雷达成像技术对钢筋混凝土桥梁的无损检测英文文献和中文翻译
A multidisciplinary team of investigators with experience in GPR, electromagnetics, structural engineering and scientific instrument development, from the University of Vermont and consultants from Massachusetts worked on the project. The investigators from the University of Vermont included Professors Dryver R. Huston and Prof. Peter L. Fuhr and several graduate and undergraduate students. The Massachusetts-based investigators were Dr. Kenneth Maser of Infrasense, Inc. and Dr. William Weedon of Applied Radar, Inc.
The overall result of the project was that most of the proposed objectives were met. A working high-frequency (0.5 – 6.0 GHz) system was built and tested on damaged and undamaged slabs in both the laboratory and the field. Damage in the form of thin air-filled delaminations and accelerated corrosion was identified in the laboratory. The field results are a little less certain because of the unknown state of the underlying roadway. The state of the art for GPR has advanced considerably in the past several years. Some of the modern imaging techniques show promise for routine use in GPR surveys of bridge decks. It is recommended that future GPR systems for roadways operate at frequencies above 2 GHz and that they include synthetic aperture radar imaging techniques.
The bridge infrastructure of the United States is distressed. The United States Department of Transportation estimated in early 1994 that as many as 40% of the total number of bridges in this country are structurally deficient, with repair costs estimated in the billions of dollars (Smith, 1995; and Halabe et al. 1995). The leading cause is the deterioration of the bridge deck. Deterioration is due primarily to two mechanisms: 1) Freeze/thaw damage to the concrete (punky concrete), and 2) Corrosion-induced delamination resulting from infiltration of chlorides introduced by winter road salting operations or by ocean spray. Unfortunately, bridge deterioration – including rebar corrosion, delaminations and disintegrating concrete – is often hidden under an asphalt overlay (Maser and Kim Roddis, 1990). Efficiently managing maintenance activities for bridge decks requires tools that can assess the integrity or state of deterioration. One of the major problems with concrete deterioration is that its severity and extent is difficult to assess. The mechanisms of deterioration occur below the surface, and their manifestations are not readily seen in visual inspections. Consequently, agencies are forced to program, prioritize, and set budgets for the repair and replacement of many structures whose conditions are virtually unknown. This has led to "surprises" during construction, and to cost overruns and excess repairs.
Current techniques for condition assessment are slow, labor intensive, intrusive to traffic, and do not produce an accurate estimate of the quantity of deteriorated concrete. These techniques, which include core sampling, corrosion (half-cell) potentials, and chloride ion measurements, are well documented (NCHRP, 1979). Corrosion potentials and chloride ion measurements infer corrosion, but do not address unseen freeze/thaw damage. A more reliable technique, the chain drag, does not work with either asphalt overlays or in heavy traffic conditions with high ambient noise. Alternative non-destructive evaluation (NDE) techniques offer the possibility of more efficiently and effectively assessing the state of a bridge deck.
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