Thermally modified timber (TMT) for decking applications – determination of relevant surface properties

IRG/WP 11-40544

L Meyer, C Brischke, C R Welzbacher

In recent years thermally modified timber (TMT) entered various market segments. It is used for facades, horticultural equipment, garden furniture, and also for kitchen and bathroom cabinets. However, flooring turned out to be the most important application for TMT, either as interior parquet or as exterior decking. Besides durability and dimensional stability, which had been the initial target properties of TMT, research activities need to focus also on flooring relevant properties. The performance of flooring is mainly characterized by its optical appearance, thermal behaviour and different mechanical properties, e. g. hardness and bending strength. Consequently, in the frame of a worldwide inter-laboratory test on quality measures for TMT, which was initiated in the frame of IRG in 2008, studies on the sensitivity of TMT on typical flooring loads were considered. Within this study color and heat flux density measurements were conducted to determine the suitability of TMT in terms of thermal comfort. The heat flux density was barely affected by the heat treatment, because it is mainly determined by the material density. Thermal modification did not lead to a remarkable loss, neither in density nor in heat flux. However, timber turned out to be preferential compared to mineral or polymer-based flooring materials suffering from less thermal comfort. The most important mechanical load for flooring was regarded in static and dynamic hardness tests. As TMT is known to be especially susceptible to dynamic loads, a method for determination of dynamic hardness was developed and applied to differently severe treated TMT. The development based on the Brinell hardness principle and aimed on examining differences between static and dynamic loads on hardness as well as on the possibility to convert both hardness values into each other. Extensive hardness tests with 24 different native wood species and TMT were conducted. The dynamic hardness decreased with increasing treatment intensity (in maximum by 20 %), whereby the axial hardness was significantly less affected compared to radial hardness. Furthermore, the reduction in hardness was found to be reliably predictable by color measurements.

Keywords: Brinell hardness, dynamic hardness, heat flux density, quality control, thermal comfort

Conference: 11-05-08/12 Queenstown, New Zealand

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