Initial investigation into the effect of iron silicate addition to metakaolin-based geopolymers

Geopolymer cement is a sustainable, high performance alternative to ordinary Portland cement. An increasing interest in the development and use of geopolymer cement has led to new research into the use of available waste materials and by-products. Aside from the typical geopolymeric materials such as metakaolin, fly ash and GGBS, other materials such as red mud and mining wastes have been found to have potential. Produced and landfilled in Bulgaria, iron-silicate fines (ISF) have been identified as an alternative material which can enhance the properties of geopolymers, as reactive component in metakaolin-based geopolymer mortars. To date, ISF has not been considered for use as a geopolymeric material. This paper presents the results of an initial study into the potential use of ISF as a component of metakaolin-based geopolymers. The effect of ISF of geopolymer mortars is considered. Increasing the ratio of ISF was found to significantly increase the mortar flow, but also increase the setting time of the mortar. The replacement of metakaolin with ISF, up to 20 %, improved the 7 day compressive strength by more than 13 %. The potential use of a synthetic geopolymer aggregate, containing ISF, as a high polished stone value aggregate was also considered. Initial testing suggest a good resistance to coarse polishing, but a much lower resistance to fine polishing. However, the study has identified that ISF has good potential for use in geopolymer applications.