Scientists turn human poop into concrete and it's surprisingly 42% stronger

Scientists found that treated faecal sludge biochar can replace part of cement in concrete and improve strength. The study points to a greener use for human waste while reducing cement demand and possible heavy metal leaching.

In Short

• Researchers used treated faecal sludge from sanitation systems to create biochar
• They tested mixes for strength, porosity, water absorption and drying shrinkage
• Best results came when biochar replaced five to ten per cent cement

What if human waste could one day help build stronger buildings?

Scientists have found that a material made from treated faecal sludge can partially replace cement in concrete and, at the right concentration, significantly improve its strength.

The research, published in Scientific Reports, explored the use of biochar derived from faecal sludge, treated human waste collected from septic tanks and sanitation systems, as a partial replacement for cement in concrete.

Specialised treatment plants collect and process faecal sludge.

Researchers converted the material into biochar, a carbon-rich substance, and mixed it into concrete to study whether it could make the construction material stronger and more sustainable.

The results were striking.

Concrete containing a 10% replacement of cement with faecal sludge-derived biochar showed a 21% increase in compressive strength and a 42% increase in flexural strength after 91 days of curing.

Compressive strength measures how much pressure concrete can withstand, while flexural strength indicates how well it resists bending and cracking.

The researchers tested different amounts of biochar and examined several properties, including strength, water absorption, porosity and drying shrinkage.

The findings suggested that replacing between 5% and 10% of cement with biochar could improve concrete performance. At a higher 15% replacement level, water absorption and porosity were comparable to conventional concrete after 28 days.

The material also appeared to remain stable over time. After 120 days, mortar containing 10% biochar showed drying shrinkage similar to ordinary Portland cement mortar, indicating that the material could maintain its shape and stability over longer periods.

Another potentially important finding involved harmful heavy metals. The study reported a reduction in heavy metal concentrations in concrete specimens as biochar content increased, which could potentially reduce the leaching of harmful substances into the environment.

The research could offer a double environmental benefit: finding a productive use for treated human waste while reducing the amount of cement needed in concrete.

Cement production is energy-intensive and a major contributor to global carbon emissions. While more research and real-world testing will be needed before faecal sludge-derived biochar can be widely used in construction, the study points towards an unusual possibility.

Tomorrow's buildings could partly be built using what we flush away today.

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