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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
×
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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2011. Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders. Washington, DC: The National Academies Press. doi: 10.17226/14613.
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62.1 Overview Figure 2-1 presents a flowchart for the project. The general approach adopted for NCHRP Project 9-36 was to improve existing technologies rather than develop a completely new aging procedure. The project started with a review of existing binder aging procedures to identify viable candidate methods for possible improvement. Two viable methods were identified: the Stirred Air Flow Test (SAFT) and the Modified German Rotating Flask (MGRF) (1, 2). Figures 2-2 and 2-3 are schemat- ics of these two devices. The SAFT uses air blowing to simulate short-term aging of the binder. Air from a nozzle submerged in the binder is dispersed in the binder by an impeller mounted to an external motor. The SAFT also includes a condenser to collect volatile compounds that are released during the aging process. The MGRF uses a rotary evaporator similar to that specified in ASTM D5404 and AASHTO T319 for recovery of binders after solvent extraction. In the MGRF, air is intro- duced into the rotating flask to age the binder. The exhaust gases from the MGRF are not collected; mass change measure- ments are used to quantify binder volatility. From the review, it was determined that both the SAFT and the MGRF are rel- atively inexpensive, easy to perform, applicable to both neat and modified binders, and—based on available literature— can reasonably reproduce the level of aging that occurs in the RTFOT. However, it was not clear from the review if either test could be extended to long-term aging. The selection study was, therefore, conducted to choose one of these methods for further development. The selection study investigated whether, at a temperature of 100°C, either test can adequately mix air with stiff modified binders to produce a level of aging simi- lar to that obtained in the PAV. From this study, the SAFT was selected for further development. The additional devel- opment for the SAFT included (1) a volatile collection system (VCS) study to design an improved system for quantifying the volatility of binders tested in the SAFT and (2) a SAFT opti- mization study to determine operating parameters for the SAFT so that for neat binders, it would reproduce the level of aging obtained with the RTFOT. The last study that was con- ducted in NCHRP Project 9-36 was the verification study. In this study, the properties of binders aged in both the SAFT and the MGRF were compared to properties of binders aged in the RTFOT and the properties of binders from mixtures that were short-term oven-aged in accordance with the perform- ance-testing procedure in AASHTO R30. Initially, only the SAFT was included in the study, but the study was expanded to include the MGRF. The verification study served as the basis for the final proposals for short-term aging that are the primary product of NCHRP Project 9-36. Each of the studies shown in Figure 2-1 is described in greater detail in the sections that follow. 2.2 Identify Viable Candidate Methods 2.2.1 Ideal Aging Procedure for Specification Testing A critical review of existing binder aging procedures was conducted to identify viable candidates for improvement in NCHRP Project 9-36. To guide this critical review, the fol- lowing requirements for ideal short- and long-term aging procedures for specification testing in the United States were developed. 1. Both long-term and short-term aging must be simulated. The aging of asphalt binders, whether in the field or during accelerated laboratory aging, is a very complex process that has received considerable attention from researchers for many years. It is generally agreed that the aging process occurs in two distinct steps: (1) during construction (plant mixing, placement, and compaction) and (2) during the service life of the pavement. During construction, the aging occurs at an elevated temperature, and there is opportunity for the asphalt binder to both oxidize and to lose volatile C H A P T E R 2 Research Approach

7compounds. In contrast, aging during the service life of a pavement occurs at a much lower temperature where oxi- dation is the primary aging mechanism. There is relatively little volatile compound loss during the service life of a pavement. Therefore, the ideal binder aging procedure must accommodate both the short-term aging that occurs during the construction process as well as the long-term aging that occurs during the service life of a pavement. 2. Simulated laboratory aging must be conducted at two temperatures, one representing conditions at the hot mix plant and the other as close as possible to pavement service temperatures. Short-term aging is simulated with the RTFOT. In this test the asphalt binder is exposed to a stream of air at 163°C, which is representative of mixing and compaction temperatures. For a pavement, maximum service temperatures range from 58° to 70°C. Research con- ducted during the SHRP asphalt research program clearly demonstrated that the aging mechanisms that occur in the laboratory during simulated aging change significantly when the aging temperature rises above approximately 110°C. This finding limits the extent to which temperature can be used to accelerate the simulation of long-term aging. Consequently, the short- and long-term aging must be conducted at different temperatures. Previous studies also indicate that the long-term aging mechanism, and its asso- ciated kinetics, is more reliably simulated when the accel- erated aging is conducted as close as possible to the service temperature. Selection Study (Evaluate Extendibility to Long-Term Aging) Identify Viable Candidate Methods Volatile Collection System Study SAFT Optimization Study Verification Study Stirred Air Flow Test Modified German Rotating Flask Recommendations Figure 2-1. Flowchart for NCHRP Project 9-36. Figure 2-2. Schematic of the prototype Stirred Air Flow Test (1).

83. The short-term aging process must include a procedure for capturing and measuring volatile loss. During the mixing and compaction process, some of the material of lighter molecular weight can vaporize and escape into the atmosphere. This is, in part, essentially an extension of the distillation process. As well, components—primarily oils used in the preparation of modified asphalt binders—also may vaporize and escape into the atmosphere. The RTFOT provides a means of measuring mass change, which includes the loss of mass resulting from volatilization as well as mass gain that can result from oxidation. Volatile loss is more significant to the paving industry than mass change. Volatile loss should be more directly related to “blue smoke” than mass change, wherein excessive vapors are lost to the atmosphere, causing an environmental problem. Further, volatile loss provides better control than mass change over certain undesirable refining practices (for example, when a hard base stock is “cut” with oils). Therefore, the ideal binder aging procedure should capture the volatile com- pounds that are lost during the simulation of short-term aging. For the purposes of a specification test, it is not nec- essary to characterize these materials, but simply to collect and weigh them. Including such a procedure in the short- term aging process also should be of benefit to research studies where it may be desirable to characterize the nature of the volatile compounds. 4. Sufficient material must be available for characterizing the physical properties of the asphalt binder after short- and long-term aging. The ideal aging procedure, as envi- sioned within the context of this project, will be used for specification purposes. The specifications for asphalt binders are based upon physical properties. Consequently, the ideal aging procedure must yield sufficient material to characterize the physical properties of the asphalt binder. Adequate material must be available after the short- and long-term aging steps. 5. The long-term aging must be completed within 46 hours. Whereas the short-term aging can be conducted at tem- peratures representative of the hot mix plant and at real- istic times (less than 4 hours), the long-term aging must be accelerated by some means in order to meet the needs of both the producers and users of the asphalt binder. Cur- rently, both pressure and temperature are used to acceler- ate the aging process in the PAV. This results in a 20-hour test. During the SHRP asphalt research program, a 144- hour test conducted at 60°C was proposed. Industry strongly objected to this protocol and, consequently, the aging temperature was increased to 100°C. It is clear that a specification test that can be used for quality control and acceptance purposes, and that is applicable to U.S. prac- tice, cannot be of 1-week duration. Recognizing that there must be a compromise between test reliability and Figure 2-3. Schematic of the Modified German Rotating Flask (2).

test length, the long-term aging test must be completed within approximately 46 hours (2-day cycle time for equipment). As discussed with the NCHRP project panel, limiting the long-term aging procedure to a 1-day test may be too restrictive in terms of developing a reliable long-term aging test. On the other hand, a test that requires more than 2 days to complete will be unacceptable to the industry. 6. The short- and long-term aging procedure must be applicable to both neat and modified asphalt binders. One of the primary reasons for NCHRP Project 9-36 is that the RTFOT is not applicable to some modified binders. Some modified asphalt binders do not roll uniformly within the bottle during the test, thereby negating a basic assumption of the test (i.e., that during the test the asphalt binder is exposed, in the form of a thin film, to the stream of air). A second problem with the RTFOT is that some modified binders tend to “crawl” out of the bottle during the test. These problems were addressed during NCHRP 9- 10 by placing steel rods in the RTFOT bottles. Subse- quent work by FHWA showed that the steel rods were not effective. During the long-term aging process, the asphalt binder must form a film, or be stirred in a manner that is equally applicable to neat or modified binders. This is especially of concern during the simulation of long-term aging where oxidation is the aging mechanism. In order for the long-term test to be equally applicable to neat and modified binders, the availability of oxygen must be inde- pendent of the type of binder. 7. The long-term aging test must accommodate binder- and modifier-specific aging kinetics. The rate of harden- ing, whether in the field or in the laboratory under accel- erated conditions, is binder-specific. Different binders are affected differently by changes in temperature or length of exposure during accelerated long-term aging. In other words, aging kinetics are binder-specific. The current PAV test may simulate the aging that occurs in 5 years for one binder and 10 years for another binder. The fact that the PAV test does not treat all binders equally was well known to researchers during the SHRP asphalt research program. To further complicate the matter, aging kinetics are also modifier-specific and differ from the aging kinetics of asphalt binders. To characterize aging kinetics, physical property measurements must be made at multiple times or temperatures, or a combination thereof. Although it is unrealistic to expect that a complete characterization of aging kinetics will be part of a future specification, the ideal long-term aging test should, as a minimum, provide for sampling at multiple aging times. During the SHRP asphalt research program, researchers noted that the aging process caused a shift in the rheological master curve as opposed to a change in the shape of the rheological mas- ter curve. This was demonstrated with both laboratory- and field-aged materials. Thus, aging kinetics can be cap- tured by using a very limited rheological testing protocol. The ideal aging procedure will allow sampling at multiple aging times so that aging kinetics can be included in a future specification. 8. The aging test procedure must not expose the operators to unsafe or hazardous conditions. Safety is a key issue that must be considered in any laboratory procedure. Of pri- mary concern with respect to an ideal aging test is the aging atmosphere during the long-term test. Some researchers have suggested the use of pure oxygen as the aging envi- ronment, but there are concerns over the safety of the use of pure oxygen in commercial laboratories. Further, the use of high pressure, regardless of atmosphere, is to be avoided if possible. 9. Equipment for the aging procedure must have a reason- able cost, be reliable, easy to operate and clean, and be configurable for both the short-and long-term aging procedures. There are a number of other features that an ideal procedure must embody. Without elaborating, the equipment must be reasonably priced, reliable, easy to operate, and easy to clean (especially with respect to the use of solvents). Although the operating conditions for short-term aging and long-term aging must be different, this does not necessarily militate against the use of the same equipment for both short-term aging and long-term aging. Various scenarios are possible, and the same equipment might be used for both long-term and short-term aging, but the temperature may be changed. On the other hand, the equipment may be the same but operated under different conditions as, for example, a container switched between replicate devices operated at different temperatures. A summary listing of the key features of the ideal aging pro- cedure for specification testing is presented as follows. This list was used to guide the review of existing tests and the selection of viable procedures. The ideal aging procedure should • Simulate both long-term and short-term aging; • Be performed at two temperatures, one representing condi- tions at the hot mix plant and the other representing, as close as possible, service temperatures; • Include a procedure for capturing and measuring volatile loss during short-term aging; • Provide sufficient material for characterizing the physical properties of the binder after short- and long-term aging; • Complete long-term aging within 46 hours; • Be applicable to both neat and modified asphalt binders; • Accommodate binder- and modifier-specific aging kinetics in the long-term aging; • Be safe and technician-friendly; and 9

10 • Use reasonably priced equipment that can be shared between the short- and long-term procedures. 2.2.2 Review and Selection Process A three-step process was used to select promising proce- dures for further evaluation in NCHRP Project 9-36. The first step included two activities that were conducted simultane- ously at the beginning of the project. These were the devel- opment of the requirements of the ideal aging procedure for specification testing as discussed previously in Section 2.2.1, and a review of literature and research in progress associated with binder aging methods. Excellent literature reviews on the aging of asphalt binders and mixtures were conducted during the SHRP asphalt research program (3–5). These formed the basis for the expanded literature review performed during this study. Approximately 90 references that post-date the SHRP asphalt research were identified and reviewed. Much of this information was published in the European literature, espe- cially that of Eurobitume and RILEM. Several ongoing stud- ies associated with the development of improved binder aging methods were identified, and contact was made with the prin- cipals conducting these studies. The work in progress that was reviewed included • Efforts at the Western Research Institute under FHWA Con- tract DTFH61-99-C-00022, “Fundamentals of Asphalts and Modified Asphalts II,” associated with the chemistry of binder aging; • FHWA studies to evaluate the Modified Rolling Thin Film Oven Test, MGRF, and SAFT; • Texas Department of Transportation studies associated with the development and implementation of the SAFT; • Activities in the European Committee for Standardiza- tion (CEN) Task Group on Binder Aging (CEN TC336 SG1 TG3); and • Shell Global Solutions’ research associated with the devel- opment of the Long-Term Rotating Flask Test. Appendix A (available on the TRB website) presents a comprehensive bibliography related to binder aging that was assembled by adding the references identified in this project to the unpublished literature review prepared during the SHRP asphalt research (3). Relevant findings from the literature review and the review of research in progress are presented in Chapter 3 of this report. The second step in the evaluation and selection process was the selection of candidate procedures from those identi- fied through the literature review and the review of research in progress. Procedures based on (1) microwave technology, (2) thin films, and (3) air blowing were identified in the review of the literature and research in progress. Consideration of the fundamental aging process in these three approaches and the requirements of the ideal aging procedure for specification testing were used to select approaches and candidate procedures for further consideration. This step eliminated microwave technology. The third step in the evaluation and selection process con- sisted of a detailed comparison of candidate procedures based on the two viable approaches with the requirements of the ideal aging procedure. This step also included the considera- tion of a hybrid procedure combining meritorious elements of the various procedures reviewed. From this step, two exist- ing procedures, the MGRF and the SAFT, were identified as promising methods for further consideration. 2.3 Selection Study The objective of the selection study was to evaluate whether the two promising short-term aging tests, the MGRF and the SAFT, can be extended to long-term aging. The extension of either of these to a low-temperature, long-term aging test using air at atmospheric pressure depends on the mixing efficiency of the device. The selection study evaluated the mixing effi- ciency of the devices at conditions representative of those that should be used in a long-term aging test. In this study, the level of aging obtained for long-term conditions was compared to that obtained in the PAV. Table 2-1 presents the conditions selected by the research team for developing prototype versions of long-term aging tests based on the MGRF and the SAFT. The selection study was conducted in two parts. The first part of the study was an assessment of various modifications that could be made easily to the MGRF and the SAFT to pro- duce prototype long-term versions of these tests. The goal in this effort was to obtain approximately the same degree of aging that occurs in the PAV subject to the constraints on tem- perature, atmosphere, and time given in Table 2-1. The binders used in this part of the study were a neat PG 58-28, a styrene- butadiene-styrene (SBS) modified PG 82-22, and a low-density polyethylene (LDPE) modified PG 76-22. Table 2-2 presents the test conditions that were varied during this first part of the selection study. The suitability of each of the various configurations was assessed based on • The degree of aging obtained relative to the PAV for the PG 58-28 and the PG 82-22, Condition Value Temperature 100°C max Atmosphere Air at atmospheric pressure Duration < 48 hours Quantity Per current short-term testing protocol Degree of Aging Approximate PAV aging Table 2-1. Summary of conditions for long-term aging used in the selection study.

• Visual assessment of the degree of mixing during the test, • Visual assessment of separation for the two polymer modi- fied binders, and • Potential for implementation as a specification test. The second part of the selection study was a formal exper- iment designed to address whether the degree of aging in the prototype long-term versions of the tests was affected by the large differences in viscosities for neat and modified binders at the selected aging temperature of 100°C. To emphasize the significance of the “viscosity effect,” in the PAV condition, the unmodified binder has the consistency of light cream whereas the modified binder has the consistency of molasses. Versions of the long-term tests judged successful based on the first part of the selection study were subjected to this formal experiment. In this experiment, the PG 58-28 and the SBS- modified PG 82-22 were aged in the prototype long-term ver- sion of the test and in the PAV. Rheological measurements at high, intermediate, and low pavement temperatures were used to compare the level of aging to that produced by the PAV. Replication was included in this experiment to permit statisti- cal analysis of the differences in aging that were observed. Based on the results of the selection study, the SAFT was chosen for further development as an improved procedure for short-term aging of binders. Relevant findings from the selec- tion study are presented in Chapter 3 of this report. The selec- tion study is documented in detail in Appendix B (available on the TRB website). 2.4 Volatile Collection System Study The prototype SAFT included a volatile collection system (VCS), which consisted of a copper coil condenser operated at ambient temperature. Data published for several binders during the development of the SAFT showed that the mass of volatiles collected was a factor of 10 lower than the mass change in the RTFOT (1). Since mass change during the RTFOT includes mass loss due to volatilization and mass gain due to oxidation, the RTFOT mass change was expected to be less than the mass of the volatiles collected with the SAFT. Several possible causes for this discrepancy were identified including 1. Condensation of volatile compounds on the lid of the SAFT before they entered the air-cooled condenser, 2. Inefficiency of the air-cooled condenser allowing volatiles to pass completely through the VCS, 3. Production of fewer volatile compounds in the SAFT com- pared to the RTFOT due to the shorter duration of the SAFT conditioning procedure and the lower airflow rate used in the SAFT, 4. Rapid saturation of the small air bubbles produced in the SAFT with volatiles so that they are not able to absorb addi- tional volatiles as they move upward through the binder, and 5. Suppression of volatilization caused by the build up of air pressure in the SAFT. The VCS study consisted of a series of small experiments to evaluate these potential causes and to design a more effective VCS for the SAFT. The product of the VCS study was an improved VCS system employing reusable adsorbents that are commonly employed for chromatographic analyses. Findings from the VCS study are presented in Chapter 3. The VCS study is documented in Appendix C (available on the TRB website). 2.5 SAFT Optimization Study During NCHRP Project 9-36, the Texas Department of Transportation contracted with James Cox and Sons, Inc., to produce a commercial version of the SAFT. Figure 2-4 shows photographs of the prototype and commercial versions of the SAFT. The major difference between the prototype and com- mercial versions is how the binder in the aging vessel is heated. In the prototype device, the aging vessel was heated by direct contact with a heating mantle, while the commercial version used an oven to heat the aging vessel. Because the aging vessel was in direct contact with the heating mantle in the prototype, the aging vessel and the binder in contact with it were exposed to very high temperatures during the heat-up portion of the test. In the commercial version, the oven was limited to a tem- perature approximately 13°C above the test temperature, so the temperature of the aging vessel and the binder in contact with it were much lower. This resulted in less aging in the com- mercial version compared to the prototype for the same oper- ating parameters. The difference in aging between the proto- type and commercial versions of the SAFT necessitated a study to optimize the operating parameters of the commercial version of the SAFT to reproduce the aging from the RTFOT for neat binders. This study was called the SAFT optimization study. The SAFT optimization study included two parts. The first part was a series of tests to verify that the heat-up phase of the test does not result in significant aging of the binder. During the heat-up phase, the temperature of the binder is increased from approximately 100°C to the testing temperature of 163°C 11 Test Conditions Investigated Modified German Rotating Flask Morton versus smooth flask Rotational speed Mixing enhancers Scrapers Stirred Air Flow Test Impeller type Position of air supply Rotational speed of impeller Table 2-2. Summary of conditions investi- gated during the selection study.

12 while nitrogen flows through the SAFT vessel. Since the start- ing temperature (temperature of the binder after charging the SAFT vessel) cannot be accurately controlled, it is critical that the heat-up phase not contribute significantly to the degree of aging that occurs in the test. The second component of the SAFT optimization study was an experiment to determine the effects of impeller speed, airflow rate, and test duration on the degree of aging measured by the high pavement tempera- ture rheology of the binder. From this component of the SAFT optimization study, operating parameters for the commercial SAFT were selected. These operating parameters were used in the verification study described in the next section. Findings from the SAFT optimization study are presented in Chapter 3. The SAFT optimization study is documented in Appendix D (available on the TRB website). 2.6 Verification Study The objective of the verification study was to (1) verify that the commercial version of the SAFT and the MGRF reproduce the degree of aging obtained in the RTFOT for a wide range of neat binders and (2) compare the aging from the SAFT, MGRF, and RTFOT with that from mixture samples aged in a forced draft oven in accordance with the performance testing pro- tocol contained in AASHTO R30. Initially, the verification study only included the SAFT, but it was expanded at the request of the NCHRP project panel to include the MGRF. The verification study consisted of two parts: (1) the RTFOT verification experiment and (2) the oven-aged mixtures exper- iment. The RTFOT verification experiment, which included dynamic shear rheometer (DSR) and bending beam rheome- ter (BBR) measurements, was designed to provide master curves for the binders in the tank condition and after SAFT, MGRF, and RTFOT conditioning. These binder master curves served two purposes: (1) to allow a comparison of the rheolog- ical properties of material conditioned in the SAFT, MGRF, and RTFOT and (2) to allow a comparison of the master curves measured for the binders and the master curves back-calculated from mixture properties. In the oven-aged mixtures experi- ment, hot mix asphalt was prepared with the binders from the RTFOT verification experiment and aged in accordance with the performance testing protocol in AASHTO R30. Dynamic modulus master curve tests were performed on the mixture samples. From the mixture modulus master curves, the binder stiffness was estimated using the Hirsch Model (6) and com- pared to the measured stiffnesses obtained from the SAFT, Figure 2-4. Prototype SAFT (left) and commercial SAFT (right).

MGRF, and RTFOT. The verification study was the last study conducted in NCHRP Project 9-36 and provided the basis for making the final recommendation with respect to a replace- ment for the RTFOT. Findings from the verification study are presented in Chapter 3. The verification study is documented in Appendix E (available on the TRB website). 2.7 Materials 2.7.1 Binders NCHRP Project 9-36 used 13 different asphalt binders: seven neat binders and six modified binders. The binders were selected to provide a wide range of physical and chemi- cal properties and modification processes. Tables 2-3 and 2-4 present AASHTO M320 properties for the binders used in Project 9-36. The neat binders included a PG 58-28 from the Paulsboro, New Jersey, refinery of the Citgo Asphalt Refining Company (Citgo) and six binders (AAC-1, AAD-2, AAF-1, AAM-1, ABL-1, and ABM-2) from the FHWA Materials Reference Library (MRL). Detailed information on the chemical com- position of the MRL binders is contained elsewhere (7). The modified binders were selected to represent a range of binder grades, modifiers, and modification processes. These included an airblown binder, two binders modified with SBS, one binder modified with Elvaloy, one binder modified with LDPE, and one binder modified with ethyl vinyl acetate (EVA). All of the modified binders except the EVA binder were obtained from commercial sources. A commercial source supplying EVA-modified binders for paving applications could not be identified; therefore, the EVA binder was pro- duced in the laboratory of Advanced Asphalt Technologies, LLC, by modifying a PG 64-22 binder from the Paulsboro, New Jersey, refinery of Citgo with 7 percent by weight Repsol Quimica PA-420. The Repsol Quimica PA-420 was obtained from Momentum Technologies, Inc. The airblown binder graded as a PG 76-16. It was obtained from Western Refin- ing’s El Paso, Texas, refinery. Citgoflex is an SBS-modified binder produced in several grades by Citgo. The Citgoflex binder used in NCHRP Project 9-36 was a PG 82-22 grade and was obtained from Citgo’s Paulsboro, New Jersey, refin- ery. The second SBS-modified binder was that included in the FHWA Pooled Fund Study TPF-5(019), Full Scale Accelerated Performance Testing for Superpave and Structural Validation. 13 Condition Test Method CITGO 58-28 AAC-1 AAD-2 AAF-1 AAM-1 ABL-1 ABM-2 Viscosity at 135 °C, Pa·s AASHTO T316 0.23 0.18 0.26 0.34 0.55 0.42 0.19 Unaged Temperature for G*/sinδ of 1.00 kPa at 10 rad/s, °C AASHTO T315 59.7 56.5 57.0 65.4 67.7 68.5 62.7 Mass Change, % AASHTO T240 -0.358 -0.058 -1.058 -0.008 +0.122 -0.654 -0.348 RTFO Aged Residue Temperature for G*/sinδ of 2.20 kPa at 10 rad/s, °C AASHTO T315 59.8 56.3 65.6 67.0 68.0 69.5 60.7 Temperature for G*sinδ of 5000 kPa at 10 rad/s, °C AASHTO T315 13.0 17.7 11.9 27.2 19.0 17.5 25.2 Temperature for Creep Stiffness of 300 MPa, at 60 s, °C AASHTO T313 -20.1 -18.1 -23.7 -12.2 -16.6 -19.6 -6.0 PAV Aged Residue Temperature for m-value of 0.300 at 60 s, °C AASHTO T313 -23.1 -16.7 -24.6 -9.8 -11.3 -19.9 -10.2 M320 Grade 58-28 52-22 52-28 64-16 64-16 64-28 58-16 Table 2-3. AASHTO M320 properties for the neat binders used in NCHRP 9-36. Condition Test Method Airblown Citgoflex ALF Elvaloy Novophalt EVA Modifier Airblown SBS SBS Elvaloy LDPE EVA Viscosity at 135 °C, Pa·s AASHTO T316 0.79 2.94 1.20 0.65 1.72 2.07 Unaged Temperature for G*/sinδ of 1.00 kPa at 10 rad/s, °C AASHTO T315 77.3 88.5 73.6 67.4 77.9 82.9 Mass Change, % AASHTO T240 +0.031 -0.196 -0.207 -0.173 -0.132 -0.132 RTFO Aged Residue Temperature for G*/sinδ of 2.20 kPa at 10 rad/s, °C AASHTO T315 80.3 85.2 75.4 69.9 78.9 81.0 Temperature for G*sinδ of 5000 kPa at 10 rad/s, °C AASHTO T315 22.2 23.6 5.8 16.0 22.0 16.5 Temperature for Creep Stiffness of 300 MPa, at 60 s, °C AASHTO T313 -17.2 -14.5 -29.8 -19.1 -14.2 -15.4 PAV Aged Residue Temperature for m-value of 0.300 at 60 s, °C AASHTO T313 -8.1 -14.1 -27.1 -18.6 -11.1 -12.9 M320 Grade 76-16 82-22 70-34 64-28 76-16 76 –22 Table 2-4. AASHTO M320 properties for the modified binders used in NCHRP 9-36.

14 binder. Pertinent volumetric properties at the optimum binder content are summarized in Table 2-5. For the oven-aged mixture experiment, mixtures were produced using the six MRL binders and the six modified binders from Tables 2-3 and 2-4. The same binder content of 5.5 percent was used in each of the 12 mixtures produced. 0 10 20 30 40 50 60 70 80 90 100 SIEVE SIZE, mm 0.075 0.15 0.3 0.6 1.18 2.36 4.75 9.5 12.5 Figure 2-5. Gradation of the 9.5-mm limestone mixture. Property Sieve Size, mm Value 12.5 100 9.5 94 4.75 50 2.36 32 1.18 20 0.600 13 0.300 9 0.150 6 Gradation 0.075 5.1 Asphalt Content, % 5.5 Ndesign 100 VMA, % 15.8 VFA, % 72.6 Dust/Binder Ratio (Weight Basis) 1.0 Fine Aggregate Angularity, % 46.0 Coarse Aggregate Angularity, % 100/100 Flat and Elongated Particles, % 0.8 Sand Equivalent 75 Surface Area, m2/kg 4.40 Table 2-5. Volumetric properties for the 9.5-mm limestone mixture. This binder graded as a PG 70-34. The Elvaloy binder was pro- vided by Mathy Construction. It graded as a PG 64-28. Finally, the Novophalt binder was provided by Advanced Asphalt Tech- nologies, LLC. This binder contains recycled LDPE and graded as a PG 76-16. The Citgo PG 58-28 was used in the selection study, the VCS study, and the SAFT optimization study. MRL binders AAD, AAM, and ABL2 were used in the VCS study and the SAFT optimization study. The Citgoflex and Novophalt binders also were used in the selection study. All of the MRL binders and all of the modified binders were used in the verification study. 2.7.2 Aggregate Because research completed during SHRP showed a rela- tively minor effect of aggregate type on short-term mixture aging (4), only one aggregate and one gradation were used in the oven-aged mixture experiment of the verification study. The aggregate was a limestone from Frazier Quarry, Incorpo- rated’s North Quarry in Harrisonburg, Virginia. This aggre- gate was used extensively in various mixture volumetric studies completed in NCHRP Projects 9-25 and 9-31 (8). Figure 2-5 shows the gradation of the coarse graded 9.5-mm nominal maximum aggregate size mixture that was used. The optimum binder content for this mixture was selected using a PG 64-22

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Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Report 709: Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders provides a proposed method of testing for short-term laboratory aging of neat and modified asphalt binders using the modified German rotating flask as an alternative to the rolling thin film oven test.

The following appendixes A-E to NCHRP Report 709 are only available in electronic format:

Appendix A: Binder Aging Bibliography

Appendix B: Selection Study Report

Appendix C: Volatile Collection System Study Report

Appendix D: SAFT Optimization Study Report

Appendix E: Verification Study Report

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