Effects of the nature of chemical activator on the compressive strength of calcined clay geopolymer mortar

Low purity kaolin clay is presently receiving attention as a promising aluminosilicate source that has the potential of extending the application of geopolymers because of its global abundance and low embodied energy, but its strength performance depends substantially on the calcination process, mineralogy of the clay, type and proportion of chemical activator etc. This work focuses on comparing the compressive strength of calcined clay geopolymer mortars activated by three forms of chemical activators. Three groups of geopolymer mortar mixes were prepared and tested, group one utilizes
sodium hydroxide solution (NaOH) prepared by adding 68% water to the pellets 24 hrs prior to mixing, group two based on sodium silicate solution derived by adding 55.9% water to sodium metasilicate pentahydrate (Na2SiO3.5H2O) 24 hrs prior to mixing, while the group three mixes were activated with industry produced Na2SiO3 solution that has 54.5% solid component. The results show that high compressive strength is achieved by developing calcined clay geopolymer mortar using high viscosity industry produced sodium silicate solution, while very low strength is achieved by utilizing sodium silicate containing chemically bounded water. The result further shows that the
compressive strength of the geopolymer mortars are enhanced by sealed curing of the samples.