Thermo-Hydro-Mechanical Treatment of Australian Sawlog and Pulplog Hardwood Resources

Australian sawn-board product is regulated by timber’s physical and mechanical properties to ensure safe operating performances in context specific applications. Contemporary and emerging timber resources, however, are lacking the traditional properties of commercially sawn products, namely density. One technique used to improve timber properties is densification through thermo-hydro-mechanical (THM) treatments (Rautkari et al., 2010; Sandberg et al., 2013; 2007). The objective of this study was to assess the change in timber properties of several Australian wood species densified using a THM treatment to identify if these modified species could be utilised in regulated building applications. Three hardwood species from different forest management schemes were tested in this study: Eucalptus obliqua, E. nitens, and E. globulus. E. obliqua was sourced from regrowth sawlog (60 year-old), E. nitens from plantation sawlog (26 year-old) and plantation pulplog (16 year-old) and E. globulus from plantation pulplog (26 yearold). Australian Standard (AS) 3959:2018—Construction of buildings in bushfire-prone areas— states E. obliqua and E. globulus are suitable for general construction with a density ≥750kg/ m3 and E. nitens is suitable for window and door joinery with a density ≥650kg/m3. Air-dry densities measured from each species, according to their respective forest management scheme, suggest sawn-board products from these resources are lower in density than required for use in building construction in bushfire prone areas; E. obliqua ~595 kg/m3, E. nitens (sawlog) ~560 kg/m3, E. nitens ~525 kg/m3 and E. globulus ~520 kg/m3. By using THM treatment, samples were densified to 67% and 53% of their original thickness (15mm) to demonstrate modified sawnboard can meet AS for use in construction and joinery; E. obliqua ~875 kg/m3 and ~980 kg/m3, E. nitens (sawlog) ~775 kg/m3 and ~1015 kg/m3, E. nitens ~680 kg/m3 and ~940 kg/m3 and E. globulus ~775 kg/m3 and ~870 kg/m3 at 67% and 53%, respectively.