Future Forward: Can Cross-Laminated Timber Replace Concrete and Steel?
What Is CLT?
Cross-laminated timber (CLT) is part of what’s collectively called “mass timber” that includes glue-
laminated beams, nail-laminated timber and CLT. SmartLam Technologies makes large panels of CLT—no typical size, but its current press is 10 feet by 40 feet by about 14 inches deep. CLT is made with successive layers of dimensional lumber that are typically laid perpendicular to one another. Each layer has an adhesive applied, and then the layers are hydraulically compressed for a specific amount of time to create a monolithic slab of wood that “pound for pound” is stronger than concrete or steel.
“It has some interesting material properties,” notes Malmquist. “It appears like a concrete slab, but it actually behaves more like steel because of its ductility.”
Wood is a carbon store, so in the net carbon equation, CLT isn’t carbon neutral, but close, as opposed to very high carbon emissions in concrete and steel. Malmquist notes that in the United States, construction materials and activities contribute more to carbon emissions than automobiles.
“Wood arguably is the only renewable building material; it can literally be harvested,” he adds. “And our adhesive is kitchen grade—you can eat it, which again goes to the environmental side and sustainability.”
Most of the tree stock used to make CLT is 12-inch diameter or less, making it sustainably harvestable. According to Malmquist, the company’s production capability on the new plant is about 48 billion board feet annually, which is about 12,000 logging trucks. He notes that it takes the North American forest only five hours and 12 minutes to regenerate that amount of wood fiber.
Why CLT over Steel or Concrete?
Lesser weight is a key benefit of CLT, and speed of build is another incentive. Unlike concrete, which is poured into place, CLT panels are custom milled to become part of a building system that’s lifted into place onsite. Considering it’s made of wood, fire resistance is a surprising area in which CLT outperforms steel and concrete in tests performed in Europe, where CLT has been in use for more than 25 years. Similar tests in the United States support these findings.
“I have a really compelling photo that I use in presentations where there are two failed steel I-beams draped over a timber beam, where the timber survived the fire, and the steel I-beams deformed and failed,” notes Malmquist. “Have you ever tried to light a log with a Bic lighter? There’s just so much mass there. The fire event will burn into the wood to a certain extent, lose its oxygen source and self extinguish. That is the hallmark of the mass timber; it will self extinguish and still have the residual structural capabilities.”
The Future of CLT
“One of my favorite aspects of CLT is the diversity in the product line we produce,” adds Malmquist. “It has such great versatility, and it can be applied in several different marketplaces.”
He cites a wide range of projects CLT currently is used for, such as crane mats or access mats for industrial projects; erecting multi-story buildings; furniture; agricultural buildings; train stations; and modular elevator shafts, which can be built much faster via CLT than with typical concrete masonry units.
To help find more uses of CLT, SmartLam Technologies invests about 20 percent of its resources into research and development, which also includes testing for fire, seismic and acoustic performance.
“We’re trying to develop ways to improve the performance of this product in a natural and sustainable way,” adds Malmquist. “It’s really understanding how this material works, and what things we can pull out of it.”
SmarLam Technologies currently has a plant in northwest Montana, and within three years it plans to build a plant in the northeast and then the southeast as the market continues to develop and expand.