Optimization of Curing Parameters of Class C Fly-Ash-Based Alkali-Activated Mortar

The optimum curing temperatures and durations for alkali-activated mortar (AAM) synthesized using five different types of Class C fly ash (FAs) were investigated. The calcium content of the FAs ranged from 21 to 37%. For each FA, three AAM mixtures having different Alk/FA and SS/SH were prepared. Different curing temperatures ranging from 40 to 85°C (104 to 185°F) and curing durations ranging from 4 to 48 hours were investigated. Furthermore, two curing regimes having a constant ambient temperature of 30°C (86°F) and a variable ambient temperature were investigated for a curing duration of 7 days. The compressive strength of each mixture, after being subjected to the different curing regimes, was determined. A statistical model was developed, using the response surface methodology (RSM) approach, to predict the compressive strength of the mixtures. The results showed that AAM mixtures synthesized using FAs that had a relatively high calcium content displayed their highest compressive strengths at a combination of longer curing durations of 48 hours and low curing temperatures of 40 to 55°C (104 to 131°F), while a short curing duration of 16 to 24 hours and high temperatures of 70 to 85°C (158 to 185°F) were preferred for mixtures with relatively low-calcium FAs. The consumed curing energy for each mixture was also measured and correlated to the achieved compressive strength. In addition, different microstructural analysis tests were used to explain the results