The Superpave Mix Design System: Anatomy of a Research Program (2012) / Chapter Skim
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20 Chapter 4. Research Phase The research phase began in 1987 after funding for the program was secured.
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21 This emphasis was reinforced and further defined in the May 1986 "Brown Book." This document stated that a specific constraint or guideline for the asphalt program was as follows (1) : "…the final product will be performance-based specifications for asphalt, with or without modification, and the development of an asphalt-aggregate mixture analysis system (AAMAS)
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22 National Research Council Concrete & Structures Highway Operations & Maintenance LTPP Asphalt Contractors A-001 Contractor Technical Staff Loaned Staff Expert Task Groups Executive Committee SHRP Executive DirectorInformation Transfer Asphalt Program Manager Asphalt Advisory Committee Figure 7 Asphalt Program Structure (dashed lines indicate advisory status)
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23 Table 2 Major Asphalt Research Contracts: Proposed vs. Actual (based on 1 and 4)
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24 Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Ja nM ar Ap rJu n Ju l-S ep O ct -D ec Contract Number and Name Contractor/Location Amount ($1,000) A-001: Asphalt Experimental Design, Coordination, and Control of Materials University of Texas at Austin, Austin, TX Tom Kennedy, PI $6,188 A-002A: Binder Characterization and Evaluation Western Research Institute, Laramie, WY Claine Peterson, PI Ray Roberston and Dave Anderson, Co-PI $9,033 A-002B: Novel Approaches for Investigating Asphalt Binders University of Southern California Costas Synolakis and Victor Chang, Co-PI $893 A-002C: Nuclear Magnetic Resonance (NMR)
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25 Contract Number and Name Contractor/Location Amount ($1,000) A-001: Asphalt Experimental Design, Coordination, and Control of Materials University of Texas at Austin, Austin, TX Tom Kennedy, PI $6,188 A-002A: Binder Characterization and Evaluation Western Research Institute, Laramie, WY Claine Peterson, PI Ray Roberston and Dave Anderson, Co-PI $9,033 A-002B: Novel Approaches for Investigating Asphalt Binders University of Southern California Costas Synolakis and Victor Chang, Co-PI $893 A-002C: Nuclear Magnetic Resonance (NMR)
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26 To achieve the research goals, the program was envisioned to progress in four phases as follows and as shown in Figure 8: 1. Conceptualization - The physicochemical properties of asphalt binders and mechanical/structural properties of asphalt-aggregate mixes that affect pavement performance were to be identified.
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27 Figure 8 Strategy to Achieve Key Products (after 5) Economic Assessment and Implementation Performance-Based Specification P ro du ct D ev el op m en t Second –Stage Field Asphalt-Aggregate Mixture Test Development for First-Stage Validation of Asphalt Binder Asphalt-Aggregate Mixture Test Development for Asphalt-Aggregate Mix Analysis System Asphalt-Aggregate Interaction Performance-Based Physical Tests Composition Characterization Materials Selection Adoption Validation July 1991 Mar 1993 July 1990 Jan 1988 Conceptualization Definition Jan.
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28 Contract A-005 (Performance Models and Validation of Test Results) : Validate relationships between asphalt binder and asphalt-aggregate mixture properties and pavement performance (second-stage validation)
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29 4.2.2.2 Aggregate Selection Process A similar approach was employed in the selection of the aggregates. The aggregates were chosen based on known chemical, physical, geologic and petrographic properties as these properties related to perceived performance in asphalt-aggregate mixes.
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30 Figure 10 Geographical distribution of aggregates sampled for the Materials Reference Library
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31 March 1993 January 1991 January 1990 October 1987 Statistically-designed lab experiments to identify property-performance relationships Development and validation of property-performance relationships in mixes Validation with field results Performance-Based Specifications 4.2.3 Validation and Analysis of Research Data A central problem of the asphalt research program was how best to translate the large volumes of research results generated by more than twenty contractors into a coherent set of performance-based specifications. The following narrative outlines the validation strategy employed.
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32 available information, running the gamut from reliable data from controlled field experiments to personal observations by experienced engineers, would have to be identified, assessed and combined in an accelerated validation process in order to reach the pinnacle of the pyramid within the 5½-year program. Each level of the pyramid would require a different set of analytical techniques and assumptions.
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33 performance data gathered from both full-scale pavement test facilities such as the FHWA Accelerated Load Facility (ALF) and in situ field pavements studies, typified by the SHRP LTPP General and Specific Pavement Study (GPS and SPS)
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34 Figure 12 Strategy to achieve performance-based asphalt binder specification (5) A-005 Develop and validate models A-005 Validate A-002A with field data (Phase 2)
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35 Note: ALT = Accelerated Laboratory Tests 4.2.4 Mid-course Assessment At the August 1990 "Mid-course Assessment" meeting (3) , SHRP Executive Director Damian Kulash asked the 400+ attendees – representatives of state highway agencies, industry, and research organizations – to help SHRP look with fresh eyes at each part of the program and to decide where best to concentrate efforts to get the most out of the research.
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36 Tests of physical properties referenced in the binder specification should have a sound correlation with the underlying chemical properties of the asphalt. There should be a balance between chemical and physical tests.
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37 4.3 BINDER-RELATED RESEARCH Much of the research phase was spent exploring binder chemistry. This section outlines the guiding philosophy behind the research; the people, contracts and hypotheses employed in the work; and the eventual evolution of the binder specification.
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38 Chemical Composition and Performance of Asphalts Hypothesizing that the chemical composition determined its physical (rheological) properties, the focus of the research was on the separation of asphalt into chemically distinct fractions.
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39 Chemical Composition and Performance of Modified Asphalts Logically, the working hypotheses employed in the area of modified binders were similar conceptually to those discussed for unmodified asphalts. Additionally, a working concept was advanced to investigate the molecular forces which produce an elastic network (entanglement)
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40 It was envisioned that these fundamental results would provide a direct link between the asphaltaggregate chemistry and the pavement performance properties in terms of fundamental engineering properties as measured by accelerated laboratory test procedures. Chemical Composition and Model Conceptualization The model investigated considered interactions between the asphalt and aggregate surfaces occurring in three zones or regions as shown in Figure 15.
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41 4.3.3 Evolution of Binder Specification Had the SHRP Asphalt Program evolved as originally envisioned, the binder specifications would be based on the chemical composition of asphalt and common laboratory testing terminology would include IEC and FTIR instead of the now-familiar BBR, DSR and PAV. The asphalt program began with an intensive laboratory investigation to relate the chemical and physical properties of asphalt to the behavior of asphalt mixes and pavement performance.
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42 "Strawman" Specification for Asphalt Binders Graded at 0°C (32 F°)
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43 Aged Asphalt Binder Grades AB 1- AB 2- AB 3- AB 4- 1 2 3 1 2 3 1 2 3 1 2 3 Highest mean monthly temperature °F <80 80-90 90-100 >100 Lowest anticipated temperature °F <-20 -10 to -20 >-10 <-20 -10 to -20 >-10 <-20 -10 to -20 >-10 <-20 -10 to -20 >-10 Temperature dependency Low-Temperature Cracking Low-temperature stiffness at -10°F, psi (Bending Beam Test, SHRP B001) Permanent Deformation Dynamic stiffness at 140°F (Indentation Test, SHRP B002)
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44 4.4 ASPHALT-AGGREGATE MIX RELATED RESEARCH At the onset of SHRP, specifications assured only that the asphalt binder would respond in a predictable, consistent manner during plant production and placement. There was, however, no minimum level of pavement performance warranted, or even intended, in any but a peripheral sense.
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45 • Although there was significant money and effort devoted to fundamental research on aggregate properties that affect adhesion and absorption, there were no provisions to address the more routine but critical factors which affect hot-mix asphalt performance; e.g., physical/mechanical properties of aggregate and aggregate gradation. Accordingly, the narrative in 4.5.6, The Delphi Story, is presented to describe how these critical but heretofore neglected elements of aggregate properties were addressed in the asphalt program.
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46 Climatic Zone Wet-No Freeze Dry-No Freeze Wet-Freeze Dry-Freeze Highest mean monthly temperature, °F 90-100 >100 90-100 >100 90-100 >100 90-100 >100 Lowest anticipated temperature, °F -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 -10 to -20 >-10 Traffic Level1 L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H L M H Low-Temperature Cracking Stress at cracking, psi Temperature at Cracking, °F (Thermal Stress-Restrained Tensile Test, SHRP M001) Thermally-Induced Fatigue Cracking Cycles to Failure, Nf (Thermal Stress-Restrained Tensile Test, SHRP M001)
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47 Figure 19 Environmental Regimes Defined by LTPP
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48 Figure 20 Restricted Zone for Aggregate Gradation 4.4.2 Hypotheses and Models Employed in the Mix Research A thorough treatment of the hypotheses and models employed in the asphalt mix research is found elsewhere (5)
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49 4.4.2.2 Contract A-005 Performance Models and Validation of Test Results Bob Lytton of Texas A&M University and Rey Roque of Pennsylvania State University led this effort. Ideally, the second-stage validation of important relationships between asphalt properties and field performance could be accomplished through a long-term study of controlled field experiments.
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50 4.5 PRODUCTS Superpave (Superior Performing Asphalt Pavements) was the final product of the SHRP Asphalt Program.
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