Use of Heat‐Treated Water Treatment Residuals in Fly Ash‐Based Geopolymers

Geopolymerization is a developing field that can beneficially use heat‐treated water treatment residuals (WTRs) to create fly ash‐based geopolymers. In this study, geopolymers made only from fly ash (FA) and from FA plus calcined WTRs (FA–WTRs) were evaluated. The proper calcining condition for WTRs is 900°C for 1 h and the optimum amount of WTRs to mix with FA is 10 wt%. Compressive strength of samples cured at 75°C for 24 h can reach 68.1 MPa, and when cured at 23°C for 28 days the values were >50 MPa. Further studies were conducted on FA and FA–WTRs geopolymer samples cured at 75°C for 8 h followed by 23°C for 28 d. X‐ray diffraction patterns of geopolymers made from FA indicate the presence of amorphous geopolymeric and calcium silicate hydrate (C–S–H) gels, and a type of zoelite similar to gismondine. When WTRs replaced some of the FA, amorphous geopolymeric gels are mainly formed. Scanning electron micrographs indicate spherical unreactivated FA and other particles are combined and surround the geopolymeric and C–S–H gels. Utilization of WTRs in creation of FA‐based geopolymers can lead to a new type of cementitious binder.