Interfacial interaction mechanism and theoretical bond strength model between UHPC-CA and steel bar

The bond property is the basis of the bear collectively load between the steel bar and Ultra-High Performance Concrete with Coarse Aggregate (UHPC-CA). In this paper, the theoretical calculation method of bond strength between UHPC-CA and high-strength steel bar is studied. The chemical adhesion strength, friction coefficient, and mechanical interlock process of the two were investigated respectively through the refined bond property tests. The failure model is established from the interlock failure characteristics, and the bond strength is obtained theoretically. Results show that the chemical adhesion strength and friction coefficient between UHPC-CA and steel bars are 0.07 MPa and 0.5, respectively. The friction coefficient between UHPC-CA is 1.15. The interlock failure process of UHPC-CA and steel bars can be divided into three stages: uncracked stage, crack development stage, and split stage. The crack develops at an angle of 52° to the steel bar's axis and tends to stagnate at a height of 4.5 times the rib. A theoretical bond strength model is established and it is proved that the model is applicable not only to UHPC-CA but also to UHPC. This study can provide a theoretical basis for determining the anchorage length of steel bars in the design of UHPC-CA/UHPC structure, and can also provide a reference for the formulation of relevant standards.