Researchers find ways to make low-quality hardwoods useful for structural applications

What may be considered lower grade West Virginia hardwood lumber can serve as an affordable, sustainable alternative to traditional building materials like softwood, steel and concrete, according to West Virginia University professor Joseph McNeel.

The professor and director of the WVU Appalachian Hardwood Center at the Davis College of Agriculture, Natural Resources and Design has been testing the effectiveness of yellow poplar, an abundant West Virginia species, as a source of engineered wood building material. Yellow poplar grows straight, has small limbs and processes easily, making it well suited for construction.

“Half of the hardwood harvested for sawtimber in West Virginia is considered low-quality lumber because it has too many knots and other defects,” McNeel said. “It’s used for pallets, boxes, railroad ties and flooring. But you can take those low-quality hardwoods and create something with significant added value.”

While traditional lumber comes as a single piece, it’s possible to create a sturdy, durable product by gluing and pressing multiple pieces together in layers. These large, thick panels are known as cross-laminated timbers. CLTs come from lower grade material. They’re used for long spans in walls, floors and roofs and do well as load-bearing elements. The panels are typically manufactured using softwoods — spruce, fir and pine — but not with hardwoods.

Research conducted by McNeel and his colleagues suggests that certain Appalachian hardwoods, like yellow poplar, work well in structural applications.

“One reason we liked yellow poplar was because it has been tested extensively in the past for structural applications,” he said.

In the lab, the team has created panels of three, five and seven layers using a press that can apply 250 pounds of pressure per square inch. The researchers tested the panels’ bending and breaking strength and subjected samples to harsh conditions like water saturation and dehydration. Tests were performed multiple times to see if the glue bonds held and results indicated the panels will perform well in construction.

The next step will be to get yellow poplar accepted as a permittable raw material by the American Panel Association. At that point, CLT manufacturing companies will be able to use yellow poplar CLTs in commercial construction. McNeel said this will be useful not only for the construction industry, but also for the forest product companies throughout Appalachia, where much of the hardwood ends up being used in low-value items.

The potential success of CLT use hinges on a region’s ability to produce them. The panels are difficult to transport — one 3-foot-by-10-foot panel weighs 600-700 pounds — so hardwood manufacturing facilities need to be close to the market to reduce the cost, he said.

McNeel and his colleagues are also looking at uses for red oak, another Appalachian hardwood, in the construction of timber mats, which are wooden structures used to support heavy duty equipment working on sensitive sites.

“They’re used where soils degrade quickly with traffic, wetland sites and in applications like gas exploration, logging and electrical powerline maintenance,” he said. “When you’re out in the field and you need to have something that will hold up a large piece of equipment, you’ll use timber mats.”

The mats are made predominantly out of red oak, which outlasts all the other components and can endure harsh climatic conditions.

“There are no restrictions or regulations for those mats,” he said. “They’re going to be destroyed after you’ve repeatedly run heavy equipment over them. So, if we test these panels and they work effectively, we’ll try and get that out to a lot of Appalachian hardwood lumber mills and say, ‘You could get into this business. You could learn how to make these timber mats using CLT technology.’”

In addition to economic benefits, McNeel said he believes CLTs may be useful in crises and humanitarian efforts.

“They could be put together in a pinch by FEMA or in any emergency situation where people need housing,” he said. “There are a lot of potential uses for these products. We’ve just scratched the surface.”

McNeel’s research team includes Curt Hassler, research professor; Balazs Bencsik, postdoctoral candidate; Jon Norris, master’s degree candidate; and Levente Denes, associate professor in the WVU Wood Science and Technology Program.