Optimization of the Recycling of Concrete in Concrete Application to an Airport Slab

The use of demolished concrete as recycled aggregate in new concrete is a promising solution within the context of sustainable development. However, this application is still limited in the construction sector due to the lack of knowledge. In that context, Ifsttar (France) and the French industry's major players have finished in 2012 a 3 year collaborative research to provide a better comprehension of the influence of such recycled concrete aggregates on the properties of concrete. The paper first describes the context and the issues of the research. In the second part, the methodology used is presented. It mainly consisted in producing a first generation of different concrete mixes with natural aggregates. They were then crushed and recycled in a second generation of mixes. The cycle was repeated a last time to produce a third generation of concrete mixes. Concrete production and crushing were conducted in semi-industrial conditions, but under a strict control, in order to guaranty the quality and the traceability of the different materials thus produced. Concrete performances as well as recycled aggregates properties were investigated for each generation. These data represented a rich experimental basis which was analyzed and used to develop a set of semi-empirical models, linking the properties of concrete with those of recycled aggregates they are made of, but also the properties of recycled aggregates to those concrete which they are produced. The paper makes a focus on a specific concrete property to demonstrate how these models can be used to elaborate (multi)recycling scenarii. The last part of this paper is dedicated to a real case of recycling, consisting in renewing an airport area by a slab containing only aggregates recycled from old slabs. The paper concludes on the next collaborative research engaged in France research on this subject within the scope of the national Project "Recybéton".