Influence of curing schedule on the integrity of geopolymers

The curing at ambient and controlled relative humidity (RH) with mild heating (40–60°C) of a metakaolinite-based geopolymer of molar ratios Si/Al and Na/Al of 2 and 1 respectively was studied. To obtain these geopolymers in a crack-free state, rapid drying during curing should be avoided. Curing at a lower RH (e.g. 30%) is preferable to that at a higher RH (e.g. 70%). Curing in an RH oven does not offer any advantage over curing at ambient followed by mild heating (40–60°C) in sealed containers. The compositions of the geopolymers were then varied somewhat to see the effect on open porosity for the same curing schedule. The compositions with Si/Al = 1.86 and Na/Al < 0.8 had an increased tendency to crack, probably due to the larger water loss during curing. The lowest open porosity of <1% was obtained for a geopolymer of composition Si/Al = 2.14 and Na/Al = 0.87, but this developed some cracks after 1 year. However, the geopolymer of composition, Si/Al = 2, Na/Al = 1, on which most of the work was carried out when cured correctly did not crack even after 1 year.