Engineered wood products (EWPs) are being increasingly used as construction materials. EWPs are currently being made using synthetic adhesives or metal fasteners, which lead to poor recyclability and reusability. Therefore, this review paper focused on emerging adhesive- and metal-free assembling techniques including wood dowels, rotary-dowel welding, wooden nails, and dovetail joining as alternative ways of making prefabricated EWPs. This will contribute towards green construction and optimising the building process to minimise its negative impact on the environment and its inhabitants, while maximising the positive aspects of the finished structure. The respective advantages and shortcomings will be compared with those of equivalent EWPs. In general, the dowel-laminated timber (DLT) provides sufficient load-bearing capacity and even better ductility than EWPs of equivalent size, but its relatively low stiffness under a bending load limits its application as a structural element. Optimised manufacturing parameters such as dowel species, dowel spacing, dowel diameter, dowel insertion angle, dowel shape, etc. could be studied to improve the stiffness. The improved mechanical properties and tight fitting due to set-recovery of densified wood support its use as sustainable alternatives to hardwood dowels in DLT to overcome problems such as the loosening of connections over time and dimensional instability. The rotary welding technology could also enhance the strength and long-term performance of dowel-type joints, but its poor water resistance needs further investigation. The main obstacles to implementing DLT products in the market are missing technical information and design guidelines based on national codes.

Thermo-hydro-mechanical (THM)-densified timber is rarely used in construction, although its mechanical properties are in many cases excellent. The main reason for its rare use is set-recovery, which reduces the degree of densification over time so that the mechanical properties deteriorate. Our knowledge of the long-term creep of densified timber is insufficient and a full understanding of its long-term behaviour is still lacking. The purpose of this study was to examine the behaviour under long-term loading of Scots pine sapwood densified in an open system at 170–200 °C. The influence of the THM densification process on the creep properties was studied on (1) unmodified specimens, (2) THM-densified specimens, (3) THM-densified specimens that had been further thermally treated, and (4) low-molecular-weight phenol-formaldehyde resin-impregnated and THM-densified specimens. All specimens were loaded at 20 ± 2 °C and 65 ± 5% relative humidity for 14 days under 3-point bending at 35% of the short-term ultimate load, and the bending deformation was registered. The THM densification doubled the density, causing a significant increase in the modulus of rupture but no change in the modulus of elasticity, and reduced the equilibrium moisture content and creep compliance. Post-thermal modification and resin impregnation improved the dimensional stability and further reduced the creep compliance in bending. The results demonstrate that THM densification combined with resin-impregnation or thermal modification reduces the creep of Scots pine timber under a long-term bending load in a constant climate.

Thermo-hydro-mechanical (THM) densification is a well-known procedure for improving the properties of low-density wood species, but the long-term behaviour of the densified wood under constant load has not been reported and may restrain its use in construction. This study has investigated the influence of THM densification on the creep behaviour in bending of beech and pine under constant climatic conditions. The specimens were loaded in three-point bending at applied stress level of 35% of the ultimate strength for 14 days at 20 ± 2°C and 65 ± 5% relative humidity (RH), and the bending deformation was registered. The THM densification doubled the density, increased the modulus of elasticity and the modulus of rupture, and reduced the equilibrium moisture content and creep compliance. The results demonstrate that THM densification can be an effective method to improve the short-term and long-term performance of wood in constructions.

This study presents a wood modification process using Fast Pyrolysis Bio-Oil (FPBO) as a fully biobased alternative to conventional, fossil-based and potentially toxic preservatives such as copper salts, organic biocides, and creosote. Standard FPBO was used in the development of 10 formulations, which were systematically characterized in terms of pot life, viscosity evolution, density, and pH. Radiata pine samples were subsequently impregnated using a bench-scale reactor, with specimens prepared in multiple geometries to assess treatment performance across different dimensions. The modified wood was comprehensively characterized with respect to moisture uptake, dimensional stability, density, mechanical strength, fixation efficiency, biological durability, and VOC emissions. Additional screening focused on properties relevant to outdoor applications, including aesthetic appearance and colour uniformity after UV exposure. The results enabled the identification of three top-performing formulations, treatments H, A, and E, which exhibited the most favourable balance between durability, environmental performance, and structural integrity. Overall, the findings demonstrate the strong potential of FPBO-based impregnation as a sustainable, multifunctional, and high-performance alternative for advanced wood protection systems.