Compressive Strength and Sustainability Assessment of Mortar Incorporating Rice Husk Biochar as a Sustainable Cement Replacement

Document Type : Original Article

Authors

1 Department of Civil Engineering, Cha. C, Islamic Azad University, Chalus, Iran

2 Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract

The cement industry is a major contributor to global CO2 emissions, highlighting the need for sustainable supplementary cementitious materials (SCMs) capable of reducing cement consumption while maintaining mechanical performance. This study investigated the effects of raw rice husk (SH), rice husk biochar (BSH), and calcined rice husk ash (CSH) as partial replacements for ordinary Portland cement. Mortar mixtures incorporating 3%, 5%, and 8% of each material were evaluated in terms of workability, compressive strength, normalized compressive strength, and strength development up to 28 days. In addition, a cradle-to-gate life cycle assessment (LCA) was performed to quantify greenhouse gas (GHG) emissions, cumulative energy demand (CED), and environmental impacts using the ReCiPe endpoint method. The results showed that the processing method of rice husk significantly influenced both mechanical and environmental performance. Among the investigated materials, CSH improved workability because of its filler effect and fine particle size. The mixture containing 3% CSH and BSH achieved the highest 28-day compressive strength (43.4 and 41.1 MPa, respectively), corresponding to 143.6% and 136.0% of the reference mixture's compressive strength (i.e., a 43.6% and 36.0% increase), respectively. Biochar enhanced long-term strength through internal curing, whereas SH exhibited slower early-age strength development but substantial later-age strength gain. The LCA results indicated that replacing 8% of cement with RH reduced CO₂ emissions, cumulative energy demand, and the overall ReCiPe endpoint impact by 7.7%, 6.7%, and 4.8%, respectively, compared with the control mixture, while CSH also provided considerable environmental benefits. Overall, SH-derived materials offer an effective strategy for producing low-carbon cementitious mortars. The 3% CSH mixture delivered the best mechanical performance, whereas the 8% SH mixture achieved the greatest environmental benefits, demonstrating the importance of balancing engineering performance and sustainability.

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Main Subjects

References

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History

  • Receive Date: 07 July 2026
  • Revise Date: 09 August 2026
  • Accept Date: 21 September 2026
  • First Publish Date: 21 September 2026

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