Determination of Co2 capture in rendering mortars produced with recycled construction and demolition waste by thermogravimetry

Cement industries generate about 7% of global CO2 emissions. To reduce these emissions, this sector aims to improve energy efficiency reducing the clinker content in cement and carbon capture deployment. The CO2 captured in cementitious materials occurs due to the carbonation reaction. This study aims to evaluate the CO2 uptake capacity in rendering mortars produced with recycled construction and demolition waste (CDW) by natural carbonation. Mortars were produced by replacing sand for CDW at rates of 0; 25; 50; 75, and 100% were naturally carbonated in a laboratory environment. Specimens were submitted to the compression test, bulk density, and water absorption. The carbonation profile was determined by phenolphthalein spray test over time. The CO2 captured was evaluated by thermogravimetry. The kinetic model showed that the carbonation reaction occurs more quickly in mortars with a higher substitution content, which is related to the increase in the porosity of the system improving the diffusion processes of CO2, leading to an increase in the carbonation depth. In addition, as the replacement level of CDW increases, the water absorption increases in contrast with the diminishing of the bulk density. Up to 50% of replacement level, samples with CDW showed higher compressive strength than the other cases. Moreover, results showed that the cement mortars with 50 to 75% of sand replacement by CDW, presented the highest amount of CO2 captured at 69 days, leading to 85 kg of CO2 per m3 of mortar. The CO2 capturing through natural carbonation of rendering mortar can be considered as a compensatory strategy in the cycle of life assessment of these materials.