Abstract: Due to the heterogeneity of fly ash, it is difficult to anticipate the potential reactivity of fly ash. The leaching process of different fly ash under different conditions of time, temperature and alkali concentration (fly ash is first dissolved in lye, and its residue is dissociated in acid solution) . Inductively Coupled Plasma Optical Emission Spectrometer(ICP-OES) and chemical analysis results show that temperature, reaction time and alkali concentration all affect the dissolution rate and leaching content of fly ash. The leaching reactive n(Si)/n(Al) of fly ash was 2.3—2.7, and the total leaching amount of silica and aluminum from fly ash was positively correlated with the strength of geopolymers. It is found that the grading of fly ash used in cement system is not completely applicable to geopolymer system. XRD, FTIR and SEM analysis results show that fly ash is composed of reactive parts and inert parts. The active substances dissolve rapidly in the alkali dissolution process, the acid completely dissociates the gel formed during the geo-polymerization process, and the leaching process can more accurately characterize the content of reactive substances in fly ash. Therefore, alkali-acid combined determination method can be used to quantitatively estimate the reactant content and reactive n(Si)/n(Al) of fly ash, to simply and rapidly predict the potential reactivity of fly ash used in geopolymer systems, and to design the fly ash-based geopolymer.
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