Two　fine　powders　collected　from　construction　and　demolition　wastes　(CDW),　i.e.,　recycled　concrete　powder　(RCP)　and　recycled　clay　brick　powder　(RBP),　were　used　as　partial　alternatives　to　cement　for　mortar　preparation.　The　effects　of　RCP/RBP　on　fluidity/strength　of　mortar　at　varying　replacement　rates　were　experimentally　investigated　meanwhile　the　mechanism　was　discussed　according　to　hydration　process　characterized　by　hydration　heat　flow,　compositions　of　hydration　products,　hydration　degree,　as　well　as　the　pore　structure　of　blended　mortars.　Extended　analysis　was　also　conducted　on　cost　performance　and　CO2　emission　of　the　blended　mortar　by　considering　the　mortar　strength　simultaneously.　Test　results　showed　that　RCP/RBP　at　a　dosage　no　larger　than　30%　had　marginal　influence　on　water　demand　of　paste;　the　mortar　fluidity　was　even　improved　at　replacement　rates　lower　than　20%.　The　strength,　especially　compressive　strength　of　mortar　was　reduced　but　the　reduction　was　not　obvious　given　the　RCP　and　RBP　dosages　were　below　10%　and　20%,　respectively.　Both　RCP　and　RBP　can　facilitate　early　cement　hydration　and　improve　the　28-day　hydration　degree　likely　due　to　the　nucleation　effects.　The　finer　RBP　also　refined　large　pores　in　mortar　while　RCP　increased　the　total　porosity　and　made　pore　coarser.　This　work　also　confirmed　that　both　RCP/RBP　can　improve　the　cost　performance　of　mortar　and　help　achieve　extra　environmental　profits　by　reducing　CO2　emission　given　their　dosage　did　not　exceed　20%.　RBP　should　be　a　more　favorable　alternative　than　RCP　to　OPC　for　preparing　more　cost-effective　and　lower-carbon　cementitious　materials　with　ensured　fluidity　and　strength.　©　2023　Elsevier　Ltd