Effect of <i>n</i>(SiO₂)/<i>n</i>(Al₂O₃) molar ratio on physical properties and microstructure of foamed geopolymer

Abstract

The foaming geopolymer was prepared by experiments using circulating fluidized bed combustion fly ash (CFAS),silica fume (SF),water glass (WG),NaOH and H2O2,and silica fume was used to adjust the n(SiO2)/n(Al2O3) molar ratio of the geopolymers,the fresh paste was tested for foaming expansion factor and foaming rate.The strength and apparent density of the paste were tested after hardening.This paper analyzed the pore size distribution by Image-Pro Plus software,and the microstructures of the foamed geopolymers were analyzed by X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM).The results show that the increase of the molar ratio of n(SiO2)/n(Al2O3) accelerates the hydration reaction rate,and the appropriate ratio makes the foaming time advance.The wavelength shift in the FTIR indicates that the Si—O and Al—O bonds rearrange after alkali-excited,and the appropriate ratio is favorable for the rearrangement reaction of the geopolymer and increases the degree of polymerization.The product such as zeolite was formed found by XRD pattens.When the n(SiO2)/n(Al2O3) molar ratio is 2.79,the strength and apparent density of the specimen in 28 d are 1.06 MPa and 231 g/L,and the microstructure of the specimen has good compactness.

Keywords

• molar ratio
• geopolymer
• strength
• pore size distribution