Performance of geopolymer high strength concrete wall panels and cylinders when exposed to a hydrocarbon fire

•Geopolymer concretes have no signs of spalling when exposed to a hydrocarbon fire.•Residual strength of 60% was maintained after fire exposure.•Geopolymers have excellent fire resistance due to low thermal incompatibility. This study presents an investigation of the effect of hydrocarbon fire exposure on the residual compressive strength properties of geopolymer concrete panels and cylinders. Gladstone flyash was utilized as the binder whilst the alkaline solution/fly-ash ratio and sodium silicate to sodium hydroxide (Na2SiO3/NaOH) ratio was 0.4 and 2.5 respectively. The compressive strength at the test date was 64MPa. Two different cylindrical specimens’ sizes (150 and 100mm diameter×300 and 200mm high) were exposed on all sides to the hydrocarbon fire scenario for 120min whilst panels of 1075×1075×200mm were exposed on one side for the same time duration. Results showed that no significant spalling occurred in any of the specimens and the mass loss during heating was between 2.70 and 4.65% respectively which was attributed due to moisture loss. Low differential gradients and thermal incompatibility between the geopolymer paste and aggregates provides geopolymer concrete with superior spalling resistance than Ordinary Portland cement concrete. Residual compressive strength testing showed that the panels maintained approximately 60% of their initial compressive strength indicating that geopolymer concrete specimens can maintain sufficient load bearing capacity in the event of fire exposure. The residual strength profiles indicated that specimen size effect was also exhibited with the remaining strength of the cylinders being approximately 10 and 20% for the 100mm and 150mm dimeter specimens respectively. The dull red color exhibited in all specimens after fire testing indicated the presence of high iron content in the geopolymer matrix. Insitu temperature analysis showed that the geopolymer concrete had excellent heat resistance capabilities with temperatures at a depth of 100mm from the exposed surface ranging between 39°C and 45°C after 30min of fire exposure even though the temperature at exposed surface exceeds 1000°C. This is reinforced by the fact that the geopolymer has a high heat storage capacity as indicated by the geopolymers lower thermal diffusivity than OPC concrete.