Carbonation Treatment of RCA Concrete: A Preliminary Investigation

Strategies to reduce the environmental impact of the concrete industry include enhancing the CO2 sequestration using the material as a durable carbon sink. At this aim, early-age carbon curing has been proposed and seems to be a promising method for CO2 sequestration. However, studies on this treatment are still limited and do not allow to clearly evaluate its environmental benefits and its effects on concrete properties. In this work, both moist and carbon curing treatments were performed on concretes made with natural aggregate (Ref) and recycled concrete aggregate (RCA). In particular, concretes were either moist cured for 7, 14 and 28 days or carbon cured for 7 and 14 days. In addition, combined curing was also tested, performing carbon curing for 7 and 14 days, followed by moist curing up to a total of 28 days. After the different curing times, compressive strength, modulus of elasticity and resistivity were measured, together with the carbonation depth by means of phenolphthalein test. At all the curing times the use of RCA in partial replacement of natural aggregate led to a slight worsening of the mechanical properties. The carbonation treatment both in Ref and RCA concretes allowed to permanently store the CO2 guarantying comparable performances. Moreover, the combined curing had a beneficial effect in partially restoring the alkalinity of the cement paste.