Bond Strength of Ultra-High-Performance Concrete Under Direct Tension Pullout

Bond occurs at the interface between the reinforcing bars and the cover concrete and enables force transfer between the two media. Thirteen specimens comprising four distinct UHPC or ECC (Engineered Cementitious Composite) material compositions and two different values cover thicknesses to the embedded bar were tested. Experimental results were compared with bond strength values obtained from beam tests where anchorage length in the constant moment region and material properties were the same. Bond strength measurements obtained from the DTP setup were half the corresponding values obtained from beam specimens, whereas the DTP setup showed more sensitivity to the increase of the cover thickness. Detailed nonlinear finite element analysis was conducted using two alternative levels of approximation in modeling the bar matrix interface. The occurrence of unaccounted for confining pressures and restraint effects were shown in conventional pullout methods, while the DTP setup provided the most conservative estimate of bond strength.