A. Satoh et alii, Frattura ed Integrità Strutturale, 34 (2015) 397-405; DOI: 10.3221/IGF-ESIS.34.44 397 Focussed on Crack Paths Improvement of adhesion performance of mortar-repair interface with inducing crack path into repair A. Satoh Kumamoto University, Japan M. Satoh, K. Yamada Akita Prefectural University, Japan , A BSTRACT . The most important performance for repair materials is adhesion to the substrate. The authors experimentally find out that high modulus fine aggregates in repair material enhance strength of it as well as the strength of the interface repaired with it, compared to the ordinary repair without fine aggregates. This paper elaborates the mechanisms for that with fractographic observation and FEM analysis based on the results of experiment. Also the authors discuss the ways for enhancing the strength and ductility of the repaired mortar. K EYWORDS . Interface; Concrete; Repair; Strength; Ductility. I NTRODUCTION he adhesive performance is one of the most important issues for applying repair materials to existing reinforced concrete structures. There should be many analytical studies for getting the fruitful results from experiments to achieve high performance of surface adhesion. Though there are so many experimental studies [1-3] which discuss enhancement of the strength of interface, there have been very few analytical studies on mortar (or concrete)-to-repair interface [4-6]. There are two ways already known for enhancing the interfacial performance: one is the surface roughness to be repaired and the other is the performance of the repair material. For the former point, it is a generally accepted idea that the roughness should be very large. The authors analytically revealed the roughness of the interface before repairing has the dominating effects to the adhesive performance [6]. Zhang experimentally revealed that the treated roughness of the surface to be repaired is best when the average height of the treated surface is half size of coarse aggregates [7]. But for the latter point, there is no accepted idea whether the strength of the repair material should be high or low. The authors investigated the composition and the performance of the repair material (polymer cement mortar) commercially available, and find out that it does not include fine aggregates and the strength of it is not so high [3]. It is a matter of course that the adhesion performance is limited to the weakest strength among the substrate, interface and the repair. Also the strength of the interface is below the strength of repair. But if the repair is too strong and the crack path extends along the interface, the fracture is very brittle, which should be avoided. Then the most favorable crack path extends in the repair with sufficient adhesive strength in the interface. T