Combustion performance of engineered bamboo from cone calorimeter tests Shanghai Research Institute of Building Sciences University of Pittsburgh Dr. Qingfeng Xu and Dr. Kent A. Harries

Outline Introduction Materials and methods Combustion properties Comparison with typical timber Conclusion

Introduction Combustion properties of engineered bamboo are critical to the safety of bamboo building construction Few studies of the fire performance of engineered bamboo are available. 3

4 Introduction In this study: Two typical engineered bamboo – laminated bamboo and bamboo scrimber – evaluated using cone calorimeter tests Laminated bamboo 4 Bamboo scrimber

Outline Introduction Materials and methods Combustion properties Comparison with typical timber Conclusion

Sample size: 100mm×100mm×50mm, (1mm tolerance) Materials and methods Specimens - manufactured from Moso bamboo strips with polyurethane adhesive Sample size: 100mm×100mm×50mm, (1mm tolerance) laminated bamboo bamboo scrimber heat flux ⊥ to grain ∥ to grain density 677 kg/m3 1071 kg/m3 MC 10.5% 10.9% 6

7 Materials and methods Cone Calorimeter Few tests are available for bamboo, however cone calorimeter tests are often used to measure the combustion characteristics of timber exposed to constant external heat flux. Such tests correlate well with results from full- scale room fires (Chung 2010; Grexa and Lubke 2001; Lee et al. 2011; Spearpoint and Quintiere 2001). Compared to full-scale tests, cone calorimeter tests are a convenient and less- expensive means of obtaining charring properties of timber, treated lumber and engineered wood products (White and Tran 1996). 7

8 Materials and methods Cone Calorimeter Test Protocol Heat flux： 25 kW/m2, 50 kW/m2 and 75 kW/m2 Temperature： 588 ℃, 757 ℃, and 853 ℃ Exposure time： 5 to 60 minutes in 5 minute increments 8

Outline Introduction Materials and methods Combustion properties Comparison with typical timber Conclusion

10 Combustion properties Time to Ignition Time to ignition (tign) is the time required to establish sustained flaming on the sample surface due to heat radiation and is an important factor for evaluating the burning behaviour of materials. tign-1/2 is proportional to the imposed heat flux. Both materials are thermally thick. Critical heat flux, ignition temperature, and thermal response parameter are estimated. 10

11 Combustion properties Time to Ignition Laminate-perpendicular Laminate-parallel Scrimber-perpendicular Scrimber-parallel calorimeter heat flux (kW/m2) 25 50 75 time to ignition (seconds) 132 18 9 147 28 12 189 33 15 313 59 23 Critical heat flux (kW/m2) 6 7 8 Ignition temperature (oC) 297 320 340 Thermal response parameter (kWs1/2/m2) 235 269 376 Laminated bamboo (grain ⊥ heat flux) is the most flammable. Laminated bamboo (grain ∥ heat flux) and bamboo scrimber (grain ⊥ heat flux) are similar. Bamboo scrimber (grain ∥ heat flux) is the least flammable. 11

12 Combustion properties Heat Release Rate Heat release rate is defined as the heat released per unit area for samples under a constant imposed heat flux, is the most important input parameter required in zone and field models since it controls the characteristic of the fire and indicates the contribution to the development of a fire. Laminated ⊥ Laminated ∥ Scrimber ⊥ Scrimber ∥ The heat release rate increases suddenly at ignition. A second peak was observed before the end of test at higher heat flux levels. The average and peak heat release rates of bamboo scrimber (grain ∥ heat flux) were lower than others. 12

13 Combustion properties Mass Loss Rate Mass loss rate is the rate of change of sample mass during the burning process. The mass loss rate is closely related with the heat release rate, specific extinction area, and CO yield. A lower mass loss rate is indicative of a lower propensity for flame spread. Laminated ⊥ Laminated ∥ Scrimber ⊥ Scrimber ∥ The mass loss rate increased sharply when the specimen ignited and decreased gradually thereafter eventually stabilising at a near-zero rate. The mass loss rate increased with increasing heat flux and was slightly greater for bamboo scrimber (due to high resin content). 13

14 Combustion properties Specific extinction area – index for smoke production Laminated bamboo (heat flux ⊥) exhibited notably higher values. Effective heat of combustion – indicates burning intensity This value increased marginally with increasing heat flux. Results indicating incomplete combustion at low level of heat flux. Laminate-perpendicular Laminate-parallel Scrimber-perpendicular Scrimber-parallel Calorimeter heat flux (kW/m2) 25 50 75 Specific extinction area (m2/kg) -5 1 43 2 -3 27 26 -1 15 Effective heat of combustion (MJ/kg) 11 13 12 8 9 7 10 CO yield (g/kg) 23 78 58 76 CO2 yield (g/kg) 960 1019 981 688 950 936 722 923 861 553 849 842 14

Post-ignition large flames (100-200 s) Gradual burn to end of test Combustion properties Charring behaviour Smoke decreased sharply and flame expanded immediately at ignition. A large flame last about 100 to 200 seconds, and then degraded gradually to an essentially steady state. Post-ignition large flames (100-200 s) Gradual burn to end of test Initial heating Ignition 15

16 Combustion properties Charring layers Laminated bamboo (⊥) Bamboo scrimber (⊥) Bamboo scrimber (∥) 16

17 Combustion properties Charring depth 25 kW/m2 50 kW/m2 75 kW/m2 Charring depth increased with increasing heat flux and exposure time. Charring depth is approximately linear with exposure time. Charring depths for bamboo scrimber are much smaller than those for laminated bamboo. 17

18 Combustion properties Charring rate Laminated ⊥ Laminated ∥ Scrimber ⊥ Scrimber ∥ Charring rate was generally observed to increase with heat flux, and decrease with fire exposure time. Charring rate tended to be essentially constant when the fire exposure time exceeded 30 min. Charring rates for bamboo scrimber are smaller than those for laminated bamboo. 18

19 Combustion properties Charring rate prediction The average charring rate for specimens exposed to a heat flux of 50 kW/m2 for 30–60 min are proposed to be representative for use in fire design (Tsantaridis and Ostman, 1998). Both EC and Australian standards underestimate the average charring rates for laminated bamboo but are reasonably predictive of bamboo scrimber. Laminate-perpendicular Laminate-parallel Scrimber-perpendicular Scrimber-parallel Average char rate (30-60 min) 0.76 0.44 0.58 EC 5 (EN1995-1-2 2004) predicted char rate 0.65 (softwood) 0.65 (softwood) 0.50 (hardwood) 0.50 (hardwood) AS1720.4 (AS1720.4 2006) predicted char rate 0.57 0.47 19

Outline Introduction Materials and methods Combustion properties Comparison with typical timber Conclusion

Comparison with typical timber Laminated bamboo and Bamboo Scrimber placed in context with typical softwood (Douglas Fir) and hardwood (Merbau) (Xu et al. 2015) laminated bamboo bamboo scrimber Douglas Fir Merbau ⊥ ∥ density (kg/m3) 677 1071 470 860 time to ignition (sec.) 18 28 33 59 23 148 critical heat flux (kW/m2) 6 7 8 40 ignition temp. (oC) 297 320 340 478 643 peak heat release rate (kW/m2) 235 239 231 204 151 110 time to peak heat release rate (sec.) 52 56 82 55 248 average heat release rate in 5 min. (kW/m2) 135 121 118 116 61 30 specific extinction area (m2/kg) 1 -3 2 -5 9 effective heat of combustion (MJ/kg) 13 11 10 4 CO2 yield (g/kg) 1019 950 923 849 862 390 charring depth at 30 min (mm) 25 27 16 19 32 14 average charring rate 30-60 min (mm/min) 0.76 0.44 0.58 1.11 0.41 21

Outline Introduction Materials and methods Combustion properties Comparison with typical timber Conclusion

Conclusions Bamboo scrimber is more resistant to fire reflecting the fact that it is almost twice as dense as laminated bamboo. The orientation of the grain has negligible influence on fire performance. Bamboo scrimber performed comparably, if not marginally better, than typical softwood (Douglas Fir) Laminated bamboo exhibited poorer fire performance than typical softwood (Douglas Fir). 23

References Laminated Bamboo and Scrimber: Xu, Q., Chen, L., Harries, K.A., and Li, X. (2017) Combustion performance of engineered bamboo from cone calorimeter tests, European Journal of Wood and Wood Products, Vol. 75, pp 161-173. Cone Calorimetry, Softwood and Hardwood: Xu, Q., Chen, L., Harries, K.A., Zhang, F. and Liu, Q. (2015) Combustion and charring properties of five common constructional wood species from cone calorimeter tests, Journal of Construction and Building Materials, Vol. 96, pp 416-427. 24