In a significant stride towards sustainable construction, researchers have quantified the carbon capture potential of concrete made with recycled aggregates from construction and demolition waste (CDW). The study, led by Eduardo Rigo from the Graduate Program of Civil Engineering at the Federal University of Latin American Integration, Brazil, and published in the journal “Case Studies in Construction Materials,” offers promising insights into reducing the cement industry’s carbon footprint.
The cement industry is a major contributor to global carbon dioxide emissions, accounting for approximately 7% of the total. However, cementitious materials and CDW can capture CO₂ through a process called carbonation. Rigo and his team aimed to accurately quantify this CO₂ capture potential using thermogravimetric analysis (TGA), a method that measures the change in weight of a sample as it is heated, decomposing the material and releasing gases.
The researchers characterized the materials using various techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), and laser granulometry. They then created concrete mixtures with different water-to-cement ratios and varying levels of recycled aggregate (RA) replacement. “We wanted to understand how the use of fine and coarse mixed recycled aggregates affects the concrete’s properties, emissions, and carbon capture potential,” Rigo explained.
The study found that the concrete’s carbon capture varied between 12 and 94 kg CO₂ per cubic meter, with the highest values coming from concrete with fine aggregates and a lower water-to-cement ratio. Notably, concretes with 100% RA exhibited lower CO₂ emissions and had the potential to capture up to 19% of the emissions from cement production. “This is a significant finding, as it demonstrates that recycled aggregate concrete can contribute to the circularity of the carbon market,” Rigo said.
However, the research also revealed that as the replacement rate of RA increased, the concrete’s mechanical properties decreased, and the carbonation depth and capillary water absorption increased, which could negatively impact durability. Compressive strength losses ranging from 16% to 38% were recorded, depending on the replacement content and concrete’s water-to-cement ratio.
Despite these challenges, the study highlights the potential of recycled aggregate concrete to reduce emissions and capture CO₂. “Optimizing the mix design with admixtures is essential to mitigate losses in physical and mechanical properties,” Rigo noted. This could pave the way for more sustainable construction practices and contribute to the energy sector’s efforts to reduce carbon emissions.
The findings of this research could shape future developments in the field by encouraging the use of recycled materials in concrete production. By doing so, the construction industry can reduce its reliance on virgin materials, lower its carbon footprint, and contribute to a more sustainable future. As the world grapples with the challenges of climate change, such innovations are not just welcome but necessary.