Experimental study on flexural fatigue behavior of composite T-beams in ultra-high performance concrete reinforced and normal-strength concrete

Abstract

The purpose of this study is to investigate the flexural fatigue properties of reinforced ultra-high performance concrete (RUHPC) T-beams, and composite T-beams of normal-strength concrete-RUHPC (NC-RUHPC) and damaged reinforced concrete (RC) strengthened with RUHPC (RC-RUHPC) under constant-amplitude low-cycle fatigue tests. Firstly, the loading value in the fatigue test was obtained by static load tests. Then, the relationship between fatigue deflection, bending stiffness, fatigue crack width, fatigue crack width growth rate, and fatigue life of RUHPC, NC-RUHPC, and RC-RUHPC T-beams were studied with the fatigue tests. The test results show that one main crack is only formed near the midspan in the later stage of fatigue loading, other bending cracks are micro-cracks, and their propagation is slow and short. The fatigue fracture of steel bars embedded in tested beams occurs after more than 3.7 million cycles. When the steel bars are undergoing fatigue fracture, their stress is significantly lower than the yield strength, and two kinds of fracture surfaces are produced: intergranular fracture and transgranular fracture; the mechanical properties of steel bars are changed in the strength index and plasticity index after fatigue fracture. The cost of UHPC and other materials can be reduced by using NC-RUHPC or RC-RUHPC T-beams in practice.