reveal minimal changes in surface morphology and chemical composition. Quantitative TGA analysis shows that at 1 day, CMT and CS exhibit a dilution effect similar to other SCMs. At 28 days, LS, CS, and CMT surpass the dilution line, with LS demonstrating the highest bound water and calcium hydroxide content. This study demonstrates the proof of concept that the modified R 3 test can serve as a rapid screening method for assessing SCM reactivity. In addition, the results provide a benchmark for the performance of CMT and CS before further activation strategies are explored, contributing to the broader effort of utilizing copper mine wastes as alternative SCMs.