An investigation of non-destructive testing techniques for concrete structures

Concrete is the most commonly preferred material for the construction of a wide range of different types of civil structures. Concrete is a composite material produced by mixing aggregate, cement, water and chemical admixtures. It is an adaptable material, which can be conveniently mixed to meet various design and structural requirement whilst it can practically be formed in almost any useful shape. However, the in-service lifetime of concrete structures is drastically reduced when cracking, dynamic displacement or distortion are not immediately detected so as appropriate repairs can be carried out in time. Several important existing structures are inching closer to their end of their serviceable lifetime. Therefore, the application of quantitative non-destructive testing and conditioning monitoring techniques is becoming more important and a necessity in order to accurately and reliably evaluate the overall structural integrity of existing and future concrete structures. This research study is concerned with the investigation of advanced quantitative condition monitoring techniques for concrete structures. More specifically, the combination of Ultrasonic Pulse Velocity (UPV), Acoustic Emission (AE) testing and Visual Inspection (VI) have been selected in order to perform quantitative quality control of concrete beam specimens with different strength levels specifically manufactured for the present research study. The UPV method operational principles are based on the transmission of ultrasonic waves through the thickness of the concrete components. Any differences in the ultrasonic wave velocity measured can be used to effectively evaluate the actual strength of the concrete in a quantitative manner. On the other hand, AE testing is a passive technique, which can be employed to quantitatively monitor damage propagation in concrete structures as well as other materials in order to determine the tactual level of structural degradation with time. Experiments were conducted using a range of different concrete specimen types including both cube and beam-shaped ones with intentionally varying quality. AE data were acquired during compressive and flexural tests performed on the concrete samples manufactured. Various statistical analysis methodologies such as cumulative energy have been considered in trying to effectively quantify damage evolution. This thesis summarises the key findings of this research effort