Experimental Study on Bonding Properties between Finishing Rolled Rebar and Grouting Material

Abstract

In bearing capacity testing of prestressed concrete pipe piles, grouting material is filled up to the bottom of the pipe pile, which is equipped with a finishing rolled rebar. The reaction force of the reaction beam is transferred to the anchor pile through the bonding force between the finishing rolled rebar and grouting material. Therefore, investigating the bonding properties between the finishing rolled rebar and grouting material is essential to remove barriers to the application of the anchor pile method in bearing capacity testing of the prestressed concrete pipe pile. In this study, the bonding properties of 11 groups of specimens were studied through pull-out tests, and the effects of the cover thickness, diameter, and anchorage length of reinforcement on the bond strength between finishing rolled rebar and grouting material as well as on the bond stress-slip curve were explored. The test results showed that the bond stress-slip curve between finishing rolled rebar and grouting material can be divided into two stages, i.e., slip stage and splitting failure stage. In the slip stage, a linear relationship exists between bond stress and slip amount, and microcracks appear in the grouting material around the finishing rolled rebar. In the splitting failure stage, the slip amount increases rapidly under uplift load. Finally, the grouting material around the finishing rolled rebar forms a failure zone, and splitting failure occurs. The bonding capacity and bond strength between finishing rolled rebar and grouting material increase with the increasing cover thickness of the rebar. The bond strength is the maximum for a relative cover thickness of 3.0, and the difference between the maximum and minimum values is more than 9%. The bonding capacity between rebar and grouting material increases slightly with the increasing rebar diameter, but the bond strength decreases with the diameter, and the difference between the maximum and minimum bond strengths is more than 21%. As the contact area between finishing rolled rebar and grouting material increases, the bonding capacity between them increases with the increasing anchorage length of the rebar. However, the bond strength first increases, then decreases, and finally stabilizes with the increasing anchorage length, and the difference between the maximum and minimum bond strengths exceeds 14.64%.