Determination of Stress State of a Uniaxially Loaded Concrete Element Using Amplitude of an Ultrasonic Pulse

The nondestructive evaluation of concrete structures using ultrasonic waves has been an important tool in the structural health monitoring (SHM). It can be used to assess homogeneity, uniformity, integrity and stress state of a concrete. The latter is dependent on a phenomenon called acoustoelastic effect which relates stress state of a material to pulse velocity, however apart from pulse velocity, amplitude of the waves is highly stress dependent. This research paper presents an experimental study to quantify change in ultrasonic wave amplitude when concrete element is subjected to stress and propose a novel relationship between amplitude and stress. Experiments were conducted on cylindrical concrete specimens subjected to uniaxial loading and changes in ultrasonic wave velocity and amplitudes were observed. The study concluded that amplitude holds greater potential in determination of stress state and may be used as a primary tool for the same. Velocity exhibited linear increase with applied stress, an average change of approximately 4%. Conversely, the amplitude of an ultrasonic pulse increased linearly by more than 120% under stress. As the system approached failure, there were rapid fluctuations in amplitude, which could be interpreted as an early indicator of impending failure.