1、Standard Method of Test for In-Place Density of Asphalt Mixtures by Nuclear Methods AASHTO Designation: T 355-151American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2c T 355-1 AASHTO Standard Method of Test for In-Plac
2、e Density of Asphalt Mixtures by Nuclear Methods AASHTO Designation: T 355-1511. SCOPE 1.1. This test method describes the procedure for determining the in-place density of asphalt mixtures by use of nuclear gauge. The density of the material is determined by the backscatter/air-gap ratio method. 1.
3、2. DensityThe total density of asphalt mixtures is determined by the attenuation of gamma radiation where the source and detector(s) remain on the surface (backscatter method). 1.2.1. The density in mass per unit volume of the material under test is determined by comparing the detected rate of gamma
4、 radiation with previously established calibration data. 1.3. SI Unitsthe values stated in SI units are to be regarded as the standard. The inch-pound equivalents may be approximate. It is common practice in the engineering profession to concurrently use pounds to represent both a unit of mass (lbm)
5、 and of force (lbf). This implicitly combines two systems of units, that is, the absolute system and the gravitational system. 1.3.1. In the U.S. Customary units system, the pound (lbf) represents a unit of force (weight). However, the use of balances or scales recording pounds of mass (lbm) or reco
6、rding density (lbm/ft3) should not be regarded as nonconformance with this standard. 1.4. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices
7、and determine the applicability of regulatory limitations prior to use. See Section 6, Hazards. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 168, Sampling Bituminous Paving Mixtures T 191,
8、 Density of Soil In-Place by the Sand-Cone Method T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 331, Bulk Specific Gravity (Gmb) and Density of Compacted Hot Mix Asphalt (HMA) Using Automatic Vacuum Sealing Method 2.2. ASTM Standards: D2216, Standard Test M
9、ethods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-2 AASHTO D2937, Standard Test Method for Density of So
10、il in Place by the Drive-Cylinder Method D7013/D7013M, Standard Guide for Calibration Facility Setup for Nuclear Surface Gauges 3. SIGNIFICANCE 3.1. This test method is useful as a rapid, nondestructive technique for the determination of the in-place density of asphalt mixtures. 3.2. This test metho
11、d is used for quality control and acceptance testing of compacted asphalt mixtures for construction and for research and development. 3.3. DensityThe fundamental assumptions inherent in the methods are that Compton scattering is the dominant interaction and that the material under test is homogeneou
12、s. 3.3.1. Test results may be affected by chemical composition, sample heterogeneity, and to a lesser degree, material density and the surface texture of the material being tested. 3.4. The test results can be used to establish the optimum rolling effort and evaluate the job mix formula for in-place
13、 properties. The nondestructive nature allows for repetitive measurements at a single test location and statistical analysis of the results. Note 1For in-place density results, correlation with cores is recommended (see Appendix X1). 4. INTERFERENCES 4.1. In-Place Density Interferences: 4.1.1. The c
14、hemical composition of the sample may affect the measurement, and adjustments may be necessary. 4.1.2. The gauge is more sensitive to the density of the material in close proximity to the surface. Note 2The nuclear gauge density measurements are somewhat biased to the surface layers of the material
15、being tested. This method is more sensitive to the material within the first several inches from the surface. 4.1.3. Other radioactive sources must not be within 10 m (30 ft) of the gauge in operation. 4.1.4. Large objects must be at least 3 m (10 ft) away. 4.1.5. Use the gauge manufacturers correct
16、ion procedure when the gauge will be closer than 600 mm (24 in.) to any vertical mass, or less than 300 mm (12 in.) from a vertical pavement edge. 5. APPARATUS 5.1. Nuclear Density Gauge (Either Density/Moisture or Density Gauge)While exact details of construction of the gauge may vary, the system s
17、hall consist of: 5.1.1. Instruction ManualFor the specific make and model of gauge. 5.1.2. Radiation SourceA sealed source of high-energy gamma radiation such as cesium or radium. 5.1.3. Gamma DetectorAny type of gamma detector such as a Geiger-Mueller tube(s). 2015 by the American Association of St
18、ate Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-3 AASHTO 5.2. Reference StandardA block of material used for checking gauge operations, for correcting source decay, and to establish conditions for a reproducible reference count r
19、ate. 5.3. Site Preparation DeviceA plate, straightedge, or other suitable leveling tool. 5.4. Transport CaseFor properly shipping and housing the gauge and tools. 5.5. Filler MaterialFine-graded sand from the source used to produce the asphalt pavement or other acceptable materials. 5.6. Radioactive
20、 materials information and calibration packet containing: 5.6.1. Daily standard count log; 5.6.2. Factory and laboratory calibration data sheet; 5.6.3. Leak test certificate; 5.6.4. Shippers declaration for dangerous goods; 5.6.5. Procedure memo for storing, transporting, and handling nuclear testin
21、g equipment; and 5.6.6. Other radioactive materials documentation as required by local regulatory requirements. 6. HAZARDS 6.1. The gauge utilizes radioactive materials that may be hazardous to the health of the users unless proper precautions are taken. Users of the gauge must become familiar with
22、applicable safety procedures and government regulations. 6.2. Effective user instructions together with routine safety procedures, such as source leak tests, recording and evaluation of film badge data, etc., are a recommended part of the operation and storage of this gauge. 7. CALIBRATION 7.1. Cali
23、bration of the gauge will be in accordance with Annexes A1 and A2 (if applicable). (See also ASTM D7013/D7013M.) 8. STANDARDIZATION 8.1. All nuclear density gauges are subject to long-term aging of the radioactive sources, detectors, and electronic systems, which may change the relationship between
24、count rates and the material density. To offset this aging, gauges are calibrated as a ratio of the measurement count rate to a count rate made on a reference standard or to an air-gap count (for the backscatter/air-gap ratio method). The reference count rate should be in the same or higher order of
25、 magnitude than the range of measurement count rates over the useful range of the gauge. 8.2. Standardization of the gauge on the reference standard is required at the start of each days use and a permanent record of these data shall be retained. Standard counts should be taken in the same environme
26、ntal conditions as the actual measurement counts. The standardization shall be 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-4 AASHTO performed with the gauge at least 10 m (30 ft) away fro
27、m other radioactive sources and clear of large masses or other items which may affect the reference count rates. 8.2.1. Turn on the gauge and allow for stabilization according to the manufacturers recommendations. If the gauge is to be used either continuously or intermittently during the day, it is
28、 best to leave it in the “power on” condition to prevent having to repeat the stabilization (refer to manufacturer recommendations). This will provide more stable, consistent results. 8.2.2. Using the reference standard, take at least four repetitive readings at the normal measurement period and obt
29、ain the mean. If available on the gauge, one measurement of four or more times the normal period is acceptable. This constitutes one standardization check. Use the procedure recommended by the gauge manufacturer for determining compliance with the gauge calibration curves. Without specific recommend
30、ations from the gauge manufacturer, use the procedure in Section 8.2.3. 8.2.3. If the mean of the four repetitive readings is outside the limits set by Equation 1, repeat the standardization check. If the second standardization check satisfies Equation 1, the gauge is considered in satisfactory oper
31、ating condition. If the second standardization check does not satisfy Equation 1, the gauge should be checked and verified according to Sections A1.8 and A2.5. If the verification shows that there is no significant change in the calibration curve, a new reference standard count, No, should be establ
32、ished. If the verification check shows that there is a significant difference in the calibration curve, repair and recalibrate the gauge. ( )1.96 /so oN N NF= (1) where: Ns= value of current standardization count, No= average of the past four values of Nstaken for prior usage, and F = factory pre-sc
33、ale factor (contact gauge manufacturer for the factor). 9. PROCEDURE 9.1. Select a relatively smooth and flat test location where the gauge will be at least 3 m (10 ft) away from any large objects. Follow the gauge manufacturers correction procedures when closer than 600 mm (24 in.) to a vertical ma
34、ss or less than 300 mm (12 in.) from a vertical pavement edge. 9.2. Prepare the test site in the following manner: 9.2.1. Maintain maximum contact between the base of the gauge and the surface of the material under test. Use filler material to fill surface voids. Spread a small amount of filler mate
35、rial over the test site surface and distribute it evenly. Strike off the surface with a straightedge (such as a lathe or flat-bar steel) to remove excess material. 9.3. Backscatter or Backscatter/Air-Gap Ratio Method of In-Place Nuclear Density and Moisture Content: 9.3.1. Place the gauge on the tes
36、t site. Using a crayon or chalk, mark the outline or footprint of the gauge. Then place the gauge in the backscatter position. 9.3.2. Take a 1-min test and record the (wet) density reading. 9.3.3. Rotate the gauge 90 degrees centered over the original footprint (see Figure 1). Mark the outline or fo
37、otprint of the gauge. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-5 AASHTO 9.3.4. Take another 1-min test and record the (wet) density reading. 9.3.5. If the difference between the two 1-
38、min tests is greater than 40 kg/m3(2.5 lb/ft3), retest in both directions. If the difference of the retests is still greater than 40 kg/m3(2.5 lb/ft3), test at 180 and 270 degrees. 9.3.6. The density reported for each test site shall be the average of the two individual 1-min (wet) density readings.
39、 Figure 1Footprint of the Gauge Test Site with Core Location in the Center of the Footprint 10. CALCULATION OF RESULTS 10.1. Percent Compaction: 10.1.1. It may be desired to express the in-place density as a percentage of some other density, for example, the laboratory densities determined in accord
40、ance with T 209. This relation can be determined by dividing the in-place density by the laboratory density and multiplying by 100. In-Place Density100 % CompactionMaximum Density=(2) 11. REPORT 11.1. The report shall include the following: 11.1.1. Standardization and adjustment data for the date of
41、 the tests; 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-6 AASHTO 11.1.2. Make, model, and serial number of the test gauge; 11.1.3. Name of the operator(s); 11.1.4. Date of last instrument
42、 calibration or calibration verification; 11.1.5. Test site identification; 11.1.6. Thickness of layer tested; 11.1.7. Density in kg/m3or unit weights in lb/ft3; 11.1.8. Percent compaction and percent compaction corrected with cores, when applicable; and 11.1.9. Any adjustments made in the reported
43、values and reasons for the adjustment. 12. PRECISION AND BIAS 12.1. No precision or bias statements are available at this time. 13. KEYWORDS 13.1. Compaction test; construction control; density; moisture content; nuclear methods; quality control; water content. ANNEXES (Mandatory Information) A1. (W
44、ET) DENSITY CALIBRATION AND VERIFICATION A1.1. CalibrationNewly acquired gauges shall be calibrated initially. Existing gauges shall be calibrated after repairs that may affect the gauge geometry. Existing gauges shall be calibrated to reestablish calibration curves, tables, or equivalent coefficien
45、ts if the gauge does not meet the specified tolerances in the verification process. If the owner does not establish a verification procedure, the gauge shall be calibrated at a minimum frequency of 24 months. A1.2. VerificationExisting gauges shall be verified at a minimum frequency of 12 months. Th
46、e verification process and resultant tolerances obtained over the depths that the gauge shall be formally recorded and documented. If the verification process indicates a variance beyond the specified tolerances, the gauge shall be calibrated. A1.3. The calibration response of the gauge shall be wit
47、hin 16 kg/m3(1.0 lb/ft3) on the blocks on which the gauge was calibrated. This calibration may be done by the manufacturer, the user, or an independent vendor. Nuclear gauge response is influenced by the chemical composition of measured materials. This response must be taken into account in establis
48、hing the assigned standard block density. The blocks used for calibration shall be capable of generating a general and reliable curve covering the entire density range of materials tested in the field. The density of these standard blocks shall be determined to an accuracy of 0.2 percent. A1.3.1. Re
49、-establish or verify the density of the blocks used to calibrate or verify calibrations any time the blocks are transported to another location, damaged, altered in any way or at a period not to 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 355-7 AASHTO exceed 5 years. Density of blocks composed of natural materials such as soil or rock shall be verified annually. A1.4. Sufficient data shall be taken on each density standard block to e
