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The growing interest in structural health monitoring (SHM) and the recent technological progress have encouraged the research community to study and develop innovative sensors and monitoring methods, like the acoustic emissions (AE) technique. The number of publications on this method has increased exponentially in the last decade. However, most of the experimental validations of AE techniques are based on tests carried out in laboratory conditions on specimens or individual structural elements, and the applications to full-scale bridges in operation are typically concerned with damage states that do not jeopardize their safety. In this paper, we analyze the results of AE monitoring of a full-size prestressed concrete highway bridge subjected to a load test up to its failure. The bridge was built in 1968 and regularly maintained over the years. It is representative, by type, age, and deterioration state, of similar bridges in operation on the Italian highway network. Based on these results, we discuss the effectiveness of AE monitoring of in-service structures under regular traffic and exceptional load transits. We aim to answer the following questions: (i) Can AE discriminate whether a viaduct has local damages, such as concrete cracks? (ii) Can AE identify damage initiation, for instance, during an exceptional load transit? (iii) Can AE provide qualitative and quantitative information on damage propagation? (iv) Is it worth to invest on AE monitoring rather than “traditional” monitoring, such as crack-opening sensors?
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