A sustainable, carbon-negative concrete formula with strength nearly matching traditional concrete has been created at Washington State University (WSU).
Reported in the Global Construction Review, WSU researchers have discovered that adding charcoal to cement can result in a concrete that absorbs more carbon than is created by its production thanks to chemical reactions in the setting process.
In an experimental study, scientists infused typical cement with eco-friendly biochar, a charcoal produced from organic waste, that had been reinforced with concrete wastewater.
The biochar demonstrated an ability to absorb up to 23% of its weight in carbon dioxide from the atmosphere, while still attaining a strength similar to regular cement.
The findings have important implications for the concrete industry, which is notorious for its high energy consumption and carbon emissions.
Led by Zhipeng Li, a PhD student, the research is detailed in Materials Letters, a peer-reviewed journal.
“We’re very excited that this will contribute to the mission of zero-carbon built environment,” said Xianming Shi, professor in the WSU Department of Civil and Environmental Engineering and the corresponding author on the paper.
The most destructive material on Earth
According to Statista, more than 4 billion tonnes of global concrete is produced annually. Production of concrete has stalled over the past decade with concrete recognised by some as ‘the most destructive material on Earth.’
The manufacture of regular cement necessitates high temperatures and the burning of fuels. Furthermore, the decomposition of limestone, a primary component of cement, releases carbon dioxide, resulting in cement production contributing to nearly 8% of all human-caused carbon emissions worldwide.
To create an eco-friendlier alternative to cement, researchers have explored the use of biochar. However, even a small addition of biochar – as little as 3% – can significantly weaken the concrete’s strength.
The researchers successfully incorporated up to 30% biochar into their cement mix after treating the biochar in the concrete washout wastewater.
After 28 days, the biochar-amended cement reached a comparable compressive strength of approximately 1815 kg per 645 sq mm, akin to that of regular cement.
Concrete could sequester carbon for the materials lifespan
This research could pave the way for more environmentally sustainable cement manufacturing methods, reducing the industry’s carbon footprint.
“We’re committed to finding novel ways to divert waste streams to beneficial uses in concrete; once we identify those waste streams, the next step is to see how we can wave the magic wand of chemistry and turn them into a resource,” said Xianming Shi.
“The trick is really in the interfacial engineering – how you engineer the interfaces in the concrete. Most other researchers were only able to add up to 3% biochar to replace cement, but we’re demonstrating the use of much higher dosages of biochar because we’ve figured out how to engineer the surface of the biochar,” he said.
The newly developed concrete is anticipated to sequester carbon dioxide for the duration of the material’s lifespan, which is generally about 30 years for pavement and 75 years for bridges.
To bring this technology to market, the researchers are collaborating with the Office of Commercialisation at Washington State to safeguard their intellectual property rights. They have filed a provisional patent application to protect their carbon-negative concrete invention.
