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.
Highlights
Coal fly ash, as the main solid waste produced by coal-fired power plants, was generated with a significant increase year by year
The active components including active silica and activated alumina existed in fly ash can be dissolved and pozzolanic reaction occurred with aqueous alkali to form cementious paste [20,21,22]
High Na2O/SiO2 molar ratio would lead to rapid reaction rates, and early precipitation of some geopolymer gels would block potential formation of more amorphous gel and cause more unreated active components left in fly ash [24]
Summary
As the main solid waste produced by coal-fired power plants, was generated with a significant increase year by year. Poor comprehensive utilization resulted in the bulk storage of fly ash, which had posed a serious threat to the ecological environment and human health [1,2]. It has become the issue of essential importance to be solved urgently to utilize fly ash in large-scale. Compared to the common cement, geopolymer is a collection of excellent performance including high strength, low hydration heat, energy saving, low-carbon environment, good durability and encapsulation [5,6,7,8]. Geopolymer has been widely regarded as the most promising alternative to cement in the future [9]
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