At 1000 oC, the residual strengths were very low for all the tested mixtures. The GPH, GPN and OPC concrete samples retained average residual compressive strengths of 18%, 16% and 11% respectively. The severe strength loss of the specimens at this tem- perature occurred mainly because of the extensive cracking of the specimens. Furthermore, there was spalling of substrates in the OPC concrete specimens. The OPC concrete specimens suffered disintegration because of the greater loss of bonding between the binder and aggregates as a result of complete dehydration. The high thermal strain in the samples due to rapid heating rate of fire is the main contributing factor of the strength loss in concrete at this temperature. Generally, the less cracking and spalling, and higher residual compressive strength of fly ash based geopolymer concrete as compared to OPC concrete indicate its better perfor- mance after high temperature fire exposure. This observation is consistent with the higher fracture energy of geopolymer concrete as compared to OPC concrete of similar compressive strength, as shown in a previous study [31].