1、Designation: D 6087 08Standard Test Method forEvaluating Asphalt-Covered Concrete Bridge Decks UsingGround Penetrating Radar1This standard is issued under the fixed designation D 6087; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers several ground penetratingradar (GPR) evaluation procedures that can be used to
3、evaluatethe condition of concrete bridge decks overlaid with asphalticconcrete wearing surfaces. These procedures can also be usedfor bridge decks overlaid with portland cement concrete andfor bridge decks without an overlay. Specifically, this testmethod predicts the presence or absence of concrete
4、 or rebardeterioration at or above the level of the top layer of reinforc-ing bar.1.2 Deterioration in concrete bridge decks is manifested bythe corrosion of embedded reinforcement or the decompositionof concrete, or both. The most serious form of deterioration isthat which is caused by corrosion of
5、 embedded reinforcement.Corrosion may be initiated by deicing salts, used for snow andice control in the winter months, penetrating the concrete. Inarid climates, the corrosion can be initiated by chloride ionscontained in the mix ingredients. Deterioration may also beinitiated by the intrusion of w
6、ater and aggravated by subse-quent freeze/thaw cycles causing damage to the concrete andsubsequent debonding of the reinforcing steel with the sur-rounding compromised concrete.1.2.1 As the reinforcing steel corrodes, it expands andcreates a crack or subsurface fracture plane in the concrete ator ju
7、st above the level of the reinforcement. The fracture plane,or delamination, may be localized or may extend over asubstantial area, especially if the concrete cover to the rein-forcement is small. It is not uncommon for more than onedelamination to occur on different planes between the concretesurfa
8、ce and the reinforcing steel. Delaminations are not visibleon the concrete surface. However, if repairs are not made, thedelaminations progress to open spalls and, with continuedcorrosion, eventually affect the structural integrity of the deck.1.2.2 The portion of concrete contaminated with excessiv
9、echlorides is generally structurally deficient compared withnon-contaminated concrete. Additionally, the chloride-contaminated concrete provides a pathway for the chloride ionsto initiate corrosion of the reinforcing steel. It is therefore ofparticular interest in bridge deck condition investigation
10、s tolocate not only the areas of active reinforcement corrosion, butalso areas of chloride-contaminated and otherwise deterioratedconcrete.1.3 This test method may not be suitable for evaluatingbridges with delaminations that are localized over the diameterof the reinforcement, or for those bridges
11、that have cathodicprotection (coke breeze as cathode) installed on the bridge orfor which a conductive aggregate has been used in the asphalt(that is, blast furnace slag). This is because metals are perfectreflectors of electromagnetic waves, since the wave imped-ances for metals are zero.1.4 A prec
12、ision and bias statement has not been developedat this time. Therefore, this standard should not be used foracceptance or rejection of a material for purchasing purposes.1.5 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parentheses are forinformation
13、only.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific
14、precau-tionary statements are given in Section 5.2. Summary of Test Method2.1 The data collection equipment consists of a short-pulseGPR device, data acquisition device, recording device, anddata processing and interpretation equipment. The user makesrepeated passes with the data collection equipmen
15、t in adirection parallel or perpendicular to the centerline across abridge deck at specified locations. Bridge deck condition isquantified based on the data obtained.3. Significance and Use3.1 This test method provides information on the conditionof concrete bridge decks overlaid with asphaltic conc
16、retewithout necessitating removal of the overlay, or other destruc-tive procedures.1This test method is under the jurisdiction of ASTM Committee D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.32 onBridges and Structures.Current edition approved July 1, 2008. Pub
17、lished July 2008. Originally approvedin 1997. Last previous edition approved in 2007 as D 6087 07.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2 This test method also provides information on thecondition of bridge decks without
18、overlays and with portlandcement concrete overlays.3.3 A systematic approach to bridge deck rehabilitationrequires considerable data on the condition of the decks. In thepast, data has been collected using the traditional methods ofvisual inspection supplemented by physical testing and coring.Such m
19、ethods have proven to be tedious, expensive, and oflimited accuracy. Consequently, GPR provides a mechanism torapidly survey bridges in an efficient, non-destructive manner.3.4 Information on the condition of asphalt-covered con-crete bridge decks is needed to estimate bridge deck conditionfor maint
20、enance and rehabilitation, to provide cost-effectiveinformation necessary for rehabilitation contracts.3.5 GPR is currently the only non-destructive method thatcan evaluate bridge deck condition on bridge decks containingan asphalt overlay.4. Apparatus4.1 GPR SystemThere are two categories of GPR sy
21、s-tems, depending on the type of antenna utilized for datacollection.4.1.1 GPR systems using air-launched horn antennas withcenter frequencies 1 GHz and greater. The equipment mayconsist of an air-coupled, short-pulse monostatic or bistaticantenna(s) with sufficient center frequency to provide theac
22、curate measurement ofa5cm(2in.) thick asphalt pavement.4.1.2 GPR systems using ground-coupled antennas withcentral frequencies greater than 1 GHz.4.2 Data Acquisition SystemA data acquisition system,consisting of equipment for gathering GPR data at the mini-mum data rates specified in 4.1.1 and 4.1.
23、2. The system shall becapable of accurately acquiring GPR data with a minimum of60-dB dynamic range.4.3 Distance Measurement SystemA distance measure-ment system consisting of a fifth-wheel or appropriate distancemeasurement instrument (DMI) with accuracy of 6100mm/km (66.5 in./mile) and a resolutio
24、n of 25 mm (1 in.).NOTE 1Fig. 1 shows a functional block diagram for multiple GPRsand support equipment.5. Hazards5.1 During operation of the GPR system, observe themanufacturers safety directions at all times. When conductinginspections, ensure that appropriate traffic protection is utilizedin acco
25、rdance with accepted standards.5.2 Electromagnetic emissions from the GPR apparatus, ifthe system is improperly operated, could potentially interferewith commercial communications, especially if the antenna isnot properly oriented toward the ground. Ensure that all suchemissions from the system comp
26、ly with Part 15 of the FederalCommunications Commission (FCC) Regulations.6. Procedure6.1 Conditions for Testing:6.1.1 If soil, aggregate, or other particulate debris is presenton the bridge deck surface, clean the bridge deck.6.1.2 Test the bridge deck in a surface dry condition.6.2 System Performa
27、nce ComplianceThe system shouldbe calibrated and performance verified in accordance with themanufacturers recommendations and specifications. The fol-lowing information is included for reference only and describestypical calibration procedures for different types of systems.Compliance with the follo
28、wing procedures is not required andthe manufacturers calibration procedure takes preference. Forair-launched antennas, this test shall consist of the following:6.2.1 Signal-to-Noise Ratio:FIG. 1 Block Diagram of GPR and Support EquipmentD60870826.2.1.1 Signal-to-Noise Ratio TestPosition the antenna
29、atits far field distance approximately equal to maximum dimen-sion of antenna aperture above a square metal plate with awidth of 43 antenna aperture, minimum. Turn on the GPR unitand allow to operate for a 20-min warm-up period or the timerecommended by the manufacturer. After warming up the unit,re
30、cord 100 waveforms. Then evaluate the recorded waveformfor signal-to-noise ratio. The signal-to-noise ratio is describedby the following equation:Signal Level Amp!Noise Level An!. 20 26.0 dB! (1)6.2.1.2 This will be performed on each of the 100 wave-forms and the average signal-to-noise value of the
31、 100 wave-forms will be taken as the “signal-to-noise of the system.”Noise voltage (An) is defined as the maximum amplitudeoccurring between metal plate reflection and region up to 50 %of the time window after the metal plate reflection, normallyused with the antenna (that is, 1.0 GHz/20 ns: 10 ns.)
32、. Thesignal level (Amp) is defined as the amplitude of the echo fromthe metal plate.6.2.1.3 The signal-to-noise ratio test results for the GPR unitshould be greater than or equal to 20 (+26.0 dB).6.2.2 Signal Stability:6.2.2.1 Signal Stability TestUse the same test configura-tion as described in the
33、 signal-to-noise ratio test. Record 100traces at the maximum data acquisition rate. Evaluate thesignal stability using the following equation:Amax AminAavg, 0.01 1%! (2)where:Amax= the maximum amplitude of the metal plate reflec-tion for all 100 traces,Amin= the minimum amplitude of the metal plate
34、reflec-tion for all 100 traces, andAavg= the average trace amplitude of all 100 traces.6.2.2.2 The signal stability test results for the GPR systemshould be less than or equal to 1 %.6.2.3 Linearity in the Time Axis and Time Window Accu-racy:6.2.3.1 Variations in Time Calibration FactorUse thesame t
35、est configuration as described in the signal-to-noise ratiotest, except that the metal plate can be replaced by anyreflecting object. Collect a single waveform and measure thedistance from the antenna to the reflector. Perform this test atthree different distances corresponding to approximately 15,3
36、0, and 50 % of the time window normally used with thesystem. The time delay between the echo from the aperture ofthe transmitting antenna and that from the reflecting object ismeasured as time t1(where subscript1represents position 1,and so forth). The difference between t2and t1and between t3and t2
37、represents the travel time for a fixed distance in air. Thefactor Ci represents the speed between distance i and i+1. Theallowable variation in measured speed is shown as follows:C1C2Mean of C1and C2, 2 %, (3)where:C1= Distance from Position 2 to Position 1T1C2= Distance from Position 3 to Position
38、2t26.2.3.2 The variation in time calibration factor should beless than 2 %.6.2.4 Long-Term Stability Test:6.2.4.1 Long-Term Amplitude VariationUse the same testconfiguration as described in the signal-to-noise ratio test.Switch on the GPR and allow to operate for 2 h continuously.As a minimum, captu
39、re a single waveform every 1 min, 120total. Calculate the amplitude of a metal plate reflection andplot against time for each waveform. For the system to performadequately, the amplitude of reflection should remain constantafter a short warm-up period. The stability criteria is asfollows:AmaxA20A20,
40、 0.03 3%! (4)where:A20= the amplitude measured after 20 min, andAmax= the largest amplitude measured between 20 minand 120 min.6.3 Pre-Operation Measurement:6.3.1 Free Space Signal (FSP)The equipment manufac-turer may require the GPR antenna to be mounted in anoperational configuration, and 100 wave
41、forms gathered in theabsence of the material to be inspected. Use the average of 100waveforms as a template for clutter removal.6.3.2 Flat Metal Plate (FMP)Position the GPR in anoperation configuration, and gather 100 waveforms whileilluminating a flat plate with dimensions recommended by themanufac
42、turer. This is a measure of the emitted energy to beused in subsequent measurements, and as a template fordecorrelation or background removal, or both.6.4 GPR Data Acquisition:6.4.1 Air-Launched Antenna Systems:6.4.1.1 Make GPR inspection passes in a longitudinal direc-tion parallel to the centerlin
43、e of the bridge deck with theantenna mounted to maintain a manufacturer-recommendeddistance from the bridge deck surface.6.4.1.2 Use a transverse distance (dt) between GPR inspec-tion passes 1 m (3 ft) is suggested.6.4.1.3 Use a longitudinal distance (dl) between GPR scans#150 mm (6 in.).6.4.1.4 Det
44、ermine the starting location for passes, that is, atabutments, joints, or a predetermined location.6.4.1.5 Determine the optimum speed of operation forcontiguous longitudinal coverage based on GPR range sweeprate and the scan-spacing.6.4.2 Ground-Coupled Antenna Systems:6.4.2.1 Make GPR inspection p
45、asses either parallel to thedirection of traffic, or perpendicular to the direction of traffic,depending on the direction of the top layer of reinforcing. Thepass direction should be chosen so that the antenna crossesover the top layer of reinforcing at an angle nearest to 90.D60870836.4.2.2 Use a t
46、ransverse distance (dt) between GPR inspec-tion passes 0.6 m (2 ft).6.4.2.3 Use a longitudinal distance (dl) between GPR scansnecessary to obtain sufficient data 150 mm (6 in.) is sug-gested.6.4.2.4 Determine the starting location for passes, that is, atabutments, joints, or a predetermined location
47、.7. Data Processing7.1 There are two different accepted GPR data processingmethodologies. Both methods employ reflection amplitudes.The first method, the bottom deck reflection attenuation tech-nique, calculates deterioration based on the relative reflectionamplitudes from the bridge deck bottom rel
48、ative to the bridgedeck surface. The second method, the top reinforcing reflectionattenuation technique, utilizes the relative reflection amplitudesfrom the top layer of reinforcing to assess deterioration.7.2 Deterioration Measurements at Top Reinforcing Steelusing the Bottom Deck Reflection Attenu
49、ation Technique:7.2.1 Measure and record the applied signal strength, Vt,atthe deck surface.7.2.2 Measure and record the maximum signal strength ofthe deck bottom echo, Vbs.7.2.3 If Vbsis$0.0264 Vtfor a longitudinal GPR inspectionpass, proceed to 7.2.5. (The number 0.0264 is a constantderived from research data.)7.2.4 If Vbsis 0.0264 Vtafter repeating the longitudinalGPR inspection pass, the data are not reliable for determiningremoval quantities of bridge deck concrete. Processing of thedata will require an alternative technique, such as the techniquedescribed
