Building a picture of bamboo’s strengths

A team of architects and engineers has mapped the way heat flows across the cell walls of bamboo, providing a clearer picture of how variations in thermal conductivity are linked to its elegant structure.

It’s an important step, the researchers say, in fulfilling the potential to use bamboo and other renewable, plant-based materials for structural as well as design purposes.

Laminated bamboo is increasingly popular as a flooring material because it is hard and durable. It also has a stiffness and strength comparable to engineered wood products, but for applications in buildings, its thermal properties also are important. 

“Thermal conductivity, for instance, dictates the rate of temperature increase through a material, which affects fire behaviour and building energy performance,” Darshil Shah and colleagues write in the journal Scientific Reports. 

“Energy use in buildings (e.g. space heating and cooling) accounts for over 30% of global energy consumption and CO2 emission. In this regard, material choices and their thermal performance have a notable role in improving building energy intensities”. 

The new study was a collaboration between Shah and Michael Ramage from Department of Architecture at the University of Cambridge, UK, and Johannes Konnerth and Claudia Gusenbauer from the University of Natural Resources and Life Sciences Vienna, Austria. 

They used advanced scanning thermal microscopy to study cross-sections of the vascular tissue that transports fluid and nutrients within the bamboo plant. The resulting images revealed an intricate fibre structure with alternating layers of thick and thin cell walls. 

Peaks of thermal conductivity within the bamboo structure coincide with the thicker walls, where chains of cellulose – the basic structural component of plant cell walls – are laid down almost parallel to the plant stem. 

These thicker layers also give bamboo its strength and stiffness. In contrast, the thinner cell walls have lower thermal conductivity due to cellulose chains being almost at a right angle to the plant stem.

“Nature is an amazing architect; bamboo is structured in a really clever way,” says Shah. “It grows by one millimetre every 90 seconds, making it one of the fastest growing plant materials. 

“Through the images we collected, we can see that it does this by generating a naturally cross-laminated fibre structure.”

The researchers say a better understanding of bamboo’s thermal properties will not just provide insights into how to reduce the energy consumption of bamboo buildings. It also will enable modelling of the way bamboo components behave when exposed to fire.

“Through our work we can see that heat travels along the structure-supporting thick cell wall fibres in bamboo, so if exposed to the heat of a fire the bamboo might soften more quickly in the direction of those fibres.” Shah says. 

“This helps us work out how to reinforce the building appropriately.”

The team now plans to look at what happens to heat flow in bamboo when its surface is burned and forms char.