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Fatigue behaviour of concrete has become an increasingly popular topic in the last century, especially with the development of railway bridges. Fatigue loading may appear in various forms, from physically applied loads, to indirect loads, including corrosion and thermal fatigue among others. These fatigue loadings may occur independently or in conjunction with the applied fatigue loadings, which could exacerbate the fatigue process and likely decrease the lifespan of the structure. The mechanisms of fatigue failure in concrete may be divided into three phases: (1) crack initiation, (2) progressive growth of micro-cracks, and (3) convergence of micro-cracks to form macro-cracks. In fibre reinforced concrete (FRC), energy is dissipated in the wake of the crack tip, which increases the load carrying capacity, thereby providing post-cracking ductility. Unlike ferrous materials, concrete was found to exhibit no fatigue limit after 2 million load cycles. However, its performance may be influenced by stress levels, load frequency, boundary conditions, matrix composition, and number of applied cycles. In this paper, the flexural fatigue behaviour of pre-cracked steel fibre reinforced concrete was investigated. Various pre-cracks and load levels were considered. X-ray Computed Tomography (CT) scans were implemented to determine the extent of damage to the fibres within the concrete matrix after fatigue loading.

In fibre reinforced concrete (FRC), energy is dissipated in the wake of the crack tip through the actions of fibre bridging and fibre pull out. This is the main mechanism which inhibits crack growth, thus increasing the load carrying capacity of FRC by providing post–cracking ductility. Furthermore, the same mechanism is present when FRC undergoes fatigue loading. Typical applications for FRC which undergo significant fatigue loading during their service life include paving applications such as bridge decks, highways and industrial floors. The continuous exposure to cyclic loading results in a decrease in apparent stiffness of the material, which may lead to fatigue failure [1, 2]. Fatigue failures are almost always unexpected, and can have a catastrophic outcome [3, 4]. Thus, the fatigue characteristics become vital performance and design parameters [1]. In this paper, the mechanisms of fatigue failure of pre-damaged hooked-end steel fibre reinforced concrete (SFRC) are investigated at a single fibre level. An initial pre-damage was applied to the fibres before the cyclic loading commenced. The pre–pull out ranged from 0.6 mm to 2.5 mm, and the cyclic loading was applied at 70% and 85% of the maximum static pull out capacity of the fibre embedded in the concrete.

Concrete is a popular construction material used all around the globe. It is strong in compression and weak in tension. To mitigate this tensile weakness, various reinforcement methods have been used over the years, of these, fibre reinforced concrete (FRC) has gained popularity. Fibres not only improve the tensile strength of the concrete matrix, but also control crack propagation through crack bridging action. The goal of this study is to investigate the long-term behaviour of FRC pavements through conduction of static and fatigue meso-scale level tests using different steel fibres. To achieve this goal, the influence of different fibre geometries and embedment angles on the pull-out behaviour of fibres in FRC was investigated first. This was carried out by examining 60mm Dramix 3D steel and 5D steel fibres at single fibre level. The embedment depth was kept constant at half the fibre length, and the fibre embedment angles were tested at 0°, 15° and 30°. The average maximum pull-out load, Amax, was determined first through static tests then fatigue tests were carried out using 85% of the Amax value on pre-damaged samples. These tests indicated that an increase in fibre embedment angle and number of hooks leads to additional anchorage of the fibre. Fibre pull-out was found to be the dominant fibre failure mechanism for the static single fibre pull-out tests (SFPTs).