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- Use of the impact-echo method in nondestructive measurements of the thickness of new concrete pavements / by Clemeña, G. G.(Gerardo G.)(CARDINAL)314479; Virginia Transportation Research Council.(CARDINAL)195142;
Includes bibliographical references (page 31).Final report;The nondestructive impact-echo (IE) method offers a simple means for introducing compressional stress waves into a concrete element or slab and measuring the resonance frequencies associated with the reflections of the waves from any internal voids and the bottom of the slab. It is relatively effective for detecting internal voids or delaminations in concrete, which is the application for which it was developed. It may also be possible to use the method for indirect measurement of the thickness of a slab if the wave propagation velocity in the concrete is known. This study was conducted to determine whether the IE method, by itself, could replace the use of coring for quality-assurance measurements of the thickness of concrete slabs in newly built pavements. The results from tests conducted on three pavements indicated that the wave velocity varied so much, not only between pavements but also within a pavement, that unacceptable errors can result when an average velocity is determined (through limited coring) for a pavement and subsequently assumed for the entire pavement. To reduce the error to an acceptable level, the wave velocity at any test location must be measured to within an acceptable accuracy by another independent method. In pursuit of this approach, an indirect-transmission procedure based on ultrasonic (UT) measurement was incorporated and tested. This combined IE/UT procedure was able to measure thickness with absolute errors of 5 mm in one pavement and 7 mm in another, at a 90% probability. These results can be considered encouraging since the current procedure requires that the length of a core reported to the nearest 3 mm be the average of several measurements around the core and, in some cores, these measurements can have a spread of as much as 13 mm. In addition, it is expected that these errors can be reduced easily with the use of a transducer with a smaller contact face that would be less sensitive to roughness on the surface of grooved concrete pavements.Sponsored by Virginia Department of Transportation, in cooperation with the Federal Highway Administration, under project no.- Subjects: Technical reports.; Pavements, Concrete; Pavements, Concrete; Ultrasonic testing.;
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- The use of ground-penetrating radar in the surveying of overlaid bridge decks : summary report / by Clemeña, G. G.(Gerardo G.)(CARDINAL)314479; Virginia Transportation Research Council.(CARDINAL)195142;
Includes bibliographical references (page 13).Final report.It was shown in a previous study that the presence of delamination in concrete can be detected by the appearance of a distinctive signature in the analog radar reflection profiles recorded when a concrete deck is scanned with ground-penetrating radar. As a follow-up, radar was used on eleven overlaid bridge decks to assess the overall reliability of the technique when applied to the nondestructive inspection of such decks, using the identified radar signature as an indicator of the presence of concrete delamination. The radar results were verified by soundings conducted on the test decks after their overlays were removed. Among the decks tested, the average success rate of radar in detecting real concrete delamination was found to be 82 ± 20 percent (at 95 percentile). In addition, false indication of the presence of delamination had been observed. It was suspected, however, that the presence of debonding and damage in the overlay in some locations contributed extensively to this type of errors since such damages in the decks would likely manifest themselves as anomalies in the reflection profiles close to that associated with concrete delamination. On the other hand, although some concrete delaminations were missed by radar, these misses often involved relatively small delaminated areas. For future studies, it is recommended that additional radar parameters (including localized increased reflectivity at the bituminous/concrete interface, polarity change in the reflection at the interface, distortions in the reflection from the rebars, and attenuation of reflection from the concrete slab) be examined. These parameters can be related to other types of damages often found in overlaid decks in conjunction with the concrete delaminations.Sponsored by Virginia Department of Transportation, in cooperation with the Federal Highway Administration, under contract no.- Subjects: Technical reports.; Concrete bridges; Ground penetrating radar.; Pavements;
- Available copies: 1 / Total copies: 1
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- Everything you need to write great essays you can learn from watching movies / by Douglas, Jay,Ph.D.(CARDINAL)399575;
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- Subjects: English language; Essay; Motion picture authorship.; Report writing.;
- Available copies: 1 / Total copies: 1
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