A Manual for Design of Hot-Mix Asphalt with Commentary (2011) / Chapter Skim
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From page 65... ...
This chapter also discusses various performance tests that can be used to assess HMA mixture performance and presents an introduction to the MEPDG and how this software can be used to complement the mixture design process. 65 C H A P T E R 6 Evaluating the Performance of Asphalt Concrete Mixtures
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From page 66... ...
A downward arrow indicates that the performance indicator deteriorates with an increase in the compositional factor. The relationship between binder stiffness and fatigue resistance depends on the pavement structure; for thin pavement structures, increasing binder stiffness will decrease fatigue resistance, while for thick pavement 66 A Manual for Design of Hot Mix Asphalt with Commentary Component Factor Resistance to Rutting and Permanent Deformation Resistance to Fatigue Cracking Resistance to Lo w Temperature Cracking Resistance to Moisture Damage Durability/ Resistance to Penetration by Water and Air Increasing High Temperature Binder Grade ↑↑↑ Increasing Low Temperature Binder Grade ↓↓↓Asphalt Binder Increasing Intermediate Temperature Binder Stiffness ↑↓ Increasing Aggregate Angularity ↑↑ Increasing Proportion of Flat and Elongated Particles Increasing Nominal Maximum Aggregate Size ↓ ↓ ↓ Increasing Mineral Filler Content and/or Dust/Binder Ratio ↑↑ ↑ Aggregates Increasing Clay Content ↓ Increasing Design Compaction Level ↑↑ ↑↑ Increasing Design Air Void Content ↑↑ Increasing Design VMA and/or Design Binder Content ↓↓ ↑ ↓ Volumetric Properties Increasing Field Air Void Content ↓↓ ↓↓ ↓ ↓↓ ↓↓↓ Typical Effects of Increasing Given Factor within Normal Specification Limits While Other Factors Are Held Constant within Normal Specification Limits Table 6-1.
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From page 67... ...
The information presented in Table 6-1 and the more detailed discussion on the relationships among binder properties, aggregate properties, mixture composition, and pavement performance that is given later in this chapter are based on several sources, most importantly NCHRP Report 539: Aggregate Properties and the Performance of Superpave-Designed Hot Mix Asphalt and NCHRP Report 567: Volumetric Requirements for Superpave Mix Design. Binder Characteristics and Performance Performance Grading System As discussed in more detail in Chapter 3, the Performance Grading system for asphalt binders, AASHTO M 320, controls the properties of asphalt binders that are related to pavement performance.
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From page 68... ...
The Performance Grading system places a maximum limit on the stiffness of the binder after simulated long-term aging. Although there is much debate over this requirement and its relationship to traditional 68 A Manual for Design of Hot Mix Asphalt with Commentary Grade Adjustment for Average Vehicle Speed in kph (mph)
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From page 69... ...
Finally, increasing the mineral filler content of the HMA decreases permeability for the same in-place air void content (again, understanding that there are practical limitations to how much mineral filler can be used in HMA mixtures)
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From page 70... ...
Even though decreasing VMA and increasing design air void content will, in general, improve rut resistance, as discussed below, VMA values that are too low and design air void values that are too high will often produce mixtures with poor durability. This is why there are both minimum and maximum values for VMA and air void content.
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From page 71... ...
Rut resistance can be evaluated in the AMPT using the dynamic modulus test, the flow number test, or the flow time test. Use of the dynamic modulus test to evaluate rut resistance was developed in conjunction with the MEPDG and is discussed in detail in NCHRP Report 580: Simple Performance Tests for Permanent Deformation of Hot Mix Asphalt -- Volume 1: The E*
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From page 72... ...
The Asphalt Mixture Performance Tester Figure 6-1 shows the AMPT. It is a relatively small, computer-controlled test machine that can perform various tests on HMA over a temperature range of 4 to 60°C.
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From page 73... ...
AASHTO PP 61-09, Developing Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT)
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From page 74... ...
AASHTO PP 60-09, Preparation of Cylindrical Performance Test Specimens Using the 74 A Manual for Design of Hot Mix Asphalt with Commentary 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 1000 2000 3000 4000 5000 6000 Load Cycle Pe rm an en t S tra in , % 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 0.0040 0.0045 0.0050 Pe rm an en t S tra in R at e, % p er C yc le Permanent Strain Permanent Strain Rate Flow Number = Minimum Permanent Strain Rate Figure 6-2. Typical data from the flow number test.
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From page 75... ...
The air void content of the AMPT specimen will have a major effect on the properties measured in the AMPT. AMPT specimens used to evaluate rutting resistance should be prepared to the expected average field air void content at the time of construction, not the design air void content.
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From page 76... ...
This test was developed as a quick and inexpensive procedure for evaluating rut resistance using equipment currently available in many HMA design and quality assurance laboratories. Christensen, Bonaquist, and Jack reported an excellent relationship between rutting resistance and the indirect tensile strength at high temperature in a 2000 publication.
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From page 77... ...
These values are >10,000 for mixes produced with PG 64-XX binder, >15,000 for mixes produced with PG 70-XX binder, and >20,000 for mixes produced with PG 76-XX binder. Additional information on the use of the APA and Hamburg Wheel-Track testing as performance tests for use in the mix design process is given in Chapter 8.
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From page 78... ...
By controlling VBE, the mixture design process controls the fatigue life of the mixture. As discussed previously, VBE, is controlled in the design method described in this manual by controlling both the VMA and the design air void content.
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From page 79... ...
Sawed ends are needed to attach the deformation measuring equipment. IDT testing is usually conducted on specimens compacted to the anticipated in-place air void content and exposed to long-term oven aging in accordance with AASHTO R 30.
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From page 80... ...
80 A Manual for Design of Hot Mix Asphalt with Commentary 0 2 4 6 8 10 12 14 16 18 20 0 4000 60002000 8000 1200010000 14000 16000 18000 20000 Number of Passes R ut D ep th , m m Creep Slope Stripping Slope Stripping Inflection Point Figure 6-9. Typical rut depth versus wheel pass curve from AASHTO T 324.
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From page 81... ...
Non-conventional materials might include recycled materials such as ground glass, ground tire rubber, ground or shredded plastic Evaluating the Performance of Asphalt Concrete Mixtures 81 Property Recommended Test Design Traffic Levels for Which Property Should be Evaluated Moisture Sensitivity AASHTO T 283 All Permanent Deformation Flow Number or Dynamic Modulus, AASHTO TP 79-09 3 Million ESAL and greater Fatigue Cracking None NA Thermal Cracking None NA Table 6-4. Recommended performance tests for HMA made with conventional materials including most modified binders.
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From page 82... ...
MEPDG Input Levels The MEPDG requires a large amount of information about the pavement being analyzed. This includes data concerning traffic, climate, subgrade soils, the condition of existing pavements for rehabilitation design, and the thicknesses and material properties for each layer of the pavement, including existing pavement layers for rehabilitation design.
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From page 83... ...
The alligator and longitudinal cracking models also require in-place volumetric properties of the HMA layers, specifically the air void content and the effective binder content. These volumetric Evaluating the Performance of Asphalt Concrete Mixtures 83
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From page 84... ...
If rutting will be used in conjunction with other forms of distress to judge the acceptability of the HMA mixture, then a complete analysis using the MEPDG must be performed. In this case, 84 A Manual for Design of Hot Mix Asphalt with Commentary HMA Property Rutting Thermal Cracking Alligator Cracking Longitudinal Cracking Reflection Cracking Roughness Dynamic Modulus X X X Indirect*
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From page 85... ...
Thermal cracking is expressed as feet of transverse cracking per lane mile. Surface Roughness Within the MEPDG, the change in roughness in a pavement section depends on the initial roughness, the predicted rutting and cracking, and site factors including pavement age, soil type, freezing index, and precipitation.
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From page 86... ...
Decreasing in-place air void content 1% will increase the dynamic modulus approximately 5%. 86 A Manual for Design of Hot Mix Asphalt with Commentary
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From page 87... ...
Increasing the effective binder content and decreasing the in-place air void content of the lowest HMA layer will substantially decrease the predicted alligator cracking in the pavement. As discussed previously, use of dense-graded mixtures with higher design VMA will decrease the predicted alligator cracking compared to that for mixtures with more typical VMA values.
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From page 88... ...
88 A Manual for Design of Hot Mix Asphalt with Commentary HMA Property Rutting Thermal Cracking Alligator Cracking HMA ≥ 5 in Alligator Cracking HMA < 3 in Longitudinal Cracking High Temperature Binder Grade Increase to improve Increase to improve Decrease to improve Decrease to improve Low Temperature Binder Grade Decrease to improve Design VMA Decrease to improve Increase to improve Increase to improve Increase to improve Design VFA Increase to improve Filler Content Increase to improve In-Place Air Void Content Decrease to improve Decrease to improve Decrease to improve Decrease to improve Decrease to improve Table 6-6. Summary of effect of mixture composition on performance predictions.
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From page 89... ...
PP 61-09, Developing Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT)
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From page 90... ...
Evaluation of Indirect Tensile Strength to Identify Asphalt Concrete Rutting Potential, Asphalt Technology Program, Department of Civil and Environmental Engineering, West Virginia University, Morgantown, WV, May. 90 A Manual for Design of Hot Mix Asphalt with Commentary
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