1、Designation: D4748 10Standard Test Method forDetermining the Thickness of Bound Pavement LayersUsing Short-Pulse Radar1This standard is issued under the fixed designation D4748; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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 the nondestructive determina-tion of the thickness of bound pavement layers using Groun
3、dPenetrating Radar (GPR).1.2 This test method may not be suitable for application topavements which exhibit increased conductivity due to theincreased attenuation of the electromagnetic signal. Examplesof scenarios which may cause this are: extremely moist or wet(saturated) pavements if free electro
4、lytes are present and slagaggregate with high iron content.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is there
5、sponsibility 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 hazardstatements are given in Section 11.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Roc
6、k, and ContainedFluidsD6087 Test Method for Evaluating Asphalt-Covered Con-crete Bridge Decks Using Ground Penetrating RadarD6429 Guide for Selecting Surface Geophysical MethodsD6432 Guide for Using the Surface Ground PenetratingRadar Method for Subsurface InvestigationE1778 Terminology Relating to
7、Pavement Distress3. Terminology3.1 Definitions:3.1.1 Definitions shall be in accordance with the terms andsymbols given in Terminologies D653 and E1778.3.1.2 Additional definitions can be found in section 3.1.3 ofGuide D6432, and in Ref (1).33.1.3 Additional definitions:3.1.3.1 bound pavement layeru
8、pper layers of a pavementstructure consisting of aggregate materials mixed with cemen-titious binder such as bitumen or Portland cement paste.Examples of bound pavement layers include bituminous con-crete, portland cement concrete, and stabilized bases. Boundpavement layers do not include granular b
9、ase and subbasematerials.3.1.3.2 unbound pavement layerlower layers of a pave-ment structure consisting of untreated aggregate materials suchas sand, gravel, crushed stone, slag, and other stabilizedmaterials. Unbound pavement layers include base, subbase andcompacted subgrade.4. Apparatus4.1 The ap
10、paratus may consist of a vehicle or a cart that isequipped with the following:4.1.1 One or more GPR antennas mounted on the vehicle,cart, or on a trailer4.1.1.1 The antenna for this application typically has acenter frequency that ranges from 1.0 to 2.6 GHz.Atypical 1.0GHz antenna usually has a reso
11、lution sufficient to determine aminimum layer thickness of 40 mm (1.5 in.) to an accuracy of65.0 mm (60.2 in.).Antennas emitting short pulses containinga center frequency of 2.0 GHz and higher provide resolutionsufficient for determination of a minimum layer thickness lessthan 25 mm (1.0 in.) to an
12、accuracy of 62.5 mm (60.1 in.).4.1.1.2 Two basic types of antenna systems are in use:(1) Air-launched antennas that are specifically designed toradiate into the air and are to be used at some distance abovethe pavement surface, typically 20 to 50 cm (8 to 20 inches).(2) Ground-coupled antennas that
13、are specifically designedto operate in contact with the pavement surface.4.1.2 Control Unit consisting of a transmitter, receiver, andtiming control electronics. It transmits and receives low-powerbroad band Radio Frequency (RF) signals through the antenna.1This test method is under the jurisdiction
14、 of ASTM Committee E17 on Vehicle- Pavement Systems and is the direct responsibility of Subcommittee E17.41 onPavement Testing and Evaluation.Current edition approved Dec. 1, 2010. Published March 2011. Originallyapproved in 1987. Last previous edition approved in 2006 as D4748 06. DOI:10.1520/D4748
15、-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of r
16、eferences at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.The RF signals are then converted into a signal suitable fordisplay and resulting interpretation.4.1.3 Distance Measuring Instrument (DMI) with an a
17、ccu-racy of 6190 mm/km (61ft/mile) and a resolution of 305 mm(12 in.) or better.4.1.4 An optional Global Positioning System (GPS) with aninstantaneous positioning accuracy of1m(3ft.) or better.4.1.5 Personal computer suitable for data acquisition, dis-play and storage.4.2 The schematic drawing in Fi
18、g. 1 illustrates a typicalequipment configuration5. Summary of Test Method5.1 Since this test method is based upon measurementsperformed by a GPR system, a brief description of theoperating principles of a system is included herein.5.2 The GPR system transmits and receives electromagneticsignals by
19、means of an antenna.As the transmitted electromag-netic wave propagates through the pavement layers, the waveis refracted and reflected at layer interfaces and received by theantenna. The received signal is recorded by the GPR system interms of amplitude and two-way travel time. Fig. 2 and Fig. 3sho
20、w the schematics of the two antennas types (air-launchedand ground-coupled) and the typical data collected from them.Fig. 4 shows an example of the air-launched GPR data stackedin series with respect to the travel distance along the surveyline.5.3 Layer thickness can be determined using the followin
21、gequation if the velocity and the two-way travel time for theradar wave to travel through a given layer are known.T 5 v 3Dt2(1)where:T = layer thickness,v = velocity of the radar wave through a given material,Dt = two-way travel time through layer.The GPR system measures two-way travel time, so it i
22、seasily obtainable from analysis of the data. For monostaticGPR systems, the velocity of the radar wave can be estimatedfrom the following relationship:v 5c=r(2)where:c = speed of light in air, 300 mm/nsec (11.8 in/nsec),r = relative dielectric constant of layer,Substituting Eq. (2) in Eq. (1) resul
23、ts in the followingequation for layer thickness. Note that this equation is neces-sarily different for bistatic antennas in order to accommodatefor the separation distance between the transmit and receiveantennas.T 5Dt 3 c2=r(4)NOTE 1Definitions of the terms monostatic and bistatic are providedin Se
24、ctions 3.1.3.17 and 3.1.3.4, respectively, of Guide D6432. Forconvenience, these definitions are excerpted from Guide D6432 andrepeated below.Monostatic (1) a survey method that utilizes a single antenna actingas both the transmitter and receiver of EM waves. (2) Two antennas, onetransmitting and on
25、e receiving, that are separated by a small distancerelative to the depth of interest are sometimes referred to as operating in“monostatic mode”.Bistatic the survey method that utilizes two antennas. One antennaradiates the EM waves and the other antenna receives the reflected waves.5.4 The relative
26、dielectric constant or the radar wave veloc-ity of a layer can be obtained in one of three ways: (1) metalplate calibration; (2) ground truth cores at locations where GPRdata were collected; or (3) Common Midpoint (CMP) method.5.4.1 Metal plate calibrationThe metal plate calibrationprocedure involve
27、s obtaining GPR data with the antennaplaced at operating height over a large metal plate, then usingthe amplitude of the metal plate reflection in an equation thatalso incorporates the amplitude of the pavement reflection tocalculate the pavement dielectric constant. This method onlyapplies to air-c
28、oupled GPR antennas. This method allowscalibration at every GPR scan location.FIG. 1 Equipment ConfigurationD4748 1025.4.2 Ground truth coreThis procedure involves coringthe pavement at a known location where GPR data have beenobtained. The radar wave velocity at the core location iscalculated using
29、 the core thickness and the two-way travel timeof the radar reflection from the pavement bottom. This methodassumes that the velocity is uniform over the test area.5.4.3 Common midpoint methodThis procedure involvescollecting data while moving two ground-coupled GPR anten-nas away from each other wh
30、ile transmitting from one antennaand receiving on the other antenna. Mathematical equations areused to calculate the dielectric constant of the pavement basedon the change in two-way travel time of the reflection frompavement bottom versus separation distance between the twoantennas.5.5 The ability
31、to detect a layer depends on the contrastbetween the dielectric constant of that layer and the layerbeneath. A sufficient contrast for thickness determinationusually exists between asphaltic layers and unbound pavementlayers such as soil or aggregate base materials. Such a contrastmay not always be
32、sufficient between concrete and aggregatebase materials, between individual layers of asphalt, or be-tween concrete and cement stabilized base materials. Relativedielectric constants of typical pavement materials are given inTable 1 of this standard and also in Table 1 of Guide D6432.5.6 At some dep
33、th, the reflections at the layer interfacescannot be detected by the GPR. This maximum penetrationdepth is a complex function of GPR system parameters such astransmitted power, receiver sensitivity, center frequency andFIG. 2 Schematics of air-launched antennaD4748 103bandwidth of the GPR system and
34、 signal processing, as well asthe electromagnetic properties of the pavement materials andenvironmental factors such as moisture content.6. Significance and Use6.1 This test method permits accurate and nondestructivethickness determination of bound pavement layers. As such,this test method is widely
35、 applicable as a pavement system-assessment technique.6.2 Although this test method, under the right conditions,can be highly accurate as a layer-thickness indicator, consis-tently reliable interpretation of the received radar signal todetermine layer thicknesses can be performed only by anexperienc
36、ed data analyst. Such experience can be gainedthrough use of the system and through training coursessupplied by various equipment manufacturers or consultingcompanies. Alternatively, the operator may wish to use com-puter software to automatically track the layer boundaries andlayer thickness, where
37、 applicable.7. Calibration and Standardization7.1 The system should be calibrated and its performanceshould be verified per the manufacturers specifications. Typi-cal calibration procedures can be found in Section 6.2 of GuideD6087 and shall not be repeated in this standard. However, itis the manufa
38、cturers specifications that take preference, asemphasized in D6087.8. Procedure8.1 Determine the following prior to the survey:FIG. 3 Schematics of ground-coupled antennaD4748 1048.1.1 Transverse offset of the longitudinal scan line to besurveyed. Typically, the scan lines are in the wheel paths and
39、/oralong the center of the lane of interest.8.1.2 Number of scans per unit distance or the spacingbetween GPR scans. The speed of the traverse is dependent onthe number of scans per unit distance. For air-launched GPRantennas, the traverse speed is constrained only by the desiredspacing of radar sca
40、ns. For typical ground coupled antennas,the traverse speed is limited to approximately 8 km/h (5 mph)in order to maintain steady ground contact.8.2 Warm up the GPR system prior to the survey for aperiod recommended by the manufacturer, typically between30 minutes and an hour.8.3 Calibrate the GPR sy
41、stem per the manufacturer specifi-cations if any.8.4 Continuously traverse the radar antenna along the lon-gitudinal scan line to be tested with minimal vehicle wander.8.4.1 Ensure that the collected GPR data is associated withat least one reference location so that the thickness informationcan be r
42、eported accurately with respect to the roadway stationand transverse offset.8.5 Process the GPR data using a software available for theanalysis. The outcome of this process should be a thicknessprofile of the bound pavement layer with respect to theroadway station.9. Interferences9.1 Determinations
43、made with GPR are adversely affectedby surface and subsurface water. Standing water on the surfaceof the pavement decreases the amount of energy that penetratesthe pavement. This effect is difficult to measure and may varydramatically over a short time interval due to variations in thethickness of t
44、he water layer caused by run-off or evaporation.However, in general, testing shall not be conducted in thepresence of standing water.9.2 The apparatus is subject to interference from othersources of electromagnetic radiation. Interference from nearbyhighpower transmitters manifests itself as large,
45、high-frequency variations in the radar return across the entiremeasurement depth. Other sources of intermittent interferencemay include mobile phones and radios. Testing shall not beconducted in the presence of observed interference.9.3 Large objects such as vehicles have the potential tointerfere w
46、ith the radar return. A conservative, equipmentindependent approach to minimize the effects of large objectsis to maintain these objects at a distance outside the zone ofinfluence as calculated by the following expression:d 5t2 3 k(4)FIG. 4 Series of GPR data displayed with respect to travel distanc
47、eTABLE 1 Relative Dielectric Constants and radar wave velocitythrough the materialsMaterialRelativedielectricconstantsRadar velocity,m/nsRadar velocity,inch/nsAir 1 0.30 11.8Water 81 0.03 1.3Asphalt 2 to 4 0.15 to 0.21 5.9 to 8.4Clay 2 to 10 0.05 to 0.21 1.9 to 8.4Concrete 4 to 10 0.010 to 0.15 3.7
48、to 5.9Granite 5 to 8 0.11 to 0.15 4.4 to 5.9Limestone 4 to 8 0.10 to 0.15 4.2 to 5.9Sand 4 to 6 0.12 to 0.15 4.8 to 5.9Sandstone 2 to 3 0.17 to 0.21 6.8 to 8.4Sandy Soil 4 to 6 0.12 to 0.15 4.8 to 5.9Clayey Soil 4 to 6 0.12 to 0.15 4.8 to 5.9Gravel 4 to 8 0.10 to 0.15 4.2 to 5.9D4748 105whereD = the
49、 zone of influence,K = multiplication constant, 3.28 for d in meters (1 for d infeet), andT = time in nanoseconds of the measured data10. Report10.1 Report at a minimum, the following information:10.1.1 Location and limits of the survey (project ID andbeginning/ending stations).10.1.2 Survey date and weather conditions.10.1.3 Pavement material type (Bituminous, Portland ce-ment, or composite pavement)10.1.3.1 In case of composite pavements such as a bitumi-nous overlaid Portland cement concrete pavement, it may notalways be possible to extract the thickness of t
