Effect of reinforcement ratio, fiber orientation, and fiber chemical treatment on the direct tension behavior of rebar-reinforced UHPC

Abstract

The direct tension performance of rebar-reinforced ultra-high performance concrete (UHPC) was investigated in this paper. Nine series of dog-bone specimens were tested under the direct tension load at both material and component levels. The experimental variables include the reinforcement ratio, fiber orientation, and fiber chemical treatment. The experiments showed that the rebar-reinforced UHPC members exhibited the tensile failure with the rupture of steel rebars. Meanwhile, a single and localized main crack was observed, accompanied by closely spaced short and small micro-cracks. It is concluded that the addition of longitudinal reinforcement can effectively improve the post-cracking stiffness, the ability to restrain the crack width and the peak load of UHPC members under direct tension load, whereas indicated little influence on the elastic linear behavior and their first cracking load. Moreover, increasing the reinforcement ratio not only has these effects but also can significantly enhance the yield load and ultimate load. Nevertheless, increasing the reinforcement ratio has little effect on the pre-cracking stiffness and the first cracking load. In addition, the employment of parallel fiber orientation can significantly increase the post-cracking stiffness, first cracking load, yield load and peak load, and can significantly restrain the propagation of the crack width, as well as improve the tension stiffening response of UHPC. However, this method has little effect on the pre-cracking stiffness and the ultimate load. Besides, the fiber chemical treatment with ZnPh had no noticeable effect on the direct tension behavior of rebar-reinforced UHPC specimens. Finally, a formula was set up to calculate the tensile loading capacity of UHPC members and the prediction agreed well with the test results in the present and previous studies.