Two new trees support cross-laminated timber

Materials World magazine
,
9 Mar 2020
testing cross-laminated timber

Timber engineers in the USA prove that low-grade trees can boost timber supplies and the local economy.

Two species of tree have proven suitable for producing cross-laminated timber (CLT) that would supply the local timber market, and make valuable products from previously ignored resources. 

According to the research team, ‘CLT provides the possibility of a substantial market for underutilised and lower-quality tree species’. 

Native to north-eastern USA, the eastern hemlock and eastern white pine could be used to manufacture large quantities of CLT for use in the construction of walls, floors, roofing and a multitude of home building elements. 

While encouraging greater use of timber in building construction would support the forestry industry and local communities, as well as helping designers and architects to lower the overall carbon footprint of building projects, there are additional benefits to making use of these particular trees. 

Eastern hemlock, for instance, is generally considered a forest fire hazard. The wood is too low quality for most purposes and is prone to ring shake defects. Further, it is often attacked by an insect that eventually kills it, leaving large stocks of dead trees to rot on the forest floor. 

Therefore, finding a use for this tree species would not only benefit forestry management in the area, but create revenue from an otherwise neglected resource. 

A new use for dead wood 

University of Massachusetts Amherst, USA, Professor of Wood Mechanics and Timber Engineering, Peggi Clouston, led the project to examine these two tree species for more demanding purposes. 

According to Clouston, ‘Turning this particular species into CLT turns a very low-value material into a very high-value building product’. The wider intention was to explore new ways to support the timber market, and increase efficiency and uptake of timber engineering in wider construction projects. 

At the university’s Wood Mechanics Lab in the School of Earth and Sustainability, Clouston’s team tested these two species of tree to confirm their suitability for CLT 

They first produced 17 composite building panels of 99m × 305m × 3.048m, by gluing together three layers of board from each of the trees. 

These were put through the lab’s strength testing equipment to determine if they could support large and very large structures, such as buildings. The machines focused on major and minor axis bending properties and major axis shear properties. 

Results showed that both species met the legal specifications for timber under the American National Standards Institute/American Plywood Association PRG 320 regulation for CLT, and that eastern hemlock outperformed pine. 

As such, the team is now recommended the opportunity for a local business in the area that could take advantage of this bounty. 

Feasibility of two north-eastern species in three-layer ANSI-approved cross-laminated timber, published in Journal of Materials in Civil Engineering, can be read here: bit.ly/2PXiK3S


Image: Putting a CLT panel through the strength testing machine. Credit: Peggi Clouston/UMass Amherst.