Coupling of attrition and accelerated carbonation for CO2 sequestration in recycled concrete aggregates

An accelerated carbonation method was applied to improve the ability of recycled aggregates to store CO2 through the rolling carbonation process; moreover, recycled concrete aggregates' physicochemical properties to produce secondary aggregates for civil engineering applications were explored and evaluated. The carbonation tests were carried out in a laboratory-scale air-proof rotating drum equipped with a CO2 feeding system. Performing carbonation in a rotating drum promotes selective attrition of concrete aggregates. The process accelerates the carbonation by removing the carbonated zones on the surface of coarse aggregates and then facilitating the access of CO2 to un-carbonated zones. The tests were performed at normal atmospheric conditions, with a partial pressure of CO2 kept at about 0.75 bar. The optimal initial moisture of the concrete aggregate was found. The main tests were conducted on 10/20 mm aggregate, but it was shown that the carbonation process was 20% faster for smaller size aggregate (5/8 mm). The rolling speed, initial moisture content, and mass amount played an important role in CO2 sequestration. The most efficient rotating carbonation condition was reached at 100 rpm, aggregate moisture around 8%, and 500 g of aggregates in a 5 L reactor at any partial pressure. The dynamic process highly increased the carbonation kinetics compared with static carbonation of the same duration. The CO2 sequestered was up 80 mg/g of aggregate, estimated to be around 60% of the potential of CO2 capture of the tested recycled concrete aggregate. The number of revolutions appears to be a relevant process parameter concerning the carbonation kinetics. The carbonation duration acts in a complementary way as in a static process. Some physical properties of the recycled concrete aggregate were determined. As a result, the carbonation process reduced water absorption and enhanced the density of the aggregates.