Ultrasonic Testing of Damage in Concrete under Uniaxial Compression

Experiments using ultrasound were conducted to evaluate microcrack growth and degradation of elastic properties in cement-based materials during uniaxial compression. Prismatic specimens (76.2 x 76.2 x 152.4 mm) made of three concrete mixtures, mortar, and hardened cement paste were used in the experiments. The specimens were subjected to monotonic axial loading until failure while ultrasonic shear and longitudinal pulses were recorded. Changes in the amplitude, velocity, and frequency contents of the pulses were correlated to the increasing levels of stress. Two scalar damage models were applied to evaluate whether the concrete damage induced by axial loading leads to the independent degradation of the two moduli of elastic isotropy or only one. The first model considers the degradation of the secant modulus of elasticity alone. The second approach assumes degradation of two independent moduli of elasticity assuming damage to remain isotropic. The ultrasonic damage estimators based on pulse velocity were defined and compared with the mechanical measurements.