Microscopic analysis of nano-modified fly ash by fluidized bed reactor-vapor deposition

摘要

The nano-modification and hydration mechanisms of fly ash (FA) modified by fluidized bed reactor-vapor deposition (FBR-VD) has been analyzed microscopically. The experimental fluidized bed reactor (FBR) and chemicals such as HCl (HC), H2SO4 (HS), NaOH (NH), and NaCl (NC) were used to modify the FA. The results show that the strength of samples modified by NH, HC, and NC increased at different ages, where the strength ratio of the sample modified by NC before 3 d exceeds 120%, while the strength of the FA-cement paste modified by HS decreased slightly in the early stage but increased in the later stage. By comparing FA and Ca(OH)(2) (CH) contents of different samples, it could be concluded that modifiers can activate the pozzolanic activity of FA and allow it to participate in the secondary hydration reaction earlier, resulting in higher the intensity of the FA-cement paste. The FBR-VD method can effectively deposit different modifiers as nanometer-sized particles on the surface of FA, causing them to react with FA, and through the changes in the binding energy of the elements, it was proved that the modifiers can break the glass network structure of FA and efficiently stimulate the pozzolanic activity of FA. In the FA-cement hardened paste, the surface of the modified FA permitted the deposition of more hydration products than that of the unmodified FA, and the quantity of deposition as well as form of different modified samples was different. Modifiers had a remarkable effect on the FA-cement hardened paste, effectively promoting the pozzolanic effect of FA and improving the strength of the hardened cement. (C) 2020 Elsevier Ltd. All rights reserved.