Fire-induced spalling in hybrid polyethylene fiber-reinforced engineered cementitious composite panels

Polyethylene (PE) fibre-reinforced engineered cementitious composites (ECC) offer high ductility and durability, however concerns over fire performance, particularly spalling resistance, continue to limit their adoption. This study evaluates single and hybrid PE fibre-reinforced ECC with high-volume slag and MgO under fire exposure, examining spalling resistance at both material and structural scales. Key test parameters include PE fibre length (9, 12, 18 mm), fibre type (single or hybrid with polypropylene (PP) and basalt fibre), and panel size (300 ×300 mm, 200 ×200 mm, 100 ×100 mm) and thickness (20, 50 mm). A novel 1-directional (1-D) spalling test is also developed and compared with a traditional 3-directional (3-D) furnace test. Material-scale tests showed that replacing 12 mm, 0.75 % PE fibre with basalt improved strength retention at elevated temperatures by approximately 5–7 %, achieving a total retention of 37–40 %. However, large-scale tests revealed poor spalling resistance with this mix as full-thickness spalling occurred in 300 × 300 × 50 mm panels. Spalling resistance improved with longer PE fibres (18 mm) or the addition of PP fibres, with a hybrid mix (12 mm 0.3 % PP, 1.25 % PE, 0.75 % basalt) demonstrating superior performance. Further analysis indicated that fibre melting may not be the primary mechanism for spalling resistance; rather, fibre distribution and bonding with the matrix are critical for forming an effective network for vapour pressure dissipation.