Review on the impact of metakaolin-based geopolymer's reaction chemistry, nanostructure and factors on its properties

The low carbon footprint and superior properties of geopolymer make it a potentially suitable alternative to ordinary Portland cement, which has been one of the dominating research focuses in the last decades. However, the mechanisms of geopolymeric reactions and the nanostructure of geopolymer are still questionable. Besides, some undesired properties in geopolymer synthesis limit the field application of geopolymers. This paper focused on the current knowledge of the reaction chemistry and nanostructure of geopolymer and factors affecting metakaolin-based geopolymer synthesis. A systematic summary of the reaction process, chemical bonds in geopolymer, and models of geopolymer were provided to better understand the reaction mechanisms of geopolymerization. Various factors important to geopolymer's properties, including Si/Al ratio, Na/Al ratio, type of alkaline activator and alkali cation, water/solid ratio, and curing condition, were comprehensively reviewed to guide the geopolymer synthesis. Through this review, we hope to promote this field's continued growth and development and encourage the wider adoption of geopolymers as a sustainable alternative to traditional construction materials.