ABSTRACT
The aim of this study is to confirm the eco-respectability of recycled aggregates concrete (RAC). Comparisons are performed according to the normative criteria of Life Cycle Assessment (LCA) methodology applied to construction materials (EN 15804 standard). Thus, this study aims to compare the environmental impacts of RAC (Recycled Aggregate Concrete) as compared to NAC (Natural Aggregate Concrete). A multicriteria analysis of the factors impacting the LCA of such concretes is proposed in a case study (cement content and cement type, aggregate substitution rate, transport 490distances of aggregates and concrete). The first focus is the study of the influence of the concrete composition (quantity of RA, the cement dosage, and the water content). Then, optimized formulations of concrete with close mechanical strengths are performed in order to obtain the same cement content and the same efficient water content. Four substitution rates are tested: 0S0G; 10S10G; 30S30G; 100S100G. In order to study the sensitivity to transport, several transport distances of NA and RA are proposed. It allows studying the integrated management of demolition waste streams in several towns. Finally, LCA of experimental construction sites are performed.
The study of the concrete composition influence indicates that the use of recycled aggregates in concrete formulations leads to an increase of environmental impacts at different levels, when the standardized mechanical strength required is reached by the cement content adjustment. Moreover, with cement content similar for the RAC and the NAC (optimized formulations), when the situation of the area leads to the proximity of the concrete production site with the production sites of NA or RA, the use of RA cannot be justified by a sufficient decrease in transport in view of its resulting impacts. Concerning LCA of concrete for experimental sites, the origins of aggregates (RA or NA) play a relatively low role, due to the reduced part in the slab studied of RAC with high RA content.
Finally, the environmental benefit of the use of RA is ensured by calculating the avoided burdens in addition to an LCA, which quantifies the damage of the manufacturing of such concrete (the amount of saved NA or the consumption of the area of landfill avoided).
