Date of Award

1-1-2013

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

First Advisor

Paul Ziehl

Abstract

Evaluating the integrity of concrete structures is an essential procedure to ensure structural safety and durability. Non-destructive testing (NDT) is needed for localizing and characterizing the growing damage in existing structures and also for quality control of new structures. Visual inspection is a commonly used method; however it is not suitable for early detection of damage and very dependent on the experience of the inspector. More research is needed to establish advanced methods for structural health diagnosis such as acoustic emission (AE). Acoustic emission is notably sensitive to active damage in concrete structures. This thesis includes three studies that mainly investigate the effectiveness of AE for condition assessment.

The first study aims to present a review of AE-based methods for evaluating the state of in-service structures during load testing. Discussion on the reliability of the proposed methods for different types of structures is provided. Acceptance criteria and quantification limits are summarized based on previous researches. AE has shown promising results in assessing the structural condition of concrete members and its ability to detect micro-cracking is well established. The extensive applications of AE accomplished in field are fairly discussed and some recommendations were given for effective diagnosis. This study attempts to pave the way for the standardization of AE as an inspection and evaluation method for in-service concrete structures.

The second study discusses the feasibility of utilizing AE for corrosion detection and quantification. The high sensitivity of AE enables it of detecting the weak stresses emerged due to corrosion initiation and propagation. The ability of AE to monitor the corrosion process was proven by several studies on small and medium scale specimens. Locating the corrosion damage by AE was successfully achieved in laboratory. Quantifying the corrosion damage is examined by means of intensity grading charts for cracked and un-cracked prestressed concrete specimens. However, further research is needed to establish the quantification limits and to extrapolate the results to in-service structures.

The third study investigated the ability of AE to detect damage in prestressed concrete specimens. The study included eight beams that were monitored during cyclic load tests. Five specimens were preconditioned to different levels to present possible practical circumstances. Index of damage based on AE-cumulative energy was investigated for damage assessment. The results were in well agreement with the observed damage. However, this method is not convenient for field application as it involves exceeding the maximum admissible damage during the test. Thus, a modification to the index is proposed to facilitate field implementations. The modified index of damage showed a clear trend with the growing damage and the detection of yielding point was enabled in both cracked and un-cracked specimens.

The studies presented in this thesis provide an overview of different AE-based methods that can serve as guidance for future researchers as well as a case of study for a newly developed method. The outcomes of these studies verify the viability of using AE for structural health diagnosis. AE showed promising ability for corrosion damage assessment. However most of AE-methods require the aid of a benchmark for absolute conclusions. Further investigation is needed for the standardization of AE as an independent non-destructive evaluation method.

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