Bamboo Bio-Concrete: Eco-Friendly Innovations in Construction
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By Nidhi DhullJul 1 2024Reviewed by Susha Cheriyedath, M.Sc.
A recent article published in Sustainability comprehensively examined the influence of bamboo particles on the physical properties and durability indicators of bamboo bio-concrete (BBC) through experimental measurements.
Study: Bamboo Bio-Concrete: Eco-Friendly Innovations in Construction . Image Credit: Cocos.Bounty/Shutterstock.com
Background
As the construction sector is moving towards renewable raw materials to reduce greenhouse gas emissions, several alternative building materials are being investigated to reduce their carbon footprint. These alternatives generally use bio-aggregates to produce new sustainable construction materials while improving the thermal characteristics of the buildings.
Large-volume fractions of bio-aggregates, including bamboo waste, wood shavings, rice husk, and hemp, are used to develop bio-based cement mixtures. The bio-concretes synthesized from such cement mixes are lightweight, thermal insulators, and can potentially reduce the overall ecological impact of the construction industry.
However, bio-aggregates are characterized by high porosity. Thus, the traditional design rules generally applied for producing ordinary cement-based structures are not applicable in the case of bio-concrete. In this context, this study involved comprehensive experiments to examine the potential of treated bamboo aggregates to produce bio-concrete.
Methods
The bamboo waste used in this study was obtained from a Brazilian company that uses the culms as construction elements. Bamboo particles (BPs) were prepared from these bio-aggregates by crushing, refining, and sieving. Additionally, Brazilian Portland cement was used for BBC production.
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The extractives present in bio-aggregates can negatively impact cement setting and hardening. However, washing the aggregates in hot water can reduce such effects. Thus, an isothermal calorimetry test was performed to determine the ideal number of BP washing cycles for proper cement hydration. Accordingly, BPs were washed in hot water (80 °C) for one hour before producing BBC.
After air-drying the BPs, the elongated pile method was employed for homogenization. Subsequently, four different BBC composites were produced by varying cement-to-bamboo as 2.5 and 3 wt.%, equivalents to 50% and 45% BP volume fractions, respectively. The water-to-cement (w/c) ratio was 0.4 and 0.5 to ensure a minimum standard consistency index of 255 mm for good workability.
A flow table test was conducted to assess the workability of BBC in the fresh state. Alternatively, its apparent density was analyzed using six cylindrical specimens (diameter: 50 mm, height: 100 mm) cured for 28 days. Additionally, the insulating capacity of BBCs was assessed through a thermal conductivity test utilizing eight specimens (diameter: 50 mm, height: 20 mm).
Water absorption by capillarity was measured for 28 days on four cylindrical specimens for each BBC composite. Finally, a drying shrinkage test was performed using four prismatic samples for each bio-concrete, measuring the length variation and mass loss for 90 days.
Results and Discussion
The isothermal calorimetry test revealed that hot-water (80 °C) washing of BPs effectively prevented cement hydration delay. Consequently, all the prepared BBC mixtures were homogeneous in the fresh state. Their spread varied between 268 mm and 290 mm, indicating good workability with easy molding.
The BBC specimens’ thermal conductivity and density varied from 0.315 to 0.519 W/mK and 693 to 786 kg/m3, respectively. These results indicated an insulating nature and low density of BBCs. Moreover, these values decreased with increasing content of BPs due to the latter’s highly porous structure.
The capillary behavior of the BBCs exhibited high absorption kinetics in the first hours of curing and decreased beyond ten days to reach a plateau. For a specific cement/bio-aggregate ratio, increasing the w/c ratio did not significantly change this absorption behavior. However, the capillary kinetics of BBCs increased with increasing biomass volume due to the correlation of the concrete’s water absorption coefficient to the porous structure of BP.
The BBC composite with 45% BP and 0.4 w/c experienced minimum shrinkage and mass loss on immersing in water. The deformation and weight variation increased with increasing BP proportion and w/c ratio in the concrete mix. The results of the thermal conductivity test showed that the bio-concrete is insulating, with thermal conductivity values between 0.315 and 0.519 W/mK.
The researchers divided the evolution of drying shrinkage and mass loss into variable (rapid retraction for first 20 days) and stable (gradually attained plateau with less than 3% variation) stages. This phenomenon was attributed to the porosity of the cement matrix and BPs and the relative humidity.
Conclusion
Overall, the researchers presented through investigation of the fundamental properties of BBC including density, thermal conductivity, capillary water absorption, and drying shrinkage. The lightweight and insulating BBCs prepared by incorporating bamboo aggregates proved feasible for use in various construction applications including internal partitions, false ceilings, retrofitting façades, and hollow brick walls.
However, the prepared BBCs exhibited greater deformation and weight variations with increasing bio-aggregate content and w/c ratio. Thus, the authors suggest further studies to improve the cementitious matrix of bio-concrete by replacing cement with pozzolanic materials. Additionally, their natural durability (external weathering) and biological robustness (fungal attack) need thorough assessment for practical applications.
Journal Reference
Andreola, V. M., da Gloria, M. Y. R., Pepe, M., & Filho, R. D. T. (2024). A Comprehensive Experimental Study on the Physical Performance and Durability of Bamboo Bio-Concrete. Sustainability, 16(13), 5334. DOI: 10.3390/su16135334, https://www.mdpi.com/2071-1050/16/13/5334
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