A review: The strength influence factors of slag and fly ash based alkali activated materials

Alkali-activated materials(AAM) are known to be environmentally friendly alternatives to cement-based materials because they can potentially reduce greenhouse gas emissions and reutilize industrial by-products. However, the application of AAM is still limited by the lack of mixture design regulation. Unlike cement, the very different chemical composition of the precusors and alkaline activators may result in a very fluctuating strength. In order to study the factors influencing the strength of slag and fly ash-based alkali-activated materials (BFS/FAAAM), and clarify their reaction mechanism, this paper reviews current knowledge about the mechanical properties and the reaction mechanisms of BFS/FA-AAM. The control factors of strength are BFS/binder ratio, Na2O/binder ratio, and SiO2/Na2O ratio. The ion concentrations, determined by these control factors, play a decisive role in the development of strength. Generally, the strength is proportional to the BFS/binder ratio. The best strength could be obtained at the optimum values of Na2O/binder ratio, and SiO2/Na2O ratio. The optimum values of the SiO2/binder ratio of BFS-AAM and FA-AAM are between 5.5%-8% and between 7-10%, respectively. The optimal values of the SiO2/Na2O ratio of BFS-AAM and FA-AAM are between 0.85-1.4 and between 0.6-1, respectively. For BFS/FA-AAM, the optimum ratio is still unknown. Further study is needed to investigate the effect of control factors on the mechanical properties of BFS/FA-AAM