Mechanical Property and Microstructure of Fly Ash-Based Geopolymer Activated by Sodium Silicate

Abstract

Sodium silicate is one of the common alkali activators of geopolymers. The modulus, concentration and dosage of sodium silicate have significant effects on the activation of fly ash, the strength and microstructure of geopolymer. In this paper, unconfined compressive strength test, X-ray diffraction analysis (XRD), Fourier transform infrared light (FTIR), 29Si nuclear magnetic resonance (29Si NMR), scanning electron microscope and energy disperse spectroscopy (SEMEDS), and physisorption experiment (BET) were carried out to study the effects of the sodium silicate modulus and dosage on the mechanical property and microstructure of fly ash-based geopolymer. The results indicated that the main product of the geopolymer activated by sodium silicate was hydrated sodium aluminosilicate (N-A-S-H). When modulus value decreased and meanwhile dosage of sodium silicate increased, the reorganization and polymerization of gel products were accelerated so that the integrity and continuity of the microstructure of geopolymer were improved, and then the strength increased. When the modulus of sodium silicate was 3.28, the maximum value of the strength was at the dosage of 10%. According to this study, it was investigated that modulus value and dosage of sodium silicate had obvious influence on the alkali- activated reaction of fly ash, which can provide an engineering reference for the special soil solidification with geopolymers.