Photocatalytic　coatings　applied　onto　cement-based　pavement　materials　have　been　intensely　developed　to　purify　runoff　pollution　and　vehicle　exhaust.　However,　the　masking　effect　of　the　adhesive　incorporation　often　results　in　an　unsatisfactory　purification　efficiency.　Thus,　developing　an　adhesive-free　photocatalytic　coating　with　high　stability　and　purification　efficiency　on　cement-based　pavements　is　still　urgently　needed.　Herein,　a　colloidal　graphitic　carbon　nitride　(g-C3N4)　modified　with　hydroxyl　groups　was　sprayed　onto　cement　pastes　to　prepare　a　photocatalytic　coating　on　the　cement-based　materials.　The　results　of　photocatalytic　degradation　of　Rhodamine　B　(RhB)　indicated　that　the　RhB　degradation　efficiency　and　stability　of　the　colloidal　g-C3N4-coated　cement　paste　were　significantly　improved　compared　to　pristine　g-C3N4-coated　cement　paste.　After　a　runoff-washing　trial,　photocatalytic　RhB　degradation　by　colloidal　g-C3N4-coated　cement　paste　was　13.8-fold　higher　than　that　of　pristine　g-C3N4-coated　cement　paste.　Mechanistic　studies　suggested　that　the　well-distributed　membrane　microstructure　of　colloidal　g-C3N4　and　coordinate　bonds　between　colloidal　g-C3N4　and　calcium-silicate-hydrates　were　mainly　responsible　for　the　improved　stability　and　purification　efficiency　of　colloidal　g-C3N4-coated　cement　pastes.　These　results　support　the　use　of　colloidal　g-C3N4　as　a　promising　strategy　to　prepare　photocatalytic　cement-based　pavements　with　good　stability　and　purification　efficiency.