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24 C H A P T E R 3 A survey on practices related to fabrication of specimens for asphalt performance testing was distributed to state DOTs, Canadian provinces, and partner laboratories. A total of 80% of state DOTs, along with the District of Columbia, provided a response to the survey; no responses were received from Canadian provinces. Twenty-nine partner laboratories responded to the survey and are included in the analysis. The state DOT survey (referred to as âagency surveyâ throughout this chapter) is presented in Appendix A, along with the survey responses in Appendix B. The partner laboratory survey is also presented in Appendix A, and the partner laboratory survey responses are in Appendix C. The agency and partner laboratory survey responses are presented together for each question below. State of the Practice Related to the Use of Asphalt Laboratory Performance Tests Many state DOTs (33/40) reported that they prepare asphalt concrete specimens for labora- tory performance testing. This specimen preparation and testing is conducted either in house at agency laboratories or at consultant or university laboratories in the relative proportions shown in Figure 3. The survey data show that most (16/27) partner laboratories conduct performance tests for multiple agencies as shown in Figure 4. Figure 5 and Figure 6 summarize the types of performance tests that agencies and partner laboratories report conducting, respectively. The Other category for agencies includes various forms of TSR (similar to AASHTO T 283), Thermal Stress Restrained Specimen Test (TSRST, AASHTO TP 10), Loaded Wheel Tester (different from APA or HWT), MIST (ASTM D 7890), Marshall Flow and Stability, Hveem Stability, Bending Beam Rheometer (BBR) Beam Sliver Test (AASHTO TP 125), Interlayer Bond Strength Test, Stress Sweep Rutting Test (AMPT), and Permeability Test. The other category for partner laboratories includes various forms of BBR Sliver Test (AASHTO TP 125), MR, C* Fracture Test, Repeated Simple Shear Test (AASHTO T 320), flexural frequency sweep part of AASHTO T 321, Nflex IDT as proposed by the National Center for Asphalt Technology (NCAT), Oregon Field Torque Test, Interlayer Shear Strength (AASHTO TP 114), IDT E* Test, Repeated Load Creep Recovery Test, Static Creep Test, and TSR (similar to AASHTO T 283). The HWT, SCB, and E* tests are reported to be the most commonly run tests by both agencies and partner laboratories. The partner laboratories reported running a wider variety of performance tests, while agency responses were typically limited to one or two test types. The number of agencies reporting that they use particular tests for mix design acceptance, in quality assurance processes, and routinely for research purposes is summarized in Figure 7, Figure 8, and Figure 9, respectively. Figure 10 summarizes the tests that agencies report are used State of the Practice
State of the Practice 25 18 1 13 Conducted only in-house by agency Conducted only through consultant/university labs Conducted both in-house and through consultant/university labs Figure 3. Performance testing location reported by agencies. 11 12 4 1 agency 2 - 5 agencies >5 agencies Figure 4. Number of agencies for which partner labs conduct performance tests. 10 8 10 5 2 11 3 20 1 6 14 1 3 2 4 17 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Figure 5. Performance tests that were conducted in house or by other entities that were used by agencies.
26 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories 7 9 14 13 12 26 13 23 19 17 26 7 7 4 12 18 0 5 10 15 20 25 30 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Figure 6. Number of partner labs conducting performance tests. 6 6 0 0 0 0 2 11 1 0 2 0 0 0 2 11 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Figure 7. Number of agencies using performance tests for mix design acceptance.
State of the Practice 27 1 2 8 1 2 3 1 1 1 1 1 1 1 2 1 3 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Mix Acceptance Pay Factor Adjustment Other Figure 8. Number of agencies using performance tests for quality assurance processes. 3 2 1 2 0 2 1 8 0 2 3 1 2 1 2 5 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Figure 9. Number of agencies routinely using performance tests for research.
28 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories nonroutinely for research or other purposes. The uses of tests falling into the âotherâ category are summarized in Table 10. Agencies reported that most of the performance testing is con- ducted for mix design acceptance with lower proportions being conducted for QA and routine research; a broader range of tests are reported to be run on a nonroutine basis. Partner labora- tories reported that over two-thirds (70%) of the performance testing is conducted for research purposes and the remaining conducted for mix design, mix acceptance, QA processes, or pay factor adjustments. Specimen Fabrication Practices for Laboratory Asphalt Performance Testing Table 11 and Table 12 show the percentage of agencies and partner laboratories that use each piece of equipment in the fabrication of test specimens based on the number of agencies or partner laboratories using each test (e.g., 20% of agencies that fabricate APA specimens use a mix splitter in the fabrication process). The gyratory compactor is used almost exclusively for fabricating laboratory performance-test specimens in both agency and partner laboratories. 4 2 10 2 2 9 0 14 0 4 12 0 1 1 3 8 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Figure 10. Number of agencies nonroutinely using performance tests for research or other purposes. Performance Test Type Mix Design Acceptance Quality Assurance Processes Routine Research Nonroutine BBR beam sliver x Hveem stability x x Indirect tensile strength ratio x x x x Interlayer bond strength x x x Loaded wheel x Marshall flow and stability x Moisture-induced sensitivity test x Permeability x Stress sweep rutting x Thermal stress restrained specimen x Table 10. Agency reported uses of âotherâ tests.
State of the Practice 29 Several agencies did report use of other compactor types (e.g., kneading compactor or Marshall hammer) but these were rare cases. The survey data show that ovens, saws, and temperature chambers are also frequently used pieces of equipment in the specimen fabrication process. The percentage of agencies and partner laboratories using standard, modified standard, or nonstandardized/in-house procedures for fabricating specimens for each test are shown in Figure 11 and Figure 12, respectively Primarily, agencies reported that ASTM or AASHTO standards are followed as is or with some modifications. In-house procedures are reported for only a few test types. Most often, partner laboratories reported that standardized procedures are followed by either modified or in-house procedures and are used less than 30% of the time for most tests. Over 80% of agencies and 93% of partner laboratories reported that standard dimensions are used in the fabrication of specimens for performance testing. The agency survey data showed that RPMLC and LMLC are the most common material types used for fabricating performance test specimens and that plant mixed, field compacted (PMFC or field cores) are used about half as frequently as the other types (Figure 13). Partner laborato- ries reported that laboratory mix is the most common material used to fabricate performance test specimens, followed by reheated plant mix and field cores (Figure 14). This is likely a result of the fact that partner laboratories conduct performance tests for research more often than for the QA process. The type of material used and broken down by test type is shown for agency and partner laboratories in Figure 15 and Figure 16, respectively. The three material types are used for all tests by partner laboratories. Test Type Equipment Mix Splitter Superpave Gyratory Compactor Oven Rotary Saw Coring Drill Core Drying Device Gluing Templates Gluing Jigs Temperature Conditioning Chamber Vacuum-Bag Sealing Device APA 20% (2) 70% (7) 60% (6) 10% (1) 0% (0) 0% (0) 0% (0) 0% (0) 20% (2) 10% (1) Cantabro 13% (1) 75% (6) 88% (7) 0% (0) 0% (0) 25% (2) 0% (0) 0% (0) 25% (2) 38% (3) CTIndex 50% (5) 90% (9) 90% (9) 30% (3) 0% (0) 30% (3) 0% (0) 0% (0) 40% (4) 30% (3) DCT 0% (0) 40% (2) 20% (1) 40% (2) 20% (1) 0% (0) 20% (1) 0% (0) 40% (2) 0% (0) DTCF 50% (1) 100% (2) 100% (2) 100% (2) 100% (2) 0% (0) 50% (1) 100% (2) 100% (2) 0% (0) E* 18% (2) 91% (10) 82% (9) 73% (8) 64% (7) 36% (4) 45% (5) 64% (7) 73% (8) 9% (1) FBF 0% (0) 33% (1) 67% (2) 67% (2) 0% (0) 0% (0) 33% (1) 33% (1) 67% (2) 0% (0) HWT 55% (11) 95% (19) 90% (18) 90% (18) 10% (2) 20% (4) 0% (0) 0% (0) 20% (4) 15% (3) IDT 0% (0) 100% (1) 100% (1) 0% (0) 0% (0) 0% (0) 0% (0) 0% (0) 100% (1) 0% (0) RLPD 17% (1) 83% (5) 83% (5) 83% (5) 83% (5) 17% (1) 17% (1) 33% (2) 83% (5) 0% (0) SCB 50% (7) 79% (11) 79% (11) 79% (11) 0% (0) 21% (3) 0% (0) 0% (0) 57% (8) 14% (2) SSG DTCF 100% (1) 100% (1) 100% (1) 100% (1) 100% (1) 100% (1) 0% (0) 100% (1) 100% (1) 100% (1) SSG E* 33% (1) 33% (1) 33% (1) 67% (2) 100% (3) 33% (1) 67% (2) 100% (3) 100% (3) 33% (1) SSG RLPD 0% (0) 0% (0) 0% (0) 50% (1) 100% (2) 0% (0) 50% (1) 50% (1) 100% (2) 0% (0) TxOT 0% (0) 100% (4) 100% (4) 100% (4) 25% (1) 25% (1) 25% (1) 100% (4) 75% (3) 0% (0) Other 59% (10) 76% (13) 88% (15) 29% (5) 35% (6) 24% (4) 6% (1) 12% (2) 59% (10) 24% (4) Note: Percentage of agencies that reported fabricating specimens for tests. Numbers within parentheses report actual responses. Table 11. Equipment used by agencies to fabricate performance test specimens.
30 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Test Type Equipment Mix Splitter Superpave Gyratory Compactor Oven Rotary Saw Coring Drill Core Drying Device Gluing Templates Gluing Jigs Temperature Conditioning Chamber Vacuum-Bag Sealing Device APA 29% (2) 86% (6) 71% (5) 14% (1) 14% (1) 43% (3) 0% (0) 0% (0) 71% (5) 43% (3) Cantabro 22% (2) 89% (8) 100% (9) 11% (1) 11% (1) 56% (5) 0% (0) 0% (0) 44% (4) 56% (5) CTIndex 43% (6) 100% (14) 100% (14) 43% (6) 14% (2) 50% (7) 0% (0) 0% (0) 100% (14) 57% (8) DCT 54% (7) 100% (13) 92% (12) 92% (12) 69% (9) 38% (5) 77% (10) 15% (2) 92% (12) 38% (5) DTCF 50% (6) 100% (12) 92% (11) 92% (11) 92% (11) 75% (9) 92% (11) 92% (11) 92% (11) 67% (8) E* 38% (10) 100% (26) 96% (25) 92% (24) 85% (22) 65% (17) 69% (18) 54% (14) 92% (24) 58% (15) FBF 62% (8) 38% (5) 92% (12) 92% (12) 15% (2) 38% (5) 38% (5) 8% (1) 92% (12) 23% (3) HWT 39% (9) 100% (23) 96% (22) 91% (21) 9% (2) 39% (9) 9% (2) 4% (1) 74% (17) 35% (8) IDT 37% (7) 100% (19) 95% (18) 89% (17) 32% (6) 47% (9) 74% (14) 37% (7) 89% (17) 47% (9) RLPD 47% (8) 100% (17) 94% (16) 88% (15) 88% (15) 65% (11) 47% (8) 35% (6) 88% (15) 47% (8) SCB 35% (9) 100% (26) 96% (25) 96% (25) 15% (4) 58% (15) 23% (6) 12% (3) 96% (25) 42% (11) SSG DTCF 57% (4) 86% (6) 71% (5) 86% (6) 86% (6) 86% (6) 86% (6) 86% (6) 86% (6) 43% (3) SSG E* 57% (4) 86% (6) 71% (5) 86% (6) 86% (6) 86% (6) 86% (6) 29% (2) 86% (6) 43% (3) SSG RLPD 50% (2) 100% (4) 75% (3) 75% (3) 75% (3) 75% (3) 75% (3) 25% (1) 75% (3) 25% (1) TxOT 25% (3) 100% (12) 92% (11) 92% (11) 17% (2) 58% (7) 42% (5) 67% (8) 92% (11) 33% (4) Other 22% (4) 67% (12) 78% (14) 72% (13) 50% (9) 61% (11) 28% (5) 22% (4) 72% (13) 61% (11) Note: Percentage of partner laboratories that reported fabricating specimens for tests. Numbers within parentheses report actual responses. Table 12. Equipment used by partner laboratories to fabricate performance test specimens. 6 5 7 3 2 10 1 11 6 11 1 3 2 1 9 3 1 1 1 1 9 3 1 2 2 3 2 1 2 6 0 4 8 12 16 20 24 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Standard Procedures Modified Standard In-house Procedure Figure 11. Number of agencies using different types of standards for specimen fabrication of performance test specimens.
State of the Practice 31 6 7 10 9 11 24 12 18 16 16 23 6 6 4 7 7 3 1 1 5 3 1 8 4 1 6 4 5 1 3 3 1 1 1 1 1 2 1 1 2 9 0 4 8 12 16 20 24 28 32 36 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Standard Procedures Modified Standard In-house Procedure Figure 12. Number of partner labs using different types of standards for specimen fabrication of performance test specimens. 73 76 32 Laboratory Mix, Laboratory Compacted (LMLC) Reheated Plant Mix, Laboratory Compacted (RPMLC) Plant Mix, Field Compacted (PMFC/Field Cores) Figure 13. Types of mix that agencies use in fabrication of performance test specimens. 203 176 113 Laboratory Mix, Laboratory Compacted (LMLC) Reheated Plant Mix, Laboratory Compacted (RPMLC) Plant Mix, Field Compacted (PMFC/Field Cores) Figure 14. Types of mix that partner labs use in fabrication of performance test specimens.
32 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Figure 15. Types of mix that agencies use in fabrication of performance test specimens by test type. 7 8 1 1 7 2 3 12 6 8 1 1 1 3 12 4 3 2 2 7 2 5 16 7 9 1 2 1 1 3 11 4 1 3 1 7 2 2 1 1 2 8 0 5 10 15 20 25 30 35 40 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other LMLC RPMLC Field Cores Figure 16. Types of mix that partner labs use in fabrication of performance test specimens by test type. 6 6 13 11 11 23 12 23 18 14 23 6 6 4 11 16 5 7 11 11 10 19 11 18 12 14 22 5 5 3 8 15 6 4 6 7 4 9 3 16 11 4 15 5 5 2 5 11 0 10 20 30 40 50 60 70 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other LMLC RPMLC Field Cores
State of the Practice 33 With respect to laboratory conditioning of asphalt mixtures during the specimen fab- rication process, 37% of agency survey responses indicated no laboratory conditioning, whereas the remaining 63% of responses indicated a preference for the use of loose mix aging (Figure 17). The partner laboratories indicated that loose-mix conditioning is the most prevalent in the fabrication of performance test specimens and only 9% of entities utilized unconditioned test specimens (Figure 18). A more detailed presentation of the survey data from agencies and partner laboratories regarding laboratory conditioning is provided in Figure 19 and Figure 20, respectively. Apart from the SSG RLPD, at least one agency conducts some form of laboratory conditioning during the performance-test specimen-fabrication process for each test type. The data clearly show that the use of laboratory conditioning during the specimen fabrication process is extensively used by partner laboratories for vari- ous performance tests. Figure 17. Distribution of agency lab practices with respect to laboratory conditioning during specimen fabrication for performance testing (no agencies reported both loose mix and compacted sample conditioning for a test type). 61 13 41 Loose Mix Compacted Sample No Lab Conditioning Figure 18. Distribution of partner laboratory practices with respect to laboratory conditioning during specimen fabrication for performance testing. 191 31 22 4 Loose Mix Compacted Sample No Lab Conditioning Both Loose Mix and Compacted Sample
34 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories 8 4 7 2 1 7 1 13 1 3 10 1 1 3 12 2 4 3 3 1 4 2 7 3 4 2 2 1 5 0 5 10 15 20 25 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Yes No Figure 19. Number of agency labs conducting laboratory conditioning during specimen fabrication of performance test specimens. 6 6 13 10 12 25 11 20 16 16 22 7 7 13 17 2 3 1 4 1 4 2 5 5 3 6 1 1 1 1 2 0 5 10 15 20 25 30 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Yes No Figure 20. Number of partner labs conducting laboratory conditioning during specimen fabrication of performance test specimens.
State of the Practice 35 A detailed breakdown of the distribution between loose mix and compacted sample lab- oratory conditioning procedures adopted by agencies and partner laboratories is plotted in Figure 21 and Figure 22, respectively. The survey data indicated that loose-mix conditioning is more often adopted by agencies in the performance-test specimen-fabrication process than conditioning of compacted samples. The only exception to this observation is for the FBF test; however, only three agencies responded for this test method. The SCB and IDT tests are the only ones with more than 25% of partner laboratories using compacted specimens for the laboratory conditioning process. For the tests where agencies utilize a loose mix laboratory conditioning process, the AASHTO R 30 short-term aging protocol (4 hours of loose mix laboratory conditioning at 135°C (275°F)) is followed 59% of the time (Figure 23) while it is followed almost 90% of the time by partner laboratories (Figure 24). A more detailed distribution regarding use of the AASHTO R 30 short-term laboratory-conditioning protocol by test type is plotted in Figure 25 and Figure 26. Apart from IDT and TxOT, the AASHTO R 30 short-term, labora- tory-aging protocol is favored by at least half of the agencies for all other tests. Evaluation of the survey data on loose-mix laboratory-conditioning processes other than AASHTO R 30 protocol revealed that the majority adopt 2 hours of laboratory conditioning (as opposed to 4 hours recommended by AASHTO R 30) and in many instances use the mix compaction temperature for laboratory conditioning [as opposed to temperature of 135°C (275°F) rec- ommended by AASHTO R 30]. An alteration of laboratory conditioning time to 2 hours and/ or conditioning temperature to mix compaction temperatures accounts for nine of the 25 âother processâ response in Figure 23. The most common processes other than AASHTO R 30 short-term laboratory aging used by partner laboratories are 8, 16, and 24-h conditioning at 135°C (275°F). 5 4 1 1 6 3 12 7 7 1 1 1 2 10 3 1 2 2 1 4 0 2 4 6 8 10 12 14 16 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Loose Mix Compacted Sample Figure 21. Use of loose mix versus compacted samples by agency labs for laboratory conditioning of performance test specimens (shown by test type).
6 6 13 10 11 10 19 14 15 22 6 6 4 12 13 3 1 1 3 3 1 5 1 8 2 3 0 5 10 15 20 25 30 35 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Loose Mix Compacted Sample 24 Figure 22. Use of loose mix versus compacted samples by partner labs for laboratory conditioning of performance test specimens (shown by test type). 170 21 AASHTO R 30 Short-term Aging Protocol Other Process Figure 24. Loose-mix laboratory-conditioning procedure used by partner labs during performance- test specimen fabrication. 36 25 AASHTO R 30 Short-term Aging Protocol Other Process Figure 23. Loose-mix laboratory-conditioning procedure used by agency labs during performance- test specimen fabrication.
State of the Practice 37 5 4 7 1 1 6 12 1 3 7 1 1 2 10 2 2 3 2 6 1 1 3 2 3 0 5 10 15 20 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Yes No Figure 25. Number of agencies using AASHTO R 30 short-term aging protocol for loose-mix laboratory conditioning. 5 5 12 9 10 22 17 12 14 19 5 5 10 12 1 1 1 1 1 2 2 2 1 3 1 1 1 2 1 0 5 10 15 20 25 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Yes No 10 3 Figure 26. Number of partner labs using AASHTO R 30 short-term aging protocol for loose-mix laboratory conditioning (by test type).
38 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories For survey respondents indicating that they use laboratory conditioning on compacted- asphalt-mix specimens, the survey subsequently collected information on whether conditioning is conducted on bulk specimens (prior to cutting and/or coring) or on finished test specimens. The overall distribution of survey data shows that compacted-mix laboratory conditioning is most often conducted on finished test specimens (Figure 27 and Figure 28). Only 15% of agencies indicated that they use the AASHTO R 30 long-term laboratory aging procedure [5 days at 85°C (185°F)], while most partner laboratories use this procedure, as shown in Figure 29 and Figure 30. When agencies do not use the AASHTO R 30 long-term labora- tory aging protocol, the laboratory conditioning on compacted specimens involves a shorter duration (typically 2 to 4 hours) of conditioning of the specimen at the test temperature. The type of specimen used for conditioning by partner laboratories is broken down by test type in Figure 31. Survey results indicate that over 90% of agencies and partner lab practices for performance- test specimen fabrication require a target air void level (Figure 32 and Figure 33). The only exceptions to the target air void requirement were some instances of the Cantabro test and the SSG E* and RLPD tests. One agency using small-scale geometry tests indicated that these 4 9 Lab conditioning on bulk specimen (prior to cutting and/or coring) Lab conditioning on finished test specimen (after cutting and/or coring to get to final test specimen geometry) Figure 27. Distribution of agency laboratory practices regarding laboratory conditioning of compacted specimens. 13 16 Lab conditioning on bulk specimen (prior to cutting and/or coring) Lab conditioning on finished test specimen (after cutting and/or coring to get to final test specimen geometry) Figure 28. Distribution of partner laboratory practices regarding laboratory conditioning of compacted specimens.
State of the Practice 39 2 11 AASHTO R 30 Long-term Aging Protocol Other Process Figure 29. Preference of agency labs regarding protocol for long-term laboratory conditioning of compacted specimens for performance testing. 24 5 AASHTO R 30 Long-term Aging Protocol Other Process Figure 30. Preference of agency labs regarding protocol for long-term laboratory conditioning of compacted specimens for performance testing. are often conducted on field cores, and thus air voids are not targeted during the specimen fabrication process. Figure 34 and Figure 35 show the distribution of agency and partner laboratory air void requirements with respect to AASHTO/ASTM specifications and use of air void requirement on bulk sample versus finished test specimen, respectively. Most agencies and partner laborato- ries follow the recommendations provided in AASHTO and ASTM test methods for the corre- sponding performance test. For the remainder, agencies more frequently target air voids on bulk specimens, while partner laboratories target air voids on final test specimens. With respect to the target air void level, the survey data showed that 7% is the most com- monly adopted value by agencies and partner laboratories, as seen in Figure 36 and Figure 37. The other target air void levels used by agencies are 4, 5, and 6%; while partner laborato- ries use 5 and 8% target air voids. Agencies most commonly use a tolerance of ± 1% on target air voids (Figure 38) while the majority of partner laboratories allow ± 0.5% tolerance (Figure 39).
40 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories 101 9 Target Air Void Required Target Air Void Not Required Figure 32. Distribution of agency laboratory practices regarding requirements of target air void level for performance test specimens. 1 1 2 1 1 3 2 1 1 2 1 1 2 1 6 1 2 0 2 4 6 8 10 APA Cantabro CTIndex DCT DTCF E* FBF HWT IDT RLPD SCB SSG DTCF SSG E* SSG RLPD TxOT Other Lab conditioning on bulk specimen (prior to cutting and/or coring) Lab conditioning on finished test specimen (after cutting and/or coring to get to final test specimen geometry) Figure 31. Distribution of partner laboratory practices regarding laboratory conditioning of compacted specimens (by test type).
207 20 Target Air Void Required Target Air Void Not Required Figure 33. Distribution of partner laboratory practices regarding requirements of target air void level for performance test specimens. 58 26 19 Target air void requirement as per AASHTO/ASTM specification for the performance test. Requirements not detailed in test specification or deviated from test specification: Target air void required on bulk compacted sample prior to test specimen fabrication. Requirements not detailed in test specification or deviated from test specification: Target air void required on finalized test specimen. Figure 34. Agency laboratory practices regarding target air void requirements for performance test specimens. 161 34 53 Requirements not detailed in test specification or deviated from test specification: Target air void required on bulk compacted sample prior to test specimen fabrication. Requirements not detailed in test specification or deviated from test specification: Target air void required on finalized test specimen. Target air void requirement as per AASHTO/ASTM specification for the performance test. Figure 35. Partner laboratory practices regarding target air void requirements for performance test specimens.
42 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Figure 37. Target air void level requirements for performance test specimens as used by partner labs. 60 17 Target air void level of 7% Target air void level other than 7% Figure 38. Allowable tolerances to target air void level for performance test specimens as used by agency labs. 16 21 3 Target air void level tolerance of ±0.5% Target air void level tolerance of ±1% Target air void level tolerance other than ±0.5% and ±1% 26 14 Target air void level of 7% Target air void level other than 7% Figure 36. Target air void level requirements for performance test specimens as used by agency labs.
State of the Practice 43 Figure 39. Allowable tolerances to target air void level for performance test specimens as used by partner labs. 82 8 Target air void level tolerance of ±0.5% Target air void level tolerance of ±1% Survey data for agency and partner-laboratory practices regarding maximum allowable storage times during the performance-test specimen-fabrication process are documented in Table 13 and Table 14, respectively. The majority of agencies do not have a fixed maximum allowable storage time, while a substantially larger number of partner laboratories reported that they have restrictions on the maximum storage times. For example, only one out of 11 agencies that use the E* test reported that they limit the maximum storage time between finalized-test-specimen preparation and mechanical testing as opposed to nine partner labo- ratories having such restriction (out of 29 that conduct this test). Furthermore, the partner lab practices have more maximum allowable storage limitations during each phase of the specimen fabrication process. The most commonly used storage-time restriction by agencies is between the finalized-test-specimen fabrication and mechanical testing (most often a 1-day limit). Comments provided by agency survey takers indicated that a majority of agencies attempt to fabricate performance test specimens as soon as their laboratory operations allow. The results in Table 14 also illustrate that there is a very wide range of storage time limits in use by partner labo- ratories; even within the same category and for the same test laboratories have limits ranging from 3 days to 180 days. The survey results regarding the preparation of mixture and test specimens for storage are shown in Figure 40 and Figure 41. The majority of agency respondents indicated that no specific preparations are undertaken for storage of samples and specimens. Most partner laboratories reported that they do not use any preparation method to store test specimens, but many store loose mixture in an airtight container prior to compaction. Partner lab responses for âotherâ preparation methods for storage included use of wax-lined boxes, storage in metal containers (unsealed) in climate-controlled spaces, and storage in coolers and freezers. Challenges and Knowledge Gaps Both agencies and partner laboratories reported that the most frequent challenge encoun- tered in fabrication of performance test specimens is meeting the air void requirements on the bulk or test specimens, as shown in Figure 42 and Figure 43. This is followed by challenges meeting dimensional requirements, equipment issues, and operator training. While these are the most common issues faced in the fabrication of test specimens, many agencies also commented
44 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Test Type Number of Agencies Using the Test Between Loose-Mix Sampling and Laboratory Compaction Between Preparation of Compacted (Bulk) Specimen and Finalized Test Specimen Between Finalized - Test- Specimen Fabrication and Mechanical Testing Between Repeated Mechanical Testing (if Multiple Tests Are Conducted on Same Specimens) APA 10 NA NA 1 (1) 1 (1) Cantabro 8 NA NA NA NA CTIndex 10 1 (1) NA 2 (1, 3) NA DCT 5 NA NA NA NA DTCF 2 NA NA NA NA E* 11 NA 1 (3) NA NA FBF 3 NA NA NA NA HWT 20 1 (1) 1 (1) 2 (1, 3) 1 (2) IDT 1 NA NA 1 (3) NA RLPD 6 NA NA NA NA SCB 14 1 (1) 1 (1) 1 (1) 1 (2) SSG DTCF 1 NA NA 1 (14) NA SSG E* 3 NA NA 1 (14) NA SSG RLPD 2 NA NA NA NA TxOT 4 NA NA NA NA Other 17 3 ( , 1)1 6/ 2 (1, 1) 2 (1, 14) 1 (2) Note: Maximum number of days allowed for storage is shown in parentheses. NA = No performance tests were conducted in the study. Number of Agencies with Requirement for Maximum Storage Times Before, During, and After Specimen Fabrication for the Performance Tests (allowable maximum storage times in days) Table 13. Agency-reported allowable maximum storage times during performance-test specimen-fabrication process. that these issues were relatively infrequent. Less than 20% of partner laboratories reported that meeting dimensional requirements, operator training, and shelf storage times are frequent issues. Temperature tolerances and ambient laboratory conditions were not reported as fre- quent challenges. Only half of the agencies reported that they track specimen rejection rates, while 80% of part- ner laboratories track them. Those agencies that track rejection rates reported that they range from 5 to 25%, with 10 to 15% being the most commonly reported range. Partner laboratories
State of the Practice 45 Test Type Number of Partner Labs Using the Test Between Loose - Mix Sampling and Laboratory Compaction Between Preparation of Compacted (Bulk) Specimen and Finalized Test Specimen Between Finalized -Test- Specimen Fabrication and Mechanical Testing Between Repeated Mechanical Testing (if Multiple Tests Are Conducted on Same Specimens) APA 8 2 (3, 30) 1 (5) 1 (5) NA Cantabro 9 1 (5) 2 (5, 7) 2 (5, 30) NA CTIndex 14 4 (3, 30, 180) 6 (3, 5, 7) 7 (1, 3, 5, 7, 10, 30) 2 (7) DCT 14 1 (3) 2 (3, 5) 4 (2, 3, 10, 30) 1 (7) DTCF 13 3( 5, 30, 180) 3 (3, 3, 14) 3 (2, 10, 14) 2 (2, 14) E* 29 6 (3, 30, 180) 8 (3, 5, 7, 14) 9 (2, 3, 5, 7, 10, 14, 30) 5 (2, 3, 7, 90) FBF 13 4 (3, 30, 180) 4 (3, 5, 7) 5 (2, 5, 10, 30) 1 (14) HWT 25 4 (3, 30, 180) 6 (3, 5, 7) 7 (2, 3, 5, 10, 30) 1 (7) IDT 21 3 (3, 5, 30) 5 (3, 5) 6 (2, 3, 5, 10) 2 (7, 14) RLPD 19 4 (3, 30, 180) 6 (3, 5, 7) 7 (2, 3, 5, 7, 10, 30) 2 (7) SCB 28 4 (3, 30, 180) 6 (3, 5, 7) 7 (2, 3, 5, 10, 30) 1 (7) SSG DTCF 8 2 (3, 180) 1 (14) 1 (14) 1 (2) SSG E* 8 2 (3, 180) 1 (14) 1 (14) 2 (2, 90) SSG RLPD 5 1 (3) NA NA NA TxOT 14 3 (3, 5) 4 (3, 5, 7) 5 (2, 3, 5, 10) NA Other 19 3 (3, 180) 5 (1, 3, 7) 3 (7, 30) 1 (7) Note: Maximum number of days allowed for storage is shown in parentheses. NA = No performance tests were conducted in the study. Number of Partner Laboratories with Requirement for Maximum Storage Times Before, During, and After Specimen Fabrication for the Performance Tests (allowable maximum storage times in days) Table 14. Partner laboratory reported allowable maximum storage times during performance-test-specimen fabrication process. reported that rejection rates typically range from 5% to 20%, with a few reporting higher numbers. A total of 83% of agencies reported that they are satisfied with the current rejection rate, and those that are not satisfied reported that rejection rates less than 5% to 10% are desired. Partner laboratories noted that the rejection rate depends on operator experience and the type of speci- men being fabricated. A total of 90% of the partner laboratories are satisfied with the current rejection rate. Almost 30% of agencies and 40% of the partner laboratories reported that they have observed gaps in knowledge that make it challenging to successfully fabricate performance
46 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories 9 19 18 15 3 3 3 3 1 16 4 4 4 5 5 8 3 0 5 10 15 20 25 30 35 40 Between loose mix sampling and laboratory compaction Between preparation of compacted (bulk) specimen and finalized test specimen Between finalized test specimen fabrication and mechanical testing Between repeated mechanical testing (if multiple tests are conducted on same specimens) N um be r o f P ar tn er L ab s Other Left in air-tight container Vacuum Sealed Wrapped in Plastic Film No preparation Figure 41. Distribution of partner lab practices with respect to preparation of performance test specimens for storage (data labels show number of responses for each option). 20 25 23 21 1 4 1 1 1 4 1 1 1 0 5 10 15 20 25 30 N um be r o f A ge nc ie s Other Left in air-tight container Wrapped in Plastic Film No preparation Between repeated mechanical testing (if multiple tests are conducted on same specimens) Between preparation of compacted (bulk) specimen and finalized test specimen Between loose mix sampling and laboratory compaction Between finalized test specimen fabrication and mechanical testing Figure 40. Distribution of agency practices with respect to preparation of performance test specimens for storage (data labels show number of responses for each option). test specimens. The reported gaps include limited guidance on achieving air void ranges (including variation within gyratory specimens and measurement methodology), allow- able time frames for testing, and laboratory aging protocols. Agencies also included the need for staff training and experience. Several agencies also reported that they are relatively new to specimen fabrication for performance testing and expect that continued experience will increase confidence and consistency. Several partner laboratories also questioned the necessity of some of the tolerances and the impact of this variability on the measured properties.
State of the Practice 47 Figure 42. Most frequent issues agencies encountered in fabricating specimens. 6 9 19 12 11 14 9 0 2 4 6 8 10 12 14 16 18 20 Dimensions on Bulk Specimen Dimensions on Test Specimen Air Voids on Bulk Specimen Air Voids on Test Specimen Operator Training/Skill Levels Equipment Others Figure 43. Most frequent issues partner labs encountered in fabricating test specimens. 3 4 15 21 1 5 15 3 0 5 10 15 20 25 Dimensions on Bulk Specimen Dimensions on Test Specimen Air Voids on Bulk Specimen Air Voids on Test Specimen Exceeding Shelf Storage Times Operator Training/Skill Levels Equipment Others
48 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Only eight agencies reported that they are currently sponsoring or planning to sponsor research related to the fabrication of laboratory specimens for performance testing. The descrip- tions of research provided in the survey responses indicate that these agencies are looking at performance-engineered mixture design approaches, various testing types, and long-term aging in the laboratory. Chapter Summary The survey indicated that the majority of state agencies (33/40) fabricate specimens for asphalt-mixture performance tests; the fabrication and tests are conducted both in-house and at partner laboratories. With the exception of the APA, HWT, and Cantabro tests, most agencies indicated that performance tests are run most often for research purposes or on a nonroutine basis. Most of the partner laboratories (16/27) responding to the survey indicated that they fabricate specimens and conduct performance tests for more than one agency. Both agency and partner laboratories reported that a gyratory compactor is used almost exclusively for fabricating laboratory performance-test specimens and that ovens, saws, and temperature chambers are also frequently used pieces of equipment. ASTM or AASHTO standards as written or with some modifications are primarily used for fabrication of test specimens by both agency and partner laboratories. Agencies reported that RPMLC and LMLC material types are most commonly used (with equal frequency) to fabricate performance test specimens, while partner laboratories report that LMLC material is used most frequently. Loose-mix conditioning following the AASHTO R 30 short-term aging procedure is most commonly used by both agency and partner laboratories. For laboratories that condition compacted specimens, agency results indicate that this is most often performed on final test specimens using a process other than AASHTO R 30, while most partner laboratories report that they use AASHTO R 30. Most laboratories have air void requirements for fabrication of performance test specimens, with the most common target air void level being 7%. However, agencies reported a typical tolerance of ±1%, while most partner laboratories report a tolerance of ±0.5%. The survey results indicated that most agencies do not have storage time restrictions and do not have specific preparation requirements for mixture samples or specimens. Many agencies indi- cated that specimens are fabricated and tested as quickly as operations allow. More partner laboratories reported storage time restrictions at various phases of performance-test specimen fabrication, but the limits are widely variable (1 to 180 days). Partner laboratories reported that loose mix is commonly stored in airtight containers prior to compaction. The most frequent challenge in fabricating performance test specimens reported by both agencies and partner laboratories is meeting air void requirements. Approximately half of the agencies and 80% of the partner laboratories reported that they track rejection rates; typical rejection rates are reported to be 5 to 25%, with 10 to 15% being most common. Almost 30% of agencies and 40% of partner laboratories reported they have observed gaps in knowledge that make it challenging to successfully fabricate performance test specimens. The reported gaps include staff training and experience, limited guidance on achieving air void ranges, allowable time frames for testing, and laboratory aging protocols.
