Synthesis and Characterization of Coal Fly Ash-based Foamed Geopolymer

Fly ash, a residue arising from the combustion of pulverized coal, is one of the major wastes generated in coal-fired power stations. Several utilization options of fly ash are currently being practised in many countries in an effort to minimize waste and protect the environment. This paper studied the potential use of fly ash from South African power utilities in the production of foamed geopolymeric materials which may be suitable for various applications including the building industry. The foamed geopolymers were synthesized through alkali activation of the fly ash and subsequent hydrothermal treatment procedure. This was done by mixing fly ash (FA) with sodium hydroxide (NaOH) and ultrapure water to form a paste, before introducing sodium hypochlorite solution (NaOCl, foaming agent) into the existing paste. The resulting mixture was then placed in the oven to produce the foamed geopolymer. The mixing was done using FA: NaOH: NaOCl: H2O mass ratio of 3.03: 1.00: 1.14: 1.00. The chemical composition, mineralogy, morphology and molecular structure of the starting material (fly ash) and the synthesized product (foamed geopolymer) were analyzed using XRF, XRD, SEM and FTIR respectively. The porosity and the bulk density of the foamed geopolymer was also determined using mercury porosimetry.