This　paper　presents　the　effect　of　alkali　dosage　on　the　mechanical　properties　and　water　resistance　of　alkali-activated　brick　powder　geopolymers　(BPG)　by　measurements　of　compressive　and　flexural　strengths,　bulk　density,　water　absorption　and　softening　coefficient.　To　reveal　the　micromechanism　of　BPG　under　varied　alkali　dosage,　the　mineralogical　phases,　reaction　degree,　micromorphology,　and　pore　structure　of　BPG　are　analyzed　by　techniques　of　XRD,　TGA,　SEM　and　MIP,　respectively.　Furthermore,　the　environmental　impacts　of　BPG　are　evaluated　by　considering　CO2-e　emission　and　energy　consumption.　Results　show　that　the　BPG　prepared　with　low　alkali　dosage　(2%　or　4%　Na2O)　exhibits　the　loose　microstructure　with　few　amorphous　gels　and　relatively　high　porosity　(including　high　proportion　of　capillary　pores)　resulting　in　the　relatively　poor　mechanical　properties　and　water　resistance.　However,　a　higher　alkali　dosage　(6%　or　8%　Na2O)　promotes　the　geopolymerization　reaction　resulting　in　the　denser　microstructure　with　more　amorphous　gels　and　relatively　lower　porosity,　thereby　greatly　enhancing　the　mechanical　properties　and　water　resistance　with　maximal　flexural　strength,　compressive　strength　and　softening　coefficient　of　2.2　MPa,　31.1　MPa　and　0.77　respectively.　Water　immersion　may　cause　Na+　and　OH　to　dissolve　from　BPG　matrix　resulting　in　a　charge　imbalance　of　three-dimensional　network　structures,　which　will　further　lead　to　strength　degradation.　In　comparison　to　ordinary　Portland　cement　paste,　BPG　can　reduce　CO2-e　emission　by　about　40%-70%　and　energy　consumption　by　about　20%-50%.　The　optimal　mixing　parameters　have　an　alkali　dosage　of　6%,　a　silicate　modulus　of　1.6　and　a　water-to-binder　of　0.3　by　considering　the　compressive　strength　and　environmental　impacts.