The prediction of physical (wood density, mass loss) and mechanical (bending properties, compressive strength parallel to grain, and Brinell hardness) properties of heat-treated sessile oak (Quercus petraea L.) by FT-NIR spectroscopy, colour change, and partial least squares regression (PLS) was studied. Samples of oak sapwood and heartwood were treated for 4 h at temperatures at 170, 190, and 210°C. FT-NIR spectra (100 scans and 4 cm⁻¹) and colour parameters (CIE L*a*b* system) were collected on the radial surface before and after heat treatment. The applied heat treatment changed wood properties, darkened the colour and reduced the colour difference between heartwood and sapwood. According to the residual prediction deviation (RPD), most models obtained could be used for preliminary wood quality screening (1.5 < RPD < 2.0) and the properties of heartwood were better predicted than those of sapwood. Mass loss prediction by colour change can be used for quality control while for the other properties FT-NIR provided a more clear picture of the heat-treated oak wood and can serve as a quality indicator.

This paper addresses the challenges in evaluating the structural performance of built structures using non-destructive methods and in situ tests. Such an examination of structural properties, without their sampling, is a diagnostic improvement, especially for historical heritage buildings, where it is not allowed to violate their physical integrity. Therefore, the research proposes a non-destructive testing method based on the equalization of the mechanically and non-destructively determined parameters of the strength of built-in timber. The research included three phases: (1) a preliminary examination; (2) a calibration procedure of the non-destructive method, and (3) in situ application of the established non-destructive method. The preliminary examination involved testing specimens using X-rays and ultrasonic waves by directing them, analogous to mechanical testing, in the fibers’ longitudinal, radial, and tangential directions. In the second phase, it was shown that equalizing the parameters of mechanical and non-destructive testing using ultrasound and X-rays of timber was feasible. Furthermore, mechanical calibration was conducted to establish an applicable non-destructive in situ method. Finally, in the third phase, an in situ assessment of timber architectural elements confirms the effectiveness of the suggested non-destructive approach in diagnosing architectural structures.

This study aimed to compare two thermal modification (TM) schedules—with short and long heating phases—and their influence on the properties of maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) wood. Two TM runs were conducted in industrial conditions (open system, steam atmosphere; substantially longer method compared to the processes usually described in the literature), with the same peak phase (200 °C, 3 h), but with different heating rates—slow (1.1 °C/h) and fast (2.5 °C/h). The results revealed that both TMs significantly reduced hygroscopicity and swelling of wood, but the influence of slow heating rate—through prolonged exposure of wood to relatively high temperatures—on dimensional stability was more pronounced. The modulus of elasticity, compressive strength and Brinell hardness remained mostly unchanged after TM (except for fast-modified maple), while the modulus of rupture was strongly reduced by TM in both species. It is assumed—at least in the case of maple wood—that a combination of initial moisture content above 8% and fast heating rate during TM can cause more intensive degradation of wood polymers. Relatively small differences in colour between slow- and fast-modified wood were found. The results confirmed the hypothesis that the heating phase is an important part of the TM schedule, and it can directly affect (together with peak temperature and time) certain wood properties.