This　study　investigated　the　mechanical　properties　of　concrete　of　strength　grade　C30　and　C35,　containing　different　content　(10%–50%)　of　a　composite　admixture　of　ferronickel　slag　and　blast　furnace　slag　powder　(referred　to　as　F-S　powder　and　F-S　concrete　hereafter,　respectively).　The　mechanical　properties　include　axial　compressive　strength,　elastic　modulus,　Poisson＇s　ratio,　splitting　tensile　strength,　and　the　compressive　stress-strain　relationship.　The　difference　in　mechanical　properties　between　F-S　concrete　and　conventional　concrete　was　analyzed.　Test　results　indicated　that　the　positive　correlation　of　conventional　concrete　between　the　axial　compressive　strength,　elastic　modulus,　splitting　tensile　strength,　and　cubic　compressive　strength　was　applicable　to　F-S　concrete　irresponsible　of　the　specific　F-S　powder　content.　Both　Poisson＇s　ratio　and　the　failure　mode　under　compression　for　F-S　concrete　were　identical　to　those　of　conventional　concrete.　The　shape　characteristics　and　fitting　parameters　of　the　stress-strain　curve　were　mainly　related　to　F-S　concrete　strength　grade　but　had　little　connection　with　the　specific　F-S　powder　content.　Furthermore,　based　on　tested　data,　the　stress-strain　constitutive　equations　were　established　for　F-S　concrete,　which　provides　a　reference　for　the　test　analysis　of　large　specimens　and　corresponding　engineering　application.　©　2019　Elsevier　Ltd