New sustainable cement reduces emissions and maintains strength

Engineers from the University of São Paulo and Princeton have created a new method to recycle cement waste into a low-carbon alternative. This new type of cement is as strong as traditional Portland cement but produces fewer carbon emissions. Construction and demolition waste is a major problem, generating significant amounts of refuse. In the United States, this waste is more than double that of household waste. Most construction debris ends up in landfills or is used for low-quality applications. The researchers are excited to show that cement waste can be recycled for high-quality uses. In their study published in ACS Sustainable Chemistry & Engineering, the researchers found that mixtures containing up to 80% recycled cement performed as well as traditional cement while producing much lower emissions. Portland cement is responsible for about 8% of the world’s carbon emissions due to its high carbon intensity. If widely used, this recycled cement could potentially reduce emissions from the cement industry by up to 61%. This estimate is much higher than previous projections. The recycling process uses heat. Waste concrete is ground into powder and heated to 500 °C. This restores its properties without generating additional carbon dioxide emissions. Although the recycled cement alone is weak, combining it with finely ground Portland cement or limestone improves its strength and workability. The new cement can support a more circular economy in construction. The researchers estimated that it emits 198 to 320 kilograms of carbon dioxide per metric ton, which is 40% less than existing alternatives. This method could transform how cities manage construction materials. However, some challenges remain. Better sorting and processing methods for demolition waste are needed. The technology may work best in cities with older buildings rather than in areas with mostly new construction. Additionally, building codes may need updating to accommodate this new material. The research collaboration began when Professor Angulo visited Princeton in 2023. This partnership has helped both teams improve their understanding and research capabilities. They are now looking to answer questions about the durability and effectiveness of recycled cement over time. This cooperation is expected to advance knowledge in this important area of sustainable construction.