Fire behaviour of waterborne intumescent coatings on timber substrate for bushfire exposure

• Published in: Fire safety journal 2023-10, Vol.140, p.103836, Article 103836
• Main Authors: Baena, Juan Carlos, Wang, Cheng, Kabir, Imrana I., Khalid, Arslan, Nazir, Muhammad Tariq, Yuen, Anthony Chun Yin, Ahmad, Faiz, Yeoh, Guan Heng
• Format: Article
• Language: English
• Subjects: Ammonium polyphosphate; Bushfire attack level; Expandable graphite; Intumescent coating; Timber substrate; Waterborne acrylic resin
• ISSN: 0379-7112
• DOI: 10.1016/j.firesaf.2023.103836

The fire behaviour of radiata pine timber, treated with intumescent coatings and exposed to heat flux conditions equivalent to a high-risk bushfire attack level (BAL) is investigated. The experiment is designed for coated timber exposed to bushfire attack levels greater than 19 kW/m2 and up to 29 kW/m2 (BAL-29) in accordance with AS 3959. The timber was coated with a DFT of 400 μm of the developed intumescent formulations based on expandable graphite (EG), ammonium polyphosphate (APP) and a waterborne acrylic resin with high adhesion strength. The coated timbers were tested according to AS3959, for a BAL-29 rating, using a cone calorimeter at 25 kW/m2 for 10 min. Most of the coated samples reported a substantial reduction in the peak heat release rate (p-HRR) and average HRR with values not greater than 100 kW/m2 and 60 kW/m2, respectively. These results satisfy the requirements for bushfire-resistant timber at BAL-29 rating. Formulation 4 (F4), with EG:APP ratio of 3:1 and resin content of 45 wt% was identified as the most cost-effective formulation. Coatings with high loading of EG and APP provided the best fire protection to the timber substrate, however, a larger char with a less compact structure is formed. •High adhesion strength was reported by the waterborne acrylic resin.•A cost-effective coating with 3:1 EG:APP ratio and 45 wt% resin was identified.•A substantial reduction in p-HRR was reported by the coated timber.•Key factors affecting the performance of the intumescent coating were identified.