In a new study published in the JSE Journal of Science and Engineering, researchers Rida Respati, Salampak, Fatma Sarie, and Adi Jaya from Universitas Palangkaraya investigated a solution to a significant challenge in road construction: the poor bearing capacity of peat soil. They explored the potential of using a combination of 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 and cement to stabilize peat soil, which is abundant in regions like Central Kalimantan Province, Indonesia, but is typically unsuitable for road subgrades due to its high water content, low density, and high compressibility. The research demonstrates that adding a mixture of cement and biochar derived from coconut shells can significantly enhance the soil’s load-bearing strength, making it a viable material for road construction subgrades.

The study focused on improving the California Bearing Ratio (CBR) value, a key indicator of a soil’s ability to support road loads. The original peat soil had a CBR value of 2.2%. To improve this, the researchers tested various combinations of cement and biochar. The biochar content was kept constant at 5%, while the cement content was varied at 5%, 6%, 7%, and 8%. The results showed a direct correlation between the amount of cement added and the increase in the soil’s CBR value. With a mixture of 5% biochar and 5% cement, the CBR value increased to 4.6%. The addition of 6% cement and 5% biochar raised the value to 6.4%. A combination of 7% cement and 5% biochar yielded a CBR value of 7.2%. The most significant improvement was observed with the highest cement concentration tested. When 8% cement was combined with 5% biochar, the CBR value reached 9.0%.

This substantial increase in the CBR value has practical implications for road construction. According to the study, a CBR value of 4.6% or 6.4% is suitable for a road subgrade, while values of 7.2% and 9.0% allow the material to function as a sub-base layer. This is a critical finding, as it suggests that the combination of biochar and cement can not only make peat soil usable for road construction but can also potentially elevate its function to a higher structural layer.

The researchers attribute these improvements to the synergistic properties of the materials. Cement provides mechanical strength, while biochar improves the physical properties of the soil and helps bind water. The use of biochar also reduces the amount of cement required for stabilization, making the process more sustainable. This method offers a dual benefit: it improves soil performance for infrastructure projects and contributes to climate change mitigation by reducing carbon emissions and enhancing carbon storage in the soil.

The study concludes that the combination of 8% cement and 5% biochar is an effective and recommended method for stabilizing peat soil, transforming it into a functional subgrade for light to moderate traffic roads. This innovative approach provides a viable and environmentally conscious solution to a longstanding problem in civil engineering.

SOURCE: Respati, R., Salampak, Sarie, F., & Jaya, A. (2025). Innovation in Road Construction Materials: A Study on the Combination of Biochar and Cement in Improving Subgrade Bearing Capacity. JSE Journal of Science and Engineering, 4(1), 48-57.