[Article] Rice husk ash reduces the damage rate of compressed earth blocks

Most research on earthen construction still faces the same structural limitations: insufficient mechanical strength, brittle failure behavior, dependence on cement stabilization, and a persistent gap between laboratory validation and real-world housing deployment. At the same time, the discussion on low-carbon materials often remains qualitative, without clear benchmarks. A practical threshold is increasingly emerging in the field: for a masonry unit to be considered truly low-carbon, its embodied emissions should typically fall below 0.10–0.15 kg CO₂ per kg of brick, significantly lower than conventional fired or cement-based units.

In this context, the PhD work of Marian Valenzuela (Chile) provides an important contribution. The study investigates the use of rice husk ash (RHA) as a stabilizing agent in compressed earth blocks (CEBs), not only in terms of compressive strength, but more importantly through the lens of damage evolution and failure behavior. The results show a substantial reduction in damage rate, up to approximately 88%, with a clear transition from brittle collapse toward a more ductile and controlled mechanical response. This shift is critical, particularly in seismic contexts, where material behavior under stress defines structural safety more than peak strength alone.

What makes this work particularly relevant is that it goes beyond simple material substitution. Rice husk ash is not an inert filler; it acts as a reactive pozzolanic binder, improving inter-particle cohesion and contributing to the formation of cementitious phases. This opens the possibility to significantly reduce cement content while enhancing performance, directly impacting both durability and embodied carbon.

At the Sustainable Building Design Lab (ULiège), this research is part of a broader and more strategic trajectory. The objective is not only to optimize a material in isolation, but to connect these findings to scalable housing systems. This is where the HABIMO project in Burkina Faso becomes essential. HABIMO moves from the material scale to the building and socio-economic scale, aiming to develop affordable, bioclimatic housing based on compressed earth blocks, reduce dependence on imported cement, and integrate local resources and production chains. The challenge is therefore not only technical but also economic and cultural, particularly in contexts where earth construction still faces issues of perception and acceptance.

The real shift lies here. The question is no longer whether compressed earth blocks can be improved, but whether they can meet four conditions simultaneously: structural reliability, low embodied carbon within defined thresholds, economic viability, and scalability in real contexts. Connecting material innovation, such as RHA stabilization, with system-level approaches like HABIMO is a necessary step toward that goal.

🤝 This work is only possible through strong collaboration across contexts. I would like to acknowledge the excellent contribution of the Chilean research team, in particular Marian Valenzuela and Prof. Víctor Tuninetti (Universidad de La Frontera, Chile), whose work advances the understanding of the mechanical performance and resilience of compressed earth blocks. I also want to recognize the committed partners in Burkina Faso, Adamah MESSAN, Philbert Nshimiyimana, PhD, Luc Courard, @Simon-Pierre Salassy, involved in the HABIMO project, including colleagues at 2iE, and field actors on social acceptance.

👏 Valenzuela, M., Tuninetti, V.& Attia, S. (2025). Rice husk ash reduces damage rate of CEB under uniaxial compression. Procedia Structural Integrity, 68, 386-390. doi:10.1016/j.prostr.2025.06.070
👏 Valenzuela, M., Tuninetti, V., Ciudad, G. et al. Designing sustainable cement free compositions with rice husk ash to improve mechanical performance in next generation ecoblocks. Sci Rep 15, 14920 (2025). https://doi.org/10.1038/s41598-025-97963-8

📘 Full article https://hdl.handle.net/2268/334426
📚 Learn more about our research https://www.sbd.uliege.be/
💻 Subscribe to my newsletter https://lnkd.in/diTVT5eq
🅱️ Bilibili b23.tv/bzjL3bn or 🎬 YouTube https://lnkd.in/erHrfkNf
🌐 Explore previous posts and resources https://www.shadyattia.org
🔗 Follow all my professional links, including WeChat 🟩💬 微信 https://lnkd.in/eN3xZhhZ

CompressedEarthBlocks #LowCarbonMaterials #CircularConstruction #AffordableHousing #HABIMO #BuildingScience #Decarbonization #SustainableConstruction