Bonding Behaviour of Bamboo Reinforcement in Rammed Earth

Incorporating reinforcement in earthen elements considerably increases the range of architectural options available to designers and is essential in earthquake-prone areas. Modern construction specifies steel reinforcement for such situations. However, steel reinforcement can be prohibitively expensive in low-to-middle income countries and bamboo is therefore a popular reinforcing material where it is available. As a natural material which is fast growing, cheap, and sequesters carbon as it grows, bamboo has become the focus of attention for opportunities to replace high-carbon materials, for example steel, in construction. However, how effectively bamboo bonds to and reinforces the surrounding earth requires research. This paper presents experimental results measuring the push-out strength of bamboo reinforcement embedded in rammed earth and how the mechanism is affected by the bamboo's surface area, the suction present in the soil matrix, and the placement of the bamboo nodes. The results demonstrate that shrinkage can detach the bamboo from the earth, eliminating bonding between the reinforcement and the surrounding matrix. However, the presence of bamboo nodes close to the top or bottom of a compacted layer, where they can mobilise the strength of more dense material, considerably improved the bonding as they project across the shrinkage gap (c.0.75 mm). Improving our understanding of how bamboo interacts with earthen materials will permit safer construction in some of the world's poorest regions and create new opportunities for other nations to reduce their carbon footprints.