Adhesive Strength and Fire Resistance of Structural Glued Laminated Timber

In Japan, resorcinol-formaldehyde (RF) resin and phenol-resorcinol-formaldehyde (PRF) resin are regarded as heat-resistant adhesives used for manufacturing quasi-fireproof structural glued laminated timber (GLT). Other adhesives can be used but have to be approved individually by Japanese Agricultural Standards. Adhesive strength generally decreases with rising temperatures, and this affects the fire resistance of GLT. In order to clarify this relation quantitatively, structural GLT beams using different types of adhesives were made and their fire performances were evaluated. The adhesive shear strengths in laminated wood and dynamic viscoelastic properties of resin films at elevated temperature were evaluated. Adhesives used were PRF resin, six kinds of aqueous polymer isocyanate (API) resin and poly(vinyl acetate) (PVAc) resin. The PRF-GLT beams and API-GLT beams exhibited the fire performance required for 45-minute fire test. The adhesive shear strengths were RF > API > PVAc at 100, 150 and 200 C. In particular, PVAc strength decreased drastically, and the adhesive strength at 150 C was zero. The dynamic viscoelastic properties of resin films supported these results. The fire resistance degradation of GLT beam was dominated by the loss of lamina and it depended on the adhesive shear strength. According to the analysis of temperature profiles in GLT beam during the fire test, a GLT beam specimen is expected to be 45-minute quasi-fireproof required for the Building Standard Law of Japan if the adhesive shear strength at 200 C is enough to keep lamina from dropping.

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