Top-bar effect of steel bars in self-consolidating concrete (SCC)

Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation, and use in congested reinforced concrete structures characterized by difficult casting conditions without applying vibration. The bond characteristics of such SCCs are very important for their application in practical construction. This paper presents the results of an investigation dealing with the local bond strength between self-consolidating concrete and steel reinforcing bars. Twelve concrete specimens grouped in two series made of normal concrete (NC) and SCC were tested. In each specimen, three steel bars were embedded in concrete at different locations: bottom, middle and the top of the specimen. Cover thickness varied for different embedded bars. Bond strength and slip of each steel bar were measured in a pullout test. The type of bond failure was by splitting for all specimens. Test results were compared with the values calculated by two proposed equations and ACI 318 Code. Based on the results of this study, the local bond strength of top bars for SCC is about 20% less than that for NC. For the bottom bars, however, the results were almost the same. Comparison of the local bond strength between test results with the values calculated by ACI 318 Code shows that in the case of SCC, the location factor of ACI Code should be increased.