Nondestructive Evaluation of Prestressed Concrete Structures by Means of Acoustic Emissions Monitoring

Abstract

The acoustic emission (AE) technique has been found to be an informative nondestructive testing (NDT) method for evaluation of structures constructed with certain materials. While AE evaluation procedures and evaluation criteria have been proposed for nonprestressed concrete structures, standardized AE evaluation criteria for prestressed concrete beams are not available. The main objective of the study described in this dissertation was to develop and evaluate practical AE methods for integrity assessment of in-service prestressed concrete structures. The study encompassed a laboratory investigation of the AE response of prestressed concrete beams as well as a field investigation of the AE response of an in-service prestressed concrete bridge. The results of this study indicate that AE monitoring holds promise for nondestructive evaluation of prestressed concrete structures. For the laboratory study, AE was monitored while sixteen prestressed concrete T-beams?twelve beams constructed with self-consolidating concrete (SCC) and four beams constructed with conventionally consolidated concrete?were loaded in cycles of increasing intensity to failure. Several AE parameters, such as amplitude, duration, and signal strength, were investigated in relation to the structural integrity of the beams. Three previously proposed AE criteria for integrity evaluation of reinforced concrete members were evaluated with respect to the behavior of these prestressed concrete specimens. A new evaluation method based on the signal strength moment was proposed and proved effective for indicating the integrity of the prestressed concrete beams. The behavior and AE response of the SCC beams were compared with those of conventionally consolidated prestressed concrete beams. In addition, the effectiveness of the recently proposed ACI 437 Cyclic Load Test (CLT) NDT method for concrete structures was evaluated vis-à-vis the behavior of the laboratory specimens. Results indicated good agreement between the CLT assessment criteria and two of the AE evaluation criteria for prestressed concrete beams. For the field investigation, two spans of a damaged highway bridge were load tested to investigate the practical effectiveness of AE monitoring for in-service prestressed concrete bridges. Procedures for in-situ AE evaluation of prestressed concrete bridges were proposed and evaluated by comparing the AE results from the load tests with the corresponding structural deformations.