Parameters Affecting Direct Shear Bond Between Existing Concrete and New Concrete

Bonding of new concrete on existing concrete for repair or strengthening of structures must consider the various transferring forces that occurred at the joint. One of the important transferring forces is shear force at the joint which depends on various parameters. This research is to study the parameters affecting the direct shear bond between existing concrete and new concrete. The samples used for the test were a cylindrical shape with 150 mm in diameter and 300 mm in length. The existing concrete and the new concrete were connected at the middle of the sample. The parameters of this study were: (1) three different surface roughness of existing concrete, i.e. smooth, slight rough, and very rough surface; (2) two types of new concrete, i.e. plain concrete and steel fiber reinforced concrete; (3) compressive strengths of concrete; and (4) installation of a chemical anchor at the joint. The results were found that the increase in surface roughness of the existing concrete increased significantly the direct shear bond and energy absorption. The use of steel fiber and higher compressive strength in new concrete would increase slightly the bond strength and its displacement as well as energy absorption. The use of steel fiber reinforced concrete and cast in existing concrete having very rough surface would increase bond strength about 2.28%. This might be caused by steel fibers to increase the locking at the interface, In addition, the installation of a chemical anchor at the interface would increase significantly the bond strength and its displacement at 55% and 166%, respectively. Finally, the statistical analysis by using Multiple Linear Regression was found that the parameters affecting direct shear bond with 0.05 significance were surface roughness of existing concrete and installation of chemical anchor at the joint. The equation used to predict the test results were consistent with the results obtained from the test with R² = 0.9539 and F = 28.9824.