Accelerated carbonation of recycled concrete aggregates and its implications for the production of recycling concrete

Abstract

During the demolition and recycling process the specific surface area per volume of concrete is significantly increased. As a result, the potential for CO2 absorption by carbonation of the cement hydrates is enhanced. In this study, recycled concrete aggregates (RCA) with varying moisture contents are carbonated with 100% CO2 at atmospheric pressure. The changes in the properties of RCA are characterized and they are used for the production of recycling concrete. There is only a minor impact of carbonation on bulk density and water adsorption of the RCA. The accelerated carbonation leads to the formation of calcium carbonate and decalcified calcium-silicate-hydrate (C-S-H) present in patches on the surface of RCA particles. Using slurry instead of tap water decreases concrete flow and generally increases compressive strength. Using carbonated instead of uncarbonated RCA leads to a faster decrease of flow with time and to a higher compressive strength of the recycling concrete compared to uncarbonated RCA. The higher strength linked to the use of carbonated RCA offers the potential to decrease the clinker content of the recycling concrete.