Investigation of the Properties of Metakaolin-Based Geopolymer Materials Using Ferrisilicates as Additives Synthesised in Sodium Hydroxide Solution or Distilled Water

The main objective of this work is to investigate the behaviour of ferrisilicates prepared from hematite and two silica sources (rice husk ash and silica fume) on the compressive strength of geopolymer materials. Some ferrisilicates were synthesised in 2M sodium hydroxide solution. Others were prepared using distilled water as a solvent. The Fe2O3/SiO2 molar ratio contained in the ferrisilicates is set to 0.2. Metakaolin and sodium silicate solution with a molar ratio of SiO2/Na2O of 1.6 were used as the aluminosilicate and hardener in this work. The control geopolymer compressive strength is 53.34 MPa. For ferrisilicates prepared in alkaline solution using rice husk ash and silica fume, their compressive strength values are 71.91 and 77.72 MPa, respectively. The compressive strengths of the geopolymer materials made from ferrisilicates prepared in distilled water using rice husk ash and silica fume are 74.13 and 44.73 MPa, respectively. In the presence of ferrisilicate obtained by dissolving silica fume and hematite in sodium hydroxide solution, the maximum compressive strength of 77.72 MPa was obtained. When ferrisilicates from the mixture of silica fume, hematite, and distilled water are used as an additive, the minimum compressive strength of 43.73 MPa is achieved. It can be concluded that additives synthesised in an alkaline medium and those obtained in distilled water with rice husk ash improve compressive strength. On the other hand, the compressive strength of the geopolymer material that uses the additive produced with silica fume in distilled water is lower (44.73 MPa).