Complete recycling of concrete

Abstract of RECYBETON Phase 2

The second phase of the National Project RECYBETON ( was conducted by its 46 partners from August 2013 to February 2015.

In subject 1 “Technologies and processes”, a significant work has been performed on sorting technologies used for recycled concrete aggregates, at the laboratory scale. For example, the capability of the “water jig process” (sorting by densitometry) has been studied with several series of tests that allowed drawing initial conclusions about its relevance. Optical technologies and NIR (Near Infra Red) applied to the sorting of recycled aggregates have also been studied in laboratory; they probably will refine sorting trailing. Regarding the manufacturing processes, the influence of mixing on the rheology of recycled concrete was characterized according to different parameters such as the type and configuration of the mixer, mixing time or initial water content of aggregates. After working on the cement potential of crushed concrete sand in phase 1 of the project, the feasibility of using fine and sand of crushed concrete as a mineral addition in new concretes has been studied in this phase 2.

Subject 2 “Materials and structure” provided important inputs on the spatial and temporal variability of recycled aggregates. Cracking of recycled concrete was characterized in laboratory on samples of concrete coming from an experimental site. A predictive model was also confronted with the experimental results. As regards the behaviour of concrete recycled in the hardened state, the adhesion steel / concrete was studied using different tests: pullout tests, test on ties, beam tests.

The applicability of the “RAG” approach (alkali-aggregate reaction) has been the subject of a specific research, the objective being to clearly identify in the current recommendations the points that need to be reviewed in the case of concrete containing recycled aggregates. Finally, the ANR project ECOREB (ECO-construction by the recycling of concrete) provided important results on the mechanical behaviour and durability of recycled concrete.

As part of the subject 3 “Sustainable development”, a first action was devoted to the characterization of the environmental behaviour of recycled concrete and the results are used to show that the contribution of recycled aggregates does not result in a significant change in the release. In the second action research teams have focused on the environmental performance of concrete with different proportions of recycled aggregates. LCA (Life Cycle Analysis) were performed using two different softwares: GaBi based on an own database and SimaPro based on the Ecoinvent database.

Subject 4 “Standard and normative issues” is a subject that interact with all the previous themes. Further to work of phase 1, this working group was interested in feedbacks of countries other than France and helped to identify both barriers and incentives of the development of recycling of concrete into concrete. There is a fairly strong disparity in the use of recycled aggregates in structural concrete.

Finally, two experimental construction sites were realized in the framework of the National Project RECYBETON. The first relates to a parking pavement of about 2100 m2 achieved with concrete with substitution rate of natural aggregates by recycled aggregates varying from 0 to 100%. The second experimental site is a bridge dedicated to cycling, for which part of the concrete contains 20% recycled aggregates.

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Président : Jacques ROUDIER (IREX)
Directeur : Horacio COLINA (ATILH)
Directeur Scientifique : François de LARRARD (LAFARGE LCR)

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