Factors affecting the compressive strength of class C fly ash geopolymer

The compressive strength of geopolymer prepared from a class C fly ash (CFA) at different curing conditions and mass ratio of water to fly ash were investigated. The geopolymer was activated with a mixed solution of sodium hydroxide (NaOH) and sodium silicate. The results revealed that the obtained compressive strength was in the range of 11.7 similar to 61.9MPa and the compressive strength decreased with the increment of the mass ratio of water to CFA (W/F). The geopolymer samples with the highest strength were obtained when W/F was 0.30 with proper delay time id before being demoulded and then followed by curing at 60 degrees C for 24h. For geopolymer with lower W/F (0.30), its optimum curing temperature was better not higher than 60C, however, for the higher W/F, the curing temperature was suit to more than 70 degrees C.