Accelerated carbonation of construction waste powders: A circular economy strategy for CO₂ mitigation in cementitious materials

This paper investigates the carbon dioxide (CO₂) fixation potential of different Construction and Demolition Waste Powders (CDWP) for application as Supplementary Cementitious Material (SCM). Powders from a mixed and concrete source with three different particle size distributions were evaluated, and the powders were mineralized by accelerated carbonation for 2, 8, 24, 48, and 168 h at 23 ± 2 ºC, 60 ± 10% relative humidity, and 15% CO₂ concentration. The pre- and post-treatment powders' physical-chemical properties were evaluated using analytical techniques (TGA, XRD, FTIR, SEM), and CO₂ fixation was quantified by thermogravimetry analysis. The carbonated powders were applied in mortars considering a 25% Portland cement replacement level, which were evaluated for CO₂ emissions and compressive strength at 28 days. It was verified that the CO₂ fixation process and powder source are more relevant than particle size distribution. Concrete powders could fix between 33.5 and 54.7 kg CO₂/t when mixed type fixed, at a maximum of 12 kg CO₂/t. The application of concrete powders, when mineralized for 2 h with a 25% cement replacement level, results in a 25% reduction in CO₂ emissions per m³ of mortar compared to a Filler Portland Cement (FPC). The CO₂ application for CDWP mineralization as SCM showed promising results, highlighting waste recycling, reductions in Portland cement-associated emissions, and high relevance to both the circular economy and the carbon market.