Acoustoelastic effect in concrete material under uni-axial compressive loading

This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δc=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions.