ABSTRACT
This section presents the construction of a conventional truss bridge of the Nîmes Montpellier rail bypass project using recycled coarse aggregates (RA). This full-scale experiment is combined with laboratory study. For this structure, a C35/45 concrete was required to comply with an environmental class XC4 XF1 defined in NF EN206/CN. Two recycled concrete mixes were designed: the first one was limited to 20% RA according to NF EN206/CN for this kind of environmental class, and the second one explored the impact of a higher content of 40% RA replacing a totally natural 6/14 coarse aggregate. Chemical, mineralogical, and physical properties of the selected RAs were determined. Concretes were studied in laboratory as usual for this kind of structure; in addition, further characterizations were performed (water porosity, oxygen permeability, carbonation depth, and shrinkage assessments) to evaluate the impact of RA ratio on concrete durability. Laboratory studies reveal that fresh concrete and hardened concrete properties of both 40% and 20% RA mixes were in agreement with requirement specification. The bridge was built with the 20% RA mix and standard concrete mix. No particular difficulties were observed neither in concrete production 396nor in its placement. One sacrificial wall element to allow core sampling was cast at the same time as the structure to follow concrete properties over time. More than 2 years after construction, no particular defaults were observed, and the measurements of durability parameters on core samples were as expected. This experience shows that RAs could be generalized even in engineered structures without major difficulties, probably, even at higher than 20% content as proved by the positive results obtained for the 40% mix.
