How Thermal Modification Affects the Short-Term Bending Creep Behaviour of Fraxinus Excelsior Wood

Among wood types used in industry, ash wood is one of the most commonly heat-treated species. It is widely applied for outdoor applications such as cladding, terrace boards, and garden furniture, as well as in indoor applications that require high dimensional stability. Although the mechanical properties of thermally modified ash have been extensively studied, its creep behaviour under sustained load remains insufficiently described. This study evaluates the short-term creep behaviour of ash wood thermally modified at 210 °C under bending stress, based on deflection measurements at different stress levels and under controlled humidity conditions. Untreated ash wood with comparable moisture content served as a reference. The results show that thermally modified wood exhibited lower creep compliance than untreated wood at all applied stress levels. After 24 h of loading, the absolute reduction in total creep compliance was 3.7% at 40% stress and 20.3% at 60% stress relative to control wood. The difference between modified and unmodified wood became more pronounced as the load level increased. These findings indicate that thermal modification can reduce the tendency of ash wood to creep under short-term loading conditions. Given the limited test duration and the use of small specimens, the results should be interpreted with caution and cannot be directly extrapolated to structural-scale applications. Nevertheless, the study provides new knowledge and is an interesting basis for further investigation of the creep behaviour of thermally modified wood under long-term loading and variable environmental conditions.