Large timber durability testing program takes major step forward; efforts to characterise timber fire performance continue

The FWPA-supported National Centre for Timber Durability and Design Life continues to collaborate with research partners around Australia to gather evidence-based data, systems and tools to underpin consumer confidence in the performance of timber products.

Here, we offer a round-up of some key activities being led or supported by the centre team, including an update on an extensive testing program covering timber application for outdoor use, and work to provide a broader basis for characterising and predicting timber fire performance.

Earlier this year, the centre announced the launch of a significant testing program, with a specific focus on various timber materials used in Hazard Class H3, covering outdoor applications that are above ground and exposed to the weather. The project represents the first time in 30 years that such a diverse range of species, products and preservatives have been tested.

The knowledge gained will arm the construction industry with more extensive and accurate information on timber durability than ever before. The team is striving to develop a more accurate understanding of timber properties, to support structural engineers when selecting the appropriate timber for a particular application and, as a consequence, create improved confidence and uptake.

Led by FWPA’s National Centre for Timber Durability and Design Life in collaboration with the Queensland Department of Agriculture and Fisheries (DAF), the ambitious project is now up and running, with DAF test sites at Nambour near the Sunshine Coast, and South Johnstone in Far North Queensland, both established and operational.

During the next five years and beyond, the trial will consider in excess of 40 different materials, with more than 8,000 test samples in total, ranging from plywood to laminated veneer lumber (LVL), oriented strand board (OSB), solid wood, heartwood of spotted gum, and merbau (kwila), as well as a wood-plastic composite.

A range of traditional wood preservatives and more recently developed treatments will also be tested, to gauge the effectiveness of various species and treatment combinations under different conditions. The tests will gather important data on durability performance associated with the treatments, using a range of traditional visual assessments, alongside additional tests that can detect any changes to the timber’s engineering properties.

Methods used will include ground proximity tests, where blocks are placed directly onto concrete above the ground. Also included is an above-ground ‘sandwich test’ previously used in the USA, in which wooden blocks are strapped together to create ‘timber sandwiches’ that are exposed on racks above the ground. Additional testing will see beams placed on timber supports located on concrete above the ground, to assess changes in flexural properties.

The goal is to gather information on the durability of the tested materials, which can be used to enhance existing CSIRO service-life prediction models. Current models were developed more than 20 years ago, and so today have significant limitations. In particular, this latest work will provide important data on the performance of more recently developed preservatives and modified wood systems.

Characterising the fire performance of Far North Queensland hardwoods

Elsewhere, Dr Felix Wiesner, of the University of Queensland, has completed a preliminary study examining the fire performance of a number of Far North Queensland hardwoods. The study is focused on relating timber characteristics to fire performance, and intended to provide a broader basis for characterising and predicting fire performance.

While results are still being analysed, the preliminary work has highlighted the need for additional research to help better assess the performance of timber samples during these tests.

Dr Wiesner has begun preparations to assess ongoing smouldering in durability-treated exterior products following a wildfire. This research will investigate the extent to which copper-based treatments facilitate smouldering (or ‘afterglow’) in timber following a fire has passed through.

Understanding and quantifying the extent of this smouldering is critical for ensuring the design life of timber infrastructure is not cut short by fires that might otherwise have caused only minor damage. 

Collaborating with our colleagues in Tasmania and South Australia

Dr Babar Hassan, who joined the National Centre for Timber Durability and Design Life as research fellow earlier this year, has been actively engaged with our University of Tasmania partners, to explore new methods for enhancing the durability of refractory hardwoods — meaning those that are liable to crack, split and warp — for above ground applications.

A small trial has been established to explore the use of borate preservatives (or ‘boron diffusion’) to offer protection against fungal and insect attack, followed by over-treatment with a conventional preservative. This approach has been successfully adopted in North America to protect railway sleepers, and could create new opportunities for using difficult-to-treat hardwoods in exterior applications.

In addition, Dr Hassan recently completed a preliminary treatment test of the softwood timber being evaluated as part of work underway at the University of South Australia (UniSA), mentioned elsewhere in this edition of R&DWorks, to determine the mechanical properties of softwood sawn timber.

The UniSA researchers are capturing a representative sample of softwood sawn-timber production from 13 participating Australian sawmills over a full year. They will then analyse test results to provide accurate information to industry on the structural properties of sawn timber products, providing robust evidence to clearly demonstrate the many performance benefits associated with timber.

As part of our collaboration with the UniSA team, we expect to receive portions of samples tested during their studies, so we can explore treatability differences across the various growing ranges.

The National Centre for Timber Durability and Design Life was established in 2016 at the University of the Sunshine Coast, and takes a national approach. Since its inception, the centre has made significant progress in building links between industry, academia and customers, nationally and internationally, to put Australia at the forefront of international best practice.