Small-Diameter Scots Pine and Birch Timber as Raw Materials for Engineered Wood Products
Authors
Henrik Heräjärvi
The Finnish Forest Research Institute
Aki Jouhiaho
TTS Institute
Vesa Tammiruusu
Metsähallitus
Erkki Verkasalo
The Finnish Forest Research Institute
Abstract
In the future, the building industries will need predictable, homogeneous and cost-competitive wood products with structural safety in increasing quantity and quality. This can be provided by, e.g., breaking solid wood and reconstructing the structure in a way that the degrading influence of knots, cracks, decay and other natural irregularities in wood will be eliminated. Beams, panels or boards made by this principle are called the engineered wood products (EWP). The purpose of this study was to investigate the possibilities to utilize small-diameter Scots pine and birch timber for production of EWPs that are reconstituted of strands. The wood technological characteristics of the tree species used in these products worldwide were studied based on the literature, and the findings were compared to the characteristics of domestic woods. In addition, test specimens were manufactured from domestic raw materials of Scots pine and birch species, and tested in order to examine the differences between woods from young trees from the first commercial thinnings and top sections of mature trees from final cuttings as a raw material. According to the literature review, the average basic density and, consequently, many mechanical properties of pine and birch grown in Finland do not markedly differ from those of the numerous foreign species used for EWPs. The empirical tests indicated that beams (air-dry density ca. 620-800 kgm-3) with relatively auspicious static stiffness (ca. 6000-8500 MPa) and bending strength (ca. 32-42 MPa) could be manufactured from timber equal to or smaller than pulpwood in diameter.
