Influence of calcium nitrate and sodium nitrate on strength development and properties in quicklime(CaO)-activated Class F fly ash system

The single use of CaO has been regarded as relatively unsuccessful in fly ash activation when no other additives are used together, as it produces a considerably lower strength compared to other types of activators (e.g., alkaline activators). This study investigated two potential additives of nitrate compounds (i.e., Ca(NO3)(2) and NaNO3) to improve the strength of a CaO-activated fly ash system. The results showed that the use of Ca(NO3)(2) was greatly beneficial in the strength improvement of the binder system primarily due to the significant increase in (1) the dissolution degree of fly ash, (2) C-S-H formation, and (3) pore size refinement from early days; however, NaNO3 was much less advantageous in strength improvement, although it also aided in dissolving fly ash.