Potassium alkali concentration and heat treatment affected metakaolin-based geopolymer

Geopolymers prepared using KOH and K2SiO3 alkali solution instead of the more common NaOH and Na2SiO3 are reported. The influence of KOH concentration, curing temperature and heat treatment on the properties of metakaolin-based geopolymers were studied. The KOH concentrations were varied at 6, 8, 10, 20, 30 and 40 M, the K2SiO3/KOH ratios used were 1 and 1.5 and curing temperatures of 40 °C and 60 °C for 24 h were applied. Results showed that geopolymer with 10 M KOH, cured at 40 °C, 24 h and heat treated at 550 °C gave the highest compressive strength at 28 days. The heat treatment process caused the porosity of geopolymer increased because water was eliminated from the geopolymer structure by the applied heat, therefore, the density decreased whereas the water absorption and the porosity of geopolymer specimens increased. The microstructure of heat-treated specimens showed more mature geopolymer matrix than that of non heat-treated ones leading to higher compressive strength in the former geopolymers and had ceramic-like property.