Effect of Loading Frequency on Flexural Fatigue Behaviour of Concrete

Frequency of loading plays a signicant role in influencing the fatigue response of concrete. It is widely accepted in the literature that concrete fatigue life increases with increase in loading frequency. This behaviour is counter-intuitive, as the specimen is expected to fail in less number of cycles when subjected to higher loading frequency. This paper aims at understanding the fracture and failure mechanisms responsible for this counter intuitive behaviour through an experimental investigation. The flexural fatigue experiments are performed on concrete beam specimens subjected to three different loading frequencies: 0.5 Hz, 2 Hz and 4 Hz with the aid of acoustic emission technique. The mechanical and acoustic emission results reveal that the increased fatigue life for specimens subjected to higher loading frequencies is attributed to the widely distributed and randomly oriented micro cracks that can blunt the effect of high stresses by increasing the energy required to cause failure. The concrete specimens subjected to lower loading frequencies tend to exhibit brittle behaviour and consequently fail at lower number of fatigue load cycles.