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Every concrete structure has concrete-to-concrete surfaces as placing joints whichare discontinuous planes in concrete produced during construction, which shouldinseparably adhere to each other for better performance. The adhesion of newlycast concrete with old concrete is the most critical issue for retrofitting existingconcrete structure. The first issue to study for improving mechanical properties ofinterfacial adhesion performance in concrete is the thorough understanding of themechanism of interfacial fracture. For that purpose, tension softening diagram(TSD) is the best resort. It means that TSD comprises the most fundamentalfeatures of fracture mechanics parameters [1] including tension softening initialstress (ft), critical crack width (Wcr) and fracture energy (GF).