Abstract: In the purpose of selecting a concrete most suitable for bonding, three kinds of concrete (ordinary Portland cement, slag cement, and composite Portland cement) were bonded by three binders respectively, and the bonding effect were compared with split tensile strength as the evaluation indicator. Furthermore, the equivalent coefficient β of bonding strength, which is an index of evaluation the strength of bonding between new and old concrete, is proposed for the first time. It is the ratio of splitting tensile strength of a bonded concrete to splitting tensile strength of standard specimen of the concrete. Comparison of β among the three concretes revealed that the bonding effect of three binders on ordinary Portland cement is better than that of the other two, with the 28 d bonding strength reaching 86% of the tensile strength of standard specimen, which suggest that ordinary Portland cement is the most suitable for bonding among the three concretes.

Key words: bonding between new and old concrete, short age, binder, bonding strength, equivalent coefficient