Utilization of Low Sulfur Fly Ash from Circulating Fluidized Bed Combustion Burner as Geopolymer Binder

Circulating fluidized bed combustion (CFBC) burner is gaining increasing popularity due to its compact size, high efficiency, and lower burning temperature compared with the pulverized coal combustion (PCC) burner. Normally, fly ash produced from CFBC burner is not rounded, requires higher water content, and has high sulfur content. Due to its drawbacks, CFBC fly ash is rarely used as cementitious material or geopolymer precursor. This study focuses on comparing variations in the concentration of NaOH solution and in the ratio of alkaline activators to the properties of low sulfur CFBC fly ash-based geopolymer mortars. It was concluded that the fly ash has the potential to be utilized as a geopolymer precursor although with an increase in water demand. The geopolymer mortar shows good compressive strength and stability. The highest compressive strength of 33.4 MPa at 90 days was achieved at NaOH concentration of 8 M and ratio of sodium silicate solution to sodium hydroxide solution of 2.5 with excellent stability