Glulam beams: Performance of PVA and PUR adhesives on bending strengths of locally selected Nigerian timber species

The applicability of structural timber to construction is due to its desirable qualities such as lightweight, aesthetics and eco-friendliness. However, continuous use of timber for structural purposes comes with the challenge posed by the anisotropic nature of various timber species. Advanced societies have developed and modified their sawn timber species in form of glue-laminated structural members such as beams, columns, joist etc. Nigeria timber species are yet to be fully explored along glued-laminated beams production. This paper assesses the suitability of three selected Nigerian timber species namely; Gmelina Arborea (ML), Terminalia superba (AF) and Pycnanthus angolensis (AK) for production of glued-laminated (glulam) beams. They are locally known respectively as Melina (ML), Afara (AF) and Akomu (AK). The applicability and glue-ability of the glues and their ultimate effect on the flexural strength were investigated through the use of two different types of glue components namely; polyvinyl acetate (PVA) and polyurethane (PUR) glue. The physical properties of the timber species such as moisture content (MC) and densities were determined using BS EN 408. The beams produced which are 1680mm by 150mm by 120mm in dimension were subjected to two points loading system to determine their flexural strengths and failure loads in accordance with ASTM D-198. The flexural strengths results indicated that Pycnanthus angolensis offered most resistance to bending loads with an average flexural strength value of 16.04N/mm2 when PUR glue was used and 13.04N/mm2 when PVA glue was used. The ANOVA result showed that glue types have significant effect on the flexural strength at confidence level of 95%. It was concluded that Pycnanthus angolensis is most suitable for structural applications. PUR is considered the better glue in terms of strength and glue-ability while PVA glue is considered better in terms of workability and applicability based on almost perfect glue line integrity achieved