Fiber Reinforced Concrete (FRC) is recognized as a promising material in the field of new construction and repair. Major advantages are increased toughness and damage resistance, improved durability and thus sustainability. Structural effectiveness and durability of concrete repairs represent a major issue of our time. These two aspects are addressed in this thesis through a multifaceted survey. New possibilities for the application of High Performance FRC in structural repair are investigated by means of combined experimental and numerical analysis. Ultra-thin floor diaphragms for seismic retrofit of buildings, structural strengthening of R/C beams, and seismic retrofit of bridge pier columns are considered. Moreover, a study on bond strength, toughness, and damage resistance of interfaces between substrate and repairs is presented. A new approach to inherent interface characterization is proposed and fundamental considerations on interface properties are included.