Enhanced reactivity of geopolymers produced from fluidized bed combustion bottom ash

Abstract

In this study, waste bottom ash obtained from fluidized bed combustion of low-grade South African coal in a bubbling fluidized bed reactor was used to produce geopolymers. The geopolymers were cured using both a conventional oven and a household microwave. An alkaline solution of Na2SiO3/NaOH (1:0.5) was mixed on a 1:1 ratio with a mixture of bottom ash/kaolin (1:1) mixture. Thereafter the resulting mixture was mixed with sand on a 1:0.5 ratio. Characterization of the geopolymers carried out using the following techniques, scanning electron microscope (SEM-EDX) analysis, compressive strength test, Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. A household microwave and a conventional oven were used to enhance the geopolymerisation process and strength of the geopolymers. The results showed that the microwave curing enhanced the reactivity and compressive strength of the geopolymers. The microwave and oven cured geopolymer had the highest Si/Al ratio of 4.42 and reached a reasonable high compressive strength test of 31 MPa in 7 days compared to geopolymers cured with a conventional oven only or with a microwave only. The microwave radiation followed by conventional oven curing reduced the heat curing time and energy but improved the reactivity and strength of the geopolymer.

Keywords

• Geopolymer
• Bottom ash
• Geopolymerisation
• Microwave
• Conventional oven