Abstract
In this paper, a new innovative technology for the treatment of returned concrete is proposed. This method is based on the application of physical–mechanical processes that allow to obtain new quality products: recycled aggregates, microfiltered water and cement sludge. Specifically, by means of a mechanical system equipped with buffer and Archimedes screws, fine (d < 5 mm) and coarse (d > 5 mm) aggregates are obtained. 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) and no type of potentially toxic additive is added. In this context, this paper investigates the feasibility of using all these components as new raw materials for sustainable concrete production. In particular, according to the requirements imposed by technical standards, an experimental program was developed, aimed at evaluating the physical, chemical, and mechanical properties of the analyzed materials. The results showed that both recycled aggregates, the microfiltered water and the cement sludge can be used to produce new structural concrete. In particular, it was proven that also the cement sludge, which generally represents the most critical component destined for disposal, can be reused as filler in the partial replacement of sand.
Highlights
The results showed a significant increase in the California bearing ratio (CBR) value of the soils treated with cement sludge but a greater sensitivity to water variations compared to soils without cement sludge
As stated by Ferrari et al [22], the properties of the aggregates obtained from the recovery of returned concrete are strongly related to those of the original aggregates used in the initial concrete mixture
This is mainly due to the fact that the returned fresh concrete is subjected to an efficient washing process that completely eliminates all the cement paste adhered to the original natural aggregate
Summary
According to the ERMCO Report [2] and Ferrari et al [3], in European industrialized countries, approximately 2–3% of the concrete produced returns to the batching plants at the end of the day Based on this estimate, the returned concrete produced in Italy consists of approximately 710,000 cubic meters per year. As stated by Verian et al [9], contaminants and adhered mortar in the recycled aggregates should be minimized and their use kept to a limited percentage (30%)
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