Structural concrete with recycled aggregate: advances in mechanical properties, durability and sustainability

A large number of tests has been carried out in the last 15 years all around the world to study the possibility to use recycled concrete aggregates (RCA) to produce structural concrete. Earlier tests indicated that RCA concrete had lower properties in comparison to ordinary concrete, such as lower elastic modulus, a more brittle post-elastic behavior, lower workability, higher shrinkage and creep. Most of these issues have been addressed to the content of cement mortar remaining in adhesion to the aggregate after the recycling processes and that cannot be totally eliminated without high economic and ecological costs. This cement mortar which has undergone the crushing process creates zones of weakness in the RCA, causes higher water absorption, higher concrete porosity and causes the decay of the aforementioned properties. More recent tests prove that Recycled Concrete shows this peculiar problems only with a percentage of substitution of standard aggregates with RCA higher than 30%. Under this percentage recycled aggregate concrete (RAC) can be considered as a standard concrete, on condition that an appropriate mix design is performed.