Carbonation of recycled concrete aggregates affected by alkali-silica reaction

Concrete recycling has become a major challenge for the construction industry. Using recycled concrete aggregates (RCA) in structural applications is limited due to their often lesser mechanical and durability performances. Alkali-silica reaction (RAS), in particular, is a pathology which could affect recycled concretes to an even larger extend than in the original concrete, due to the higher alkalis content of these aggregate. The present work attempts to study the effects of RCA carbonation in order to reduce the quantity of alkali hydroxides and the mobility of the alkali ions in the cement paste for preventing water-swelling gel formation. Concrete samples were produced from reactive natural aggregates, crushed at different expansion levels and the obtained RCA were submitted to CO2. Their alkali reactivity was assessed through an autoclave mortar bar test and comparison with not carbonated RCA and original natural aggregates was performed. Reactivity of carbonated RCA is less important that the one of original natural reactive aggregates, but however higher than the acceptable limit. Carbonation enables to still reduce this reactivity by 20 to 50%.