Understanding the microstructure of alternative binder systems – banahCEM a metakaolin based geopolymer

Geopolymer binders have emerged as an alternative to Portland Cement systems for specialist applications due to their improved durability and environmental impact. Geopolymer binders can be made by combining alkali activators... [ view full abstract ]

Geopolymer binders have emerged as an alternative to Portland Cement systems for specialist applications due to their improved durability and environmental impact. Geopolymer binders can be made by combining alkali activators with precursor materials including high purity dehydroxylated kaolin (metakaolin) or pulverised fuel ash. Although the technical and engineering properties of these materials can now be controlled to a high degree of precision, there is still much to be learnt about the underlying chemical reactions and the microstructure of the material. banahCEM is a geopolymer binder made from a calcined iron-rich kaolinitic clay. To aid in the understanding of the geopolymer system a SEM microstructural analysis of banahCEM has been carried out in comparison to high-purity metakaolin based geopolymer. Results indicate that there are several visible phases in the banahCEM geopolymer: 1) Geopolymer (alkali aluminosilicate) binder gel, 2) Partially reacted/relic metakaolin particles, 3) Reacted metakaolin particles, and 4) Impurities. Geopolymer produced from high-purity metakaolin is also composed of a geopolymer binder and relic metakaolin particles (phases 1 & 2). However, the size, proportion and distribution of the phases differ. By better understanding the microstructure of the geopolymer system, we in turn can learn how the mix proportions affect the properties and microstructure. However, and more importantly, we can manipulate the geopolymer system to suit a specific area of application, for example, increase the capacity to resist acid and chemical attacks.