An experimental study on the mix design optimization of fly ash-based geopolymers

Abstract

Geopolymers are materials suitable for utilization in the construction industry due to their superior properties, such as high strength and good durability. The properties of geopolymers can be configured due to mix design and synthesis conditions. In this study, the mix designs providing the highest compressive strength were investigated. For this purpose the sodium hydroxide/sodium silicate ratios and alkali activator/fly ash ratios were differentiated in the geopolymer synthesis. Fly ash was used as raw material. Geopolymer samples were cured at 80 °C for 16 h and aged for 7 and 28 days in laboratory. The highest compressive strength was obtained as 27.36 MPa with alkali activator/fly ash ratio of 0.4 and sodium hydroxide/sodium silicate ratio of 1.0. The degree of reaction values were determined for all the geopolymer samples. Fourier Transform infrared spectroscopy (FTIR) was used for determining the chemical bonds in the structure. The spectrum of the samples revealed that more aluminosilicate gel formed for the sample providing the highest compressive strength.