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https://hdl.handle.net/11681/4685| Title: | Technologies for improving the evaluation and repair of concrete bridge decks : ultrasonic pulse echo and polymer injection |
| Authors: | University of Nebraska--Lincoln. Center for Infrastructure Research. Construction Productivity Advancement Research Program (U.S.) Alexander, A. Michel. Haskins, Richard W. Cook, Robert. Baishya, Mantu C. Kelly, Michael. |
| Keywords: | Concrete bridges Evaluation Maintenance Repair Polymer injection Bridge decks Concrete decks Ultrasonic pulse echo |
| Publisher: | Structures Laboratory (U.S.) Engineer Research and Development Center (U.S.) |
| Description: | Technical Report Abstract: A significant number of concrete bridge decks, both public- and nonpublic use, in the United States are subjected to a variety of detrimental environmental conditions. Many of the decks are in northern regions and are subject to cold weather, some of these are subjected to further degradation from the applications of deicing salts. The current major distress noted is the occurrence of shallow delaminations resulting in horizontal voids below the surface of the decks. It appears the majority of the delaminations are caused by freezing and thawing action, by chloride attack that corrodes the reinforcement, and by alkali-silica reaction. All three attack mechanisms require the presence of moisture. Efforts to design and place a dense, impermeable concrete are hindered at times due to the porous nature of concrete. As the concrete ages, a micro-system of tension cracks and other surface imperfections can develop, exposing the matrix to water and chloride infiltration. Water infiltration alone can lead to accelerated alkali-silica reaction and steel-reinforcement corrosion. Surface spalling not only reduces ride quality, but it leads to more serious problems including structural deterioration and failure. Many concrete sealers and penetrants on the market are designed to protect concrete by improving and enhancing its physical properties. Surface sealers such as silane, silicones, and siloxanes have been developed to prevent the infiltration of moisture and chlorides. Penetrants such as high molecular weight methacrylate (HMWM) and epoxies have been developed to penetrate and fill cracks and porous areas in the concrete, sealing it against the infiltration of air, water, and chloride. Once the concrete is effectively sealed, both the progression of alkali-silica reaction and the corrosion of the reinforcing steel are arrested. These materials are also designed to bond to the concrete and thus to the structural integrity of the concrete. Once the delamination voids are filled, the structural integrity of the pavement is regained without the cost and downtime of an overlay. A case study is presented to determine the effectiveness of low-pressure injection of HMWM and epoxy material into delamination voids as a repair process for bridge decks. Test results, together with other physical property testing and modeling, are presented. Also included are suggested procedures, conclusions, and future test programs. Currently, the only standard method of detecting delaminations in concrete bridge decks is the chain drag (ASTM Standard D 4580), "Standard Practice for Measuring Delaminations in Concrete Bridge Decks by Sounding"). As this method depends on someone having an "ear" for hearing the discriminating sound from a delamination, it is subjective. An objective method was needed to evaluate delaminations in bridge decks. The U.S. Army Engineer Waterways Experiment Station (WES) made significant advancements in the development of a new high-frequency, high-resolution, ultrasonic pulse echo (UPE) system for evaluating delaminations in concrete bridge decks. Improvement of various functions was accomplished by the following means: The signal quality was improved by the design of new transducers. The face of the transducers was angled to better direct the transmitted and received energy. Transducer materials were matched in their acoustic impedance to permit better efficiency of transmission and reception. An improved type of lead metaniobate was used as the piezoelectric material. The speed of data acquisition was improved by the development of the rolling pond and a digital oscilloscope. The transducers were immersed in a thin layer of water kept in place by the rolling pond. The rolling pond consists of two large drums covered with a soft rubber and belt-driven pulleys which were covered in a rubber material. As the rolling pond moved along the deck, it provided a continuous rubber seal against the concrete surface and prevented the water from leaking from the protected space. The speed of data acquisition was improved by approximately 700X. The identification of signals was improved by fabricating a store of physical models and developing a ray-based software model. Numerous concrete models were fabricated with varying thicknesses and with various simulated flaws and defects. These models were used in conjunction with the ray-based software model to identify multiple reflections, p-waves, shear waves, and surface waves. The reduction of material noise (scattering from aggregate) was improved by a spectrum-processing algorithm. The presentation of results was improved by commercial software sold by MATLAB, Inc. Previously only one signal could be presented for analysis. MATLAB permitted about 200 signals to be observed in a B-scan presentation which improved the interpretation of results. Progress was made toward the computer interpretation of signals with artificial neural networks (ANNs). Signal recognition is an important application of ANNs. Progress was made on operator guidance on measurement procedure using an Expert System. The system was named SUPERSCANNER, the acronym for Scanned Ultrasonic Pulse-Echo Results by Site-Characterization of Concrete Using Artificial Neural Networks and Expert Reasoning, although time constraints did not permit the ANN and Expert systems to be implemented. The new system demonstrates its potential for commercialization and competition with or replacement of the chain drag in the future. The WES prototype field system is available for performing evaluation services for various organizations. |
| Rights: | Approved for public release; distribution is unlimited. |
| URI: | http://hdl.handle.net/11681/4685 |
| Appears in Collections: | Technical Report |
