Green scene:

The magic (bamboo) bullet?

by Stewart McCoy

In 2007, the first modern bamboo bridge capable of carrying 8-ton trucks was erected over a river in Hunan Province, China. There was a big to-do about it. The application of the technology was innovative, and much has been made about the sustainability benefits of building bridges with bamboo.

“A lot of people think bamboo is the magic bullet,” says Dr. Lynn Clark, professor of botany at Iowa State University.

Bamboo is a grass, and yet it can carry an 8-ton truck. Bamboo can also sequester more than 30% more carbon dioxide than its timber counter-parts. No wonder engineers are excited about bamboo!

What did take to build a truck-safe bamboo bridge? Can we do it in the U.S.?

The first truck-safe bamboo bridge

When the Leiyang Bridge was erected in 2007, eight workers completed it in 10 days without heavy construction equipment. The bridge is rated to safely carry a 2-axel 8-ton truck. The ultimate load that the bridge could carry is up to 80 tons—that’s 160,000 pounds!

Other bamboo bridges have reportedly carried the weight of trucks up to 5 tons. However, this bridge is the first to use glue-laminated technology and be rigorously field tested by professionals.

Is bamboo the greener alternative?

Modern engineered wood has been a contemporary material of choice for building bridges that support heavy loads. However, bamboo advocates point out the sustainable benefits of using bamboo instead of timber.

A major contributor to climate change is carbon dioxide (CO2), a greenhouse gas. Bamboo advocates often point out that bamboo removes CO2 from the atmosphere through photosynthesis at much greater rates than other plants. The removal of CO2 from the atmosphere is often referred to as sequestration.

For example, 2.5 acres of bamboo removes about 62 tons of CO2 from the atmosphere per year, while 2.5 acres of young forest removes only 15 tons of CO2 from the atmosphere per year, according to a publication by J.J.A. Janssen of Eindhoven University of Technology.

Comparing bamboo and timber life cycles

However, it’s important that such a comparison be considered in the context of plant life cycles, cautions Dr. Clark. For example, if you compare the life cycle of an Oak tree to bamboo, “things will probably even out,” says Dr. Clark.

“Bamboos could live decades to 120 years or so and then die. When they die and decompose, they release carbon back into the atmosphere,” says Dr. Clark.

“If you consider an Oak, it could be around for several hundred years, and could sequester as much or more [than bamboo],” says Dr. Clark.

A lot of numbers are thrown around promoting the benefits of bamboo. So it’s important to consider the context of statistics.

In the context we’re considering, bamboo and timber are harvested and used as building materials. Bamboo grows quickly and sequesters carbon more rapidly than trees during their respective harvesting life cycles.

So, if bamboo and trees are cut down for building materials, bamboo is generally considered to sequester more carbon dioxide than timber.

From Glulam to GluBam®!

One method of making modern bridge girders from timber is to glue together several layers of pre-cut wood; the result is glue-laminated timber or glulam. Girders are the long beams that span a bridge. You can read more about engineered wood in the January–February 2009 issue of Go!

Bamboo can also be laminated for use in bridges and for many other purposes. Lamination is a manufacturing method for protecting raw natural materials like wood and bamboo from the elements by covering them in plastic or a similar protective material.

Laminated bamboo goes pretty far back. In 1942, the U.S. government commissioned a study to determine the effectiveness of using bamboo laminates for ski poles. And laminated bamboo has long been used for floor tiles.

However, Dr. Yan Xiao, professor of civil engineer at the University of Southern California, and his collaborators at the Institute of Modern Bamboo, Timber and Composite Structures (IBTCS—part of Hunan University) are the first to develop laminated bamboo specifically for bridges. They’re calling their invention GluBam®.

One advantage to using glulam technology is that higher-grade bamboo can be layered in areas that will experience the greatest stress. Lower-grade bamboo can be layered in areas that will experience the least stress. This means engineers can control the strength (and related structural properties) of the girder. GluBam® is what allows grass to carry an 8-ton truck!

Compared to girders made of concrete and steel, glulam girders are more environmentally friendly because they require less energy to produce. Taking it a step further, GluBam® girders are considered to be even more environmentally friendly. Compared to concrete and steel, wood products rely on fewer fossil fuels during the production process, and bamboo products rely on even fewer.

The trouble with adopting modern bamboo bridges the U.S.

Inspired by Dr. Xiao’s innovative modern bamboo bridge project, researchers at Iowa State University’s Institute for Transportation (InTrans) set out to determine if similar bridges might be possible in the United States.

Unfortunately, the researchers never got past the proposal stage of the project because they ran into several unexpected problems.

A major goal of the InTrans research project was to determine if GluBam® would be a better alternative to traditional timber bridges. The researchers wanted to compare the costs and durability of the bamboo bridges.

Another major aspect of the project was to determine if bamboo could be grown locally. Using local materials cuts down on pollution associated with transporting the materials and reduces the negative impact of product production on the environment.

Unfortunately, using locally grown bamboo, as great as it sounds, was a lot more trouble than the researchers thought it would be.

The trouble with locally-grown bamboo

The research team learned that there are approximately 1,400 species of bamboo. Many of these species are adapted to climates that are warm year-round, which poses difficulties for growing bamboo in certain regions of the U.S. that have harsh winters.

In China, bamboo survives the temperate winters and puts up new shoots in the spring. In much of the U.S., bamboo shoots are often killed during the winter and the roots have to put up new shoots in the spring, making it difficult for the shoots to mature.

A related issue is that bamboo can’t be clearcut like timber. In fact, bamboo is almost always harvested by hand.

A bamboo shoot takes about 3–4 years to harden enough to be suitable for a building material. A single bamboo plant can have many shoots of varying ages, making it very difficult to harvest using a machine.

More research needs to be done

The study by J.J.A Janssen, mentioned earlier, also reports that, except for bamboo that is both grown and used locally, nearly all of the environmental cost of bamboo originates from transportation. Even with that cost, bamboo is found to be more sustainable than steel, concrete, or timber.

However, there are enough unknowns out there that bamboo is not currently viewed as a viable alternative to traditional bridge building materials in the U.S., according to Brent Phares and Jake Bigelow, the investigators on the InTrans research project.

Learn more

If you’re interested in learning more about the environmental aspects of bamboo or how bamboo is used to build structures such as houses, you can visit the Environmental Bamboo Foundation.

You can also read more about Dr. Yan Xiao and his work in the Popular Science article "The Bamboo Builder."