Characterization of ready-mixed concrete plants sludge and incorporation into mortars: Origin of pollutants, environmental characterization and impacts on mortars characteristics

Abstract Ready-mixed concrete plants (RMCP) sludge samples were studied, particularly from an environmental point of view. Their average composition (cement, sand and filler contents) was determined through chemical analysis. Based on this composition and trace-elements contents of the raw materials used in RMCP, trace-elements contents in sludge were calculated. Good correlation was obtained with the measured contents, highlighting strong dependence between sludge composition (especially cement content) and raw materials (especially cement type). Prediction of the leaching behavior appeared to be more complex, due to variability of trace-elements leachability factor (from 0.02% for Cd to 27.47% for Ba). Nevertheless, good estimation of the environmental behavior could be achieved through an empirical predictive model (correlation coefficient higher than 0.9), allowing the prediction of the inert or non-inert nature of the sludge. Particularly, this study highlighted the importance of the type of cement used in RMCP. Indeed, the use of CEM I clinker-rich cement into RMCP leads to higher chromium contents into sludge leachates, which can modify the sludge category, from inert to non-hazardous. Finally, mortars were manufactured with sludge in order to assess their influence on the environmental properties of the mortars. Incorporation of sludge into mortars did not impact significantly the leaching behavior of the monoliths, which confirms the efficiency of this stabilisation method.