New research shows spent coffee grounds can make concrete stronger and greener. RMIT University scientists heated used coffee grounds (about 350°C, no oxygen) to create a fine “biochar”. Adding 15% biochar (replacing the same fraction of sand) boosted concrete's 28-day strength by roughly 30%. A life-cycle analysis found CO₂ emissions fell by up to 26% (with fossil-fuel use down 31%) when biochar was added. Cement production itself accounts for about 8% of global CO₂.
Coffee biochar concrete
According to the study, RMIT University scientists heated coffee waste to make fine biochar, turning waste into a circular‑economy resource. The charcoal-like biochar, mixed into cement and sand, improves durability and eases reliance on scarce natural sand. The researchers report life-cycle carbon reductions of about 15–26 percent when replacing 5–15 percent of the sand with biochar. The team has already trialled coffee-concrete in a footpath pour and on part of a Victorian highways upgrade.
Towards sustainable construction
The construction industry is a huge contributor to greenhouse gases worldwide with nearly 37 per cent of its emissions (the cement manufacturing process alone emits approximately 8 per cent). Novelties such as coffee-biochar concrete are better aligned with a wider initiative of sustainable materials and circularity.
Embodied carbon in concrete can be reduced by substituting sand and cement with the recycled or other inputs (e.g. fly ash, slag or waste-derived biochar). These strategies will decrease the use of virgin resources and contribute to achieving net-zero goals, which will make buildings more environmentally friendly.
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