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To date, however, NDE measurement methods have not been widely adopted. The reasons for this are twofold: 1. The state-of-the-art has not been developed to the point where the techniques are routinely implemented in the field; and 2. There has been a lack of well planned and thought out programs to obtain the kind of basic measurements and theory that are essential to evaluating proposed non-destructive techniques (Al-Qadi et al., 1995b). Since NDE is a powerful tool in assessing the performance and characteristics of constructed facilities, the development and implementation of an accurate and widely accepted non-destructive method of assessment is desirable.
GPR is one of several NDE methods for bridge decks that has been proposed and tested over the last couple of decades. One of the potential advantages of GPR is that it is able to analyze a bridge deck rapidly without having to contact the slab. This enables configuring a test system that can evaluate bridge decks with a minimal disruption to traffic.
The leading cause of deterioration in reinforced concrete bridge decks is believed to be a progressive breakdown that begins with the application of deicing salts and harsh environmental and loading conditions and ends with the disintegration of the roadway. The intermediate steps are: 1. The diffusion of chloride ions, from these chemicals, into the concrete. 2. Once the chloride ions penetrate to the rebar surface, they break down the passive iron oxide film that normally protects the steel. 3. The breakdown of the passivation layer enables rebar corrosion to initiate. 4. As rebar steel corrodes, it expands, sometimes with an increased volume ratio of five. 5. The expansion of the corroded rebar steel causes tensile forces in the concrete, which, in turn causes cracks in the concrete. 6. The appearance of cracks in the concrete promotes further chloride ion, water and oxygen penetration to the rebars, which accelerates the corrosion process. 7. The corrosion and cracking process continues with end result being the formation of large cracks, commonly referred to as delaminations. The delaminations often run horizontally in the bridge deck from rebar to rebar, but eventually emerge at the surface in the form of large spalls, or potholes (Joyce, 1984; Manning and Holt, 1980; and Escalante et al. 1984).
In colder states, such as those in New England, the condition of concrete disintegration due to cycles of freezing and thawing appears to be as prevalent as delamination due to rebar corrosion (Maser, 1989). Concrete disintegration caused by freeze thaw damage to the cement matrix is known as scaling, and reduces the concrete to a gravely matrix which may contain either air or water (Maser and Kim Roddis, 1990; and (Maser and Kim Roddis, 1990; and Carter et al., 1986). In this mode of disintegration, moisture accumulates within the bridge deck. As the moisture freezes it expands. When the tensile force due to this expansion exceeds the tensile strength of the concrete cracking occurs. This leads to a “waterfall” effect in which the cracks grow, allowing them to retain more water that causes them to grow more. Subsurface moisture may also cause delamination between pavement layers, allowing heavy traffic to dislodge chunks of surface pavement from the weakened road, resulting in the condition referred to as spalling (Smith, 1995).
使用雷达成像技术对钢筋混凝土桥梁的无损检测
这个项目的总体目标是促进高级的雷达探地技术,这样就可以成为一个更加实用和可靠的工具来评估钢筋混凝土桥面的完整性,尤其在新英格兰特别关注桥梁的具体问题。这个项目由新英格交通运输协会(NETC)项目94-2进行融资的“使用雷达成像技术检测钢筋混凝土桥梁的无损。”该雷达探地钢筋混凝土道路项目包括数据统计,实验室和现场研究。论文网
在探地雷达,电磁学、结构工程和科学仪器的发展有经验的多学科小组的调查人员,马萨诸塞州大学的佛蒙特州和顾问负责这个项目。佛蒙特大学的调查人员包括Dryver r•休斯顿教授和彼得•l•富尔教授和几个研究生和本科生。马萨诸塞州调查员Infrasense Kenneth脉泽博士,博士Inc .)和威廉•应用雷达Weedon Inc .)
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