Understanding reactive amorphous phases of fly ash through the acidolysis

Abstract

It is well understood that the reactive components of fly ash (FA) in alkali cement are mainly donated by amorphous phases. The acidolysis method is typically employed to dissolve these amorphous phases for separate analysis; however, such method is not truly convincing, especially the testing and analysis processes. This paper investigates the hydrofluoric acid (HF, 1%) dissolution process (from 0.5 h to 20 h) of two Class-F FAs with different physical and chemical characteristics. The time-dependent quantitative analysis results indicate that in addition to amorphous phases, some crystalline phases are also dissolved in 1% HF solution. Further, the chemical statistics on the dissolved amorphous phases was extracted from the scanning electron microscopy images. Amorphous aluminosilicates in FA can be quantitatively classified into six groups, of which the three reactive amorphous aluminosilicates are defined.