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🇦🇷 Argentina /Environment & Climate

Coffee waste heated to 350°C becomes biochar that can replace some sand in concrete, boosting strength by 29.3%

From Clarín · () Spanish

Translated from Spanish and summarized by DistantNews. Read the original for the full story.

At a glance

News Documents & data Context piece
  • Researchers at Australia’s RMIT University converted spent coffee grounds into biochar for use as a partial replacement for sand in concrete.
  • Concrete containing biochar made at 350°C and replacing 15% of the sand by volume had 29.3% higher compressive strength than the conventional control mix.
  • The approach could divert coffee waste from landfills and reduce demand for natural sand, although the supplied article ends before describing further field testing.

Coffee grounds that normally end up in the bin could become part of the concrete used in construction. Researchers at Australia’s RMIT University developed a method for turning the waste into biochar and using it to replace some of the sand in a concrete mixture.

The best result came when biochar produced at 350°C replaced 15% of the sand by volume. That concrete recorded compressive strength 29.3% higher than the conventional control mixture. The study was conducted by Rajeev Roychand, Shannon Kilmartin-Lynch, Mohammad Saberian, Jie Li, Guomin Zhang and Chun Qing Li at RMIT’s School of Engineering, and was published in 2023 in the Journal of Cleaner Production.

The researchers stressed that used coffee cannot simply be mixed directly into cement. Untreated grounds release organic compounds that interfere with cement hydration and reduce the concrete’s strength. They therefore used pyrolysis, a heat treatment carried out without oxygen, at 350°C and 500°C to produce a porous, carbon-rich material known as biochar.

The team tested replacements of 5%, 10%, 15% and 20% using raw coffee waste and both types of biochar. It also examined the samples through techniques including electron microscopy and X-ray diffraction. Biochar made at 500°C produced a more fragile structure and microcracks, which weakened its performance.

The researchers linked the stronger 350°C mixture to its microscopic structure. Cement paste could penetrate the biochar’s pores, while water held in those pores supported internal curing. RMIT cited annual coffee-ground waste of about 75 million kilograms in Australia and roughly 10 billion kilograms worldwide. “With a circular economy approach, we could keep organic waste out of landfills and better preserve our natural resources, such as sand,” professor Jie Li said.

With a circular economy approach, we could keep organic waste out of landfills and better preserve our natural resources, such as sand.

· Jie LiThe RMIT professor described the environmental potential of using coffee waste in concrete.
About this summary

Originally published by Clarín in Spanish. Translated, summarized, and contextualized automatically by DistantNews, with a note on how the source frames the story. Not individually reviewed before publishing. How this works.

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