Alkali-activated　binders　based　on　metakaolin,　fly　ash　and　slag　without　curing　were　exposed　directly　in　air,　Na2SO4　and　MgSO4　solutions　for　studying　the　evolution　in　mechanical　strength　and　microstructure.　A　series　of　binders　were　synthesized　and　characterized　on　7,　21,　45,　60,　75　and　90　days,　respectively.　Compressive　strength　measurement,　scanning　electron　microscope　(SEM)　mapping,　X-ray　diffraction　(XRD)　and　unclear　magnetic　resonance　(NMR)　were　applied　in　the　study.　It　is　found　that　the　exposure　in　sulfate　solutions　leaded　to　the　deterioration　of　the　binders　by　the　dissolution　of　alkalis.　In　Na2SO4　solution,　a　higher　percentage　of　zeolite　was　formed　in　the　binders.　While　in　MgSO4,　a　precipitate　layer　(e.g.,　brucite　and　gypsum),　forming　on　the　binder　surface　plays　an　important　role　in　protecting　the　formation　of　gel,　promoting　the　compressive　strength　improvement　of　alkali-activated　slag,　and　compensating　the　decrease　in　compressive　strength　of　alkali-activated　metakaolin.　These　results　provide　clues　for　the　direct　preparation　of　alkali-activated　concrete　in　aggressive　sulfate　environment.　(C)　2020　The　Author(s).　Published　by　Elsevier　B.V.