University of Vermont Transportation Research Center

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Prefabricated and pre-stressed reinforced concrete beams and girders are integral components of many highway structures, including those build by rapid construction techniques. Concerns exist regarding the development of cracks during curing, form removal, detensioning, transport, installation, and operation. Non-destructive, Acoustic Emission (AE) sensing techniques have the potential for detecting and locating cracking in prefabricated, prestressed concrete girders used as Prefabricated Bridge Elements and Systems (PBES) in rapid construction practices as part of a Quality Assurance/Quality Control (QA/QC) program. AE sensing records transient elastic waves produced by the release of stored elastic energy resulting in plastic deformations (i.e., crack nucleation and growth) with an array of point sensors. The AE instrument system is relatively portable which can allow for it to be an option for both off-site fabrication QA/QC as well as on-site field QA/QC. This report presents a multi-stage research initiative on acoustic emission measurements of prefabricated and pre-stressed concrete beams used in highway bridge construction during detensioning, craned removal from formwork and transport to bridge sites, along with supporting laboratory tests and numerical analysis. The project objectives are: 1. Identify suitable instruments to monitor pre-stressed and/or post-tensioned concrete girders for cracking activity; 2. Design and develop a reusable instrumentation package; 3. Measure performance and condition of concrete girders during fabrication and transport; 4. Identify test protocols and possible accept/fix/reject criteria for structural elements based on information from monitoring system; and 5. Develop plans for reusing monitoring instruments on multiple bridge projects. Presented are results from laboratory, full-scale girder fabrication, and transport monitoring, along with recommendations for future testing procedures and quality assurance protocol development.