Separation and Quantification of Attached Mortar in Recycled Concrete Aggregates

Construction and demolition waste stream has generated news materials that may be re-introduced into new concrete, e.g. as recycled aggregates. The specific feature of recycled concrete aggregates is the presence of hardened mortars influencing their behaviour. This study aims to distinguish processes that allow the complete separation and quantification of attached mortar. An important point is that the laboratory developed method has to be transferable on a wider scale to be exploited on a real recycling platform. This study is linked to the recybeton national research project involving public research laboratories, institutes and private companies. After a short literature review, pointing out the relevant processes, several methods are tested in laboratory conditions to determine their efficiency. They are based on mechanical, chemical and physical principles. Efficiencies are evaluated by measuring mass losses, density variations and by carrying out visual comparisons. It appears that not any one method is 100% satisfactory as aggregates are never completely cleaned and/or are damaged. Furthermore, the global efficiency of the process is difficult to determine because of the lack of knowledge of primary aggregate properties or because of property changes during treatment. The most promising methods, of those investigated in this study, seem to be combined thermal–mechanical processes.