Indian scientists have developed a new approach to making stronger and potentially more sustainable concrete by using biochar produced from treated human waste. The research was led by civil engineer Raghuvesh Tiwari of Manipal University Jaipur.
The team used treated sewage sludge collected from a treatment plant in Warangal. The material was dried and heated at temperatures between 350 and 450 degrees Celsius in a low-oxygen environment to produce biochar, which was then ground into a fine powder.
Researchers replaced 5%, 10% and 15% of the cement in concrete samples with the waste-based biochar. They then tested the samples for strength, water absorption, shrinkage and porosity.
The results showed that concrete containing 5% biochar recorded a 20% increase in compressive strength and a 36% increase in flexural strength after 91 days. With 10% replacement, flexural strength increased by up to 42%, while compressive strength rose by 21%.
Scientists believe the porous biochar can absorb water and release it gradually as the concrete hardens, potentially supporting the chemical reactions responsible for strengthening the material. Its silica content may also contribute to the formation of strength-enhancing compounds.
However, higher biochar content did not produce better results. At 15% replacement, the concrete developed more pores and cracks, resulting in lower overall strength.
The researchers say further testing is needed before the technology can be used in real-world construction. Its performance under extreme temperatures and salt exposure, as well as the possible release of heavy metals from sewage-based materials, will require further study. The research has been accepted for publication in Scientific Reports.
