Abstract: Civil infrastructure systems such as highways, bridges, buildings represent the skeleton of any nation. The deterioration of bridges in many countries in the last few decades calls for effective methods for condition evaluation and maintenance. Since there is increasing dependency of the society on infrastructure systems such as bridges, proper design and timely monitoring and maintenance is essential. However, various factors such as neglect, overuse and lack of proper inspection and monitoring has led to accelerated deterioration of bridges, Often, unsatisfactory inspection and monitoring leads to detection of damage only at the critical state where repair cost becomes comparable with replacement cost. Assessing the extent of damage and its speedy restoration essentially requires information about the current and previous states of health of the structure. Hence there is a need for continuous monitoring of the health of the structure. This has resulted in the development of several non-destructive testing (NDT) techniques for monitoring their performance. The concept of non destructive testing (NDT) is to obtain material properties of in place specimens without the destruction of the specimen or the structure from which it is taken. It can provide knowledge that may not be possible to deduce from visual observation alone. Successful NDT tests allow locating and characterizing material conditions which might not be visible on the surface but which affects the structural durability or performance. This paper reviews various NDT methods that are currently being used in conjunction with the condition assessment of bridge component when subject to cracking, fracture and other unseen damage cases, specifically focusing on Rebound hammer Test and ultrasonic pulse velocity Test. Also this paper reviews three case studies conducted in India, Malaysia and Turkey. The case study from India determines the quality and strength of a T-beam girder bridge. 75 concrete bridges under the supervision of Public Works Department, Malaysia and 10 out of 200 reinforced concrete bridges (i.e. 10 most deficient bridges) in Turkey were selected to determine the strength and to establish a correlation between visual inspection rating and the non-destructive testing results. The investigation shows that the use of non-destructive testing methods can help reduce the backlog of deficient bridges in two ways. First, these techniques will allow inspectors to get a more accurate view of the condition of a bridge. The second way is by allowing inspectors to locate damages earlier. The studies also show that Ultrasonic pulse velocity Test is the ideal NDT method to predict the deterioration in the structures and to determine the service life of the structures. And there exists a correlation between results of non-destructive tests and condition states based on visual inspections.
Keywords: non-destructive testing, rebound hammer test, Ultrasonic Pulse velocity method, Case Studies.