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49 C H A P T E R 4 The states of Arizona, Illinois, Maine, Montana, and Texas were the five states selected for more detailed investigation. There were a number of reasons why these states were selected to be focus states. All selected states indicated a willingness to participate in follow-up case example interviews, and they represent a geographic distribution that includes both cold and warm climates and also represent a range of agency sizes. The states of Illinois, Maine, and Texas have been very active in conducting various types of performance testing of asphalt specimens. Table 15 summarizes the types of tests used by each case example state and the purposes for which they are used. During each case example interview, state agency representatives were asked to clarify and elaborate on their survey responses; there were standard additional questions asked of each agency and also questions unique to particular agencies depending upon the methods and tests used. The sections below provide the detailed case-example information for each selected state regarding mixture types, sampling and handling procedures, specimen fabrication equipment and procedures, and challenges. Arizona The Arizona Department of Transportation (Arizona DOT) reported that they prepare specimens and conduct laboratory performance testing. Arizona DOT conducts the HWT and the SCB test following the Illinois Flexibility Index Test (I-FIT) protocol (AASHTO TP 124) for research purposes on a nonroutine basis. They also fabricate specimens for university partners to run complex modulus, direct-tension cyclic-fatigue, and flow number tests for research projects. Mixture Types, Sampling, and Handling Procedures Arizona DOT reported that reheated plant mix is used to fabricate specimens for all perfor- mance tests; the mixture is sampled following AASHTO T 168. They have a specific procedure for preparing and splitting field samples (ARIZ 416e, included in Appendix E). The procedure explains the use of a mechanical (clamshell) or quartermaster splitter to reduce material to the appropriate size for sampling. A closed-end sampler (Figure 44) is used to obtain the appropriate amount of material in the laboratory for specimen fabrication. ARIZ 416e (see Appendix E) also describes the protocol for reheating material with limits on temperatures and time. Samples may be stored for indefinite periods of time at temperatures not exceeding 140°F. If necessary, the sample may be heated at 290 ± 10°F for a maximum of 3 hours. The 3-hour time period begins when the oven reaches the specified temperature. Also, Case Examples
50 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Performance Test Arizona Illinois Maine Montana Texas Cantabro - - - - Mix design acceptance CTIndex - - Nonroutine research - Routine research E* - - - - Nonroutine research HWT Nonroutine research Mix acceptance and routine research Routine research, mix design acceptance, and QA mix acceptance on select projects Routine research, mix design acceptance, and QA mix acceptance Routine research, mix design acceptance, and QA mix acceptance IDT - - - - Mix design acceptance RLPD - - Routine research - - SCB Nonroutine research Mix acceptance and Routine research - - - SSG DTCF - - Routine research - - SSG E* - - Routine research - - TxOT - - - - Routine research, mix design acceptance, and QA mix acceptance Note: Hyphens indicate that the state does not use or conduct the test. Table 15. Test types and purpose for case example states. the material may be reheated for a maximum of 1 hour at a temperature not exceeding 300°F to restore pliability during sampling. Arizona DOT reports that no laboratory conditioning is performed on mixtures or specimens beyond what is required for temperature conditioning with the HWT and SCB test procedures. They do not have procedures for preparing material for storage, and there are no requirements for maximum storage times beyond what the test specifications dictate. Typically testing is conducted immediately after specimens are fabricated, but loose mix can be stored for 4 to 8 weeks in rare cases.
Case Examples 51 Specimen Fabrication Equipment and Procedures Arizona DOT reported that a Superpave gyratory compactor is used for all specimen fabrication although 90% of their mixtures are designed using the Marshall approach. Density requirements for the HWT and SCB test are as per the specification. They reported challenges meeting density in fabricating the 160-mm-tall specimens for SCB testing and they have observed inconsistencies in the air void distribution over the height of these speci- mens. Mix splitters, ovens, and rotary saws are used for all specimen fabrication. Challenges Arizona DOT reported that the most frequent issue they encounter in the specimen fabri- cation process is that air void requirements in the bulk specimens are not met for the SCB specimens; typically, the air void levels are too high, which they attribute to the taller specimens. However, they do not track rejection rates. No gaps in knowledge that make it challenging to fabricate performance test specimens in-house have been observed, and Arizona DOT does not have plans to sponsor any research that addresses this issue. They do see a need for performance testing of friction courses, which they use extensively. Illinois The Illinois Department of Transportation (Illinois DOT) responded that they prepare specimens and conduct laboratory performance testing; the acceptance activities are con- ducted in-house only by the agency. Illinois DOT routinely conducts the Illinois modified HWT (AASHTO T 324), Illinois modified I-FIT version of the SCB (AASHTO TP 124), and the Illinois modified Lottman test (AASHTO T 283) for mix acceptance and for research purposes. Figure 44. Photographs of Arizona closed-end sampler (courtesy of Arizona DOT).
52 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Mixture Types, Sampling, and Handling Procedures For the three performance tests conducted by Illinois DOT, LMLC, PMLC, and RPMLC as well as field-cored materials are used to fabricate test specimens. Illinois DOT reports that mixtures are sampled according to the agencyâs manual of test procedures (attached in Appendix E); the sampling location is dependent on the project tonnage per mixture. The sampling location for plant-mixed materials is either behind the paver or from a material transfer vehicle (MTV). An agency-specific material blending and split- ting procedure is adopted by Illinois DOT. The procedure is comparable to the AASHTO R 47 and is described in detail in the Level 1 training manual for technicians (Appendix E). Illinois DOT reported the DOT prefers the riffle splitter of the various available splitting devices. Illinois DOT did not report a specific procedure for reheating plant-produced loose mixtures for compaction in the laboratory. The short- and long-term specimen conditioning procedures depend on the test. For HWT, Illinois DOT does not conduct any laboratory conditioning besides that conducted on laboratory-produced mixture during the volumetric mix design process on HMA. For the I-FIT procedure, loose-mix conditioning of laboratory-produced mixes similar to the conditioning during the volumetric mix design is done. An additional 2 hours of laboratory conditioning is applied to WMA mixtures for both HWT and I-FIT procedures. Thereafter, fully prepared I-FIT specimens (compacted, cut, and notched) are sub- jected to long-term oven aging at 95°C (203°F) for 3 days. The conditioning is conducted by placing finalized test specimens face down (notched side facing toward the pan) in a metal pan lined with a barrier material. Illinois DOT has found that parchment paper is a relatively reusable, inexpensive barrier material. The conditioning temperature and time was selected on the basis of research sponsored by Illinois DOT that evaluated different aging times and temperatures. Illinois DOT also reported that the choice of conducting long-term oven aging on the finalized test specimen is partly driven by practicality (not having to redo volumetrics postâoven aging, and the like). The Illinois modified AASHTO T 283 procedure eliminates the freezing component of the moisture conditioning procedure, resulting in a conditioning pro- cess that involves 24-h soaking in 60°C (140°F) water bath for compacted, saturated specimens. At present, Illinois DOT does not have a fixed storage duration time for plant-produced loose mix. The agency reported that test specimen fabrication happens as soon as possible from the time of mix sampling. If needed, Illinois DOT generally stores plant-produced loose mix in cloth bags or other storage containers. Previous Illinois DOTâsponsored and in-house research studies have shown that shelf aging of test specimens is not found to impact results of perfor- mance tests adopted by them if tested within approximately 3 weeks. The agency reported that once test specimens are fabricated, the testing is conducted very soon thereafter. Specimen Fabrication Equipment and Procedures Illinois DOT reported having agency-required modifications to the specimen fabrica- tion requirements in the AASHTO specified procedures for HWT (AASHTO T 324), I-FIT (AASHTO TP 124), and moisture susceptibility using TSR (AASHTO T 283). All performance test specimens are compacted by Illinois DOT using the SGC with 150 mm diameter. Illinois DOT targets an air void level for both I-FIT and HWT test specimens to be 7.0 ± 1.0%. The Illinois DOT manual of test procedures for materials (Appendix E) provides guidance regard- ing the bulk gyratory specimen air void level to achieve the target air void level in test speci- mens. For example, a 9.5-mm (3/8-in.) NMAS mix is recommended to be compacted to achieve gyratory-pill air void content in the range of 7.3 to 7.7% to meet the I-FITâtest-specimen air void target of 7.0 ± 1.0%. For the Illinois modified Lottman procedure, the target air void level for test specimens of 7.0 ± 1.0% is used. In addition to the current AASHTO TP 124
Case Examples 53 dimensional requirements for I-FIT test specimens, Illinois DOT reported requiring a maximum notch width of 2.25 mm (0.09 in.) and an allowable notch depth of 15 ± 1 mm (0.6 ± 0.04 in.). Illinois DOT reported that ovens, rotary saws, and a core drying device are used for all specimen fabrication as necessary. A water bath is also used for equilibrating I-FIT specimen temperature. Challenges Illinois DOT reported that the most frequent issues they encounter in the specimen fabrica- tion process is failure of bulk and prepared specimens to meet dimensional or air void require- ments. They also reported that there are infrequent occurrences of operational disruptions with respect to test specimen fabrication, and they have observed a low specimen rejection rate. Illinois DOT reported that their previous research efforts on asphalt performance test specimen fabrication included both dense-graded and SMA mixtures to ensure that research is applicable to both types of mixtures. They are currently collecting air void information on SMA bulk specimens and finalized test specimens to develop guidance for their testing manual. Illinois DOT also noted that at present there is a lack of information on performance testing requirements for cold mixes. Maine The Maine Department of Transportation (Maine DOT) reported that they prepare speci- mens and conduct laboratory performance testing; these activities are conducted in house only. Maine DOT routinely conducts the HWT, SSG E*, SSG DTCF, and RLPD for research purposes. The HWT is also conducted for mix design acceptance and QA mix acceptance on select projects. Maine DOT reported that the CTIndex test is conducted for research purposes on a nonroutine basis. Mixture Types, Sampling, and Handling Procedures Maine DOT reported that reheated plant mix is used to fabricate specimens for all per- formance tests; laboratory-mixed and laboratory-compacted material is used to fabricate specimens for CTIndex, HWT, SSG E*, SSG DTCF, and RLPD testing. Field cores are only used to fabricate specimens for the CTIndex testing. Maine DOT reported that mixture is typically sampled from the MTV or paver hopper, though material for the AMPT testing can also be obtained from the truck at the plant. They use a quartermaster on-site for splitting the newly sampled material into cardboard sample boxes. Maine DOT has a specific procedure (included in Appendix E) for the HWT. This proce- dure details temperatures and times for reheating plant material for fabrication of the HWT specimens. Maine DOT reported that they try to keep reheating to a minimum, and while they do not have specific procedures written for other test types, the procedure outlined for the HWT specimens is typically followed for the fabrication of all specimens. After mix- ture is reheated in the laboratory, Maine DOT uses a quartermaster twice and then a riffle splitter to achieve the appropriate mixture quantity for HWT and CTIndex specimen fab- rication. For fabricating the SSG E*, SSG DTCF, and RLPD specimens, a quartermaster is used twice. Loose-mixture laboratory conditioning following the AASHTO R 30 short-term aging protocol is conducted by Maine DOT for all laboratory-produced mixtures used to fabricate specimens.
54 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Maine DOT reported that the DOT wraps loose mix in plastic film for storage prior to labo- ratory compaction and that no other storage preparation is done between further specimen preparation steps. The plastic film is the most efficient method for the cardboard sampling boxes that are used. They reported that there are no requirements for maximum storage times for the HWT and CTIndex test specimens. Maine DOT requires that mechanical testing be conducted within 30 days of specimen fabrication for the SSG E*, SSG DTCF, and RLPD tests. If specimens will be stored for more than 14 days prior to testing, they are wrapped and sealed either with plastic film (cut and cored specimens) or in a cylinder mold (bulk specimens). Maine DOT reported that these time limits were based on guidance from North Carolina State Uni- versity to limit the amount of aging of the specimens and the potential impact on the results. Specimen Fabrication Equipment and Procedures Maine DOT reported that a Superpave gyratory compactor is used for all specimen fabrica- tion. Density requirements for the HWT and CTIndex test are as per the specification. The target air void levels for the SSG E* and SSG DTCF tests are 5% ± 0.7%, and are 5% ± 0.5% for the RLPD test. These values are based on their specified target in-place density of 5% ± 2.5%. Maine DOT reported that 95% of the HWT specimens and 99% of the RLPD specimens meet density requirements. Maine DOT reported that they have approximately a 25% failure rate with the small geo- metry specimens meeting density requirements, with more difficulty with the larger NMAS materials. They typically observe a 10% to 15% failure rate with 9.5-mm (3/8-in.) material and up to 40% with 19-mm (¾-in.) material. Because of this, Maine DOT is considering using the larger specimen size for 19-mm (¾-in.) mixtures in the future. Maine DOT technicians have developed a database of compaction information (Gmm, mass, gyration level, air void) for dif- ferent materials that has helped improve the success rate of meeting density requirements over time. As a result of their experiences, Maine DOT no longer measures the density of the bulk specimen. Maine DOT reported that ovens, rotary saws, and a core drying device are used for all speci- men fabrication. Gluing templates and jigs, a temperature conditioning chamber, and a vacuum sealing device are used for SSG E*, SSG DTCF, and RLPD testing. Challenges Maine DOT reported that the most frequent issue they encounter in the specimen fabrication process is that air void requirements of the final test specimen are not met; no bias has been observed on the high or low side. They also reported issues with specimen fabrication equip- ment. They have experienced challenges with asphalt-rich base materials and gap-graded rubber mixtures, particularly with gumming of core barrels. Maine DOT reported that they have not observed any gaps in knowledge that make it chal- lenging to fabricate performance test specimens in-house and do not have plans to sponsor any research that addresses this issue. They are considering testing on cold mixtures in the future. Montana The Montana Department of Transportation (Montana DOT) reported that they prepare specimens and conduct laboratory performance testing; these activities are conducted in house only. Montana DOT routinely conducts the HWT for mix design acceptance and QA mix accep- tance, as well as routine research purposes.
Case Examples 55 Mixture Types, Sampling, and Handling Procedures Montana DOT reported that laboratory-mixed and laboratory-compacted material, field cores, and reheated plant mix are used to fabricate specimens for the HWT. The plant material is typically sampled behind the paver or from the windrow (Figure 45) using the procedures outlined in MT 303 (included in Appendix E) and the material is transported in containers constructed to minimize heat loss, contamination, or damage to the sample from mishan- dling during shipment. Montana DOT reported that they do not have specific protocols for reheating cooled mixture, but attempt to minimize reheating as much as possible. They follow AASHTO T 312 to maintain compaction temperature for gyratory specimens compacted at the plant; if the paving job is close enough to the central laboratory, material will be brought there for compaction prior to cooling. AASHTO R 47 is used to reduce samples to the appropriate size for fabrication. Loose-mixture laboratory conditioning following the AASHTO R 30 short-term aging protocol is conducted by Montana DOT for all laboratory-produced mixtures used to fabricate specimens. Montana DOT reported that they do not specify any kind of preparation for storage. They reported that there are no requirements for maximum storage times but that they are committed to providing paving acceptance results within 7 business days. Typically, mix-design verification testing is completed within a day of compaction, and plant-mix gyratory specimens are tested within 3 to 4 days of compaction. Specimen Fabrication Equipment and Procedures Montana DOT reported that specimens are fabricated using a kneading compactor (MT 335, included in Appendix E) in the main laboratory and a gyratory compactor at the plants. Montana DOT has a specific procedure for the HWT (MT 334, included in Appendix E). This procedure details procedures for preparing HWT specimens using laboratory-produced mix, compacted slabs, gyratory specimens, and field cores. These procedures include guidance on specimen thickness and cutting and have equipment-specific procedures for one type of gyratory compactor. They also report that specimen thicknesses of 60 mm (2.4 in.) and 80 mm (3.1 in.) are used for testing at the central laboratory and satellite laboratories, respectively. There are no established tolerances associated with thickness; only the specification thickness range of 38 to 100 mm (1.5 to 4 in.) is used. Density requirements for the HWT are as per the specification. Montana DOT has not quantitatively observed the rejection rate of test specimens but is satisfied with the current rate. Montana DOT reported that ovens, rotary saws, and a core drill are used for specimen fabrication. Figure 45. Montana DOT windrow sampling procedure (Figure 2 from MT 303).
56 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories Challenges Montana DOT reported that the most frequent issue they encounter in the specimen fabrica- tion process is that air void requirements of the bulk specimen are not met. This is a relatively rare occurrence, but they observe that typically the air voids are on the high side as a result of the general practice of erring on the side of using less versus too much material. Montana DOT reported that they are currently gaining experience with gyratory compaction in the laboratory and are performing comparisons of cylindrical specimens and slabs. They are evaluating the difference between cutting specimens that have a thickness of 115 mm (4.5 in.) to a test specimen thickness of 60 mm (2.4 in.) versus compacting to a thickness of 60 mm (2.4 in.) directly. These evaluations are being done in-house, and they do not have plans to sponsor any research that addresses these issues. Montana DOT is interested in testing of porous mixtures in the future, as well as methods to evaluate microsurfacing types of materials. They are also interested in a durability/low-temperature cracking test to go along with the HWT in a balanced design/specification approach, and the ease of specimen fabrication is a significant factor in their evaluation of different test methods. Texas The Texas Department of Transportation (Texas DOT) reported that they prepare specimens and conduct laboratory performance testing; these activities are conducted both in-house and by consultant and university laboratories on behalf of Texas DOT. Texas DOT reported that all verification testing is conducted in house, and the majority of tests are run at their central laboratory. Interagency contracts are used with university partners for conducting tests, typi- cally when needed for forensic analysis or for research projects. Various tests and their usage by Texas DOT are summarized in Table 16. Texas DOT routinely conducts the Cantabro test, HWT, CTIndex, IDT, and TxOT. Texas DOT also conducts E* testing on a nonroutine basis for research purposes (see Table 16). Mixture Types, Sampling, and Handling Procedures Texas DOT reported that laboratory-mixed, laboratory-compacted specimens are used for all six performance tests used by their agency. Furthermore, field cores are used for E*, HWT, and TxOT tests. Finally, reheated plant mix is used to fabricate specimens for all perfor- mance tests except the E* test. Sampling of all plant-mixed materials for Texas DOT is done in Performance Test Mix Design Acceptance Mix Acceptance in QA Process Routine Usage for Research Nonroutine Usage for Research Cantabro CTIndex E* HWT IDT TxOT Table 16. Purpose of performance testing for Texas DOT.
Case Examples 57 accordance with the TEX-222-F test procedure. Texas DOT reported that approximately 90% or more of plant-mixed material for performance testing is sampled from trucks. Texas DOT also reported that in their construction contracts Texas DOT [TxDOT] explicitly states that âTxDOT reserves right to sample and test from any location.â Splitting of sampled material is conducted by Texas DOT as per the TEX-200-F test method (Appendix E). This method allows for the use of a sample splitter (aka riffle splitter); quartering cloth; quartering machine; or mix- ing on a smooth, clean surface with a large, flat scoop or shovel until blended; and quartering with a straight edge. Loose-mix conditioning of 120 minutes is used for all performance tests used by Texas DOT except for E* when mix is being compacted directly from production without letting it cool down. If mix is allowed to cool down prior to compaction (typically when it has to be shipped to another location for specimen fabrication and testing), then the conditioning time is reduced to 90 minutes. Texas DOT reported that this reduction in conditioning time is based on the hypothesis that the mix continues to age in storage containers during the cooling process and thus requires less laboratory conditioning on reheating. Specific conditioning temperatures are dependent on the binder grade of the mixtures; these are described in the TEX-206-F test method (Appendix E). Texas DOT reports that they do not have a storage time restriction on loose-mix sampling and time of compaction; however, once test specimens are fabricated, the storage time is limited to 3 days for all tests except the Texas overlay test. For that test, the storage time for final test specimen is limited to 5 days. The maximum time limits were determined by Texas DOT on the basis of internal studies that showed variations in measured performance properties (specifically for HWT and TxOT) for storage times in excess of 5 days. Specimen Fabrication Equipment and Procedures Texas DOT reported that for all plant-produced hot- and warm-mix asphalt, a Superpave gyratory compactor is used for specimen fabrication. For a small number of lime-rock asphalt and cold recycled mixes, Texas DOT also uses the Hveem stabilometer. The air void requirement for all finalized performance test specimens is 7 ± 1.0% with the exception of E*. Since the E* test is often employed by Texas DOT for forensic evaluations, the agency reported that these tests are run on specimens with the same air void level as in-place pavement. The allowable tolerance of 1.0% for specimen air voids is reported by Texas DOT to be on the basis of practicality of the fabrication process. Texas DOT reported that they have had less than a 5% specimen rejection rate for performance tests; the main causes for rejection were failure of finalized test specimens to meet air void requirements, challenges with operator training/skill levels, and equipment problems. Furthermore, most of the recent specimen rejections were reported to be the result of equipment breakdown issues. Texas DOT reported that ovens are routinely used for all specimen fabrication. Rotary saws are used for E*, HWT, and TxOT specimens, and a temperature conditioning chamber is also used for specimen conditioning of these three tests as well as the CTIndex test. Challenges Texas DOT reported that the most frequent issue they encounter in the specimen fabrica- tion process is for the TxOT, since this test has stricter dimensional tolerances and requires an epoxy-based gluing process. Specifically, operators are required to carefully glue the speci- mens to metal plates with uniform epoxy thickness and without filling up the gaps between the plates. At present, Texas DOT is evaluating the effects of long-term laboratory aging on
58 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories performance properties. Furthermore, the agency also reported that they have implemented performance testing of tack coats using shear tests (TEX 249-F) and are working on specifica- tions to require this. Chapter Summary The case examples illustrate the range of sampling and handling procedures for fabrication of performance test specimens that are used by the states. Some states have detailed guidance on some aspects (e.g., Maine and Texas have specific storage times for several types of test speci- mens) and little guidance in others (e.g., lack of specific reheating protocols). Interviewees from the five case example states consistently observed that failure to meet air void requirements was the common challenge in fabricating specimens and that operator skill and training are important.
