Acoustic monitoring for the evaluation of concrete structures and materials

Concrete structures are referred to as the basis of contemporary technical civilization. They support transportation, storage of goods and shelter humans in large numbers. Despite their long endurance, they have ceased to be considered as maintenance free. They are subject to long term loading due to own weight, dynamic loading scenarios including earthquakes, as well as environmental degradation. Thus, concrete structures should undergo inspection and evaluation of their health condition while proper maintenance actions should be proposed. To prolong their useful life span, robust monitoring methodologies should be applied. The first and basic information is extracted from visual inspection. However, this concerns only the surface distress indications. Defects may start to grow from the interior, and therefore, an assessment based solely on visual observation would not be complete. Among monitoring methodologies
that assess the full volume of the structure, acoustic emission (AE) has
started to be applied in a wide basis. AE is a passive technique that offers specific advantages like the real-time monitoring of the defects propagation, which enables to characterize the critical moments of the structure in relation to the applied operational load. Three-dimensional localization of the cracking sources is also possible if a number of sensors are used, while the parameters of the recorded waveforms exhibit strong sensitivity to the mode of cracking enabling estimations of the dominant fracture processes. Additionally, even if accessibility is limited, just a few points of the surface would be sufficient to place sensors, through which large structural volumes are inspected, highlighting the global nature of the technique. In this chapter, the basics of AE are mentioned and discussed in terms of instrumentation and correlation of AE parameters to damage of concrete structures. In addition, current studies aiming at improving the characterization reliability are also discussed.

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