Concrete with sewage-derived biochar strengthens over time, study finds
Researchers found that concrete with 5 to 10 percent of its cement replaced by sewage-derived biochar strengthens over time.
A recent study highlights the potential of biochar derived from sewage sludge to enhance concrete strength. Researchers from Manipal University, led by Jaipur Raghuvanshi Tiwari and Priyansa Mehra, investigated the effects of replacing cement with biochar in concrete mixes. Their findings, published in Scientific Reports, reveal that concrete with 5% cement replaced by biochar exhibited the highest strength across various testing periods.
Biochar, a charcoal powder produced by heating organic matter in low-oxygen conditions, was used to partially substitute cement in concrete. This approach aims to reduce cement usage, which is resource-intensive and a significant source of carbon dioxide emissions. The study found that concrete with 10% biochar replacement initially showed lower strength but surpassed standard concrete by the 13-week mark.
The research involved creating 20 different concrete mixes, varying the water-to-cement ratio and substituting 0, 5, 10, or 15% of cement with biochar. Measurements of compressive and flexural strength were taken at four, eight, and 13 weeks. Notably, concrete with 5% biochar consistently demonstrated superior strength, while the 10% mix showed significant improvement over time, indicating continued hardening beyond the typical four-week plateau.
The enhanced strength is attributed to silicon compounds in the biochar reacting with calcium hydroxide from cement, forming additional strengthening materials. Biochar particles also filled microscopic gaps between cement grains, further boosting strength. However, a 15% biochar substitution resulted in weaker concrete due to insufficient cement binding.
Heavy metal concentrations were assessed given the sewage origin of the biochar. While levels of metals like mercury and zinc were lower in the biochar-infused concrete compared to raw biochar, they increased with higher biochar substitution rates. The study acknowledged limitations, including the use of sludge from a single treatment facility and the absence of testing in extreme environmental conditions or for potential heavy metal leaching.
Source: Biochar Feed