Abstract :
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.
