Recycled　aggregate　(RA)　was　surface　treated　by　two　strengthening　slurries　prepared　with　sulphoaluminate　cement　(SAC),　with　or　without　the　addition　of　an　industrial　waste,　basalt　powder　(BP).　Test　results　show　that　the　quality　of　the　surface　treated　RA　was　improved,　reflected　by　the　increased　apparent　density　and　the　reduced　crushing　value　and　water　absorption　(by　weight),　meanwhile　the　mechanical　properties　and　the　resistance　against　chloride　and　sulphate　attacks　of　the　prepared　RAC　were　enhanced.　Based　on　the　microhardness　test　results,　the　newly　formed　ITZ(1)s　and　ITZ(3)s　in　RAC　using　the　treated　RA　demonstrated　a　sandwich-like　structure.　The　significant　enhancement　of　ITZis　and　ITZ(3)s　and　the　surface　strengthening　of　the　old　adhering　cement　mortar　explain　the　mechanism　of　RAC＇s　improvement　at　the　macro　scale.　It　was　also　found　that　by　adding　a　certain　quantity　of　BP　to　the　SAC　slurry,　RAC　demonstrated　better　performance　at　both　the　micro　and　the　macro　scales.　By　also　considering　the　environmental　benefits　by　consuming　BP　as　an　industrial　waste　in　some　regions　of　China,　the　SAC-BP　composite　slurry　deserves　more　exploration　in　further　studies.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.