Research Articles

The objective of the study was to investigate the influence of heat treatment on air-dried density, equilibrium moisture content (EMC), porosity, average surface roughness (R_a), sound transmission loss, and sound absorption coefficient of poplar (Populus nigra L.) and beech (Fagus orientalis Lipsky) woods. Specimens were exposed to four different temperature levels, namely 150 °C, 170 °C, 190 °C, and 210 °C, for 3 h. The sound absorption coefficient and sound transmission loss of test samples were determined in the frequency range of 63 Hz to 6300 Hz using an impedance tube. It was found that the density, EMC, and average surface roughness values of samples decreased with the heat treatment temperature. In contrast, as the heat treatment temperature increased, porosity of samples increased. The sound absorption coefficient and sound transmission loss of both wood species increased with the heat treatment temperature. The average sound absorption coefficients of untreated and heat-treated poplar samples were approximately 0.16 and 0.18; whereas for beech wood the corresponding values were approximately 0.15 and 0.16. The average sound transmission losses of untreated and treated poplar were approximately 22.7 and 24.0 dB, for the untreated and treated beech samples were 17.3 and 20.7 dB respectively.

Olive tree pruning waste represents a significant agricultural byproduct in Mediterranean regions. It can be regarded as a sustainable and cost-effective alternative resource to other traditional materials for buildings. It is necessary to evaluate the flammability of these materials, according to building regulations. In this preliminary study, several fire-retardant coatings were applied to the materials obtained from olive leaves mixed with a natural adhesive. The coatings included cement-based layers, hydraulic lime, gypsum plaster, intumescent varnishes containing phosphate-based compounds, and graphene-based paints. Treated samples were subjected to flame spread tests to determine their fire resistance properties according to Standard EN ISO 11925-2. The potential of using olive leaves waste as a building material when combined with appropriate fire-retardant coatings is highlighted. The findings suggest that such treatments contribute to mitigating fires and promote the sustainable use of agricultural byproducts in buildings. By applying the coatings, the fire resistance increases significantly compared to untreated samples. The ceramic coatings provided the highest level of protection by reducing the flame spread rate and increasing the time to ignition. Additionally, the treated samples exhibited increased char formation, reducing heat transfer, and delaying combustion. Further research is recommended to optimize the formulations and application methods for large-scale implementation.

Tensile, edgewise, and flatwise bending behaviors of visually graded fir (Abies nordmanniana subsp. bornmuelleriana) boards were investigated through destructive and non-destructive testing to evaluate their mechanical performance and grading accuracy. A total of 724 specimens were prepared and tested in accordance with EN 408 standards. Knot diameter ratios (narrow, mean, and parallel) were used to establish three visual grading methods. Vibration-based (PLG, Hitman) and time of flight (ToF) (Microsecond Timer, Ultrasonic Timer, and Sylvatest Duo) techniques were used for non-destructive evaluation (NDE), along with screw withdrawal tests. The results showed that although the vibration method had lower dynamic modulus of elasticity (MOEd) values ​​than the ToF method, it provided stronger correlations with tensile and bending properties. The mean and parallel knot diameter ratios provided more reliable grading results than the narrow ratio. Tensile strength was more affected by defects than bending strength, and the flatwise bending method consistently produced the highest strength values. The adjustment from global to local MOE reduced modulus values below 9000 MPa, resulting in lower strength class assignments. Overall, the vibration-based NDE method proved the most effective for predicting lumber quality, and the flatwise bending test emerged as a viable alternative to tension and edge bending methods for structural grading.

To address the loosening of mortise and tenon joints in solid wood chairs caused by prolonged use and wood expansion and contraction, this study proposes a reinforcement method using 3D-printed connectors based on polyethylene terephthalate-1,4-cyclohexanedimethanol (PETG) filament. First, the influence of key process parameters (extrusion extent, nozzle travel speed, and nozzle temperature) on the mechanical properties of PETG models was analyzed. Subsequently, based on the optimized process parameters, reinforcement connectors with rib structures were designed and 3D printed. The reinforcement effectiveness was evaluated by comparing the ultimate load of mortise and tenon joints with and without the reinforcement connectors. Results indicated that with the increase of extrusion extent and nozzle temperature, and the decrease of nozzle travel speed, the ultimate strength and Young’s modulus of PETG models increased, improving their mechanical properties. The optimal process parameters were determined as follows: extrusion extent of 105%, nozzle travel speed of 70 mm/s, and nozzle temperature of 250 °C. After installing the reinforcement connectors, the average ultimate load of the mortise and tenon joints reached 445.7 N, which was 34.9% higher than that of joints without reinforcement, demonstrating that the 3D-printed connectors effectively reinforced and protected the mortise and tenon joints.