Acoustic techniques for concrete evaluation: improvements, comparisons and consistency

In civil engineering, the testing of structures allows a large number of chemical, mechanical and micro–macro structural parameters to be determined. Within the scope of ultrasonic Non-Destructive Testing (NDT), which is often used to evaluate concrete, many different techniques can be employed to generate, propagate, and receive the ultrasound waves, and to process the corresponding signals. The SENSO project, developed by nine partners, provided an opportunity to test a large number of principles related to the material’s characteristics and properties. Concerning the acoustic techniques, the first approach was based on linear propagation with bulk waves and surface waves, or with backscattered waves. The second method involved nonlinear analysis using wave modulation. One aim of the SENSO project was to compare these different techniques, in order to select that having the most promising performance in the laboratory, before transferring the measurement techniques to the field. The objectives were to evaluate the porosity, degree of saturation, modulus of elasticity and compressive strength of concrete. In the present paper, the measurement techniques and measured parameters are presented, together with the improvements developed within the context of the SENSO project. The methodology used to classify and select the ultrasonic techniques is described. It takes into account the sensitivity of the method to changes in the material and associates measurement uncertainties. Finally, the most significant results to evaluate porosity, mechanical characteristics and degree of saturation of various concretes, are developed. The consistency of the results of the measurements is analysed. The advantages and drawbacks of each technique are discussed