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February / March 2002 Cover

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The Amazing Adventures of 'Superwood'


The Amazing Adventures of 'Superwood'
Composite Research Is Adding Muscle to Maine's Mild-Mannered Timbers

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Technology at The University of Maine is transforming the state's lower-grade wood species into "super wood" new value-added building materials.

Engineers and wood scientists at UMaine's Advanced Engineered Wood Composites Center (AEWC) are developing new materials by combining wood with space-age plastics, such as fiber-reinforced polymers (FRPs). The goals: stronger, cost-efficient construction materials to build structures that withstand natural disasters, such as earthquakes and hurricanes; marine piers that resist decay and pest infestation, such as shipworms; and strong bridges that last longer, offering an alternative to traditional spans of steel and concrete.

Wood composites will help the country address a variety of problems, according to Habib Dagher, AEWC director and a professor in the Department of Civil and Environmental Engineering, whose confidence in wood composite technology stems from years of testing in both the laboratory, and in existing bridges and piers.

"Our research has already demonstrated the potential for wood composites to lower costs, increase efficiency and improve the performance of structures. Our goal is to demonstrate the reliability of new applications and move as quickly as possible to the marketplace," says Dagher.

Insurance industry figures put the annual average cost of natural disasters in the United States (in damages to property and loss of life) at about $50 billion, he says. Meanwhile, according to the National Partnership for Highway Quality, 25 percent of the nation's bridges are deficient, and wooden poles and pilings need to be replaced because of rot and insect infestations.

Habib Dagher
Habib Dagher, AEWC director and professor in the Department of Civil and Environmental Engineering, has long stressed the importance of using technology to transform Maine's abundant timber resources into new, value-added products.

Wood composites products under study:

Structural beams
Building panels
Marine pilings
Rot-resistant decking
Highway guardrails
Utility pole crossbeams
Bridge decks and girders

In pursuit of its goal, AEWC opened a 33,000-square-foot laboratory for building and testing wood composite materials in 2000. Formal partnerships have been created with industry, government research labs and other universities. Research by AEWC scientists has already led to three patents, and two more applications are pending.

"In the last five years, we have focused on building a world-class laboratory. Now that we have achieved that, we are turning our attention to research and economic development," Dagher says.

At its core, the laboratory is a teaching facility where students work with faculty to develop new technology. They use sophisticated computer models to determine what happens to wood as it breaks or as adhesives permeate pores and bind the wood to other materials. They build structures that they shake, bend and twist to simulate years of wear and tear.

Working directly with the business community is John Fiutak of UMaine's Department of Industrial Cooperation. Before coming to UMaine, Fiutak ran a manufacturing facility for Willamette Industries in Albany, Ore., a major producer of engineered wood building materials. He has been meeting with landowners and managers in Maine's forest products industry to lay the groundwork for a facility in the state to make laminated wood beams, known as glulams.

One focus of Fiutak's efforts has been a product that could be Maine's first step into the engineered wood products industry. It takes advantage of low-grade red maple, hard maple, birch and beech already being produced as a residual in some mills. AEWC research has shown that when these materials are glued together into beams, they can out-perform industry standards for strength upward of 30 percent. Red maple is Maine's most abundant hardwood, but it has little commercial value.

AEWC is working on revisions to building codes to include this product, says Fiutak.

More than 75 million board feet of glulams were sold in the Northeast and Canadian Maritimes for the residential construction market in 2000, he points out, but the closest manufacturing facility is in New York state. Moreover, that facility specializes in high-end softwood products. Fiutak's vision is for a plant to turn out hardwood beams that will be custom cut to almost any length and delivered to a contractor's specifications, reducing labor costs at the building site.

While hardwood laminated beams are close to reality, the future lies in products that take advantage of the low cost and flexibility of wood and the high strength of FRPs. "Wood is one of the best materials available from the perspective of strength to cost," says Robert Lindyberg, AEWC research engineer, "but it suffers from a perception as a low-tech material. We are working to change that. Wood composites are very much high-tech."

AEWC engineers and scientists are attacking that problem on several fronts. In the laboratory, they are subjecting wood composite materials to stresses and strains that are more severe than what they might actually encounter in a structure. Samples of composites are repeatedly drowned in water and dried out. They are run through freeze-thaw cycles, bombarded with ultra-violet light and subjected to constant pounding and bending.

At issue is not only the integrity of the wood and FRP. The glue line between the two is critical. Failure there could drastically reduce performance and cause a structure to become dangerously weak. Researchers now are taking a microscopic look at how well different adhesives keep wood and FRP together.

In addition to laboratory studies, AEWC has created a network of demonstration projects to monitor the performance of bridges and piers in actual use. Most of the projects are located in Maine, but others exist in Pennsylvania and Ohio, and more are planned across the country as part of collaboration with state departments of transportation and the Federal Highway Administration.

One of those projects, a commercial marine pier in Milbridge, Maine, met performance requirements with a composite structure weighing a third as much as a conventional one made of reinforced concrete. Today, trucks drive over a deck made with laminated wood and sheets of FRP applied at AEWC.

Also in Milbridge is a two-lane road bridge built with timbers that are strapped together with half-inch thick FRP cables, a technology known as post-tensioning. The bridge has proven its worth by requiring less maintenance than a similar AEWC-built structure in Gray, Maine, that uses standard steel rods in place of the FRP. Whereas the steel rods have to be retightened frequently, the FRP cables do not.

During the first two-and-a-half years of service, the FRP cables lost 14 percent of their tension strength compared to a 67 percent loss in the steel rods. Both bridges were built to be safe even without the tensioning. UMaine has received a patent on the FRP cable technology.

An AEWC project in Pennsylvania shows that futuristic wood composite products can even have a role in historic preservation. A timber structure partially built with composite beams now carries the Delaware Canal, originally constructed in the 1830s, over Tohickon Creek. Lindyberg worked with the aqueduct's owner, the Pennsylvania Department of Conservation and Natural Resources, and the U.S. Forest Products Laboratory to design the structure.

Another AEWC project, a road bridge scheduled for construction in Crenshaw County, Ala., uses the same approach as a smaller AEWC bridge in Medway, Maine. The large load-bearing beams that support the structure will be made of laminated planks with an FRP layer on the bottom of each beam. Repeated tests at AEWC show that an FRP layer nearly doubles beam strength, even when lower-quality woods are used.

The AEWC's FRP technology also has been applied to the concrete pillar of a highway overpass in Bangor, Maine. The goal is to determine if the material can extend the life of the pillar by protecting it from road salt.

At all of the demonstration sites, AEWC engineers monitor structural performance under a variety of operating conditions. Much of the work is simple and straightforward. Researchers load dump trucks with sand, drive the trucks onto bridges and measure how far the structures sag. They also visually inspect beams and decks, and in some cases, use strain gauges to make precise measurements.

Their data show how wood-FRP hybrids perform under a range of temperatures, humidity levels and loading stresses. With more composite bridges planned in the next few years, AEWC is working with the Federal Highway Administration to develop national engineering standards for the use of wood composites in highway infrastructure.

While these structures provide a foundation for AEWC research, new ventures are giving students and faculty other opportunities. For example, in the last year, stress tests have been run on building panels strengthened with FRP. The goal is to create a product that will effectively withstand the stresses of hurricanes, earthquakes and other disasters, saving money and lives. That work is supported by a grant from the National Institute of Standards and Technology.

Repair or strengthening of existing wooden structures is another avenue that AEWC researchers have explored. In one experiment, solid beams were cut nearly in half, then patched with FRP. Tests showed that the patches restored the beams to full strength.

Through contracts with private companies, AEWC technicians now are evaluating wood composite designs for skateboards, furniture, decking, home construction materials and shelving. In each case, they are testing the ability of wood-FRP technology to add value to products used in daily life and to meet the nation's building needs in the 21st century.

by Nick Houtman
February-March, 2002

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