Carbon fixation and material improvement through CO2 treatment of coarse recycled concrete aggregates: Experimental insights and projections for Brazil by 2050

Alternatives for carbon capture, utilization, and storage (CCUS) have applications in the treatment of recycled concrete aggregates (RCA) in a process known as CO 2 mineralization. This study evaluates the influence of CO 2 treatment on RCA's physical and microstructural properties and the CO 2 fixation potential of RCAs until 2050 in the Brazilian scenario, considering the projected population growth and concrete waste generation. To produce recycled coarse aggregate, source concretes were prepared using different cement types (CP IV-32 and CP V) and water/cement (w/c) ratios (0.55 and 0.65). Following crushing and screening, the coarse particles were selected for CO 2 treatment in a carbonation chamber (RH 65%, CO 2 15%, time 24 h). CO 2 fixation by the RCA was determined through thermogravimetric analysis (TGA). Additionally, specific gravity, water absorption, X-ray microtomography (μCT), scanning electron microscope (SEM), and Vickers microhardness tests were conducted to evaluate physical and microstructural changes after treatment. Results indicate that aggregate carbonation was partial, with the w/c exerting a greater influence on CO 2 diffusion than the cement type. The RCA produced with CP IV-32 and a 0.65 w/c ratio, achieved the highest CO 2 fixation (29.10 kgCO 2 /ton), projecting a total fixation of 77.50 ktCO 2 per year in the 2050 scenario. This treatment led to the most significant physical improvements, including a 3.03% increase in specific gravity and a 7.32% reduction in water absorption. Although X-ray microtomography (μCT) confirmed a general decrease in porosity and microhardness improved, SEM analysis indicated that carbonation remained superficial and did not reach the adhered mortar near the interfacial transition zone (ITZ). Ultimately, the treatment improved RCA physical and microstructural properties and promoted CO 2 utilization and fixation, contributing to circularity and decarbonization in construction through a promising process for large-scale application. • The influence of CO 2 treatment on carbon fixation and RCA properties was evaluated. • CO 2 mineralization increased specific gravity and reduced water absorption and porosity of RCA. • Microstructural analyses (μCT, SEM, microhardness) confirmed partial carbonation and improved surface quality. • Up to 29.10 kg of CO 2 per ton of RCA was uptake in 24 h of CO 2 exposure. • The average annual CO 2 fixation potential of RCAs in Brazil until 2050 is 77.50 ktCO 2 .