1、Designation: D 2950 05Standard Test Method forDensity of Bituminous Concrete in Place by NuclearMethods1This standard is issued under the fixed designation D 2950; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method describes a test procedure
3、 for deter-mining the density of bituminous concrete by the attenuation ofgamma radiation, where the source and detector(s) remain onthe surface (Backscatter Method) or the source or detector isplaced at a known depth up to 300 mm (12 in.) while thedetector or source remains on the surface (Direct T
4、ransmissionMethod).1.2 The density, in mass per unit volume of the materialunder test, is determined by comparing the detected rate ofgamma emissions with previously established calibration data.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use.
5、 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. For specificwarning statements see Section 6 and Note 4.1.4 The values stated in SI units are to be regarded as thestan
6、dard. The inch-pound equivalents may be approximate.2. Referenced Documents2.1 ASTM Standards:2D 1188 Test Method for Bulk Specific Gravity and Densityof Compacted Bituminous Mixtures Using Paraffin-CoatedSpecimensD 1559 Test Method for Resistance to Plastic Flow ofBituminous Mixtures Using Marshall
7、 Apparatus3D 2041 Test Method for Theoretical Maximum SpecificGravity of Bituminous Paving MixturesD 2726 Test Method for Bulk Specific Gravity and Densityof Non-Absorptive Compacted Bituminous MixturesD 3665 Practice for Random Sampling of ConstructionMaterials3. Significance and Use3.1 The test me
8、thod described is useful as a rapid, nonde-structive technique for determining the in-place density ofcompacted bituminous mixtures.3.2 With proper calibration and confirmation testing, the testmethod is suitable for quality control and acceptance testing ofcompacted bituminous concrete.3.3 The test
9、 method can be used to establish the properrolling effort and pattern to achieve the required density.3.4 The non-destructive nature of the test allows repetitivemeasurements to be made at a single test location betweenroller passes and to monitor changes in density.3.5 The density results obtained
10、by this test method arerelative. Correlation with other test methods such as D 1188 orD 2726 are required to convert the results obtained using thismethod to actual density. It is recommended that at least sevencore densities and seven nuclear densities be used to establisha conversion factor. A new
11、 factor must be established at anytime a change is made in the paving mixture or in theconstruction process.4. Interferences4.1 The chemical composition of the material being testedmay significantly affect the measurement and adjustments maybe necessary. Certain elements with atomic numbers greatert
12、han 20 may cause erroneously high test values.4.2 The test method exhibits spatial bias in that the instru-ment is most sensitive to the density of the material in closestproximity to the nuclear source.4.2.1 When measuring the density of an overlay, it may benecessary to employ a correction factor
13、if the underlyingmaterial varies in thickness, mineral composition or degree ofconsolidation at different points within the project. (See AnnexA3.)1This test method is under the jurisdiction of ASTM Committee D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.21 onS
14、pecific Gravity and Density of Bituminous Mixtures.Current edition approved June 1, 2005. Published July 2005. Originally approvedin 1971. Last previous edition approved in 1997 as D 2950 91 (1997).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service
15、at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2.2 The surface roughness of the ma
16、terial being testedmay cause lower than actual density determination.4.3 Oversize aggregate particles in the source-detector pathmay cause higher than actual density determination.4.4 The sample volume being tested is approximately0.0028 m3(0.0989 ft3) for the Backscatter Method and 0.0056m3(0.198 f
17、t3) for the Direct Transmission Method. The actualsample volume varies with the apparatus and the density of thematerial. In general, the higher the density the smaller thevolume (Note 1).NOTE 1The volume of field compacted material represented by a testcan be effectively increased by repeating the
18、test at adjacent locations andaveraging the results.4.5 If samples of the measured material are to be taken forpurposes of correlation with other test methods such as D 1188or D 2726, the volume measured can be approximated by a 200mm (8 in.) diameter cylinder located directly under the centerline o
19、f the radioactive source and detector(s). The height of thecylinder to be excavated will be the depth setting of the sourcerod when using the Direct Transmission Method or approxi-mately 75 mm (3 in.) when using the Backscatter Method(Note 2).NOTE 2If the layer of bituminous concrete to be measured
20、is less thanthe depth of measurement of the instrument, corrections must be made tothe measurements to obtain accurate results due to the influence of thedensity of the underlying material. (See Annex A3. for the method used.)5. Apparatus5.1 Nuclear Device An electronic counting instrument,capable o
21、f being seated on the surface of the material undertest, and which contains:5.1.1 Gamma SourceAsealed high energy gamma sourcesuch as cesium or radium, and5.1.2 Gamma Detector Any type of gamma detector suchas a Geiger-Mueller tube(s).5.2 Reference StandardAblock of dense material used forchecking i
22、nstrument operation and to establish conditions for areproducible reference-count rate.5.3 Site Preparation DeviceAmetal plate, straightedge, orother suitable leveling tool which may be used to level the testsite to the required smoothness using fine sand or similarmaterial.5.4 Drive PinA steel rod
23、of slightly larger diameter thanthe rod in the Direct Transmission Instrument, to prepare aperpendicular hole in the material under test for inserting therod. A drill may also be used.6. Hazards6.1 This equipment utilizes radioactive materials which maybe hazardous to the health of the users unless
24、proper precau-tions are taken. Users of this equipment must become familiarwith applicable safety procedures and government regulations.6.2 Effective user instructions together with routine safetyprocedures, such as source leak tests, recording and evaluationof film badge data, etc. are a recommende
25、d part of theoperational guidelines for the use of this instrument.6.3 A regulatory agency radioactive materials license maybe required to possess this equipment.7. Calibration7.1 Calibrate the instrument in accordance with Annex A1.at least once each year. Adjust the calibrations as necessary inacc
26、ordance with Annex A2.8. Standardization and Reference Check8.1 Nuclear test devices are subject to long-term aging ofthe radioactive source, detectors, and electronic systems, whichmay change the relationship between count rate and materialdensity. To offset this aging, the apparatus may be standar
27、dizedas the ratio of the measured count rate to a count rate made ona reference standard. The reference count rate should be of thesame order of magnitude as the measured count rate over theuseful density range of the apparatus.8.2 Standardization of equipment should be performed atthe start of each
28、 days work, and a permanent record of thisdata retained.8.2.1 Perform the standardization with the apparatus locatedat least 8 m (25 ft) away from other sources of radioactivity andclear of large masses or other items which may affect thereference count rate.8.2.2 Turn on the apparatus prior to stan
29、dardization andallow it to stabilize. Follow the manufacturers recommenda-tions in order to provide the most stable and consistent results.8.2.3 Using the reference standard, take at least four repeti-tive readings at the normal measurement period and determinethe mean. If available on the apparatus
30、, one measurementperiod of four or more times the normal period is acceptable.This constitutes one standardization check.8.2.4 If the value obtained in 8.2.3 is within the followingstated limits, the apparatus is considered to be in satisfactoryoperating condition and the value may be used to determ
31、ine thecount ratios for the day of use. If the value is outside theselimits, allow additional time for the apparatus to stabilize,make sure the area is clear of sources of interference and thenconduct another standardization check. If the second standard-ization check is within the limits, the appar
32、atus may be used,but if it also fails the test, the apparatus shall be adjusted orrepaired as recommended by the manufacturer. The limits areas follows:?Ns2 No?#2.0 =No/F (1)where:Ns= value of current standardization count,No= average of the past four values of Nstaken previously,andF = value of any
33、 prescale.NOTE 3The count per measurement periods shall be the total numberof gammas detected during the timed period. The displayed value must becorrected for any prescaling which is built into the instrument. Theprescale value (F) is a divisor which reduces the actual value for thepurpose of displ
34、ay. The manufacturer will supply this value if other than1.0.8.3 Use the value of Nsto determine the count ratios for thecurrent days use of the instrument. If for any reason themeasured density becomes suspect during the days use,perform another standardization check.D29500529. Procedure9.1 In orde
35、r to provide more stable and consistent results:(1) Turn the instrument on prior to use to allow it to stabilize,and (2) Leave the power on druing the days testing.9.2 Standardize the apparatus.9.3 Select a test location in accordance wtih the projectspecifications, or, if not otherwise specified, i
36、n accordance withPractice D 3665. If the instrument will be closer than 250 mm(10 in.) to any vertical mass that may influence the result,follow the instrument manufacturers correction procedure.9.4 Maximum contact between the base of the instrumentand the surface of the material under test is criti
37、cal. Themaximum void shall not exceed 6 mm (14 in.). Use native finesor fine sand to fill the voids and level with the guide/scraperplate.9.5 For the Direct Transmission Method use the guide/scraper plate and drive the steel rod to a depth of at least 25 mm(1 in.) deeper than the desired measurement
38、 depth.NOTE 4Caution: Extreme care must be taken when driving the rodinto compacted bituminous concrete as it may cause a disturbance of thematerial which could cause errors in the measurement. Drilling may bemore suitable.9.6 Place the source in the proper position. For the DirectTransmission Metho
39、d measurements move the instrument sothat the rod is firmly against the side of the hole in the gammameasurement path.9.7 Take a count for the normal measurement period. If theBackscatter Method using the Air Gap Technique is used takean additional measurement in the air-gap position as recom-mended
40、 by the manufacturer. (See Note 2)9.8 Determine the ratio of the reading to the standard countor the air-gap count. From this ratio and the calibration andadjustment data, determine the in-place density. (See Note 5and Note 6)NOTE 5Some instruments have built-in provisions to compute theratio, bulk
41、(or wet) density, and allow an adjustment bias.NOTE 6If the depth of the bituminous concrete layer under test is lessthan the depth of measurement of the instrument, the value obtained in 9.8must be adjusted. (See Annex A3.)NOTE 7Do not leave the gage on a hot surface for an extended periodof time.
42、Prolonged high temperatures may adversely affect the instru-ments electronics. The gage should be allowed to cool between measure-ments.10. Calculation of Results10.1 Using the calibration chart, calibration tables, or equa-tion, and coefficients, or instrument direct readout feature, withappropriat
43、e calibration adjustments, determine the in-placedensity. This is the bulk (or wet) density.10.1.1 An adjustment bias can be calculated by comparingthe results from a number of instrument measurements to theresults obtained using Test Method D 2726.10.2 Compare the results obtained to samples compac
44、ted byTest Method D 1559 or with the results of test methods such asD 2041 to determine acceptability (percentage of compaction).11. Report11.1 Report the following information:11.1.1 Make, model, and serial number of the test apparatus,11.1.2 Date and source of calibration data,11.1.3 Date of test,
45、11.1.4 Standard count for the day of the test,11.1.5 Test site description including project identificationnumber, location and mixture type(s),11.1.6 Thickness of layer tested and any adjustment bias,11.1.7 Method of measurement (backscatter or direct trans-mission), depth, count rate, calculated d
46、ensity of each mea-surement and any adjustment data, and11.1.8 Percentage of compaction, if required.12. Precision and Bias12.1 Precision:12.1.1 While an instrument count precision of 10 kg/m3(0.62 lbf/ft3) for the Backscatter Method and 5 kg/m3(0.31lbf/ft3) for the Direct Transmission Method is typ
47、ical on amaterial of approximately 2.25 mg/m3(140 lbf/ft3) density,with a measurement time of one minute, it only applies to theinstrument for repetitive measurements at the same location.12.1.2 Instrument count precision is defined as the changein density that occurs corresponding to a one standard
48、 devia-tion change in the count due to the random decay of theradioactive source. The density of the material should be in theapproximate range of 2150 and 2350 kg/m3(135 to 145lbf/ft3). Both the density of the material and the time period ofthe count must be stated. It may be determined from a seri
49、es of20 or more counts taken without moving the instrument, oralternately from the calibration data using the assumption thats is equal to the=count at that density. The count must be thetrue instrument count corrected for any pre-scaling.P 5sS(2)where:P = apparatus precision in density (kg/m3or lbf/ft3),s = one standard deviation of the count, andS = the slope of the calibration curve at the defined densityvalue.12.1.3 Precision as Used on Actual Pavement SurfacesTesting has shown that there is no statistical difference in15-second, 1-minute, or 4-minute average
