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 hours 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.