Bond Strength between the Old and the New Concrete

Abstract

Bond strength is the most important criteria in any concrete repair. Bond strength is the strength at the interface between two concrete of different ages. A good bond strength is the sign of successful repair work done. There are various factors which affect the bond strength but the main factors responsible are surface roughness and the contact surface area between the concrete. Both the factors have been studied in this project.
Three different types of composite specimens were cast and two types of tests were done to determine the bond strength. As contact surface area place a major role in the strength of the bond, the interface angle between the old and the new concrete were cast at 300 and 900 to provide two different area of contact and to compare the results between them. Proper surface roughness has been provided to the old concrete to ensure better bonding. Alkali activated material like Metakaolinand Silica Fume has been used in the repair concrete to increase the bond strength by adding it as a partial replacement of sand. Three types of composite specimen have been cast keeping the old concrete as same and replacing the repair concrete with Metakaolin modified concrete and Silica Fume modified concrete and the compressive strength of the composite specimen were taken at 28 days and 60 days.Slant shear test and ertical shear test were performed to determine the bond strength of the composite specimen of two different interfacial angle.
The results revealed that the use of supplementary cementing material like Metakaolin increased the bond strength by 11% after 28 days and Silica Fume by 16% under Slant shear test.Similarly the Vertical shear test gave about 11% increase in bond strength due to Metakaolin and 39% increase in bond strength by Silica Fume.