Leaching performance of carbonated recycled concrete paste as a supplementary cementitious material: pH-dependent and long-term leaching assessment

This study investigates the pH-dependent and long-term leaching behavior of major and trace elements in mortars incorporating carbonated recycled concrete paste (cRCP) to assess its environmental compatibility as a supplementary cementitious material (SCM). pH-dependent leaching tests revealed that cRCP mortars exhibit release patterns comparable to Portland cement (CEM I) systems, indicating that incorporation of cRCP does not impair trace element retention. Long-term leaching evaluated via a 64-day Dynamic Surface Leaching Test (DSLT) demonstrate that cumulative releases of all analyzed elements remain well below regulatory limits in Germany and the Netherlands. Mortars incorporating heavy-metal-doped cRCP further demonstrate robust immobilization of Ba, Cr, Cu, Mn, Ni, and Sr, even under conservative contamination scenario. Overall, the results indicate that the leaching behavior of cRCP mortars is broadly consistent with conventional cementitious systems under the conditions investigated. This findings provide mechanistic and long-term leaching data supporting the environmental assessment of cRCP composite cements, and contributes to a better understanding of trace element retention in systems incorporating cRCP.