Promoting Internal Curing in Concrete by Replacing Sand with Sustainable Biochar

Abstract

This study focuses on promoting internal curing in concrete by partially replacing sand with sustainable biochar. Biochar, a carbon-rich by-product produced from the pyrolysis of organic waste, has excellent water absorption and retention properties that can enhance the internal curing process. The replacement of sand with biochar not only contributes to better hydration of cement but also improves the microstructure and durability of concrete. By utilizing biochar, the study aims to reduce autogenous shrinkage, enhance compressive and tensile strength, and promote eco-friendly construction practices. This approach supports sustainable waste management while lowering the carbon footprint of concrete production, making it a viable alternative for green and durable infrastructure development.

Introduction

The study investigates the use of biochar as a partial replacement for fine aggregate in concrete to improve sustainability and mechanical performance while reducing environmental impacts caused by conventional concrete materials. It highlights that excessive use of natural sand and cement leads to resource depletion and high carbon emissions, motivating the search for eco-friendly alternatives like biochar, which is a porous carbon-rich material derived from organic waste.

The experimental work used M20 grade concrete with biochar replacing fine aggregate at 0%, 1%, 3%, and 5%. Standard materials such as cement, M-sand, coarse aggregate, water, and biochar were tested, and concrete specimens (cubes, cylinders, beams) were prepared and cured for 7 and 28 days. Tests conducted included compressive strength, split tensile strength, flexural strength, and internal curing capacity.

Results show that biochar improves concrete performance in most cases. The 3% and 5% replacements generally produced higher compressive strength compared to conventional concrete, with the highest compressive strength observed at 3% and 5% replacement levels. Split tensile and flexural strength also showed slight improvements at higher replacement percentages. Internal curing results indicate that biochar enhances water retention within concrete.

Conclusion

This study investigated the use of biochar as a partial replacement for fine aggregate (sand) in concrete to promote internal curing and sustainable construction. Different percentages of biochar replacement (0%, 1%, 3%, and 5%) were tested and their mechanical properties were compared with conventional concrete. From the experimental results, it was observed that the compressive strength of concrete increased with the addition of biochar up to 3% replacement, where the maximum compressive strength of 24.44 N/mm² was obtained at 28 days. When the replacement was increased to 5%, the strength slightly decreased but still remained higher than normal concrete. The split tensile strength and flexural strength of concrete also showed improvement with the addition of biochar, indicating that biochar contributes positively to the mechanical performance of concrete. The internal curing test results showed that concrete containing 5% biochar absorbed less external water compared to normal concrete, which indicates that biochar can store water in its porous structure and gradually release it during cement hydration. This improves the internal curing effect and hydration process in concrete. From the cost analysis, it was observed that biochar concrete is slightly more expensive than conventional concrete. However, the environmental benefits, improved curing, and better performance make it a sustainable alternative for construction materials. Therefore, it can be concluded that biochar can be effectively used as a partial replacement for sand in concrete, with 3–5% replacement giving optimum performance, while also supporting sustainable and eco-friendly construction practices.

References

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Copyright

Copyright © 2026 Riya Pious, Bajeel Ahmad M, Mayas Anvar, Athira P, Muhsina Banu K. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.