Building Up Bamboo- MIT researchers study bamboo for engineered building material, similar to plywood.
Categories: Building Methods
Such bamboo products are currently being developed by several companies. The MIT project intends to gain a better understanding of these materials, so that bamboo can be more effectively used structurally. To that end, MIT researchers have now analyzed the microstructure of bamboo and found that the plant is stronger and denser than North American softwoods like pine, fir, and spruce, making the grass a promising resource for composite materials.
“Bamboo grows extensively in regions where there are rapidly developing economies, so it’s an alternative building material to concrete and steel,” says Lorna Gibson, the Matoula S. Salapatas Professor of Materials Science and Engineering at MIT. “You probably wouldn’t make a skyscraper out of bamboo, but certainly smaller structures like houses and low-rise buildings.”
Gibson and her colleagues analyzed sections of bamboo from the inside out, measuring the stiffness of each section at the microscale. As it turns out, bamboo is densest near its outer walls. The researchers used their data to develop a model that predicts the strength of a given section of bamboo.
The model may help wood processors determine how to assemble a particular bamboo product. As Gibson explains it, one section of bamboo may be more suitable for a given product than another: “If you wanted a bamboo beam that bends, maybe you’d want to put the denser material at the top and bottom and the less dense bits toward the middle, as the stresses in the beam are larger at the top and bottom and smaller in the middle. We’re looking at how we might optimize the selection of bamboo materials in the structure that you make.”
Gibson and her colleagues have published their results in the Journal of the Royal Society: Interface.
A look at bamboo, from the inside out
For their experiments, the researchers analyzed specimens of moso, the main species of bamboo used in China. Like most types of bamboo, moso grows as hollow, cylindrical stalks, or culms, segmented by nodes along the length of a stalk. Bamboo can reach heights of 20 meters — as tall as a six-story building — in just a few months. The stalks then take another few years to mature — but still much faster than a pine tree’s statelier, decades-long growth.
“One of the impressive things is how fast bamboo grows,” Gibson notes. “If you planted a pine forest versus a bamboo forest, you would find you can grow far more bamboo, and faster.”
Researchers used electron microscopy to obtain images of the bamboo microstructure and create complete, microscale cross-sections of the entire culm wall at different heights along the stalk.
The resulting images showed density gradients of vascular bundles — hollow vessels — that carry fluid up and down the stalk, surrounded by solid fibrous cells. The density of these bundles increases radially outward — a gradient that seems to grow more pronounced at higher positions along a stalk.