Evaluation of stress in concrete using ultrasonic waves
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This research investigates the use of ultrasonic waves to evaluate the stress and damage in concrete. Tests were conducted on 6 in. x 6 in. x 12 in. plain concrete specimens (f'c = 6,000psi) at different loading stages that include 20, 40, 60, and 80% of the concrete compressive strength. Unloading at each stage was also recorded to evaluate the damage in the concrete structure. Use of higher amplitude waves were used to trigger nonlinear ultrasonic behavior. Various voltage amplitudes were used in this research at various loading stages, which included 200, 400, and 900V. The data showed a difference in wave velocity (time of flight), amplitudes, and frequency components. The time of flight (TOF) increased in a linear fashion with increased damage (previous load level). However, load on the specimen (at low level of load) decreased the time of flight readings. The amplitudes of higher frequency harmonics of waveforms decreased with damage and load level. However, both the slope of the TOFs and harmonic amplitudes with load level were not the same for the specimens tested making determination of a constant to evaluate stress in concrete difficult.
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