Production and characterization of geopolymers based on mixed compositions of metakaolin and coal ashes

•Mixture of coal ashes and metakaolin were used to synthetize geopolymers.•Fluidized bed combustion (FBC) ash can be used as a partially reactive filler.•Metakaolin-FBC based geopolymers have a compressive strength of ∼30 MPa.•Geopolymer materials can be produced for the building sector.

Mixtures of coal ashes from pulverized coal combustion (PCC) or fluidized bed combustion (FBC) and metakaolin were used to synthetize geopolymers. Upon full characterization of the raw powders (chemical and mineralogical composition), geopolymerization tests were conducted using an alkali aqueous solution of NaOH/Na2SiO3 at different dilutions. The produced geopolymers were subjected to SEM analysis, as well as to leaching, thermal and mechanical tests. The final microstructure and the properties of the geopolymers indicate that FBC ash can be conveniently used as a partially reactive filler in combination with the metakaolin powder. The composite material has good thermal performance and compressive strength (∼30 MPa) suitable for the building sector.