Characterization of Fly Ash for the Production of Geopolymer Cements

Current ASTM standards can be used to provide a degree of characterization of geopolymeric materials, yet the researcher must be aware of differences between hydraulic and geopolymer cementitious materials. The current study assessed the applicability of available ASTM standards that analyze the insoluble content and oxide content of cementitious materials (ASTM C114 and C311), compressive strength (ASTM C109), leaching (ASTM C1308), and setting time (ASTM C403). It was found that the speciation of sulfur is important in fly ash precursors and can be determined using ASTM C114’s determination of sulfur trioxide content. The speciation of sulfur, unburned carbon content and particle size are important parameters for the characterization of a geopolymer precursor. Furthermore, the dissolution of geopolymer precursors should be assessed at appropriate basic pH levels to determine the content of insoluble materials. The curing conditions and resulting geopolymer microstructure must be characterized (via FT-IR) and regulated to achieve consistency across research studies on geopolymer cements.