Structure and strength of NaOH activated concretes containing fly ash or GGBFS as the sole binder

The influence of the concentration of the activating agent (4, 6, or 8 M sodium hydroxide solution), and activator-to-binder ratio (0.40, 0.50, or 0.60) on the compressive strengths, pore structure features, and microstructure of concretes containing Class F fly ash or ground granulated blast furnace slag (GGBFS) as the sole binder is reported. The starting material contents and the curing parameters (temperature and curing duration) are optimized to provide the highest compressive strengths. Statistical analysis of the compressive strength results show that the activator concentration has a larger influence on the compressive strengths of activated concretes made using fly ash and the activator-to-binder ratio influences the compressive strengths of activated GGBFS concretes to a greater degree. Activated fly ash concretes and pastes are found to be more porous and contains a larger fraction of pores greater than 10 μm in size as compared to activated GGBFS mixtures. The differences in the microstructure and the reaction products between activated fly ash and GGBFS pastes are detailed.