Etude de la carbonatation des granulats de béton recyclé altéré par la réaction alcali-silice

Concrete recycling has become a major challenge for the construction industry. The use of 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 the RCA. 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 to prevent water-swelling gel formation. Concrete samples were produced from reactive natural aggregates and crushed at different expansion levels. 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 still enables a reduction by 20 to 50% of the reactivity.