The effect of high temperatures up to 700 degrees C on compressive strength and water absorption of two alkali-activated aluminosilicate composites (one of them with river sand aggregates, the second crushed sand aggregates) and ordinary Portland cement (OPC) concretes is analyzed in this paper. Binding geopolymer material was obtained after grinding the Elazig Ferrochrome slag (EFS) as fine as cement and alkaline activating with chemical materials (NaOH-Na2SiO3). Geopolymer concrete samples were produced by using this binding material with aggregates. Produced concrete samples were exposed to temperature for 1 hour, after reaching the maximum temperature. Fire resistance and water absorption of geopolymer and OPC concrete samples was obtained experimentally. Compressive strength of river aggregates and crushed sand aggregates concrete increased at 100 and 300 degrees C temperatures compared to unexposed samples, and the maximum compressive strength for these geopolymer concrete sample was obtained at 300 degrees C. Water absorption of all concrete samples increased at 700 degrees C temperature compared to unexposed samples. But there appeared to be a slight decrease of water absorption in the all concrete samples up to 300 degrees C temperatures compared to unexposed samples. Scanning electron microscopy and XRD tests were also conducted to examine microstructure and mineralogical changes during the thermal exposure.