Fig. 4 to 6 show the sensitivity of Class F fly ash-based geopolymer concrete to the curing condition. Up to 2 days, the increase in compressive and tensile strength is almost proportional to the duration of the heat curing. A minimum of 48 h (2D curing) is
required in order to reach a compressive strength similar to the one of the reference structural OPC concrete. The scatters in the compressive and tensile strengths are reasonably low (Table 4). Fig. 5 shows that the elastic modulus is close to its maximum value of 25 GPa after 1 day of heat curing and does not change significantly with further, extended,heat curing.