Biochar　is　a　promising　carbon-negative　supplementary　cementitious　material　(SCM).　However,　traditional　biochar　lacks　active　ingredients,　and　its　porous　structure　severely　weakens　the　mechanical　properties　of　ordinary　Portland　cement　(OPC),　limiting　its　substitutability　in　cement.　To　meet　the　dual　needs　of　decarbonization　and　strength　in　cement,　this　paper　explored　the　potential　of　two　types　of　silica-rich　biochar,　rice　husk　biochar　rich　in　amorphous　silica　and　bamboo　biochar　rich　in　crystalline　silica,　as　carbon-negative　SCMs.　Here,　the　hydration,　microstructure,　and　mechanical　properties　of　rice　husk　biochar　and　bamboo　biochar　blended　cements　were　investigated.　Similar　to　bamboo　biochar,　rice　husk　biochar　reduces　flowability　and　drying　shrinkage　due　to　its　porous　structure.　However,　rice　husk　biochar　contains　a　large　amount　of　amorphous　silica,　resulting　in　the　promotion　of　hydration　of　clinker　and　a　significant　pozzolanic　effect,　which　shortens　the　setting　time　of　cement,　improves　the　weak　structure　and　bonding　interface　of　biochar,　and　further　increases　the　hydration　degree　and　polymerization　degree　of　calcium　silicate　hydrate.　Compared　with　bamboo　biochar,　rice　husk　biochar　blended　cement　exhibited　significantly　higher　compressive　strengths　at　the　same　substitutions　and　ages.　A　5%　rice　husk　biochar　blended　cement　at　28　days　exhibited　12.9%　and　29.8%　higher　compressive　strength　than　OPC　and　5%　bamboo　biochar　blended　cement,　respectively.　The　compressive　strength　of　10%　rice　husk　biochar　blended　cement　was　only　4%　lower　than　that　of　OPC　at　28　days.　From　a　life　cycle　assessment,　10%　rice　husk　biochar　blended　cement　has　the　lowest　unified　carbon　emissions　(per　MPa),　22%　and　28%　lower　than　that　of　10%　bamboo　biochar　blended　cement　and　OPC,　respectively,　showing　great　potential　for　lower　unified　carbon　emission　cementitious　materials.