Collapsibility potential of gypseous soil stabilized with fly ash geopolymer; characterization and assessment

•Geopolymer fly ash showed higher sulfate resistance than Portland cement.•Higher sulfate resistance was recorded in geopolymer fly ash class F activated with KOH.•Collapsibility potential of gypseous soil decreased when stabilized with fly ash geopolymer.•Leachate and permeability decreased in gypseous soil stabilized with geopolymer fly ash.