Ultrasonic investigation of damage progression in concrete

Coherent and diffuse ultrasonic measurements are used to monitor the state of progressive damage in concrete under compressive loading. The results obtained during a single load cycle experiment are discussed in this paper. In this experiment, uniaxial compression was gradually applied (stress-controlled) to a prismatic plain concrete specimen in small incremental steps. At each load step, the strain (and not stress) was held constant until a series of ultrasonic measurements were completed. Ultrasonic measurements were taken in two directions: parallel and perpendicular to the loading axis. Identical longitudinal (P-wave) dry-contact transducers of center frequency of about 100 KHz were used in both directions. The time scale of the signals was chosen long enough to allow the recording of ultrasonic coda. The evolutions of coherent P-wave velocities, diffuse ultrasonic wave velocities, diffusivity and diffusion (at 100 KHz) with the increasing load are demonstrated and discussed.