Corrosion of built-in steel reinforcement ranks among the most serious mechanisms of bridge structure degradation. There are many reasons for the corrosion to occur: failures occurring during the bridge construction, consequences of traffic load, or, simple, ageing of the structures. Visual inspection of a bridge provides general information on the bridge condition. However, it cannot provide any information on the internal structure and integrity of the reinforced concrete or pre-loaded elements of the bridge in question. This is why non-destructive diagnostic methods are acquiring growing importance, helping researchers to properly evaluate the condition of a bridge and decide upon the most convenient methods for maintenance, repair or refurbishment of the bridge in question or its parts and schedule them accordingly.In this domain, methods employing the non-linear acoustic spectroscopy (NEWSNonlinear Elastic Wave Spectroscopy) achieved rush advancement recently. They are based on the fact that a non-linearity, which is due to the presence of a defect, makes an extraordinary indicator of the structure damage. These new, non-destructive methods appear to be promising for application to a wide range of materials featuring relatively heavy non-homogeneities, and for a large span of sites, from micro-chip to bridge structures. The present paper deals with an experimental study of the application of non-linear ultrasonic spectroscopy methods to the detection of steel reinforcement corrosion and its consequences for reinforced concrete specimens subjected to corrosion induced degradation cycles.

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It is important to use adequately reliable non-destructive methods that would be capable of determining the reinforcement conditions in concrete structures. Three different methods: ground penetrating radar, impact-echo method, and metal magnetic memory method were used for testing laboratory-prepared reinforced concrete beams (with a reinforcing bar of the same diameter along its whole length, reinforcing bar locally impaired, and reinforcing bar interrupted). The ground-penetrating radar proved the correlation of signal parameters with the reinforcing bar condition. An impairment/interruption reinforcing bar appeared in the record from measurements in the transversal and longitudinal direction by changes of the observed depth of the reinforcing bar from the concrete surface and direct wave attenuation. The impact-echo method proved that the shifts of the dominant frequencies from the response signal correspond with the impairment/interruption of the reinforcing bar. Results of diagnostics by the metal magnetic memory method were presented by a magnetogram of the magnetic field strength and field gradient on the measured distance. The changes in the magnetic field strength proved different stress concentration zones due to the reinforcing bar condition. The used non-destructive methods showed that they are capable of indicating the different reinforcement conditions in reinforced concrete beams. This paper indicates in which cases and for what reason it is appropriate to use these three methods and in what way they differ from each other.

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Concrete is the most popular building composite material (CM). Its long-term aging properties depend on the mixture, the setting and the curing. When concrete is produced and used in the place where we want it to be for the whole of its life, it is very sensitive and easily ruined. Curing is one of the things that we do to keep concrete protected during the first week or so of its life: we maintain proper temperature (neither too hot nor too cold) and dampness. The acoustic-emission method and the electrical-property measurement technique are applied to monitor early-age concrete. The relationships between the acousticemission activity, the temperature and the electrical properties, e.g., the resistivity and the capacity of concrete at an early age were studied in this research. W. Chen et al. studied the microstructure development of hydrating cement pastes during early ages using non-destructive methods including the ultrasound P-wave propagation-velocity measurement and non-contact electrical-resistivity tests. Nevertheless, there are not many references about the continuous study of the properties of concrete during an early age. A long-time monitoring of concrete properties is necessary to determine its lifetime and quality. The acoustic-emission method was proven to be a very advantageous tool for a non-destructive monitoring of structural microchanges during the lifetime of concrete. The differences between hardened concrete mixtures detected with acoustic emission can partly determine their properties at the age of 28 d. The basic concrete property is its compressive strength after 28 d; nevertheless, this can change over a long time period, thus a continuous measuring needs to be applied. Keywords: concrete, acoustic emission, electrical properties, early age, lifetime, curing Beton je najbolj priljubljen gradbeni kompozitni material (CM). Njegove dolgoletne lastnosti so odvisne od me{anice, polo`itve in strjevanja. Ko je beton izdelan in ko ga polo`imo na mesto, kjer naj bi bil do konca trajnostne dobe, je zelo ob~utljiv in se lahko po{koduje. Strjevanje je ena od stvari, ki zahteva za{~ito betona v prvih tednih njegovega trajanja s pravilno temperaturo (niti pretoplo niti prehladno) in vla`nostjo. Metoda akusti~ne emisije in meritve elektri~nih lastnosti so bile uporabljene za kontrolo mladega betona. Preiskovana je bila odvisnost med aktivnostjo akusti~ne emisije in temperaturo, elektri~nimi lastnostmi, kot sta upornost in kapacitivnost mladega betona. W. Chen s sodelavci je {tudiral razvoj mikrostrukture mlade hidratantne cementne zmesi z neporu{nimi metodami, vklju~no z merjenjem hitrosti napredovanja ultrazvo~nih P-valov, in naredil preizkuse brezkontaktne elektri~ne upornosti. Vseeno ni veliko literaturnih virov o kontinuirnem spremljanju lastnosti mladega betona. Za dolo~itev zdr`ljivosti in kvalitete betona je potrebna dolgotrajna kontrola. Metoda akusti~ne emisije se je izkazala kot napredno orodje za neporu{no kontrolo mikrosprememb zgradbe med trajnostno dobo betona. Razlike, ugotovljene z a...