Researchers at Washington State University have demonstrated a new synergistic carbon-capture strategy, i.e., using concrete washout water and biochar together to achieve carbon-negative concrete. Their strategy enabled the biochar to capture 22.85 wt% air-borne carbon dioxide, which precipitated calcium carbonate onto the biochar. This carbon-negative cement paste consisted of 30 wt% carbon dioxide-weathered biochar and 70 wt% portland limestone cement, which achieved the 7-day and 28-day compressive strengths of 22.1 MPa and 27.6 MPa, respectively.
Global warming poses a threat to the sustainability of human society, and it is essential to find a sustainable and effective strategy to curtail anthropogenic emissions of carbon dioxide.
More than 4 billion tons of concrete are produced every year globally. Making ordinary cement requires high temperature and combustion of fuels.
The limestone used in its production also goes through decomposition which produces carbon dioxide, so that cement production is thought to be responsible for about 8% of total carbon emissions by human activities worldwide.
Scientists have tried adding biochar as a substitute in cement to make it more environmentally friendly and reduce its carbon footprint, but adding even 3% of biochar dramatically reduced the strength of the concrete.
After treating biochar in the concrete washout wastewater, Washington State University researchers Xianming Shi and Zhipeng Li were able to add up to 30% biochar to their cement mixture.
“We’re very excited that this will contribute to the mission of zero-carbon built environment,” Professor Shi said.
“The paste made of the biochar-amended cement was able to reach a compressive strength after 28 days comparable to that of ordinary cement of about 4,000 pounds per square inch.”
“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…
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