Carbon Capture Potential of Recycled Concrete Aggregates from a Full-Scale Recycling Plant in the Brazilian Federal District: A Laboratory Carbonation Study

Accelerated carbonation of recycled concrete aggregates (RCA) can fix CO₂ while modifying aggregate properties, but most reported uptake values come from laboratory-produced aggregates that do not reproduce the heterogeneity of material leaving a real recycling line. This study assesses the carbon uptake of recycled sand and two coarse RCA fractions from a single industrial recycling plant in the Federal District, Brazil, sampled in two production campaigns. Carbonation was performed at 25°C, 60% relative humidity and 3% CO₂. Uptake was quantified by the net mass gain of crushed 1.18–2.36 mm specimens kept in moisture equilibrium with the test environment, and corroborated by thermogravimetric analysis (TG). Net mass gains ranged from 0.318% to 1.358%, and specimens derived from the coarse fractions exceeded those derived from the sand (0.318–0.638%). X-ray diffraction of the non-carbonated material showed a weak calcite reflection and no detectable dolomite peaks, indicating carbonate already present in the adhered paste rather than carbonate rock. TG mass loss in the 550–950°C range increased after treatment in all six samples, evidencing CaCO₃ formation in the adhered paste. Water absorption decreased by 0.08–0.41 percentage points and oven-dry density increased by 0.016–0.023 g/cm³ in single paired determinations, consistent with pore filling by carbonate. Accelerated carbonation therefore fixes CO₂ in industrially produced recycled aggregates, and confirmation at industrial scale requires multi-plant sampling, replicated testing and a process-level carbon balance.