Strength Development and Durability of Metakaolin Geopolymer Mortars Containing Pozzolans under Different Curing Conditions

This study presents the strength development and durability of heat and non-heat-cured geopolymer mortars (GMs) produced using metakaolin (MK), ground granulated blast-furnace slag (GGBFS), silica fume (SF), ground calcined perlite (GCP), raw perlite (RP), potassium hydroxide (KOH), sodium metasilicate (Na2SiO3), standard sand, and tap water. An optimal combination of MK with various pozzolans and constant solid/liquid and alkaline activator ratios were determined. It was found that the GMs, including MK and GGBFS with a 1.45 solid/liquid ratio and 2.0 alkaline activator ratio, resulted in compressive strength at 88 MPa. Analysis of GMs was performed using scanning electron microscopy (SEM), EDX (Energy Scattered X-ray Spectrophotometer), and X-ray diffraction (XRD). According to the results obtained, mainly alumino-silicate-based formation, potassium from KOH solution, and calcium from GGBFS were determined. The SEM images showed that the grains with high silica content, approximately 6–7 µm in size, are quartz crystals and embedded in the gel structure. The heat-cured GMs were exposed to MgSO4, Na2SO4, and HCl solutions for the durability tests. The strength of the heat-cured GMs was higher than the non-heat-cured GMs, and the durability of the heat-cured GMs was found as sufficient. The use of pozzolans in GMs resulted in improvements in terms of strength and durability.