Optimization of Technological Parameters for Preparation of Geopolymers Fabricated with Pulverized Fly Ash

Abstract

Geopolymer is widely considered as an important direction for the comprehensive utilization of fly ash with its production increasing sharply year by year. The effect of mixing proportion including SiO₂/Al₂O₃ molar ratio, Na₂O/SiO₂ molar ratio and water-solid ratio on the performances of geopolymer fabricated with pulverized fly ash with a median particle size of 3.3 μm was investigated by an orthogonal test in this work, and the optimum preparation technics were also obtained. Results indicated that the compressive strength of geopolymer reached the maximum of 61.0 MPa when SiO₂/Al₂O₃ molar ratio was 3.3, Na₂O/SiO₂ molar ratio was 0.11 and the W/S ratio was 0.30 under the optimum preparation technics of aging time of 3h, mixing time of 3min and curing at 80℃ for 24h. Overall, Na₂O/SiO₂ molar ratio played the most important role on the compressive strength of geopolymer, but SiO₂/Al₂O₃ molar ratio had a minimal impact. FTIR spectrum demonstrated that the sample with the optimum proportion exhibited a more complex asymmetric stretching vibration peak, which indicated that there were more activated silicon/aluminum monomers and dimers in fly ash depolumerized and repolymerized and tetrahedral phase transitions, and then geopolymer paste with denser microstructure was formed.