A new building material is making its way into the U.S. market. Cross-laminated timber, or CLT, which has been used to construct large buildings in Europe for the last two decades is experiencing growth as a building material in the U.S. and Canada.
"As of March 2019, there are currently 545 buildings in North America either built or in the design phase using mass timber products such as CLT," said Dr. Beth Stokes, scientist in the Forest and Wildlife Research Center. "That's up from less than 20 buildings two years ago."
CLT is one type of mass timber product used to compete with steel and concrete in custom large-scale projects. Thus far, there are three manufacturers producing CLT in the U.S.—two are in the Pacific Northwest (Oregon and Montana) and a third began operations in Alabama in 2018.
Stokes, who is an assistant professor in the Department of Sustainable Bioproducts, pointed out that the turn-key building approach CLT affords has plenty of benefits.
"When you build with CLT, it's like putting a puzzle together. The pieces are manufactured specifically for the building. Everything is taken to the site and bolted into place," Stokes said. "This material cuts down on construction costs, waste, and time to completion. Additionally, it's a sustainable, renewal resource that's great for carbon sequestration, reducing a building's carbon footprint."
Stokes said one issue is protecting the product during transportation and construction before it's installed and sealed into the building envelope.
"We hope to fnd a way to protect CLT from elements such as rain, heat, and high humidity," she said.
Stokes, along with doctoral student, Gabrielly Dos Santos Bobadilha, and others, are evaluating various coatings to protect CLT. They evaluated nearly 36 coatings, which they winnowed down to 12.
"Gaby performed water repellency tests on the dozen coatings that showed the most promise. We evaluated the results and selected the top five," Stokes said.
Now the team is researching how those five coatings hold up to water, heat, fungal decay, and more.
"We have several samples exposed to natural weather events that we will observe over the next fve years. We are also conducting accelerated weathering tests, where the samples are exposed to large amounts of water and UV rays over a shorter period of time. We are measuring for things like water uptake and evaluating characteristics like color change using a spectrophotometer to determine how each individual coating best protects the CLT while maintaining a 'natural' appearance," Stokes said.
The research—in its fourth year—is part of a five-year study Stokes hopes to continue as the CLT industry grows.
"CLT is a product that's changing the building industry. Overall, CLT production is great for the timber industry because it means we can use smaller timbers to make a bigger product, potentially using a lot of the excess wood that would typically be destined for the paper and pulp industry and even some of the roundwood that those industries can't use. Additionally, our research, in particular, could also help open up a potential new market for coatings to protect this emerging timber product," she said.
This research was funded by the USDA Forest Service Forest Products Laboratory. MSU collaborators include Dr. Mike Barnes, Dr. Thomas Lim, Chris McGinnis, David Butler, Brian Mitchell, and Beau Lovelace. USDA Forest Products Laboratory collaborator is Ms. Katie Ohno, an MSU alumna.