1、Standard Practice for Troubleshooting Asphalt Specimen Volumetric Differences between Superpave Gyratory Compactors (SGCs) Used in the Design and the Field Management of Superpave Mixtures AASHTO Designation: PP 76-13 (2015)1American Association of State Highway and Transportation Officials 444 Nort
2、h Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d PP 76-1 AASHTO Standard Practice for Troubleshooting Asphalt Specimen Volumetric Differences between Superpave Gyratory Compactors (SGCs) Used in the Design and the Field Management of Superpave Mixtures AASHTO Designation: PP 76-13 (2015
3、)11. SCOPE 1.1. This method covers the procedure for troubleshooting asphalt specimen volumetric differences between Superpave gyratory compactors (SGCs) used in the design and field management of Superpave mixtures. Evaluation of SGCs should include the SGC used in the mix design, the SGC used for
4、production quality control (QC), and the SGC used for production quality assurance (QA). The evaluation will assist in the identification of within-procedure differences that may impact the field management of asphalt mixtures. 1.2. This practice may involve hazardous materials, operations, and equi
5、pment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DO
6、CUMENTS 2.1. AASHTO Standards: M 323, Superpave Volumetric Mix Design R 30, Mixture Conditioning of Hot Mix Asphalt (HMA) R 35, Superpave Volumetric Design for Asphalt Mixtures R 47, Reducing Samples of Hot Mix Asphalt (HMA) to Testing Size T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asp
7、halt (HMA) Using Saturated Surface-Dry Specimens T 168, Sampling Bituminous Paving Mixtures T 312, Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor T 344, Evaluation of Superpave Gyratory Compactor (SGC) Internal Angle of Gyration Using
8、Simulated Loading 2.2. Other Standards: ASME B46.1, Surface Texture (Surface Roughness, Waviness, and Lay) FHWA-HIF-11-032, Federal Highway Administration Technical Brief, Superpave Gyratory Compactors 2015 by the American Association of State Highway and Transportation Officials.All rights reserved
9、. Duplication is a violation of applicable law.TS-2d PP 76-2 AASHTO 3. SUMMARY OF METHOD 3.1. This method is intended to provide a uniform process to assist in the identification of within-procedure differences that may impact the field management of asphalt mixes. 3.2. The design, QC, and/or QA SGC
10、s shall be evaluated. All SGCs shall satisfy and be operated according to T 312. 3.3. Laboratory-prepared or production mix may be utilized in the evaluation. 3.4. Documentation of within-procedure differences and assessment of compacted specimens shall be utilized in the evaluation. 3.5. The evalua
11、tion shall be conducted in two phases. The initial evaluation shall use multiple operators and existing within-procedure handling practices. The second phase, if required, shall utilize a single operator and consistent, within-procedure handling practices, and one laboratory shall be used in the det
12、ermination of the compacted bulk specific gravities (Gmb) of the SGC specimens. 4. SIGNIFICANCE AND USE 4.1. SGCs fabricated to operate in accordance with T 312 create cylindrical specimens from loose asphalt mixtures through a gyratory (kneading) effort. Within-procedure differences may impact the
13、comparability of SGCs; in addition, variability within the manufacturing process may result in mechanical differences in SGC performance. 5. LABORATORY DEFINITIONS SPECIFIC TO THIS STANDARD 5.1. The laboratories used in the evaluation are identified in the following sections: 5.1.1. Mix Design Labor
14、atoryThe laboratory, SGC, and operator that produced the mix design for the mix being evaluated. 5.1.2. Field Quality Control LaboratoryThe laboratory, SGC, and operator used by the contractor to ensure the quality of the production process. 5.1.3. Field Quality Assurance LaboratoryThe laboratory, S
15、GC, and operator used by the specifying agency to assure the quality of production mixes. 5.1.4. Independent Quality Assurance LaboratoryThe laboratory, SGC, and operator employed to arbitrate differences in contractor and specifying agency results. 6. PROCEDURE: PHASE IINITIAL EVALUATION 6.1. The s
16、pecifying agency shall identify the laboratories to be included in the evaluation. 6.1.1. The operator responsible for each laboratory shall be used in the initial phase of the evaluation. 6.2. Prior to compaction of any specimens, each operator shall verify the SGC calibration and SGC mold toleranc
17、es according to T 312. 6.3. The evaluation mix shall conform to one of the following sections: 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 76-3 AASHTO 6.3.1. Laboratory-Prepared MixA mix sim
18、ilar to the anticipated production mix should be used. The mix should use the same asphalt binder anticipated for production. One laboratory shall prepare sufficient mix for four SGC specimens per evaluation. Compact each SGC specimen to 115 5 mm in height and 150 mm in diameter. (See Note 1.) Note
19、1T 312 specimen tolerances are 5 mm. Within this tolerance, all specimen final heights being within 2 mm of each other have been reported to improve correlation results. 6.3.1.1. The mixing temperature shall be determined according to T 312. 6.3.1.2. The laboratory-prepared mix shall be conditioned
20、for volumetric mix design prior to compaction according to R 30. 6.3.2. Plant-Produced MixA mix similar to the anticipated production mix should be used. The mix should use the same asphalt binder anticipated for production. One sample shall be taken from a production haul vehicle, according to T 16
21、8, of sufficient size to fabricate four SGC specimens per evaluation. Compact each SGC specimen to 115 5 mm in height and 150 mm in diameter. (See Note 1.) 6.3.2.1. The production mixing temperature shall be recorded and compared to the recommended mixing temperature determined in Section 6.3.1.1. 6
22、.3.2.2. Short-term conditioning is not required for plant produced mix. 6.4. The laboratory-prepared or production mix shall be split in accordance with T 168 and provided to each laboratory. Logistics in the laboratory may result in the cooling of mix samples prior to compaction. The cooling and re
23、heating of asphalt mixes can affect the measured volumetric properties. Reheating of the mix is not part of the mix design as specified in R 35. Any differences in handling shall be recorded. If possible, an observer from either the specifying agency or contractor should assist in recording any with
24、in-procedure differences. 6.5. The mix shall be heated to the required temperature determined in Section 6.3.1.1. Heating may be performed in either the SGC mold or in a pan. The method employed by each laboratory and operator shall be the same and shall be recorded. In addition, the make and model
25、of the oven used shall be recorded. 6.6. Compact four specimens in each SGC according to T 312 to the design number of gyrations (Ndes) anticipated for the production mix. Determine the bulk specific gravity (Gmb) of each specimen in accordance with T 166. Each individual operator shall perform the
26、compaction and Gmbtesting of the specimens. 7. REPORT 7.1. Report the following information on Phase I: 7.1.1. The results of each laboratory shall be compiled as shown in Figure 1. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a v
27、iolation of applicable law.TS-2d PP 76-4 AASHTO (Date) (LABORATORY NAME) 123 Main Street Anywhere, USA 12345 SUPERPAVE GYRATORY COMPACTOR (SGC) EVALUATION FORM Operator Name: SGC: Make: Model: Oven: Make: Model: Mix Designation: Mix Type: (_) Laboratory (_) Production Short-Term Aging: (_) 4 h (_) 2
28、 h (_) None Mixing Temperature, C: Compaction Temperature, C: Heating Method: (_) In Mold (_) In Pan Comments: _ _ _ SGC Compaction Bulk Specific Gravity (Gmb) A B C D Average X Standard Deviation(s) NiniNdesRecorded Observations: _ _ _ Figure 1Superpave Gyratory Compactor (SGC) Evaluation Form 7.2.
29、 Calculate the average Gmband standard deviation(s) of the Gmbof the four compacted specimens based on the SGC height data at the compaction levels for Niniand Ndesaccording to Equations 1 and 2. 7.3. Sample Average: 1niixXn=(1) where: n = number of specimens (4); and xi= bulk specific gravity (Gmb)
30、 of sample i. Report the average to four significant digits. 7.4. Sample Standard Deviation: ( )211niixxSn=(2) where: n = number of specimens (4); xi= bulk specific gravity (Gmb) of sample i; and x = average from Equation 1. Report the standard deviation to four significant digits. 2015 by the Ameri
31、can Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d PP 76-5 AASHTO 7.5. The sample standard deviations for the two compaction levels for each laboratory should be less than or equal to the typical values indicated in T
32、able 1. Table 1Typical Standard Deviations for Gmbof Specimens Compacted in the SGC SGC Compaction Level Typical Standard Deviation Nini0.008 Ndes0.006 7.6. The absolute difference of the averages (2ixx ) between any two laboratories should be less than or equal to the typical values indicated in Ta
33、ble 2. Table 2Typical Absolute Differences for Gmbof Specimens Compacted in the SGC SGC Compaction Level Typical Absolute Difference Nini0.022 Ndes0.015 Note 2Values for Tables 1 and 2 are based on four specimens. 8. PROCEDURE: PHASE IISINGLE-OPERATOR EVALUATION 8.1. If one or more of the SGCs evalu
34、ated does not provide results within the typical ranges as indicated in Tables 1 and 2, the second phase of the evaluation shall be conducted. 8.2. A meeting between the laboratory operators will be held to identify and discuss any within-procedure differences. (See Section 9 for discussion topics.)
35、 The specifying agency should establish a uniform procedure to address the identified differences. This procedure should be based on the consensus of the group. 8.3. Repeat Section 6 with the following exceptions: 8.3.1. A single operator shall be used throughout the evaluation. 8.3.2. The laborator
36、y-prepared mix or production mix shall be mixed or sampled, split, and allowed to cool at ambient temperature for a minimum of 12 h. The split samples shall be uniformly handled and reheated to the specified compaction temperature. 8.3.3. Figure 1 shall be used to summarize the evaluation data. 8.3.
37、4. A statistical evaluation shall be conducted using the typical values provided in Tables 1 and 2. 8.3.5. If one or more of the SGCs evaluated still does not provide results within the typical ranges, the single operator should verify the calibration of the SGCs, should verify the internal angle in
38、 accordance with T 312 using a single internal angle device, should evaluate the internal angle of the molds in accordance with Section 11, and should investigate and minimize sources of variability, or contact the SGC manufacturer for service. 9. POTENTIAL DIFFERENCES AND SOURCES OF VARIABILITY 9.1
39、. Within-procedure differences may impact the field management of asphalt mixes. The following provides topics for discussion in identifying potential differences and sources of variability. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplicati
40、on is a violation of applicable law.TS-2d PP 76-6 AASHTO Addressing the potential sources of variability should be the first step(s) taken by a laboratory that experiences difficulties in obtaining consistent, verifiable Gmbvalues for compacted asphalt mixture specimens. This is not a complete list
41、of potential differences and sources of variability. 9.1.1. SGC MaintenanceEnsure that each SGC is properly lubricated and maintained in good working order. All maintenance activities recommended by the SGC manufacturer should be performed at the specified time interval. In addition to “routine” sch
42、eduled maintenance items, each SGC should be thoroughly inspected for mechanical wear by a qualified service technician at least once per year (or more often if the unit experiences heavy usage). Studies related to the angle of gyration applied to an asphalt mixture specimen have indicated that the
43、physical condition of a given SGC affects the resulting measured angle of gyration. At a minimum, recommended maintenance items listed in the Users Manual for each SGC must be performed at the recommended task frequencies. In addition to “routine” maintenance issues, users are cautioned that parts o
44、f SGC units subject to wear (i.e., bearings, rollers) should be periodically checked for condition. SGC manufacturers can provide information related to specific parts and indications of excessive wear. SGC parts showing excessive wear should be replaced. 9.1.2. SGC CleanlinessEnsure that the SGC is
45、 clean, including all surfaces, rollers, plates, and molds. Buildup of binder and mix on the working surfaces and internal mechanisms of a compactor may lead to variations in the compaction effort supplied by the unit to the asphalt mixture specimen. For example, the effect of a small 0.1-mm “intrus
46、ion” under the gyratory compactor mold base plate can decrease the effective internal angle of gyration by approximately 0.05 degrees, a significant change. 9.1.3. SGC CalibrationIt is assumed that all SGCs are properly calibrated using current manufacturers recommendations and/or applicable specifi
47、cations. Most models of the SGC manufactured today allow for the use of both 100- and 150-mm molds. If it is not apparent which setting is in use during the calibration process, verify that each SGC is set to 150 mm per T 312. A setting of 100 mm while using 150-mm molds will result in a lower than specified consolidation pressure, which will in turn result in lower Gmbvalues. 9.1.4. SGC MoldsEnsure that SGC molds are cleaned. Buildup of binder and/or hot mix as
