The objective of this paper is to use advanced modeling capabilities to represent different cracking schemes around reinforcement steel and chloride-graded concrete to determine potential relationships between measured GPR signals and attenuation, and potential deterioration states of bridge decks.The American Society of Civil Engineers determined that, in 2009, more than 26% of bridges in the United States were structurally deficient or functionally obsolete, and that there is a significant cost associated with maintaining the current level of deficient bridges (roughly $13 billion a year, according to AASHTO). Non-destructive testing, such as ground penetrating radar (GPR) surveys, can help to determine the condition of bridges. These investigations have a significant advantage over traditional visual inspection in that the condition of the subsurface can be inferred before damage has progressed to the point of being visible at the surface. This information can be extremely valuable in the scheduling and allocation of resources for repair and rehabilitation.The examination of the data from GPR surveys reveals significant attenuation of the signal scattered from the rebar in areas of concrete contamination and rebar corrosion. However, it is unclear if this attenuation is due to geometric changes in the bridge deck, such as cracking and debonding around the corroding rebar, changes to the electromagnetic properties of the surrounding concrete, e.g. due to chloride infiltration, or a combination of the two. Using finite difference time domain modeling of electromagnetic wave scattering the contribution of these factors is considered to obtain signal attenuation matching results observed in the field. It was found that the attenuation of the signal due to severe cracking does not govern over the variation of moistures and chlorides (or permittivity and conductivity) throughout the bridge deck.Downloaded 06/28/16 to 128.210.126.199. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/

Ground penetrating radar (GPR) antennas are key elements for the operation of aircoupled, compact, low-cost systems that can be operated at road speeds to map subsurface defects such as corroded rebar, trapped moisture, voids, and pavement layers. This paper presents requirements and tradeoffs for such antennas, as well as a brief methodology for the design process to frame the context and boundary conditions of the antenna problem. Furthermore, the paper discusses a number of planar antennas that have been designed in printed circuit board (PCB) technology using low-cost, glass-reinforced epoxy laminate sheets such as FR4.The ultra-wide-band operation of antennas, along with other key parameters such as gain and beam width, is very important in the design of a useful GPR antenna for air-coupled operation. The interconnected relationship between antenna parameters limits the designs and constrains the upper bounds of the performance that can be achieved. Regulatory specifications such as FCC compliance create additional burden on the specifications and requirements.A rounded bowtie antenna, a slotted bowtie antenna and two types of Vivaldi antenna are designed, simulated, fabricated, and characterized. All are intended to operate within the 1.1-3.5 GHz frequency band and benefit from compact size while providing high gain to allow for the detection of pavement layers and rebar in bridge decks to a depth of up to 2 feet. In-field measurements of the antennas, together with the GPR system, are presented for static testing scenarios such as buried rebar in a sand box and concrete slab. The antenna testing over the sandbox and concrete slab demonstrates the great potential of utilizing the proposed antennas in air-coupled GPR systems, especially the compact rounded bowtie and slotted bowtie antennas.

No abstract

Ground penetrating radar (GPR) antennas are key elements for the operation of aircoupled, compact, low-cost systems that can be operated at road speeds in order to map subsurface defects such as corroded rebar, trapped moisture, voids, and pavement layers. This paper presents requirements and tradeoffs for such antennas as well as a brief methodology for the design process in order to frame the context and boundary conditions of the antenna problem. Furthermore, the paper discusses a number of planar antennas that have been designed in printed circuit board (PCB) technology using low-cost, glass-reinforced epoxy laminate sheets such as FR4.Ultra-wide-band operation of the antennas along with other key parameters such as gain and beamwidth are very important in the design of a useful antenna for air-coupled operation. The interconnected relationship between antenna parameters limits the designs and constrains the upper bounds of the performance that be achieved. Regulatory specifications such as FCC compliance create additional burden on the specifications and requirements.A rounded bowtie antenna, a slotted bowtie antenna and two types of Vivaldi antenna are designed, simulated, fabricated, and measured. All are intended to operate within the 1.5 -3.5 GHz frequency band and benefit from compact size while providing high gain to allow for the detection of pavement layers and rebar in bridge decks to a depth of up to 2 feet. In-field measurements of the antennas together with the GPR system are presented for static testing scenarios such as buried rebar in sand box. Symposium on the Application of Geophysics to Engineering and Environmental Problems 2013Downloaded from library.seg.org by Yale University: Geology Library on 05/16/15. For personal use only. FCC ConstraintApart from considerations of antenna performance, the FCC (Federal Communications Commission) imposes regulations on UWB systems that also have to be taken into account. Since the FCC 02-48 specification exerts strict limits on maximum average emission above 960 MHz, especially at frequency range of 960-1610 MHz. This specification restricts the power level to as low as -65.3 dBm as illustrated in Figure 1. The frequency band above 2 GHz was considered to be the key frequency of operation (Federal Communications Commission, 2002). Furthermore, in order to maintain good penetrating ability of the radar, the lower frequency band less than 900 MHz was also considered as a secondary option. Symposium on the Application of Geophysics to Engineering and Environmental Problems 2013 Downloaded from library.seg.org by Yale University: Geology Library on 05/16/15. For personal use only. Symposium on the Application of Geophysics to Engineering and Environmental Problems 2013 Downloaded from library.seg.org by Yale University: Geology Library on 05/16/15. For personal use only.