Activity of Copper and Blast Furnace Slag and Its Influence on the Properties of Cement

Reducing CO₂ emissions from cement production is currently one of the major challenges faced by the cement industry. One approach to lowering these emissions is to reduce the clinker factor by incorporating alternative mineral additives into cement. Consequently, there is a growing interest in the use of copper slags (CSs) as supplementary cementitious materials. Therefore, this study investigates the properties of cements containing substantial amounts of copper slag (up to 60%) and, for comparison, the same proportions of granulated blast furnace slag. The inclusion of substantial amounts of CS results both from the lack of studies in this area and from the potential benefits associated with the utilization of larger quantities of copper slag. The chemical, phase, and particle size composition of CS and granulated blast furnace slag added to CEM I 42.5 cement from the Odra cement plant in amounts of 20%, 40%, and 60% by weight were compared. The pozzolanic activity index of the copper slag and the hydraulic activity index of the blast furnace slag were determined. The high pozzolanic activity of the CS was attributed to its high degree of vitrification (nearly 100%). In contrast, the lower hydraulic activity of the blast furnace slag was explained by its lower glass phase content (about 90% by mass). A gradual decrease in the total heat of hydration released within the first two days was observed with increasing slag content in the cement, slightly more pronounced for copper slags. However, at later stages (2-28 days), XRD analysis indicated higher hydration activity in cements containing copper slag, resulting from its strong pozzolanic reactivity. Cements with copper slag also showed slightly lower water demand compared to those with blast furnace slag. An increase in setting time was observed with higher slag content, more noticeable for blast furnace slag. The type and amount of slag in cement reduce both yield stress and plastic viscosity. Greater reductions were observed at higher slag content. Moreover, copper slag caused greater paste fluidity, attributed to the lower amount of fine particles fraction. The addition of slag decreased flexural and compressive strength in the early period (up to 7 days), this reduction being proportional to slag content. After 90 days, mortars containing 20% and 40% copper slag achieved strength values exceeding that of the reference mortar by 4%. In contrast, at a 60% CS content, a 5% decrease was observed, while for cement with 60% BFS the decrease was 11%. This indicates that a lower copper slag content in the cement (40%) is more favorable in terms of strength.