June 06, 2020

Timber bridge could spark new Maine forest-product industry

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For many people in rural Maine, trying the travel the bumpy economic road to better times in the future could literally be a case of “You can’t get there from here.”

Faced with the prospect of replacing more than 250 rural bridges that are too narrow or weakened from wear or were built when vehicles were smaller and lighter, Maine must either build new bridges or shut down part of its transportation infrastructure to large trucks.

Expensive steel-and-concrete bridges aren’t the answer for Maine, according to Habib J. Dagher, assistant professor of civil engineering at the University of Maine. Habib and his colleagues, including Barry S. Goodell, head of wood science and technology at UM, are developing a new bridge-building industry in Maine that will use Maine timber. Local road crews will construct these timber bridges without using nails, which loosen after years of wear and tear and let water and winter road salt to seep into the bridge material.

The new design will use 2-foot-by-12-foot wood planks that are pressed together, flat side to flat side, with the edges upright. High-strength steel rods are bolted through the timbers in holes predrilled every two feet.

Road-traffic weight is distributed across the slats, rather than straight down, to lessen wear and tear.

A 3-inch layer of asphalt is laid over the timbers, and the asphalt is covered with a rubberlike, waterproof composite material. Another layer of asphalt covers this material.

A key element of the bridge design is the wood preservative that permits otherwise impervious Maine wood to absorb the special chemicals that extend the life of the timber. Goodell is studying how to more effectively preserve other Maine timber species so that native rather than imported trees can be used in the bridges.

The combination of simple bridge designs and native timber that doesn’t bear the extra expense of being imported would not only save money, Habib points out, but would also form the basis of a $600-million export industry.

Maine wood and construction technology could go international, Goodell said. As an example, he mentioned the prefabricated log homes exported from the United States to Japan.

A prototype bridge is being tested in Gray. A computer attached to the bridge is connected by phone line to a computer in Habib’s laboratory.

Marc Kusinitz is the science writer in the Office of Public Affairs at the University of Maine.

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