Characterization of class C and F fly ashes based geopolymers incorporating silica fume

Abstract

Geopolymers have been proposed as an alternative to ordinary concrete with their appropriate mechanical performances and eco-friendly impacts. In current study investigated the interaction between the class C and F fly ashes on the properties of silica fume incorporated geopolymers. For that purpose, the concentration of the alkali activator were determined according to compressive and flexural strengths. Then, the geopolymers prepared with different fly ash/silica fume ratios at specified alkali activator concentration. Mechanical, physical, chemical and microstructural properties of these geopolymers were evaluated by FT-IR, XRD, TGA, and SEM-EDX. The mechanical properties of geopolymers were enhanced remarkably by NaOH molarity and it was detected that the compressive strength and flexural strength values reached the highest (21.13 ± 1.11 MPa and 6.61 ± 0.56 MPa, respectively) at 10 M. Results were compared according to the fly ash type and the fly ash/silica fume ratios of the geopolymers. Due to the high water demand of silica fume, prominent cracks were seen in the geopolymers including 100% silica fume. Besides, inadequate mechanical properties were obtained when 100% fly ash was used. Consequently, it was clearly revealed that the properties of geopolymers obtained with only fly ash or silica fume were improved by the use of both. Finally, higher mechanical properties (σC: 31.91 ± 1.90 MPa, σF: 8.34 ± 0.23 MPa) and less cracks in the bodies were obtained with class F fly ash (75% wt.).