[Show abstract][Hide abstract] ABSTRACT: Most concrete and reinforced concrete buildings date back to the first half of the last century. Concrete proved to be a durable construction material in the recent years. However, reinforced concrete structures often experience degradation after years of service. Steadily tightening requirements for the building structure reliability give rise to the need for new diagnostic methods being capable of revealing building structure failures being about to occur soon, so that defective parts, if any, can be repaired or replaced in time. Destructive diagnostic methods have been developed during the recent years. Unfortunately, application of these methods impairs the structure integrity. Therefore, increasing attention is being paid to the development of non-destructive testing methods, among which acoustic methods are ranking as the most promising ones. These methods are mostly used for the defectoscopy of homogeneous materials and simple-shaped bodies. They have however not been elaborated enough to cope with diagnosing highly inhomogeneous materials, which is just the case of concrete. Our research focuses on studying potential applications of the acoustic emission method to testing the concrete and reinforced concrete elements and structures. A problem has arisen during our measurements of reinforced concrete elements, namely, how to distinguish the acoustic emission signal variations, which are due to steel armature corrosion, from those brought about by concrete composition changes, processing technology or material degradation induced defects. Therefore, in direct connection with the research of reinforced concrete structures, the effect of the plain concrete specimen structure on the acoustic emission signal variations has been studied.
[Show abstract][Hide abstract] ABSTRACT: Stability of building structures is one of very important issues in the field of non- destructive defectoscopy. Taking into account the fact that most of concrete and reinforced concrete structures were created in the first half of last century, it is evident that a search for new and simple defectoscopic methods, allowing the researchers to determine the integrity of these building structures or their parts, is of primary importance. It is also essential to develop and/or refine the methods designed to estimate the lifetime of building structures. The current methods of non- destructive testing of building materials are suitable for the defectoscopy of homogeneous materials and simple-shaped bodies. Their application to inhomogeneous building materials is difficult in the case of small-sized cracks and defects uniformly distributed throughout the specimen. This is why non-destructive diagnostic methods (NDT) are acquiring growing importance, helping the researchers to evaluate properly the condition of a bridge and decide upon the most convenient method maintenance, repair or refurbishment of the bridge in question or its parts and schedule them accordingly. Reconstructions of motorway bridges are frequently accompanied with long-time restrictions of the number of motorway lanes, which result in considerable delays and consequent financial losses of the motorway users. If the application of NDT methods contribute to optimizing the bridge repair interventions and their scheduling in conformity with safety rules, then the costs of researching new NDT methods are fully justified. One of the methods, which is recognized worldwide as the most promising for the mentioned purposes, is the acoustic emission (AE) method. By contrast to most other NDT methods, AE is a comprehensible method, allowing both one-shot examination and long-term monitoring of the condition of the structure under consideration or its selected parts. The present paper deals with the use of the AE method from the viewpoint of its application to diagnosing the bridge structure reinforcement corrosion and its consequences.
[Show abstract][Hide abstract] ABSTRACT: Specimens manufactured from concrete m xes differing from each other in the content of the aerating agent were studied in our experiments. The acoustic emission method has been applied to studying acoustic phenomena arising in the material under test as a concomitant to the generation of micro-defects, which in turn result from the application of an external load. Both intact specimens and specimens which had been subjected to two different freeze-thaw degradation cycles were tested. The frequency of the acou tic emission overshoots, as recorded in the course of the measurements, has been processed using the cumulative curve method. Moreover, the Kaiser effect and the Felicity effect have been analyzed and evaluated. Analyses of our experiments furnish evidence for the acoustic emission signals to be able to reflect quite truly the degradation-induced crack generation and development processes. i s t t To verify the existence of correlation, if any, between the acoustic emission parameter changes and the specimen structure integrity deterioration, additional methods have been applied to the test specimens, both non-destructive (changes in the ultrasonic impulse propagation velocity, changes in the dynamic modulus magnitude) and destructive (change in the flexural tensile strength, change in the compression strength). Our check-out measurements furnish evidence for the structure integrity deterioration to result from mechanical and thermal stressing and confirm the acoustic emission parame ers to correlate with the material structure defect occurrence.
[Show abstract][Hide abstract] ABSTRACT: Corrosion of built-in steel reinforcement ranks among the most serious mechanisms of bridge structure degradation. Visual inspection of a bridge cannot provide any information on the internal structure and integrity of the reinforced concrete elements of the bridge. This is why non-destructive diagnostic methods are acquiring growing importance, helping the researchers to evaluate properly the internal condition of a bridge. In this domain, methods employing the non-linear acoustic spectroscopy (NEWS – Nonlinear Elastic Wave Spectroscopy) achieved rush advancement recently. 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.