Utilisation of copper slags as supplementary cementitious materials in cemented paste backfill

In the Abitibi mining district of Canada, several underground mines rely on cemented paste backfill (CPB) for ground support, enhancing operational productivity and profitability. However, the rising cost of binding agents and the substantial carbon footprint associated with their production make CPB an increasingly expensive technique. To address this, the mining industry is actively seeking ways to reduce binder costs, primarily by partially replacing general use (GU) Portland cement with industrial byproducts, known as supplementary cementitious materials (SCMs). This study aims to evaluate the potential of copper slags (CS) from the Horne Smelter in Rouyn-Noranda, Quebec (Canada), as SCMs by enhancing their pozzolanic activity through mechanical, chemical and hybrid activation methods. Initial findings demonstrate that mechanical activation through grinding for a period of 40 to 80 minutes (at a fixed speed of 180 rpm) combined with chemical treatments using sodium sulphate (Na₂SO₄) at concentrations between 0.1 and 0.5 N, and alkaline activators such as lime kiln dust (5 to 15% substitution rate), effectively improve the hydration and hardening of cementitious pastes. These treatments have yielded uniaxial compressive strength (UCS) values at 28 days comparable to 100% GU binders, with UCS ratios ranging from 0.8 to 1.11. This improvement is likely due to stimulation of the reactivity of the SiO₂ glass in CS, which promotes the production of a higher volume of hydrates, notably calcium silicate hydrate, thereby reducing the overall porosity of the CPB. The valorisation of CS as SCMs in CPB reduces binder costs and promotes the sustainable use of industrial waste, aligning with modern environmental policies.