A fatigue crack propagation equation of reinforced concrete (RC) beams strengthened with a new type carbon fiber reinforced polymer was proposed in this paper on the basis of experimental and numerical methods. Fatigue crack propagation tests were performed to obtain the crack propagation rate of the strengthened RC beams. Digital image correlation method was used to capture the fatigue crack pattern. Finite element model of RC beam strengthened with carbon fiber reinforced polymer was established to determinate J‐integral of a main crack considering material nonlinearities and degradation of material properties under cyclic loading. Paris law with a parameter of J‐integral was developed on the basis of the fatigue tests and finite element analysis. This law was preliminarily verified, which can be applied for prediction of fatigue lives of the strengthened RC beams.

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To improve the weak mechanical properties of the foamed concrete that resulted from a large number of pores, a plant fiber is used as fill with the matrix. In this study, five contents of sisal fiber are added into the foamed concrete to investigate the static and fatigue performance of composites. The static and fatigue experimental results show that the sisal fiber can improve the mechanical properties of the foamed concrete. When the content of sisal fiber is less than 0.15%, the higher the content of sisal fiber, the greater the bending strength and fatigue life of the foamed concrete. In contrast, if the sisal fiber content is larger than 0.15%, the bending strength and fatigue life decrease with the increasing fiber content. From the regression analyses, the results show that the double linear relationships exist not only between the sisal fiber content and the flexural strength, but also between the sisal fiber content and the fatigue life of the foamed concrete. In this study, the optimal content of sisal fiber mixed in the foamed concrete can be inferred to be 0.133%.

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