By MJ Jacobs and Brand Wessels at Stellenbosch University

Cross Laminated Timber (CLT) is a relatively new laminar wood-based product, developed in central Europe, that is rapidly gaining market share worldwide as an environmentally sustainable building product. In South Africa we currently only have one manufacturer (XLam from Cape Town) but we hope that this situation will change over the coming decade. South Africa have unique challenges impacting on the wide scale adoption of CLT and other mass timber products. At Stellenbosch Universities’ Department of Forest and Wood Science we are involved in a range of research projects to tackle some of these technical challenges.

Adhesive bondline test samples for chemically treated wood. Image credit: Stellenbosch University

Adhesive bondline test samples for chemically treated wood. Image credit: Stellenbosch University

In South Africa structural timber and structural timber products are required to be chemically treated for protection against insect attack and fungal decay in certain parts of the country. Treating the full CLT panel after construction is not a possibility due to size constraints of the treatment vessels. An ongoing PhD and MSc study is currently investigating the bondline quality of various chemical treatments, using different adhesive systems for both SA Pine and Eucalypt CLT.

Process optimisation / cost reduction

The European and American models of CLT manufacturing result in relatively inefficient and low volume recovery rates for the full CLT value chain, resulting in high cost of manufacturing. There are several opportunities where integrating the sawmill and CLT manufacturing processes can result in a more efficient value chain. In two MSc projects, opportunities such as optimal dimensional product options, wane specifications, green bonding, and incorporation of out-of-spec defects in CLT are investigated. Both computer simulation and real-world manufacturing tests are used to optimise the manufacturing process.

Structural modelling

Accurately predicting strength and stiffness of CLT is important for the wide acceptance of CLT as a commercial building material in South Africa. Therefore, developing and comparing strength and stiffness prediction models to predict the mechanical properties of CLT is investigated. Model accuracy will be confirmed in an MSc project with destructive tests, which will also provide much needed information on failure modes and quantify the strength, stiffness, and associated variation of CLT made with local SA Pine and Eucalypt timber.

Fire resistance

Although CLT have relatively good, predictable fire behaviour compared to steel and concrete, fire engineers need accurate fire performance data from our local wood resources. The fire performance of CLT can also be further increased by treatments such as boron-based fire retardants, and the use of adhesives that perform better in fire. An MSc project involving the fire resistance of SA Pine CLT manufactured in different ways aim to quantify fire performance of this material.

CLT is transforming the low -and medium rise building landscape of the world. South Africa could be a part of this revolution, but we need to develop a local manufacturing industry that can compete with the best in the world. If we invest in local research, there is a good chance that we can reach the manufacturing cutting edge of this exciting new product.