Curing Time and Temperature Effect on the Resistance to Wet-Dry Cycles of Fly Ash Added Pumice Based Geopolymer

The effects of curing regimes varying combinations of temperatures (ambient, 60 °C, 75 °C, 90 °C, 105 °C) and durations (4h, 8h, 24h, 48h, 96h, 168h) on the performance of fly ash added pumice based geopolymer pastes were investigated in this study. The precursor raw material consists of 70% pumice dust and 30% fly ash (FA). Alkali activator was prepared by mixing 10M sodium hydroxide (SH) solution and liquid sodium silicate (SS) in the ratio of SS/SH=2. Activator to precursor ratio was fixed as 0.45. Compressive strengths were determined at the 28 days of age as well as after exposure 5 wetting-drying (w-d) cycles. In addition, Fourier Transform Infrared Spectroscopy (FTIR) tests were conducted on the fresh and hardened geopolymer pastes in order to examine the effect of curing conditions to the structural changes and reaction products. The results show that in the case of 60 °C and 75 °C, the strength of the w-d conditioned samples increased steadily as the curing time increased. However, longer curing times of more than 24 hours are not beneficial for high curing temperatures (90 °C and 105 °C). The maximum strength after the w-d cycles is obtained for the curing conditions of 60°C/168h (74.4 MPa). Also, FTIR analysis confirmed that the hardened geopolymer paste transformed into a more coordinated structure and soluble carbonate compounds were reduced at 60 °C and 168 hours curing condition.