The Effect of Alkaline Concentration and Curing Temperature on the Durability of Fly Ash Geopolymer Mortar

In this study, fly ash was used to synthesize geopolymer mortar by using an activating solution prepared from a different concentration of NaOH and a highly viscous Na-silicate. The NaOH concentration prepared were 8M, 12M, and 14M. The prepared geopolymers were cured at different temperatures (ambient, 40°C, and 60°C) and were studied to determine their strength, bond structure, mechanical properties, and resistance in an acidic and salty environment using an accelerated durability test. FTIR results showed distinctive peaks of aluminosilicate bond structures. Maximum strength was achieved for 14M samples cured at room temperature. Higher alkalinity resulted in higher compressive and flexural strength and lower water absorption. Lower water absorption capacity and higher resistance to the extreme environment were achieved for samples cured at higher temperatures and higher molarities. The maximum mass loss was 10.9% for 8M cured at ambient temperature exposed to an acidic environment.