Evaluation of deterioration in reinforced concrete structures by AE technique E. Proverbio Acoustic emission (AE) technique is gaining increasing interest for applications in civil engineering. AE indeed is a passive nonintrusive technique that can be applicable either in structural health monitoring (global evaluation) and in defect localization (local evaluation). The most promising application of such a technique seems to be however in the evaluation of growing defects. Defects such as cracks and delamination can be caused by reinforcement corrosion as well as by other concrete deterioration mechanisms (alkali silica reaction, sulphate attack, etc.) as well as originating from improper concrete casting, curing or structure setting. Damage severity can be evaluated by means of the intensity analysis (IA) through the use of different indexes such as ‘Load Ratio’, ‘Calm Ratio’, ‘Felicity Ratio’ or ‘Historical Index’. Damage evolution analysis along time could be however significantly improved by adopting some procedure already used in the field of geophysics and earth science. Among various parameters, the most significant one is the b-value which is derived from the amplitude distribution data of AE following the methods used in seismology. Several application examples applied to prestressed concrete structures are reported in the paper. 1 Introduction The development of reliable and affordable technique for monitoring and for damage evaluation of reinforced concrete structures, and in particular of prestressed concrete structures, is becoming a pressing demand since the increasing age of the structures and progression of deterioration processes. Acoustic emission (AE) technique seems to be very promising in this field since it is not invasive, allows a volume evaluation and at the same time offers the possibility to locate discrete defects. AE was widely used in studying corrosion phenomena and in particular stress corrosion cracking since the early stage of the development of the technique [1]. More recently AE technique was introduced in the civil engineering in evaluating stress corrosion cracking of reinforcing cables in prestressed concrete structure [2] as well as in the detection of corrosion of reinforcing bar and in the identification of the corrosion processes [3]. However, more than in the identification of the corrosion processes itself AE technique could show its greater potentialities in the detection of the highly acoustic emitting effects of rebar corrosion i.e. concrete cracking, concrete spalling and delamina- tion. From this point of view two different approaches can be possible for damage evaluation: i.e. long term monitoring or short term testing. In the former case a continuous acoustic auscultation have to be performed to detect the effects of corrosion progression, that could be time consuming and it requires the immobilization of the whole AE equipment, in the latter case corrosion induced damage can be detected by promoting crack propagation or crack rearrangement by momentary loading of the structure, the most damaged area will act as the most emitting source. Notwithstanding its potentialities AE still have a limited diffusion as a consequence of some difficulties yet to be overcome in the field of data handling and analysis and in particular in finding reliable correlations between AE hit parameters and source typology. Pattern recognition techniques can be used with this aim [4], signal processing is there performed at the waveform level, either by applying digital filtering, Fourier transforms or other processing such as wavelet transform, or by extracting AE features as a mean to describe the shape and content of a detected AE waveform. However, waveform registration requires high data storage capacity and sophisticated equipments. Intensity analysis (IA) is based only on the evaluation of the main AE signal parameters such as energy, counts, amplitude, without the need of the waveform record and is carried out by means of the cross evaluation of different ‘health indexes’ related to AE signal intensity and to loading condition. Materials and Corrosion 2011, 62, No. 2 DOI: 10.1002/maco.201005735 161 E. Proverbio Department Industrial Chemistry and Materials Engineering, Univer- sity of Messina, Viale Ferdinando Stagno d’Alcontres 31, 98166 (Italy) E-mail: proverbi@ingegneria.unime.it www.matcorr.com wileyonlinelibrary.com ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim