Environmental and Mechanical Performance of Green Concrete Utilizing Coarse Copper Slag Aggregate

This study investigates the environmental potential and viability of replacing natural river aggregates (RAs) with copper slag aggregates (CSAs) in concrete production. The primary objective was to assess the structural performance of these eco-concrete mixtures and determine the optimum copper slag content for structural applications. The experimental program evaluated concrete mixtures with natural river aggregate replacement levels of 20% + 20% and 50% + 100% for the 8/16 mm and 16/32 mm fractions, respectively, using coarse copper slag aggregate (CCA). The results indicate that incorporating CCA increases concrete compressive strength, successfully meeting the requirements for strength class C25/30. The petrographic assessment indicated a shift towards an aggregate mixture, in which the dominant quartzite and a constant quartz-mineral fraction of 16.5% provide a stable structure alongside the CSA grains. However, a significant increase in water penetration depth (up to 22%) was observed, highlighting the enhanced water penetration depth of these concretes. SEM microstructural analysis attributed the improved bond between the cement matrix and CCA grains to a compact interfacial transition zone. Additionally, leaching tests confirmed that heavy metals are effectively immobilized in the cement paste for mixtures with lower replacement levels (up to 20%), thereby meeting environmental standards. The study concludes that copper slag at these controlled replacement levels represents a sustainable, high-quality alternative for construction materials in drainage infrastructure. Incremental analysis in accordance with NEN 7375 showed that the tested material behaves as an insoluble matrix, with no evidence of diffusion-controlled leaching. The cumulative leaching values obtained after 64 days of testing in accordance with NEN 7375 were significantly below the regulatory limits for all components analyzed. These findings indicate a low potential for contaminant release and favorable environmental stability of the 20% replacement mixture, though further leaching evaluation is required for maximum slag contents.