Until recently, a widespread philosophy in the design of concrete repair was based on this simplistic principle: “repair like with like” (Emmons and Vaysburd, 1995). According to this principle, the properties of the repair material should be as close as possible to those of the substrate. The basic idea behind the concept is the following: if the repair material and the old concrete are too different, they may not “work” together and rapid deterioration may occur. Comparative criteria applying independently to individual properties of the repair material and of the substrate were reported by different authors (Emberson and Mays, 1990a; Plum, 1990; Yeoh et al., 1992; Cusson, 1995). Each moderate property mismatch adds to the overall larger mismatch that may lead to cracking and/or debonding. Obviously, cracking of repairs has to be minimized because it threatens not only the durability of the repair, but also the protection of the embedded reinforcing steel.