Measuring the char rate of cross laminated timber in an intermediate-scale furnace

Ten experiments were conducted in the Universityof Canterbury intermediate-scale fire resistancefurnace in an attempt to measure the charring rate ofRadiata pine cross laminated timber. The furnace wascontrolled to follow the ISO 834 standard fire curve.The furnace was unable to sustain the fast initialclimb in temperature but from approximately 10 minonwards closely matched the standard fire curve.The charring rate was measured using two methods.Thermocouples were implanted between 10 and 75mm from the exposed surface that measured thetime temperature profile within the sample. The chartemperature was defined as 300 °C and the time takento reach this point used to obtain the char rate. Usingthis method the char rate of the CLT was measured as0.83 ± 0.20 mm/min. After the experiment the charlayer was removed and manual measurements takento obtain another measure of the char rate. Thistechnique measured the CLT char rate to be 0.83 ±0.11 mm/min. Results from this work are consistentwithin experimental error with AS 1720.4 [9] andKlippel et al. [6] although the recent work by SP [10]suggests that charring rates could be higher in naturalfires.An increased char rate applied to subsequent layersrepresents the effect of delamination observedby Frangi et al. [2]. An attempt to imitate thedelamination due to failure of the adhesive layer wascarried out and it was found that the timber fibresfailed before the adhesive. Because of this observationit is thought that delamination of CLT using a one-component polyurethane adhesive is not likely to bean issue in fire conditions but further experiments areneeded to confirm this.A number of areas of further research have beenidentified and given this research was conducted in anintermediate-scale furnace then care should be takenapplying the results in the design of actual buildingsthat use CLT panels.