As　an　industrial　solid　waste　from　limestone　quarrying,　limestone　powder　(LP)　is　often　used　in　cement-based　materials　to　reduce　cost　and　carbon　dioxide　emissions.　It　is　well　known　that　the　synergistic　effect　between　LP　and　alumina-rich　supplementary　cementitious　materials　(SCMs)　influences　the　properties　of　cement-based　materials.　To　study　the　synergistic　effect　quantitatively,　the　hydration　heat,　hydration　products　and　porosity　of　cement　pastes　with　different　binders　were　investigated.　Test　results　showed　that　the　synergistic　effect　between　LP　and　fly　ash　(FA)　or　slag　(S)　improved　the　hydration　degree　and　increased　the　total　hydration　heat　of　the　pastes.　When　FA　or　S　were　incorporated　along　with　LP,　the　calcium　carbonate　consumption　at　3　days　increased　from　2.0　wt%　to　4　wt%;　at　180　days　it　increased　from　2.4　wt%　to　9.3　wt%　(with　FA)　and　11.8　wt%　(with　S).　The　incorporation　of　FA　or　S　also　increased　the　diffraction　peak　of　carboaluminate,　indicating　more　carboaluminate　was　formed.　The　synergistic　effect　between　LP　and　SCMs　refined　the　pore　structure　and　reduced　the　porosity　of　the　cement　pastes.　The　synergistic　effect　between　LP　and　FA　or　S　increased　the　density　of　the　cement　pastes　by　1.04%　or　1.41%,　respectively,　and　correspondingly　improved　the　compressive　strength　of　the　pastes.