Multi-criteria study for recycled concrete aggregate separation process

Construction and demolition waste stream has generated news materials that may be reintroduced into new concrete, e.g. as recycled aggregates. The specific feature of recycled concrete aggregates (RCA) 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. 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. Several methods are tested in laboratory conditions to determine their efficiency. They are based on mechanical, chemical and physical principles. The definition of this efficiency concept and the mortar content denomination are also discussed. Originality of this study consists in optimizing hot or cold thermal processes combined with a mechanical treatment. To perform that, a multi-criteria phase experiment was carried out and several values of the multi-criteria parameters were optimized. Results allow for a thorough knowledge of treatment efficiency. However, it appears that not any one method is 100% satisfactory as aggregates are never completely cleaned and/or are damaged

Influence of materials composition and transportation tours on life cycle assessment of recycled aggregate concrete

In a context of incitation to the waste recovery as recycled aggregates to be re-introduced into new concrete, this paper aims to compare the environmental impacts related to the composition of concrete to ones due to the transportation of the recycled aggregates, issued from demolition wastes, by implementing a life cycle assessment (LCA). This study is linked to the RECYBETON French Research Project involving public research laboratories, institutes and private companies. Life cycle assessment (LCA) of recycled aggregates concrete (RAC) in comparison with a natural aggregates concrete (NAC) are realized. The study focuses first on the influence of the composition parameters of the concrete, in particular the content of recycled aggregates, the cement dosage and type, and the water content. The use of recycled aggregates in concrete formulations increases environmental impacts at different levels. This result is due to the increase of the cement content in the samples, because a standardized mechanical strength is required. Then, optimized formulations of concrete with close mechanical strengths are performed in order to obtain the same cement content (CEM 1) and the same efficient water. Four substitution rates are tested: 0, 10%, 30% and 100%. Moreover, in order to take into account impact distance, several transport distances of natural and recycled aggregates are proposed, it allows to study the integrated management of demolition waste streams in several areas

Use of recycled aggregates of concrete in total replacement of natural materials: Influence on the determination of concrete formulation parameters

The study presented here aims to develop the use of recycled aggregate issued of concrete in total replacement of natural materials (sand and gravel). In regard to natural aggregates, recycled concrete aggregates (RCA) contain mortar that influences theirs properties and those of concrete in which they are used (RCA). The objective of this work is to analyze the characteristics of concrete with 100 % of RCA. In this way, following an experimental analysis of physical, mechanical and mineralogical properties of recycled aggregates, these characteristics lead to suggesting adaptations on formulation parameters of concrete and mortar. Moreover, it was shown that the use of superplasticizers is necessary to reach satisfactory properties of concrete