Some Progresses in the Challenges for Geopolymer

Geopolymer is manufactured by chemical activation of industrial by-products, which include blast furnace slag, fly ash, steel slag, phosphorus slag etc, with alkali activators, such as the sodium silicate, sodium carbonate and sodium hydroxide and their mixtures. It has attracted worldwide attention due to its advantages of simple production process, low energy consumption, effective utilisation of industrial by-products and reduction of greenhouse gas emissions. However, as materials vary substantially in physicochemistry properties, hardening, workability and durability of deriving geopolymer products vary accordingly. Slag-based geopolymer usually set within a very short period of time (less than 30 min), while low calcium fly ash-based geopolymer takes long time (a couple of days) to set. Geopolymer binders cured at room temperature exhibited significantly higher shrinkage than Portland cement does, while thermal cured products are very volumetrically stable. Moreover, alkali-aggregate reaction can happen when alkali-reactive aggregates are used with geopolymer binders. These issues need to be considered in large scale applications. This paper reviews the current advance in the research of geopolymer.