Enhancing the hydration properties of copper tailings cement through improving the interfacial transition zone by calcium-based activators

Copper tailings are solid waste with large discharge volumes and significant environmental pollution. After activation, their pozzolanic reactivity can be enhanced, enabling them to serve as supplementary cementitious materials (SCMs) to replace cement. The use of alkali metal salt-activated tailings as a cement substitute can result in a reduction in specimen strength over time. The application of calcium-based activators offers a promising solution to mitigate these issues. This study compares the activation effects of CaO and Ca(OH)₂ on copper tailings, examining their influence on the pozzolanic reactivity of the copper tailings. Furthermore, the process by which calcium-based activators improve the interfacial transition zone (ITZ) and hence the cement hydration properties of copper tailings is examined. The results indicate that copper tailings activated with 4 % CaO and Ca(OH)₂ exhibit activity indices of 72.81 % and 65.33 %, respectively, representing 11.68 % and 4.20 % increases compared to the control group (M0). The cumulative heat release of the CaO-activated paste samples at 72 h is 855.46 J/g, 8.96 % higher than that of the Ca(OH)₂-activated sample. The compressive strength of the CaO-activated mortar samples at 28 d reaches 32.18 MPa, representing an increase of 3.3 MPa compared to the Ca(OH)2-activated sample. It is observed that CaO demonstrates a superior activation effect over Ca(OH)₂. This is primarily due to CaO, which enhances the in-situ generation of Ca(OH)₂ at the junction of the copper tailings and the cement. This process initiates pozzolanic reactions within the copper tailings and facilitates the formation of a low-Ca/Si C-S-H gel (Ca/Si = 2.40). This process enhances the interfacial transition zone (ITZ) between copper tailings and cement, thereby increasing the hydration degree of the copper tailings-cement paste, which in turn improves the compressive strength of the samples. This study provides theoretical and practical reinforcement for cement’s continued application of copper ore tailings.