CO2 sequestration by construction and demolition waste aggregates and effect on mortars and concrete performance - An overview

Global warming is one of the greatest environmental threats worldwide. It is mainly caused by the growing amount of greenhouse gases in the atmosphere, such as argon and carbon dioxide (CO2), among others. Hence, the need to reduce these gases’ emissions, in particular CO2, is imperative. This reduction may be achieved through strategies that allow capturing and storing emitted CO2 (CCS - carbon capture and storage). Construction and demolition waste (CDW) is found in great abundance with diverse potential in the building sector. However, its incorporation as recycled aggregates (RA) in construction materials, such as mortars and concrete, is still limited. This is mainly due to its higher heterogeneity, porosity and lower strength compared to natural aggregates (NA). Several studies have been carried out focusing on the reduction of CO2 emissions and of NA exploitation, as well as improving these RA's characteristics. This article intends to provide a review of the performance of mortars and concrete with RA from CDW after undergoing a CO2 curing treatment, thus contributing to CCS. Overall, CO2 curing of RA has a positive effect on their physical and mechanical characteristics. By increasing the apparent density, their porosity and water absorption consequently decrease. Also, these treatments considerably reduce the crushing index of RA, increasing their strength. Mortars and concrete produced with carbonated recycled aggregates (CRA) show increase in workability and decrease in shrinkage in comparison to those with uncarbonated RA. The mechanical performance of these construction materials is also positively influenced. Therefore, the levels of confidence in its use should increase.