Burning Properties of Combined Glued Laminated Timber

Abstract

This study delved into the combustion properties of combined glulam bonded using polyurethane (PUR) and resorcinol-phenol-formaldehyde (RPF) adhesives. The experiment involved three distinct wood species, namely, spruce, alder, and beech, which were combined in homogeneous, non-homogeneous symmetrical, and non-homogeneous asymmetrical arrangements. These species were selected to represent a spectrum, namely, softwood (spruce), low-density hardwood (alder), and high-density hardwood (beech). The varying combinations of wood species illustrate potential compositions within structural elements, aiming to optimize mechanical bending resistance. Various parameters were measured during combustion, namely, the heat release rate (HRR), peak heat release rate (pHRR), mass loss rate (MLR), average rate of heat emission (ARHE), peak average rate of heat emission (MARHE), time to ignition (TTI), and effective heat of combustion (EHC). The findings indicate that incorporating beech wood into the composite glulam resulted in an increase in heat release, significantly altering the burning characteristics, which was particularly evident at the second peak. Conversely, the use of spruce wood exhibited the lowest heat release rate. Alder wood, when subjected to heat flux at the glued joint, displayed the highest heat emission, aligning with the results for EHC and MARHE. This observation suggests that wood species prone to early thermal decomposition emit more heat within a shorter duration. The time to ignition (TTI) was consistent, occurring between the first and second minute across all tested wood species and combinations. Notably, when subjected to heat flux, the glulam samples bonded with PUR adhesive experienced complete delamination of the initial two glued joints, whereas those bonded with RPF adhesive exhibited only partial delamination.

Study of the Influence of Heat Flow on the Time to Ignition of Spruce and Beech Wood

“…Mindykowski [60] used the time to ignition for a piece of wet spruce and compared it to the time to ignition of dry wood to create a model. One of the reasons for their results is that the ignition temperature in the experiments (directly linked to the intercept heat flux) was constant for both the dry and the moist wood [13,55,[61][62][63][64].…”

“…Images of the samples exposed to a 5 kW radiant panel heat are presented in Figure 12, and those exposed to a 10 kW radiant panel heat are shown in Figure 13. Kytka et al [64] carried out an experiment involving three distinct wood species, namely spruce, alder, and beech, which were combined in various arrangements. Various parameters were measured during combustion, namely time to ignition (TTI), mass loss rate (MLR), the heat release rate (HRR), the peak heat release rate (pHRR), the peak average rate of heat emission (MARHE), the effective heat of combustion (EHC), and the average rate of heat emission (ARHE) [50].…”

“…The experiments were conducted in a furnace at five isothermal temperatures (240 • C, 270 • C, 300 • C, 330 • C, and 360 • C) with four cube sizes (5 mm, 10 mm, 15 mm, and 20 mm). The point of pyrolysis was identified at 360 • C. After pyrolysis, a combination of internal heating and heterogenous oxidation reactions on the surface lead to ignition and combustion.Kytka et al[64] carried out an experiment involving three distinct wood species, namely spruce, alder, and beech, which were combined in various arrangements. Various parameters were measured during combustion, namely time to ignition (TTI), mass loss rate (MLR), the heat release rate (HRR), the peak heat release rate (pHRR), the peak average rate of heat emission (MARHE), the effective heat of combustion (EHC), and the average rate of heat emission (ARHE)[50].…”