A comparative investigation on the freeze–thaw resistance between dry-cured alkali-activated fly ash/slag and portland cement mortars

The present investigation analyses the freeze–thaw resistance of alkali-activated fly ash and/or ground granulated blast furnace slag (GGBFS) binders compared to ordinary Portland cement (OPC). The experimental program included 20 series of mortars of alkali-activated fly ash, alkali-activated slag, alkali-activated fly ash/slag, CEM I 42.5, and CEM I 52.5. Fly ash and slag were activated with Sodium Hydroxide (NaOH) and Dry cured at 100 °C for 72 h whereas the OPC mortars were water-cured for 28 days. After completing their curing period, the mortars were subjected to 100, 200, and 300 freeze–thaw cycles followed by testing and analysis of water absorption, porosity, flexural strength, compressive strength, and mass loss. The results reveal that dry-cured alkali-activated mortars show lower resistance to freeze–thaw damage and higher water absorption, porosity, and mass loss than OPC mortars. GGBFS mortars demonstrated significant deterioration after prolonged exposure, whereas OPC mortars, particularly CEM I 52.5R, showed remarkable self-healing properties. These findings indicate that the use of alkali-activated mortars needs to be investigated further to address their low performance under cyclic freeze–thaw stress in order to enhance their usability in cold-weather environments.