Monitoring of ultrasonic velocity in concrete specimens during compressive loading-unloading cycles

Concrete structures are constantly subjected to cracks and stress variations due to the cyclic nature of actions, which lead to opposite effects in the wave propagation velocities. This manuscript investigates the joint effect of acoustoelasticity and damage on two concrete prisms subjected to compressive loading-unloading cycles up to the limit of 75% of the compressive strength. Ultrasonic pulse velocity tests were performed through the emission of longitudinal and transversal waves propagated in the direction of loading, and A-scans were recorded at several load steps during the unloading of each cycle. The results show the relative velocity variations (Delta V/V0) caused by the damage and acoustoelastic effect have similar magnitudes, but in opposite ways. The heterogeneous and brittle behavior of concrete leads to a high dispersion in the velocity results caused by the damage during compressive loading-unloading cycles. The use of the damage state as a reference for the calculus of Delta V/ V0 reduced such a dispersion and increased velocity for higher compressive stresses. (AU)