This　study　aims　to　compare　the　effects　of　three　calcium　compounds　on　the　workability,　setting　time　and　mechanical　properties　of　red　mud　(RM)–blast　furnace　slag　(BFS)-based　geopolymers.　The　crystalline　phase,　hydration　process　and　microstructure　of　RM-BFS-based　geopolymers　were　characterized　by　X-ray　diffraction　(XRD),　heat　evolution,　X-ray　photoelectron　spectroscopy　(XPS),　and　scanning　electron　microscope　(SEM)　tests.　The　results　showed　that　an　appropriate　amount　of　calcium　compounds　can　improve　the　flowability　and　compressive　strength　of　the　geopolymers,　but　the　excessiveness　causes　a　decrease　in　strength　due　to　rapid　hardening.　Other　than　calcium　carbonate,　both　calcium　oxide　and　calcium　chloride　played　important　roles　in　accelerating　the　setting　times　of　RM-BFS-based　geopolymers.　The　acceleration　in　the　setting　times　of　geopolymers　could　be　attributed　to　the　calcium　hydroxide　produced　by　the　dissolution　of　the　calcium　compounds,　which　also　provides　nucleation　sites　for　the　geopolymerization　reaction.　This　study　gives　new　insights　into　the　effect　of　calcium　on　the　setting　times　and　mechanical　properties　of　geopolymers　in　the　geopolymerization　process.　©　2024　by　the　authors.