In this paper, we describe an experimental study of concrete behavior under a uniaxial tensile load by use of the thermally-compensated Coda Wave Interferometry (CWI) analysis. Under laboratory conditions, uniaxial tensile load cycles are imposed on a cylindrical concrete specimen, with continuous ultrasonic measurements being recorded within the scope of bias control protocols. A thermally-compensated CWI analysis of multiple scattering waves is performed in order to evaluate the stress-induced velocity variation. Concrete behavior under a tensile load can then be studied, along with CWI results from both its elastic performance (acoustoelasticity) and plastic performance (microcracking corresponding to the Kaiser effect). This work program includes a creep test with a sustained, high tensile load; the acoustoelastic coefficients are estimated before and after conducting the creep test and then used to demonstrate the effect of creep load.

The seismic imaging methods currently in the development stage need to be tested for experimental validation under controlled conditions. Yet natural media are very complex, and moreover, the parameters along the measurement profile prove difficult to evaluate independently of the seismic method itself. To satisfy this need, the ultrasonic measurement laboratory (MUSC) presented in this research has been devised to experimentally model seismic field measurements by using reduced-scale models. This facility is composed of small-scale models of the underground, an optical table with two moving arms, a laser interferometer, and adapted piezoelectric transducers used as the seismic sources. The source system has been adapted to simulate the behavior of a point-surface seismic source. This is essential to reproduce the spatial energy distribution of a surface seismic source and supersedes the sources used in the past for other reduced-scale seismic experimental models. The comparisons of experimental data collected with MUSC and numerical data simulated by means of finite-element viscoelastic modeling indicate very good agreement of time arrivals and amplitudes for a range of propagation distances until the amplitude has decreased to the system noise level. These results demonstrate that the MUSC laboratory is a system with plenty of promise for validating seismic imaging methods through testing on a perfectly known propagation model prior to field application

This paper presents an ultrasonic method, based on the nonlinear acoustic mixing of coda waves with lower-frequency swept pump waves, for providing an efficient global detection of small cracks in cementitious materials. By simultaneously comparing, forboth uncracked and cracked mortars, the ultrasonic velocity variations and decorrelation coefficients between the unperturbed and perturbed signals with pump amplitude, this method makes it possible to accurately detect cracks with widths of around 20 μm in correlation with velocity variations of approximately 0.01%. The potential influence of certain material parameters such as microscopic damage is also discussed