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This paper elaborates major factors which affect the crack path ofconcrete-to-concrete interfacial surfaces produced with placing joint. Specimens witheight types of placing joints and three types of monolithic ones were employed for theevaluation of tension softening diagram followed by surface observations of theligament after fracture test. The SEM and EPMA analysis revealed that the layer ofCa(OH)2 plays a primary role on the crack path, which was clearly detected by a mapthat indicates Ca/Si ratio. The ratio of fractured part excluding detached part on thesurface divided by the total ligament area was defined as Φ, which proved to be animportant value which is related to initial closure stress (ft) and also the maximumheight on the fractured surface (Pt). As both ft and Pt affect strength (bending strengthfb) and ductility in terms of fracture energy (GF), both fb and GF are affected by Φ.Then the most important treatment for the better mechanical performance for theinterface is removing Ca(OH)2 and obtains large Φ.