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.