The construction industry is currently facing two major challenges: the high energy consumption and greenhouse gas emissions associated with Portland cement production, and the substantial costs of repair and maintenance of concrete structures exposed to aggressive environments. Geopolymer concrete, utilizing aluminosilicate materials activated by alkaline solutions, has emerged as a sustainable and environmentally friendly alternative. However, the bond strength of geopolymer-based repair layers under aggressive environmental conditions has not been sufficiently investigated. In this study, nine mix designs were developed using different combinations of precursor materials, including ground granulated blast furnace slag (GGBFS), metakaolin, and zeolite. A constant alkaline solution-to-binder ratio of 0.5 and a sodium silicate-to-sodium hydroxide ratio of 2.5 were adopted. The sodium hydroxide concentration was varied at three levels: 8, 10, and 12 M. A total of 486 cubic and prismatic specimens were prepared and subjected to various curing conditions, including acidic environments (PH = 1 and 3) and sulfate environments with concentrations of 5% and 10%, at curing ages of 7, 28, and 90 days. Compressive strength, flexural strength, pull-off bond strength, and slant shear tests were conducted in accordance with relevant standards. The results indicated that the S100-12M mix (containing 100% slag with 12 M NaOH) exhibited the best overall performance across all exposure conditions, achieving compressive strengths in the range of 65–70 MPa and bond strength values exceeding 2.1 MPa in the pull-off test. Overall, high-molarity slag-based geopolymer concrete can be recommended as an effective repair material for use in aggressive environments.