Recycled concrete could help reduce emissions

Researchers have discovered a way to recycle concrete waste, making it a more sustainable and stronger building material. This development could lead to significant reductions in the carbon emissions associated with concrete production.

Concrete, the most-used man-made material on Earth, is responsible for about 8% of global carbon dioxide emissions. The production of concrete involves heating limestone to extreme temperatures, which releases CO2. Finding greener alternatives for concrete has been a focus for researchers aiming to reduce its environmental impact.

A team from Princeton University and the University of São Paulo (USP) has made a breakthrough in recycling concrete waste. They have found that by pulverising waste concrete and then heating it to a lower temperature of 500°C, the material can be reactivated to form a new cement with comparable strength to conventional Portland cement.

The new technique, called thermoactivation, involves heating the recycled concrete at much lower temperatures than usual. This process prevents CO2 from being released, unlike traditional cement production, which requires temperatures above 1,400°C. The research team found that by adding a small amount of fresh Portland cement, they could fill in the pores of the recycled material and achieve strength comparable to standard cement.

“This method allows us to recycle concrete waste in a way that not only reduces its environmental footprint but also results in a stronger product,” said Claire White, study co-author and professor at Princeton University. “By optimising the packing of particles, we achieve a material that behaves similarly to Portland cement.”

The new recycled material, called engineered recycled cement (eRC), has been shown to reduce emissions by up to 61%. It produces between 198 and 320 kg of CO2 per metric tonne, significantly lower than traditional cement, which emits around 846 kg per tonne.

Sérgio Angulo, research leader at USP, highlighted the potential impact of this breakthrough: “Construction waste, particularly concrete, often ends up in landfills or is used in low-grade applications. This new process demonstrates that we can recycle cement waste into a high-quality material with a much smaller environmental impact.”

The team believes that their work could play a crucial role in creating a circular economy in the concrete industry, where old concrete is reused in new construction. However, they note that for this to be truly effective, construction practices need to change, and better systems for sorting and processing demolition waste must be put in place.

The study, which was published in the journal ACS Sustainable Chemistry & Engineering, outlines how thermoactivated recycled cement could become a key material in the push for more sustainable and low-carbon construction. The team hopes this research will inspire further innovation and help meet global targets for carbon emission reductions.