A recent study in the Journal of Rock Mechanics and Geotechnical Engineering by Saberian et al., demonstrates that fine-grained wood biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More significantly improves the strength and stability of expansive clay, a soil type that poses major challenges for road construction. The research indicates that incorporating biochar can enhance the mechanical properties of this problematic soil, making it more suitable for use as a pavement subgrade material.

Expansive clays are notorious for causing damage to infrastructure. Their tendency to swell when they absorb water and shrink as they dry leads to cracking and instability in roads and building foundations. Traditionally, stabilizers such as cement and lime have been used to improve these soils. However, the production of cement and lime is energy-intensive and contributes to greenhouse gas emissions. This study explores biochar as a more sustainable alternative.

The authors assessed how fine-grained wood biochar affects the geotechnical and microstructural behavior of expansive clay. The addition of biochar led to a notable 31% increase in unconfined compressive strength, a key indicator of soil stability. Furthermore, the study revealed a reduction in swelling potential and improved California Bearing Ratio (CBR) values, which are critical for pavement design. Microstructural analyses confirmed that biochar alters the clay structure, creating a more stable and less plastic material.

These findings suggest that biochar can serve as an effective and environmentally friendly amendment for expansive clay soils in pavement construction. By improving soil strength and reducing swelling, biochar can contribute to longer-lasting, more resilient roads. This approach offers a pathway to reduce the reliance on conventional stabilizers and lower the carbon footprint of construction projects.

SOURCE: Saberian, M., Zhu, J., Roychand, R., Sun, X., Li, J., & Li, C.-Q. (2025). Effect of fine-grained wood biochar on the geotechnical and microstructural behaviour of expansive clay as pavement subgrade. Journal of Rock Mechanics and Geotechnical Engineering, 0(0).