## 5 Concluding Remarks  
In this paper, a new technology for the treatment of fresh returned concrete is presented. In particular, by means of a mechanical system equipped with buffer and Archimedes screws, it is possible to separate and recover fine (d \(\leq\) 5 mm) and coarse (d \(\geq\) 5 mm) recycled aggregates. At the same time, the water coming from the washing process is sent to a microfiltration process, where a filter membrane separates the liquid phase (microfiltered water) from the solid phase (cement sludge). To guarantee the quality of the output materials, no type of potentially toxic additive is added.  
Figure 7: Hygrometric shrinkage of concrete samples at different curing days.  
In this context, the main aim of the study was to investigate the technical and environmental feasibility of using these products as new materials for concrete production. To achieve this goal, several experimental tests were carried out on fine and coarse recycled aggregates, microfiltered water, cement sludge and concrete mixtures.  
Based on the experimental results, the following conclusions can be drawn.  
* The fine and coarse recycled aggregates produced by the proposed technology comply with all the requirements imposed by UNI EN 12620 and, therefore, can be used for new concrete production. Similar to natural aggregates, they show density values in saturated-surface-dry conditions equal to 2720 kg/m\({}^{3}\) and a water absorption value of coarse recycled aggregates of 0.9%. The presence of light organic impurities, radioactivity and alkali-silica reactivity was also not detected.
* In terms of environmental behavior, the recycled aggregates do not release any contaminants into the surrounding environment. In particular, the eluates produced fully comply with the regulatory limits established by M.D. 186/2006.
* Microfiltered water complies with all the chemical and mechanical requirements of UNI EN 1008 and can be used as new mixing water for concrete production.
* The cement sludge produced by the microfiltration process has a moisture content ranging between 53% and 61% and no longer has any hydration capacity. Therefore, it cannot be used as a partial substitute for Portland cement, but it can be used as filler in new concrete mixtures.
* Compared to the control concrete, the 50% recycled mixture reached similar compressive strength values at 28 curing days. Conversely, the cement sludge mixture generally showed a decrease in compressive strength of about 15% for C10/15 concrete grade and 7% for C25/30 and C30/37 concrete grade.  
In conclusion, it is possible to state that, consistent with the principles of circular economy, the use of the products obtained by the proposed technology for concrete production is feasible and does not significantly affect the properties of the final concrete.  
Conceptualization, S.S., A.D., L.C. and G.P.; methodology, S.S., A.D. and L.C.; investigation, A.D. and L.C.; data curation, A.D. and L.C.; writing--original draft preparation, A.D.; writing--review and editing, A.D., L.C., S.S. and G.P.; supervision, S.S. and G.P.; project administration, S.S. and G.P. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. Data Availability Statement: Data sharing not applicable. The authors wish to thank the company WAMGROUP(r) and its members for their willingness to supply the recycled materials (aggregates, washing water and cement sludge) necessary for the experimental tests, as well as for their operational and economic support to the research project development. The authors declare no conflict of interest.