Human Waste Could Make Concrete 42% Stronger, Study Finds
Synopsis
Scientists in India have developed an innovative form of concrete that uses treated human waste as a partial replacement for cement - and could make concrete substantially stronger while giving sewage waste a second life.
Scientists in India have developed an innovative form of concrete that uses treated human waste as a partial replacement for cement - and could make concrete substantially stronger while giving sewage waste a second life. The research, led by civil engineer Raghuvesh Tiwari of Manipal University Jaipur, explored the use of biochar produced from human waste collected at a treatment plant in Warangal, India.
Biochar is a carbon-rich substance created by heating organic material in an environment with very little oxygen. For the study, treated sewage sludge was first dried and then heated at temperatures ranging from 350 to 450 degrees Celsius before being pulverised into a fine powder.
Researchers then replaced 5%, 10% and 15% of the cement used in concrete with the sewage-derived biochar. The resulting samples underwent rigorous testing to assess their compressive and flexural strength, water absorption, shrinkage and porosity.
Concrete containing 5% biochar recorded a 20% rise in compressive strength and a 36% increase in flexural strength after 91 days of curing. When 10% of the cement was replaced, flexural strength climbed by as much as 42%, while compressive strength increased by 21%.
Scientists believe the porous structure of biochar may play a crucial role. It can absorb water and gradually release it as the concrete hardens, potentially supporting the chemical reactions responsible for strengthening the material. The biochar also contains silica, which can aid the formation of compounds that enhance concrete's strength.
However, more biochar did not mean stronger concrete. At a 15% replacement level, the material developed increased porosity and cracking, resulting in lower overall strength.
Despite the encouraging results, researchers caution that the technology is not yet ready for widespread use in construction. Further studies are required to determine how the material performs under extreme heat, salt exposure and freezing conditions. Researchers must also examine whether sewage-derived materials could release potentially harmful heavy metals.
The study has been accepted for publication in Scientific Reports.