Synthesis of geopolymers based on mechanically activated low‐calcium iron‐rich fly ash

Abstract

AbstractIn this work, the processes occurring during geopolymerization of low‐calcium iron‐rich (19.3% Fe2О3) fly ash (FA) mechanically activated in a planetary mill were investigated. Sodium hydroxide solution was used as an alkaline agent and curing was at 20 ± 2°C. Analysis of the initial and mechanically activated FA by selective acid dissolution method showed that after mechanical activation (MA) for 180–400 s the total reactive SiО2 and Al2О3 increased by 1%–2% while the total reactive Fe2О3 more than doubled. The compressive strengths of the geopolymers prepared using the FA mechanically activated for 0, 180, and 400 s were 1.8, 15.0, and 14.0 MPa, respectively, after curing for 28 days. Considerably greater compressive strength of the geopolymers based on the mechanically activated FA was explained by the higher reactivity of the FA induced by MA. This was evidenced by analyses of the geopolymers using Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy. As shown by microprobe analysis, the geopolymers synthesized using the mechanically activated FA were characterized by considerably higher iron oxide content in the aluminosilicate hydrogel than the geopolymers prepared using the initial FA. The advantage of MA was not only to increase the overall reactivity of FA but also to include Fe in the geopolymerization process, which improved the geopolymer strength.