Improving the properties of recycled concrete aggregates by accelerated carbonation

Large amounts of construction and demolition wastes, especially concrete wastes, are generated annually. Until now, only a small fraction of concrete wastes has been reused as recycled concrete aggregates (RCA) in the manufacture of mortar and concrete. In order to optimise the use of RCA for new concrete, it is important to improve the properties of RCA. RCA are mainly composed of an intimate mix of natural aggregates and adherent hardened cement paste, which has a much larger porosity than natural aggregates. The influence of accelerated carbonation on the properties of RCA was studied in this work. Original concrete was manufactured and crushed by a jaw crusher in the laboratory. The different fractions of laboratory-produced RCA were stored in an accelerated carbonation room. The mass loss, density, porosity and water absorption of the RCA were tested before and after carbonation. Industrial RCA were also studied for comparison with the laboratory-produced RCA. The results clearly showed that, after accelerated carbonation, the density of the RCA increased due to the transformation of portlandite into calcite. The water absorption and porosity of the RCA decreased after carbonation.