To　address　the　global　challenge　of　reducing　CO2　emissions　in　the　cement　industry,　barium　(Ba)-doped　rankinite　(C3S2)　was　successfully　developed　to　enhance　carbonation　reactivity　and　CO2　sequestration.　The　synthesis,　carbonation　strength,　reaction　products,　CO2　uptake　efficiency,　and　microstructural　evolution　were　evaluated　to　identify　the　optimal　calcium-barium　ratio　concerning　carbonation　reactivity.　The　results　revealed　that　adding　Ba　had　minimal　impact　on　the　crystal　structure　of　synthesized　C3S2　but　changed　its　crystal　morphology.　Compared　with　the　pure　C3S2　paste,　incorporating　Ba　slightly　decreased　compressive　strength　upon　2　h　of　carbonation　curing.　Still,　the　strength　increased　sharply　when　the　carbonation　curing　was　prolonged　to　24　h.　The　strength　gains　of　Ba-doped　C3S2　pastes　carbonated　for　24　h　were　mainly　due　to　the　formation　of　rich　carbonation　products　and　reduced　porosity　and　average　pore　size　within　the　paste　matrix.　These　findings　establish　a　technical　foundation　for　utilizing　Ba-doped　C3S2　in　CO2-fixing　cementitious　materials　for　producing　precast　products.　©　2025　Informa　UK　Limited,　trading　as　Taylor　&　Francis　Group.