Investigation of the Bond Strength Between Existing Concrete Substrate and UHPC as a Repair Material

Abstract

The performance of any repaired concrete structure, depends on the quality of the interfacial transition zone of the composite system formed by the repair material and the existing concrete substrate. The main aim of this paper is to evaluate the bonding behavior between normal strength concrete (NSC) substrate as an old concrete and Ultra High Performance Concrete (UHPC) as a repair material. In order to assess the bond behavior, standard slant shear test and splitting tensile test were carried out. The relation between surface roughness and bond strength in shear and indirect tension for different surfaces roughness has been assessed. The old concrete surfaces were roughened by mechanical wire brush, scarifying using an electrical grinder, scabbling by a mechanical drill and as cast without roughening. Analysis of the results indicates that bond strength increases when UHPC is used for shear and tension alike. For the scabbling technique, the shear strength yields values 251.8% higher than the those for as cast surface and 153% for tension strength. In addition, UHPC show advantages that qualify it for repairing and strengthening techniques including adding a new concrete to the existing concrete substrate. In general, rough surface preparation leads to a higher bond strength. R a coefficient is a representative parameter and related to the bond strength, particularly, for shear strength. Finally, the results showed that tension strength is less sensitive to the surface roughness level and more proportional to the repair material strength.