U.S Department 

of Transportation 

Federal Highway 

Administration 

Publication No. FHWA-SA-95-003 

February 1995 

BACKGROUND of SUPERPAVE 

ASPHALT MIXTURE DESIGN 

AND ANALYSIS 

NATIONAL ASPHALT TRAINING CENTER 

DEMONSTRATION PROJECT 101 

Innovation Through Partnerships 

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NOTICE 

This document is disseminated under the sponsorship of the Department of Transportation in 

the interest of information exchange. This publication does not constitute a standard, 

specification, or regulation. 

The United States Government does not endorse products or manufacturers. Trademarks or 

manufacturers' names appear herein only because they are considered essential to the object 

of this document. 

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Technical Report Documentation Pag 

1, Report No. 1 2. Government Accession No. 3. Recipient's Catalog No. 

I I 

4. Title and Subtitle ( 5. Report Date 

Background of SUPERPAVE 

Asphalt Mixture Design & Analysis 

November 1994 

6. Performing organization Code 

Asphalt Institute 

P.O. BOX 14052 

Lexinaton. KY 4051 2-4052 

7. Author(s) 

R.B. McGennis, R.M. Anderson, T.W. Kennedy, M. Solaimanian 

9. Performing Organization Name and Address 

I 1 1 ,Contract or Grant No. 

8. Performing Organization Report No. 

10. Work Unit No. (TRAIS) 

- - i 13. Tv~e ofRe~ort and Period Covered 

15. Supplementary Notes 

FHWA Technical Representative - J.R. Bukowski 

12. Sponsoring Agency Name and Address 

Federal Highway Administration 

Office of Technology Applications 

400 Seventh St., SW 

Washington, DC 20590 

16. Abstract 

8 

Final Report 

December 1992-November 

'tf&i 

14. Sponsoring Agency Code 

HTA-21 

This manual represents the first formal training document that embodies the complete series of SUPERPAVE 

asphalt mixture design and analysis test equipment and procedures. These tests and procedures represent the 

results df the SHRP 5-year research effort to investigate and improve asphalt cement technology. This manual 

was developed under the FHWA's National Asphalt Training Center. Students attending the center utilize this 

manual to obtain a better understanding of the underlying theory behind asphalt mixture design and analysis, as 

well as how to perform each of the new procedures. 

17. Key Words 18. Dlsfribution Statement 

I 

9. Security Classif. (of this report) 1 20. Security Classif. (of this page) 121. No. of Pages 1 22. Price 

4sphatt mix, asphalt cement, gyratory compactor, indirect 

ensile tester, level 1 design, mixture design, shear tester, 

SHRP, SUPERPAVE 

Unclassified 

No restrictions. This document is available to the 

public from the National Technical Information 

Service, Springfield, Virginia 22 161 

I Unclassified I I I 

corm DOT F 1700.7 (8-72) Reproduction of completed page authorized 

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FOREWORD 

From October 1987 through March 1993, the Strategic Highway Research 

Program (SWRP) conducted a $50 million research effort to develop new ways to specify, 

test, and design asphalt materials. Near the end of SHRP, the Federal Highway 

Administration assumed a leadership role in the implementation of SHRP research. An 

essential part of FHWA' s implementation strategy was development of a nationally 

accessible training center aimed at educating agency and industry personnel in the proper 

use and application of the final SHRP asphalt products, collectively referred to as 

SuperpaveTM. This project was administered by the FHWA's Office of Technology 

Applications and designated Demonstration Project 101, the National Asphalt Training 

Center (NATC). 

The NATC resides at the Asphalt Institute's Research Center in Lexington, 

Kentucky. While the day-to-day affairs of the NATC are directed by Institute personnel, 

course development and technical direction were duties shared by a team of engineers 

from the Asphalt Institute, the Pennsylvania State University, the University of Texas at 

Austin, National Center for Asphalt Technology, Marathon Oil Company, and FHWA. 

The objective of the educational program is to train students in the practical 

applications of SHRP asphalt products. It is composed of two parts: Superpave asphalt 

binder technology and Superpave asphalt mixture design and analysis, 

This manual represents the textbook students use as a reference throughout the 40 

hours of training in Superpave mixture design and analysis. Best efforts were made to 

present the information in an easy to understand style. It was written for laboratory 

technicians and engineers with no previous training in Superpave, but with some 

knowledge in asphalt materials and mixture design. Other instructional aids consist of 

provisional AASHTO test methods (when available) and a separate illustrated overview 

document pertaining to Superpave gyratory compaction. 

The training program consists of 40 hours of instruction. Of this 40 hours, 

students receive 12 hours of classroom instruction, 16 hours of laboratory instruction, and 

12 hours of group discussion of actual test results. By the end of the course, students will 

be familiar with Superpave asphalt mixture test procedures and equipment. This course 

emphasizes (but is not limited to) Superpave Level 1 design and analysis. 

The training program and this manual do not present any information in English 

units. Superpave test procedures were largely developed in SI or metric units. The 

NATC team believed it would be counter productive and make learning more difficult if 

material properties were shown in US. customary, as well as the original SI and metric 

units. For example, it is easy for a student to understand and remember that the gyratory 

compaction pressure is 600 kPa. To show an English conversion such as, "600 kPa (86 

psi)," serves no purpose since students have no previous knowledge of typical US. 

customary units for this test parameter. The only exception to this is that some 

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Foreword 

performance based testing software was developed (and remains) in U.S. customary units. 

The NATC team has no control over these products but encourages the software 

developers to assist the industry and this training effort by standardizing the units, in SI, 

on test output. 

Users of this manual will note that no references are cited throughout the text. 

That is because as this manual was being prepared in late 1993, very few, if any, SHRP 

research reports had been published. The authors were able to glean important 

information from draft reports and verbally from researchers involved in the numerous 

areas of the SHRP asphalt research program. The authors are indebted to the many 

individuals who graciously shared their knowledge during the early phases of the NATC. 

Users are strongly encouraged to obtain and study the reports cited in the bibliography for 

the most complete information pertaining to Superpave. 

As this edition was being prepared, Superpave was still in an emerging phase. 

Many of the AASHTO test procedures were (and still are) under development. In 

addition, Superpave testing equipment is only now becoming available. Consequently, 

some of the information herein contained may be subject to change. Users of this manual 

are resolutely encouraged to stay abreast of Superpave technology through the many 

venues that have become available as a result of SHRP. The National Asphalt Training 

Center and asphalt user-producer groups are two examples of forums that specifically 

address Superpave technology. 

Mr. John R. Bukowski of FHWA's Office of Technology Applications is the Contracting 

Officer's Technical Representative for NATC. This manual was co-authored by: 

Mr. Robert B, McGennis 

Director of Research & Engineering Services 

Asphalt Institute 

Mr. R. Michael Anderson 

Asphalt Systems EngineerAsphalt Institute 

Dr. Thomas W. Kennedy 

Engineering Foundations Professor of Civil Engineering 

The University of Texas at Austin 

Dr. Mansour Solaimanian 

Research Engineer 

The University of Texas at Austin 

November 1994 

Lexington, KY 

SuperpaveTM is a registered trademark of the Strategic Highway Research Program 

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TABLE OF CONTENTS 

I . HOW ASPHALT MIXTURES BEHAVE ............................................................................................. 1 

ASPHALT BINDER BEHAVIOR .......................................................................................... 1 

MINERAL AGGREGATE BEHAVIOR ................................................................................. 3 

ASPHALT MIXTURE BEHAVIOR ........................................................................................... 7 

Permanent Deformation ............................................................................................... 7 

Fatigue Cracking ............................................................................................................ 10 

Low Temperature Cracking ....................................................................................... 13 

CURRENT WAYS TO SPECIFY ASPHALT CEMENTS ......................................................... 14 

CURRENT ASPHALT MIXTURE DESIGN PROCEDURES ................................................... 16 

11 . SUPERPAVE TO THE RESCUE ...................................................................................................... 21 

.................................................................................................................... INTRODUCTION 21 

ASPHALT BINDERS .............................................................................................................. 21 

MINERAL AGGREGATES .................................................................................................... 26 

ASPHALT MIXTURES .......................................................................................................... 28 

PUTTING IT ALL TOGETHER ................................................................................................. 30 

111 . MATERIALS SELECTION ...................................................................................................... 33 

INTRODUCTION ................................................................................................................. 33 

ASPHALT BINDERS ................................................................................................................. 33 

SUPERPAVE Weather Database .............................................................................. 34 

Reliability ...................................................................................................................... 34 

Start with Air Temperature ........................................................................................ 35 

Convert to Pavement Temperature ................................................................................ 36 

Select Binder Grade ....................................................................................................... 37 

Effect of Loading Rate on Binder Selection ............................ .. ............................... 38 

Effect of Traffic Level on Binder Selection .................................................................. 39 

MINERAL AGGREGATE ...................................................................................................... 39 

Consensus Properties ..................................................................................................... 40 

Coarse Aggregate Angularity .......................................................................... 40 

Fine Aggregate Angularity .......................................................................... 41 

Flat, Elongated Particles ........... ................................................................... 42 

Clay Content .................................................................................................. 44 

Source Properties ......................................................................................................... 45 

Toughness ....................................................................................................... 45 

Soundness ...................................................................................................... 46 

Deleterious Materials ..................................................................................... -46 

Gradation ..................................................................................................................... 46 

ASPHALT MIXTURES .............................................................................................................. 50 

Mixture Volumetric Requirements ................................................................................ 50 

Dust Proportion ......................................................................................................... 51 

Moisture Susceptibility .............................. ............................................................. 52 

IV . ASPHALT MIXTURE VOLUMETRICS ........................................................................................... 53 

INTRODUCTION ...................................................................................................................... 53 

COMPONENT DIAGRAM APPROACH ................................................................................... 53 

SPECIFIC GRAVITY .............................................................................................................. 55 

EXAMPLE CALCULATIONS ................................................................................................... 59 

V . SUPERPAVE GYRATORY COMPACTION ...................................................................................... 65 

INTRODUCTION ....................................................................................................................... 65 

TEST EQUIPMENT .................................................................................................................... 65 

iii 

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Table of Contents 

SPECIMEN PREPARATION 68 .................................................................................................... OVERVIEW OF PROCEDURE ................................................................................................. -69 

DATA ANALYSIS AND PRESENTATION ............................................................................ 70 

CALIBRATION AND STANDARDIZATION .......................................................................... 74 

VI . VOLUMETRIC MIX DESIGN ...................................................................................................... 75 

INTRODUCTION ................................................................................................................... 75 

MATERIAL SELECTION -76 ....................................................................................................... Binder Selection ............................................................................................................. 76 

Aggregate Selection ..................................................................................................... 78 

Coarse Aggregate Angularity ......................................................................... 80 

Fine Aggregate Angularity .......................................................................... 80 

Flat and Elongated Particles .......................................................................... 81 

Clay Content (Sand Equivalent) ..................................................................... 82 

SELECT DESIGN AGGREGATE STRUCTURE ........................ ....................................... -82 

SELECT DESIGN ASPHALT BINDER CONTENT ................................................................. 103 

EVALUATE MOISTURE SENSITIVITY .......... ............. ............................................... 112 

VII . PERFORMANCE TESTING (LEVELS 2 AND 3) ............................ .. .......... 115 

INTRODUCTION ......................... ....................................................................................... 115 

PERFORMANCE MODELS .................................................................................................. 116 

TEST PARAMETERS ................ ... ................................................................................ 117 

Test Temperatures ........................... ...................................................................... 117 

Asphalt Binder Contents ................................ ..................................................... 118 

SUPERPAVE SHEAR TESTER ............................ ........................................................... 119 

Testing Apparatus ................................................................................................... ,119 

Test Control Unit ......................................................................................................... 120 

Environmental Control Unit .......................... ........................................................ 120 

Hydraulic System ................................... ................................................................ 120 

Specimen Preparation and Instrumentation .................................................................. 121 

Test Procedures ...... 123 

Volumetric Test .............................................................................................. 123 

Uniaxial Strain Test .................................................................................... 124 

Repeated Shear Test at Constant Stress Ratio ................................ ......... 125 

Repeated Shear Test at Constant Height ........................ ... ..................... 127 

Simple Shear Test at Constant Height ........................................................... 128 

Frequency Sweep Test at Constant Height ...................................................... 129 

INDIRECT TENSILE TESTER ..................... .............. ............................................... 130 

Testing Apparatus .......................................................................................................... 131 

Control Unit and Data Acquisition System ................................................................ 131 

Load Measuring Device ............................................................................................... 132 

Environmental Control Chamber .............................. .............................................. 132 

Specimen Preparation and Instrumentation .................................................................. 132 

Test Procedures ............ ........................................................................................... 133 

IDT Creep Compliance and Strength (Low Temperature Cracking 

Analysis) ........................................................................................................ 133 

IDT Strength (Fatigue Cracking Analysis) ...................................................... 134 

DATA ANALYSIS AND INTERPRETATION ...................... .......................................... -135 

APPENDIX A: SUPERPAVE ASPHALT BINDER SPECIFICATION ............... ............................ 139 

APPENDIX B: SUPERPAVE ASPHALT MIXTURE GRADATION REQUIREMENTS ..................... 141 

37.5 MM NOMINAL SIZE ......................................................................................................... 141 

25 MM NOMINAL SIZE ................................................. .... 142 

19 MM NOMINAL SIZE .............................................. ........................................... 143 

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Table of Contents 

12.5 MM NOMINAL SIZE ....................................................................................................... 144 

9.5 MM NOMINAL SIZE ....................................................................................................... 145 

APPENDIX C: SUPERPAVE CONSENSUS AGGREGATE REQUIREMENTS .................................. 147 

COARSE AGGREGATE ANGULARITY ............ ............................................................. 147 

FINE AGGREGATE ANGULARITY ............................. ........... .............................................. 147 

FLAT AND ELONGATED PARTICLES ............................................................................... 148 

CLAY CONTENT ..................................................................................................................... 148 

APPENDIX D: VOLUMETRIC ANALYSIS OF COMPACTED HOT MIX ASPHALT (HMA) ......... 149 

DESCRIPTION OF TERMS ..................................................................................................... 149 

STANDARD CONVENTIONS ................................................................................................ 150 

CALCULATIONS ..................................................................................................................... 151 

APPENDIX E: OUTLINE OF STEPS IN SUPERPAVE LEVEL 1 MIX DESIGN .............................. 153 

I . SELECTION OF MATERIALS ................ .. ................................................................... 153 

I1 . SELECTION OF DESIGN AGGREGATE STRUCTURE .................................................. 153 

I11 . SELECTION OF DESIGN ASPHALT BINDER CONTENT ..................... .................. 154 

IV . EVALUATION OF MOISTURE SENSITIVITY OF DESIGN ASPHALT 

MIXTURE USING AASHTO T283 ..................................................................................... 154 

APPENDIX F: TESTING REQUIREMENTS FOR SUPERPAVE ......................................................... 155 

SUPERPAVE LEVEL 1 .............................................................................................................. 155 

SUPERPAVE LEVEL 2 .............................................................................................................. 156 

SUPERPAVE LEVEL 3 .............................................................................................................. 157 

BIBLIOGRAPHY .................................................................................................................................... 159 

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I. 

HOW ASPHALT MIXTURES BEHAVE 

Asphalt concrete (sometimes referred to as "hot mix asphalt" or simply "HMA") is a 

paving material that consists of asphalt binder and mineral aggregate. The asphalt binder, 

which can be asphalt cement or modified asphalt cement, acts as a binding agent to glue 

aggregate particles into a cohesive mass. Because it is impervious to water, the asphalt 

binder also functions to waterproof the mixture. When bound by the asphalt binder, 

mineral aggregate acts as a stone framework to impart strength and toughness to the 

system. Because HMA contains both asphalt binder and mineral aggregate, the behavior 

of the mixture is affected by the properties of the individual components and how they 

react with each other in the system. 

ASPHALT BINDER BEHAVIOR 

Asphalt binder alone is a very interesting and challenging construction material with 

which to work. Its most important characteristic, which is both a strength and sometimes 

a weakness, is its temperature susceptibility. That is, its measured properties are very 

dependent on its temperature. That is why almost every asphalt cement and mixture 

characterization test must be accompanied by a specified test temperature. Without 

specifying a test temperature, the test result cannot be effectively interpreted. Asphalt 

cement behavior is also dependent on time of loading. The same load applied for a 

different duration will cause an asphalt to exhibit different properties. As with 

temperature, asphalt cement tests must specify a loading rate. Because asphalt cement 

behavior is dependent on temperature and duration of load, these two factors can be used 

interchangeably (Figure 1-1). That is, a slow loading rate can be simulated by high 

temperatures and fast 

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loading rate can be simulated by low temperatures. 
I. How Asphalt Mixtures Behave 

1 hour 

Figure 1-1. Asphalt Cement Time Temperature Dependency 

Asphalt cement is sometimes referred to as a visco-elastic material because it 

simultaneously displays both viscous and elastic characteristics (Figure 1-2). At high 

temperatures, asphalt cement acts almost entirely as a viscous fluid. In other words, when 

heated to a high enough temperature (e.g., > 100" C), it displays the consistency of a 

lubricating fluid such as motor oil. At very low temperatures (e.g., c 0" C), asphalt 

cement behaves mostly like an elastic solid. That is, it acts like a rubber band. When 

loaded it stretches or compresses to a different shape. When unloaded, it easily returns to 

its original shape. At intermediate temperatures, which also happen to be those in which 

pavements are expected to function, asphalt cement has characteristics of both a viscous 

fluid and an elastic solid. 

There remains another important characteristic about asphalt cement. Because it is 

composed of organic molecules, it reacts with oxygen from the environment. This 

reaction is called "oxidation" and it changes the structure and composition of the asphalt 

molecules. When an asphalt reacts with oxygen, a harder and more brittle structure 

always results and that is the origin of the terms "oxidative hardening" or "age 

hardening." Oxidation occurs more rapidly at high temperatures. That is why a 

significant amount of hardening occurs during HMA production, when the asphalt cement 

is necessarily heated to facilitate mixing and compaction. That is also why oxidation is 

more of a concern when the asphalt cement is used in a pavement in a hot, desert climate. 

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I. How Asphalt Mixtures Behave 

I I I I 

-30 25 60 135 

Temperature, C 

Figure 1-2. Visco-Elastic Behavior of Asphalt 

Modified asphalt binders are produced to alter and improve the properties of the asphalt 

to enhance the long term performance of pavements. While the modifier may affect many 

properties, the majority of modifiers attempt to reduce temperature dependency and 

oxidative hardening of asphalt cement and the moisture susceptibility of asphalt mixtures. 

MINERAL AGGREGATE BEHAVIOR 

A wide variety of mineral aggregate has been used to produce HMA. Some materials are 

referred to as natural aggregate because they are simply mined from river or glacial 

deposits and are used without further processing to manufacture HMA. These are often 

called "bank-run" or "pit-run" materials. Processed aggregate can include natural 

aggregate that has been separated into distinct size fractions, washed, crushed, or 

otherwise treated to enhance certain performance characteristics of the finished HMA. 

However, in most cases processed aggregate is quarried and the main processing consists 

of crushing and sizing. 

Synthetic aggregate consists of any material that is not mined or quarried and in many 

cases represents an industrial by-product. Blast furnace slag is one example. 

Occasionally, a synthetic aggregate will be produced to impart a desired performance 

characteristic to the HMA. For example, light-weight expanded clay or shale is 

sometimes 

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used as a component to improve the skid resistance properties of HMA. 
I. How Asphalt Mixtures Behave 

An existing pavement can be removed and reprocessed to produce new HMA. Reclaimed 

asphalt pavement or "RAP is a growing and important source of aggregate for asphalt 

pavements. 

Increasingly, waste products are used as aggregate or otherwise disposed of in asphalt 

pavements. Scrap tires and glass are the two most well known waste products that have 

been successfully "landfilled in asphalt pavements. In some cases, waste products can 

actually be used to enhance certain performance characteristics of HMA. In other cases, 

it is considered sufficient that a solid waste disposal problem has been solved and no 

performance enhancing benefit from the waste material is expected. However, it is hoped 

that performance will not be sacrificed simply to eliminate a solid waste material. 

Regardless of source, processing method, or mineralogy, aggregate is expected to provide 

a strong, stone skeleton to resist repeated load applications. Cubical, rough-textured 

aggregates provide more strength than rounded, smooth-textured aggregates (Figure 1-3). 

Even though a cubical piece and rounded piece of aggregate may possess the same 

inherent strength, cubical aggregate particles tend to lock together resulting in a stronger 

mass of material. Instead of locking together, rounded aggregate particles tend to slide by 

each other. 

Cubical Aggregate Rounded Aggregate 

Figure 1-3. Aggregate Stone Skeletons 

When a mass of aggregate is loaded, there may occur within the mass a plane where 

aggregate particles begin to slide by or "shear" with respect to each other (Figure I-4), 

which results in permanent deformation of the mass. It is at this plane where the "shear 

stress" exceeds the "shear strength" of the aggregate mass. Aggregate shear strength is of 

critical importance 

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in HMA. 
I. How Asphalt Mixtures Behave 

shear plane 

Before Load After Load 

Figure 1-4. Shear Loading Behavior of Aggregate 

Contrasting aggregate shear strength behavior can easily be observed in aggregate 

stockpiles whereby crushed (i.e., mostly cubical) aggregates form steeper, more stable 

piles than rounded aggregates. Engineers refer to the slope on stockpiles as the angle of 

repose. The angle of repose of a crushed aggregate stockpile is greater than that of an 

uncrushed aggregate stockpile (Figure 1-5). 

angle of repose 

Cubical Aggregate Rounded Aggregate 

Figure 1-5. Stockpile Behavior of Cubical and Rounded Aggregate 

Engineers explain the shearing behavior of aggregate (and many other) materials using 

Mohr-Coulomb theory, named after the individuals who originated the concept. This 

theory declares that the shear strength of an aggregate mixture is dependent on how well 

the aggregate particles hold together in a mass (often called cohesion), the stress the 

aggregates may be under, and the internal friction of the aggregate. The Mohr-Coulomb 

equation 

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used to express the shear strength of a material is: 
I. How Aspha lt Mixtures Behave 

where, z = shear strength of aggregate mixture, 

c = cohesion of aggregate, 

o = normal stress to which the aggregate is subjected, and 

$ = angle of internal friction. 

The Mohr-Coulomb shearing behavior of materials is shown in Figure 1-6. 

Figure 1-6. Mohr-Coulomb Theory 

A mass of aggregate has relatively little cohesion. Thus, the shear strength is primarily 

dependent on the resistance to movement provided by the aggregates. In addition, when 

loaded, the mass of aggregate tends to be stronger because the resulting stress tends to 

hold the aggregate more tightly together. In other words, shear strength is increased. The 

angle of internal friction indicates the ability of aggregate to interlock, and thus, create a 

mass of aggregate that is almost as strong as the individual pieces. 

A last consideration in understanding the shearing properties of aggregate is the concept 

of dilatancy. When subjecting a mass of aggregate to shearing stresses, aggregate 

particles must fracture or crawl up and over each other if movement is to occur. This 

phenomenon is called dilation because it results in an enlargement or increased volume of 

the mass of aggregate (Figure 1-7). Strong materials that are more densely packed and 

have high internal 

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friction tend to dilate more than weaker materials. 
I. How Asphalt Mixtures Behave 

Before Shearing During Shearing 

Figure 1-7. Dilation of Two Aggregate Particles When Sheared 

To ensure a strong aggregate blend for HMA, engineers typically have specified 

aggregate properties that enhance the internal friction portion of the overall shear 

strength. Normally, this is accomplished by specifying a certain percentage of crushed 

faces for the coarse portion of an aggregate blend. Because natural sands tend to be 

rounded, with poor internal friction, the amount of natural sand in a blend is often 

limited. 

ASPHALT MIXTURE BEHAVIOR 

While the individual properties of HMA components are important, asphalt mixture 

behavior is best explained by considering asphalt cement and mineral aggregate acting as 

a system. One way to understand asphalt mixture behavior is to consider the primary 

asphalt pavement distress types that engineers try to avoid: permanent deformation, 

fatigue cracking, and low temperature cracking. 

Permanent Deformation 

Permanent deformation is the distress that is characterized by a surface cross section that 

is no longer in its proper position. It is called "permanent" deformation because it 

represents an accumulation of small amounts of deformation that occur each time a load 

is applied. This deformation cannot be recovered. Wheel path rutting is the most 

common form of permanent deformation. While wheel path rutting can have many 

causes (e.g., underlying HMA weakened by moisture damage, abrasion, traffic 

densification), it 

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has two principal causes. 
I. How Asphalt Mixtures Behave 

In one case, the rutting is caused by too much repeated stress being applied to the native 

soil (i.e., subgrade), subbase, or base below the asphalt layer (Figure 1-8). Although 

stiffer paving materials will partially reduce this type of rutting, it is normally considered 

more of a structural problem rather than a materials problem. It is often the result of too 

thin a pavement section because there is simply not enough depth of cover on the 

subgrade to reduce the stress from applied loads to a tolerable level. It may also be the 

result of a subgrade that has been unexpectedly weakened by the intrusion of moisture. 

The accumulated deformation occurs in the subgrade rather than in the overlying asphalt 

layers. 

weak subgrade or underlying layer \ subgrade 

deformation 

Figure 1-8. Rutting from Weak Subgrade 

The other principal type of rutting (and that which is of most concern here) results from 

accumulated deformation in the asphalt layers. This type of rutting is caused by an 

asphalt mixture that is too low in shear strength to resist the repeated heavy loads to 

which it is subjected (Figure 1-9). Sometimes the rutting occurs in a weak asphalt surface 

course. In other cases, the surface course may not itself be prone to rutting, but may 

simply conform to an underlying asphalt course that is too weak. 

shear plane 

Figure 1-9. Rutting from Weak Mixture 

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I. How Asphalt Mixtures Behave 

When an asphalt mixture ruts, it is evidence that the mixture has poor shear strength. 

Each time a heavy truck applies a load, a small, but permanent, shear deformation occurs. 

Shear deformation is characterized by a downward and lateral movement of the mixture. 

With enough load applications a rut will appear. Rutted asphalt pavements pose a safety 

hazard because the ruts will trap enough water to cause hydroplaning and ice 

accumulation. 

Asphalt pavement rutting from weak asphalt mixtures is a high temperature phenomenon. 

That is, it most often occurs during the summer when high pavement temperatures are 

evident. While this might suggest that rutting is solely an asphalt cement problem, it is 

more correct to address rutting by considering the mineral aggregate and asphalt cement. 

In fact, the previously described Mohr-Coulomb equation (T = c + o x tan @) can again be 

used to illustrate how both materials can affect rutting. 

In this case, z is considered the shear strength of the asphalt mixture. The cohesion term 

(c) can be considered the portion of the overall mixture shear strength provided by the 

asphalt cement. Because rutting is an accumulation of very small permanent 

deformations, one way to ensure that asphalt cement provides its "fair share" of shear 

strength is to use an asphalt cement that is not only stiffer but also behaves more like an 

elastic solid at high pavement temperatures (Figure 1-10). That way, when a load is 

applied to the asphalt cement in the mixture, it tends to act more like a rubber band and 

spring back to its original position rather than stay deformed. 

I shear shear 

stress (7) stress (z) 

t "weak" binder 

I normal stress (0) normal stress (0) 

Figure 1-16. Contrasting Asphalt Binder Contribution 

to Mixture Shear Strength 

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I. How Asphalt Mixtures Behave 

Another way to increase the shear strength of an asphalt mixture is by selecting an 

aggregate that has a high degree of internal friction (+). This is accomplished by selecting 

an aggregate that is cubical, has a rough surface texture, and graded in a manner to 

develop particle-to-particle contact. Figure 1-1 1 shows the contrasting aggregate 

contribution to mixture shear strength When a load is applied to the aggregate in the 

mixture, the aggregate particles lock tightly together and function not merely as a mass of 

individual particles, but more as a large, single, elastic stone. As with the asphalt 

cement, the aggregate will act like a rubber band and spring back to its original shape 

when unloaded. That way, no deformations (i.e., permanent) are accumulated. 

shear 

stress (T) 

shear 

stress (z) 

I "weak aggregate 

t "strong" aggregate 

normal stress (o) normal stress (o) 

Figure 1-11. Contrasting Aggregate Contribution 

to Mixture Shear Strength 

While it is obvious that the largest portion of the resistance to permanent deformation of 

the mixture is provided by the aggregate, the portion provided by the asphalt binder is 

very important. Binders which have low shear characteristics due to composition or 

temperature minimize cohesion and to a certain extent, the confining "normal" stress. 

Thus the mixture begins to behave more like an unbound aggregate mass. 

Fatigue Cracking 

Like rutting, fatigue cracking is a distress type that most often occurs in wheel paths 

where repeated heavy loads are applied. An early sign of Pdtigue cracking consists of 

intermittent longitudinal wheel path cracks (i.e., in the direction of traffic). Fatigue 

cracking is a progressive type of distress because at some point, the initial cracks will 

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I. How Asphalt Mixtures Behave 

join, which in turn, causes even more cracks to form. An intermediate stage of fatigue 

cracking is sometimes called "alligator cracking" because the crack pattern resembles an 

alligator's skin (Figure 1-12), In some extreme cases, the final stage of fatigue cracking is 

disintegration when potholes form. A pothole forms when several of the pieces become 

dislodged and removed under the action of traffic. 

Figure 1-12, Alligator (Fatigue) Cracking 

Engineers have long recognized that very stiff asphalt mixtures tend to have poor fatigue 

properties when the pavement structure allows the asphalt mixture layer to deflect. 

Stiffer materials, high deflection, and high stress levels translate to lower fatigue life. 

While the mechanism of fatigue cracking is easy to understand, its cause often is not. It 

cannot be addressed as just a materials problem. Fatigue cracking is usually caused by a 

number of pavement factors that have to occur simultaneously. Obviously, repeated 

heavy loads must be present. Some engineers believe that poor subgrade drainage, 

resulting in a soft, high deflection pavement, is the principal cause of fatigue cracking. 

Poorly designed and/or poorly constructed pavement layers that are also prone to high 

deflections when loaded probably contribute to fatigue cracking. Thus, thin, very stiff 

pavement layers, subjected to high deflections from repeated heavy loads are most 

susceptible to fatigue cracking. 

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I. How Asphalt Mixtures Behave 

In many cases, fatigue cracking is merely a sign that a pavement has received the number 

of load applications for which it was designed. Consequently, it is simply "worn out" and 

in need of a planned rehabilitation. Assuming that the occurrence of fatigue cracking 

coincides approximately with the design period, it may even not be considered a failure, 

but rather the natural progression of a pavement design strategy. If the observed crachng 

occurs much sooner than the design period, it may be a sign that the pavement received 

more heavy loads, earlier than expected. 

Consequently, the best ways to overcome fatigue cracking are: 

adequately account for the anticipated number of heavy loads during design, 

keep the subgrade dry using whatever means available, 

use thicker pavements, 

use paving materials that are not excessively weakened in the presence of 

moisture, and 

use paving materials that are resilient enough to withstand normal deflections. 

In general, asphalt mixtures are unaffected and largely impervious to moisture. In some 

extreme cases however, moisture vapor has been shown to strip asphalt cement from 

mineral aggregate. While stripping of an underlying asphalt layer can manifest itself as 

fatigue cracking in an upper asphalt layer, it is not normally considered a fatigue failure. 

A more common instance of fatigue cracking being caused by a moisture weakened layer 

is with an unbound base that has too many fine particles to allow for rapid drainage of 

moisture. Unbound bases should be selected so that they do not trap moisture. 

Only the last item, selection of resilient materials, can be addressed strictly from a 

materials selection perspective. As a load is applied, horizontal tensile stresses occur 

near the bottom of an asphalt layer (Figure 1-13}. Clearly, the material in this vicinity 

must be very strong with sufficient tensile strength to withstand the applied tensile stress. 

However, to overcome fatigue cracking, material in this vicinity also must be resilient. In 

this context, resilient means that the material can withstand many load applications at 

stress levels far less than the tensile strength, 

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without cracking. 
I. How Asphalt Mixtures Behave 

stresses 

HMA must be 

strong & resilient 

Figure 1-13. Tensile Stresses at Bottom of HMA Layer 

Thus, to overcome fatigue cracking from a materials perspective, HMA must be selected 

so that it behaves like a soft elastic material. Since the tensile behavior of HMA is 

strongly influenced by asphalt cement, this is accomplished by selecting an asphalt 

cement that has upper limits placed on the elastic part of its overall stiffness. In effect, 

soft asphalts have better fatigue properties than hard asphalts. 

Low Temperature Cracking 

As its name indicates, low temperature cracking is a distress type that is caused by 

adverse environmental conditions rather than by applied traffic loads. It is characterized 

by intermittent transverse cracks (i.e., perpendicular to the direction of traffic) that occur 

at a surprisingly consistent spacing (Figure I- 14). 

Low temperature cracks form when an asphalt pavement layer shrinks in cold weather. 

As the pavement shrinks, tensile stresses build within the layer. At some point along the 

pavement, the tensile stress exceeds the tensile strength and the asphalt layer cracks. 

Thus, low temperature cracks occur primarily from a single cycle of low temperature. 

Some engineers, however, also believe it is a fatigue phenomenon due to the cumulative 

effect 

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of many cycles of cold weather. 
I. How Asphalt Mixtures Behave 

Figure 1-14. Low Temperature Cracking 

Both groups agree that asphalt binder plays the central role in low temperature cracking. 

In general, hard asphalt binders are more prone to low temperature cracking than soft 

asphalt binders. Asphalt binders that are excessively oxidized, either because they are 

unduly prone to oxidation or contained in a mixture left with too many air voids after 

construction, or both, are more prone to low temperature cracking. Thus, to overcome 

low temperature cracking engineers must use a soft binder, a binder that is not overly 

prone to aging, and control in-place air void content so that the binder is not excessively 

oxidized. 

CURRENT WAYS TO SPECIFY ASPHALT CEMENTS 

The current method to characterize asphalt cement consistency is by either penetration or 

viscosity tests as shown in Figure 1-15. Both of these tests have been used to measure the 

effect of temperature on asphalt behavior. This is done by measuring viscosity or 

penetration at two temperatures and plotting the results as shown in Figure 1- 16. 

In this example, all three asphalts are the same viscosity grade because they are within 

specified limits at 60' C. While Asphalts A and B display the same temperature 

dependency, they have much different consistencies at a11 temperatures. Asphalts A and 

C have the same consistency at low temperatures but remarkably different high 

temperature consistency. Asphalt B has the same consistency at 60° C, but shares no 

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I. How Asphalt Mixtures Behave 

other similarities with Asphalt C. Because these asphalts share the same grade, they 

might erroneously be expected to display the same characteristics during construction and 

during hot and cold weather performance conditions. 

Viscosity 

Penetration 

0 sec 5 sec 

vacuum 

Figure 1-15. Penetration and Viscosity Tests 

[ Consistency 

(pen or vis) 

hardl 

soft 

Den 

Temperature, C 

Figure 1-16. Temperature Susceptibility of Three Viscosity or 

Penetration Graded Asphalts 

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I. How Asphalt Mixtures Behave 

Although viscosity is a fundamental measure of flow, it only provides information about 

higher temperature viscous behavior, not about the low or intermediate temperature 

elastic behavior needed to completely predict performance. Penetration describes only 

the consistency at an intermediate temperature, 25" C. No low temperature properties are 

directly measured in the current grading system. Often, viscosity and penetration tests do 

not completely show the advantages or possible disadvantages of some modified asphalts. 

Because of these deficiencies, many state highway agencies have amended standard test 

procedures and specifications to better suit local conditions. In some locations, this 

proliferation of tests and specifications has caused serious problems for asphalt suppliers 

wishing to sell the same asphalt grades in several states. Often, states with very similar 

performance conditions and materials will specify remarkably different asphalts. In the 

current systems for specifying asphalt, tests are performed on unaged or "tank" asphalt 

and on asphalt that has been laboratory aged to simulate construction aging. However, no 

tests are performed on asphalts that have been aged to simulate in-service aging. 

CURRENT ASPHALT MIXTURE DESIGN PROCEDURES 

Most agencies currently use the Marshall mix design method. It is by far the most 

common procedure used in the world to design HMA. This technique was developed by 

Bruce Marshall, a former employee of the Mississippi State Highway Department. The 

U.S. Army Corps of Engineers refined and added certain features to Marshall's approach 

to the extent that it was formalized as ASTM D 1559, Resistance to Plastic Flow of 

Bituminous Mixtures Using the Marshall Apparatus. The Marshall method entails a 

laboratory experiment aimed at developing a suitable asphalt mixture by means of 

stabilitylflow and densitylvoids analyses. 

One of the strengths of the Marshall method is its attention to densitylvoids properties of 

asphalt materials. This analysis ensures that the important volumetric proportions of mix 

constituents are at their proper levels to achieve a durable HMA. Another advantage of 

the Marshall method is that the required equipment is relatively inexpensive and very 

portable, and thus, lends itself to remote quality control operations. Unfortunately, many 

engineers believe that the impact method of laboratory compaction used with the 

Marshall method does not simulate mixture densification that occurs under traffic in a 

real pavement. Furthermore, the strength parameter used in this approach, Marshall 

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I. How Asphalt Mixtures Behave 

stability (Figure 1-17), does not adequately estimate the shear strength of HMA. These 

two situations may result in asphalt mixtures prone to rutting. Consequently, there has 

been a growing feeling among asphalt technologists that the Marshall method has 

outlived its usefulness for modern asphalt mixture design. 

test 

specimen 

J 

breaking 

head 

Marshall 

load / stability 

deformation 

Figure 1-17. Marshall Stability 

The Hveem mix design procedure was developed by Francis Hveem, once the Materials 

and Research Engineer for the California Department of Transportation. Hveem and 

others developed and refined the procedure over a long period. The procedure is outlined 

in ASTM D 1560, Resistance to Deformation and Cohesion of Bituminous Mixtures by 

Means of Hveem Apparatus, and ASTM D 1561, Preparation of Bituminous Mixture Test 

Specimens by Means of California Kneading Compactor. It is not commonly used 

outside western states of the U.S. 

The Hveem method also entails a density/voids and stability analysis. Mixture resistance 

to swell in the presence of water is also determined. The Hveem method has two real 

advantages. First, the kneading method of laboratory compaction is thought by most 

engineers to better simulate the densification characteristics of HMA in a real pavement. 

Second, the strength parameter, Hveem stability (Figure 1-18), is a direct measurement of 

the internal friction component of shear strength. It measures the ability of a test 

specimen to resist lateral displacement from application of a vertical load. 

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I. How Asphalt Mixtures Behave 

load 

rubber . .-.- 

membrane 

\ 

Figure 1-18. Hveem Stability 

The disadvantage of the Hveem procedure is that the testing equipment, particularly the 

kneading compactor and Hveem stabilometer, are somewhat more expensive than 

Marshall equipment and not very portable. Furthermore, some important mixture 

volumetric properties that are related to mix durability are not routinely determined as 

part of the Hveem procedure. Some engineers believe that the method of selecting 

asphalt content in the Hveem method is too subjective and may result in non durable 

HMA with too little asphalt. 

There are other mix design procedures in common use besides the Marshall and Hveem 

procedures. For example, the Texas gyratory method is currently used by the state DOTS 

in Texas, Oklahoma, and Colorado. This procedure retains volumetric design elements of 

the Marshall method and the stability determination from the Hveem method. It is 

differentiated from the others by its method of laboratory compaction, the Texas gyratory 

compactor, which is thought by some engineers to be a suitable means of simulating 

traffic densification. While the Texas gyratory design method eliminates some of the 

disadvantages of the Marshall and Hveem methods, some believe that the operational 

characteristics of the compactor need refining to be suitable for a wider variety of design 

applications. 

Increasingly, agencies are augmenting their customary mix design procedures with 

em~irical strength testing. These tests are called empirical because their test outputs 

simply result in a go or no go decision based on the experience of the agency with the test 

calibrated to real pavements. One example of this type of testing is the Georgia Loaded 

Wheel Tester (GALWT). The GALWT subjects HMA beam specimens to repeated 

pneumatic stresses applied through a loaded wheel riding on a pressurized hose (Figure IArchived
I. How Asvhalt Mixtures Behave 

19). After the required number of load applications, beam rutting is measured and the 

mixture is either accepted or rejected. 

rolling wheel 

pressurized 

beam test specimen / 

Figure 1-19. Principle of the Georgia Loaded Wheel Tester 

The advantage of empirical strength testing is that agencies can develop very clear 

acceptkeject criteria, backed up by performance data from real pavements. This is also a 

disadvantage however, because agencies have to expend considerable resources in 

experimentation to achieve this experience. Even then the experience is only applicable 

to the materials and environmental conditions tested. New products and materials require 

additional experimentation. Furthermore, because empirical strength tests result in a 

simple acceptlreject test result and no degree of performance is measured, they are 

difficult to use for economic comparisons of alternate materials. 

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11. 

SUPERPAVE TO THE RESCUE 

INTRODUCTION 

In 1987, the Strategic Highway Research Program (SHRP) began developing a new 

system for specifying asphalt materials. The final product of the SHRP asphalt research 

program is a new system referred to as Superpave which stands for Superior Performing 

Asphalt Pavements, Superpave software is a computer program that assists engineers in 

materials selection and mix design. However, the term "Superpave" refers to more than 

just the conlputer program. Most important, it represents an improved system for 

specifying component materials, asphalt mixture design and analysis, and pavement 

performance prediction. The system includes test equipment, test methods, and criteria. 

ASPHALT BINDERS 

One portion of Superpave is a new asphalt binder specification with a new set of tests to 

match. The document is called a binder specification because it is intended to function 

equally well for modified as well as unmodified asphalts. A portion of the asphalt binder 

specification is shown in Appendix A. 

The new system for specifying asphalt binders is unique in that it is a performance based 

specification. It specifies binders on the basis of the climate and attendant pavement 

temperatures in which the binder is expected to serve. Physical property requirements 

remain the same, but the temperature at which the binder must attain the properties 

changes. For example, the high temperature, unaged binder stiffness (G*/sin 6) is 

required to be at least 1 .OO kPa. But this requirement must be achieved at higher 

temperatures if the binder is expected to serve in a hot climate. 

Performance graded (PG) binders are graded such as PG 64-22. The first number, 64, is 

often called the "high temperature grade." This means that the binder would possess 

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II. Superpave to the Rescue 

adequate physical properties at least up to 64' C. This would be the high pavement 

temperature corresponding to the climate in which the binder is actually expected to 

serve. Likewise, the second number (-22) is often called the "low temperature grade" and 

means that the binder would possess adequate physical properties in pavements at least 

down to -22' C. Additional consideration is given to the time of loading (open highway, 

city streets, intersections, etc.) and magnitude of loads (heavy trucks). 

Another key feature to binder evaluation in the Superpave system is that physical 

properties are measured on binders that have been laboratory aged to simulate their aged 

condition in a real pavement. Some binder physical property measurements are 

performed on unaged binder. Physical properties are also measured on binders that have 

been aged in the rolling thin film oven (RTFO) to simulate oxidative hardening that 

occurs during hot mixing and placing. A pressure aging vessel (PAV) is used to 

laboratory age binder to simulate the severe aging that occurs after the binder has served 

many years in a pavement (Figure II- 1). 

Rolling Thin Film Oven (RTFO) Pressure Aging Vessel (PAV) 

Figure 11-1. SHRP Binder Aging Techniques 

Binder physical properties are measured using four devices: 

dynamic shear rheometer, 

rotational viscometer, 

bending beam rheometer, and 

0 

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direct tension tester. 
II. Superpave to the Rescue 

The dynamic shear rheometer (DSR) is used to characterize the visco-elastic properties of 

the binder. It measures the complex shear modulus (G*) and phase angle (6) by 

subjecting a small sample of binder to oscillatory shear stresses while sandwiched 

between two parallel plates (Figure 11-2). 

Applied Stress Position of 

Oscillating Plate 

Plate 

\ Fixed Plate I 

1 cycle 

b 

Figure 11-2. Dynamic Shear Rheometer 

The DSR measures G* and 6 by measuring the shear strain response of the specimen to a 

fixed torque as shown in Figure 11-3. In this figure, the shear strain response of a binder 

specimen is "out of phase" with the applied stress by a certain time interval At. This time 

interval represents the time lag in strain response. Phase lag is normally reported in 

angular measurement by simply multiplying the time lag (At) by the angular frequency 

(a) to arrive at a phase angle (6). For totally elastic materials there is no lag between 

applied shear stress and shear strain response and 6 equals zero degrees. For totally 

viscous materials, strain response is completely out of phase with applied stress and 6 is 

90 degrees. Viscoelastic materials like asphalt binders posses phase angles between zero 

and 90 degrees, depending on test temperature. At high temperatures, 6 approaches 90 

degrees while at low temperatures 6 is nearly zero degrees. The binder specification uses 

either G*/sin 6 at high temperatures (> 46" C) or G%in 6 at intermediate temperatures 

(between 

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7" and 34" C) as a means of controlling asphalt stiffness. 
II. Superpave to the Rescue 

Viscoelastic: 0 c 6 < 90 O 

'L, 

Shear 

Stress 

complex shear modulus 

Resulting 

Shear 

Strain e / angular frequency 

phase angle 

Figure 11-3. Computation of G* and 6 

By controlling stiffness at high temperatures, the binder specification ensures that asphalt 

provides its fair share of the overall shear strength of the mixture in terms of high 

temperature elasticity. Likewise, the specification ensures that the binder does not 

contribute to fatigue cracking by limiting its stiffness at intermediate temperatures. 

The rotational viscometer (RTV) characterizes the stiffness of the asphalt at 135O C, 

where it acts almost entirely as a viscous fluid. It is a rotational coaxial cylinder 

viscometer that measures viscosity by the torque required to rotate a spindle submerged in 

a sample of hot asphalt (Figure 11-4) at a constant speed. The binder specification 

requires that binders have a viscosity of less than 3 Pa-s. This ensures that the binder can 

be pumped and otherwise handled during HMA manufacturing. 

applied torque 

from motor 

sample chamber 

Figure 11-4. Rotational Viscometer 

The bending beam rheometer (BBR) is used to characterize the low temperature stiffness 

properties of binders. It measures the creep stiffness (S) and logarithmic creep rate (m). 

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If. Superpave to the Rescue 

These properties are determined by measuring the response of a small binder beam 

specimen to a creep load at low temperatures (Figure 11-5). By knowing the load applied 

to the beam and the deflection at any time during the test, the creep stiffness can be 

calculated using engineering beam mechanics. The binder specification places limits on 

creep stiffness and m-value depending on the climate in which the binder will serve. 

Binders that have a low creep stiffness will not crack in cold weather. Likewise, binders 

with high m-values are more effective in shedding stresses that build in asphalt 

pavements as temperatures drop, again, ensuring that low temperature cracking will be 

minimized. 

Constant (Creep) Load 

1 deflection 

Figure 11-5. Bending Beam Rheometer 

Some binders, particularly some polymer-modified asphalts, may exhibit a higher than 

desired creep stiffness at low temperatures. However, may not crack because they retain 

their ability to stretch without fracture at low temperatures. Consequently, the binder 

specification allows a higher creep stiffness if it can be shown through the direct tension 

test (DTT) that binders are sufficiently ductile at low temperatures, The output of the 

DTT is tensile failure strain, which is measured on a small dog bone shaped specimen 

that is stretched at low temperatures until it breaks (Figure 11-6). As with the BBR, the 

DTT ensures that the binder's resistance 

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to low temperature cracking is maximized. 
II. Superpave to the Rescue 

- 

strain 

Figure 11-6. Direct Tension Tester 

MINERAL AGGREGATES 

SHRP researchers also believed that mineral aggregates played a key role in HMA 

performance. While they did not develop any new aggregate lest procedures, they refined 

existing procedures to fit within the Superpave system. Two types of aggregate 

properties are specified in the Superpave system: consensus properties and source 

properties. 

Consensus properties are those which the SHRP researchers believed were critical in 

achieving high performance HMA. These properties must be met at various levels 

depending on traffic level and position within the pavement. High traffic levels and 

surface mixtures (i.e., shallow pavement position) require more strict values for 

consensus properties. Many agencies already use these properties as quality requirements 

for aggregates used in HMA. These properties are: 

coarse aggregate angularity, 

fine aggregate angularity, 

flat, elongated particles, and 

clay content. 

By specifying coarse and fine angularity, SHRP researchers were seeking to achieve 

HMA with a high degree of internal friction and thus, high shear strength for rutting 

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II. Superpave to the Rescue 

resistance. Limiting elongated pieces ensures that the HMA will not be as susceptible to 

aggregate breakage during handling and construction and under traffic. By limiting the 

amount of clay in aggregate, the adhesive bond between asphalt binder and aggregate is 

strengthened and otherwise enhanced. 

Source properties are those which agencies often use to qualify local sources of aggregate. 

The SHRP researchers believed that achieving these properties was important, but did not 

specify critical values since they are so source specific. The source properties are: 

toughness, 

soundness, and 

deleterious materials. 

Toughness is measured by the LA abrasion test. Soundness is measured by the sodium or 

magnesium sulfate soundness test. Deleterious materials are measured by the clay lumps 

and friable particles test. These tests are already in common use by most agencies. 

To specify aggregate gradation (Appendix B), SHRP researchers refined an approach 

already in wide use by many agencies. It uses the 0.45 power gradation chart with control 

limits and a restricted zone (Figure 11-7) to develop a design aggregate structure. 

Percent Passing 

nom max 

,+escontrol point max size 

size B 

B + 

I Sieve Size, mm (raised to 0.45 power) 

Figure 11-7. Superpave Gradation Limits, 12.5 mm Mixture 

A Superpave design aggregate structure must pass between the control points while 

avoiding the restricted zone. The maximum density gradation is drawn from the 100 

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IZ. Superpave to the Rescue 

percent passing the maximum aggregate size through the origin. Maximum aggregate 

size is defined as one size larger than the nominal maximum aggregate size. Nominal 

maximum size is defined as one size larger than the first sieve size to retain more than 10 

percent. The restricted zone is used by SHRP Superpave to avoid mixtures that have a 

high proportion of fine sand relative to total sand and gradations that follow the 0.45 

power line, which do not normally have adequate voids in the mineral aggregate (VMA). 

In many instances, the restricted zone will discourage the use of fine natural sand in an 

aggregate blend. It will encourage the use of clean manufactured sand. The design 

aggregate structure approach ensures that the aggregate will develop a strong, stone 

skeleton to enhance resistance to permanent deformation while achieving sufficient void 

space for mixture durability. 

ASPHALT MIXTURES 

Two key features in the Superpave system are laboratory compaction and performance 

testing. Laboratory compaction is accomplished by means of a Superpave Gyratory 

Compactor (SGC). While this device shares some common traits with the Texas gyratory 

compactor, it is a completely new device with new operational characteristics. Its main 

utility is to fabricate test specimens. However, by capturing data during SGC 

compaction, a mix design engineer can also gain insight into the compactibility of HMA. 

The SGC can be used to design mixtures that do not exhibit tender mix behavior and do 

not densify to dangerously low air void contents under the action of traffic. 

The performance of HMA immediately after construction is influenced by mixture 

properties resulting from hot mixing and compaction. Consequently, a short term aging 

protocol was incorporated into the Superpave system. This was accomplished by 

requiring that loose mixture specimens, prior to compaction by the SGC, be oven aged for 

four hours at 135' C. 

Perhaps the most important development to arise from the SHRP asphalt research 

program was performance based tests and performance prediction models for HMA. 

Output from these tests can be used to make detailed predictions of actual pavement 

performance (Figure 11-8). In other words, test procedures and performance prediction 

models were developed that will allow an engineer to estimate the performance life of a 

prospective HMA in terms of equivalent axle loads (ESALs) or time to achieve a certain 

level of rutting, fatigue cracking, and low temperature cracking. 

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II. Superpave to the Rescue 

Performance Prediction of: 

Testing Rutting 

Results Fatigue Cracking 

Low Temperature Cracking 

Figure 11-8. Superpave Pavement Performance Prediction 

Two new performance based testing procedures were developed, the Superpave Shear 

Tester (SST) and Indirect Tensile Tester (IDT). The output from these tests is input to 

performance prediction models in Superpave to estimate actual pavement performance 

(ag., millimeters of rutting). 

The SST is a testing device that performs the following six tests on HMA specimens: 

volumetric test, 

uniaxial strain test, 

simple shear test at constant height, 

repeated shear test at constant stress ratio, 

frequency sweep test at constant height, and 

repeated shear test at constant height (option). 

The first two tests involve testing the specimen using confining pressure. To accomplish 

this, the SST has a testing chamber capable of applying confining pressure by means of 

compressed air. Test temperature is also carefully controlled by the testing chamber. The 

SST has axial and horizontal hydraulic actuators with accompanying linear variable 

differential transducers (LVDTs) to measure the response of test specimens to load. Tests 

proceed by closed-loop feedback control. This means that the response of a specimen to 

loading from one actuator is measured by an LVDT. The other actuator uses the signal 

from this LVDT to respond as required. For example, in the simple shear test at constant 

height, a shear stress is applied to the HMA specimen by the horizontal actuator, As the 

specimen is sheared, it tends to dilate. The vertical LVDT senses this dilation as a change 

in specimen height and a signal is sent to the vertical actuator to apply sufficient vertical 

load to 

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keep the specimen's height from changing. Thus, dilation is prevented. 
11. Superpave to the Rescue 

Tests using the SST are performed at a variety of temperatures to simulate actual 

pavement temperatures. While a portion of the tests are aimed at fatigue cracking, the 

SST's main utility is a means of designing against permanent deformation. 

The IDT is used to measure creep compliance and tensile strength of HMA. This test 

uses a single vertical actuator to load a test specimen across its diametral plane. It is used 

to characterize HMA as a means of designing against fatigue and low temperature 

cracking. 

In the Superpave system, the results of SST and IDT testing are input into pavement 

performance prediction models. Using these models, mix design engineers can estimate 

the combined effect of asphalt binders, aggregates, and mixture proportions. The models 

take into account the structure, condition, and properties of the existing pavement (if 

applicable) and the amount of traffic to which the proposed mixture will be subjected 

over its performance life. The output of the models is millimeters of rutting, percent area 

of fatigue cracking, and spacing (in meters) of low temperature cracks. By using this 

approach, the Superpave system accomplishes what no previous design procedure has; 

namely, it joins material properties with pavement structural properties to predict actual 

pavement performance. Thus, the benefit (or detriment) of new materials, different mix 

designs, asphalt modifiers, and other products can finally be quantified in terms of cost 

versus predicted performance. 

PUTTING IT ALL TOGETHER 

Because Superpave mixture design and analysis is more complex than those in current 

use, the extent of its use depends on the traffic level or functional classification of the 

pavement for which it is being used. Consequently, three levels of Superpave mixture 

design were developed. Their extent of use and testing requirements are shown in Table 

11- 1 . 

Table 11-1. Superpave Mix Design Levels 

Traffic, ES ALs 

ESALs 5 1 o6 

lo6 < ESALs 5 lo7 

ESALs > lo7 

Design Level 

1 

In all cases, moisture susceptibility must be evaluated using AASHTO T283. 

2 

3 

Testing Requirements' 

volumetric design 

volumetric design + performance prediction tests 

volumetric design + enhanced performance 

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prediction tests 
II. Superpave to the Rescue 

While much of the resources in SHRP were devoted to developing the SST, IDT, their 

protocols, and performance prediction models, volumetric mix design occupies a key role 

in Superpave mix design. Volumetric design, which is all that is required by a Level 1 

mixture design, entails fabrication of test specimens using the SGC and selecting asphalt 

content on the basis of air voids, voids in the mineral aggregate (VMA), voids filled with 

asphalt (VFA), and the ratio of dust to effective asphalt content. Consensus and source 

aggregate properties must be achieved. 

A Level 2 mixture design uses a volumetric mix design as a starting point. A battery of 

SST and IDT tests are performed to arrive at a series of golno go performance 

predictions. 

A Level 3 mixture design encompasses most of the facets of Levels 1 and 2. Additional 

SST and IDT tests are performed at a wider variety of temperatures. Level 3 design is the 

only protocol that utilizes SST confined specimen testing. Because of the more 

comprehensive range of tests and results, Level 3 design offers an enhanced and more 

reliable level of performance prediction. 

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111. 

MATERIALS SELECTION 

INTRODUCTION 

Superpave utilizes a completely new system for testing, specifying, and selecting asphalt 

binders. While no new aggregate tests were developed, current methods of selecting and 

specifying aggregates were refined and incorporated into the Superpave mix design 

system. Superpave asphalt mixture requirements were established from currently used 

criteria. 

ASPHALT BINDERS 

The new SHRP binder specification (a portion of which is shown in Appendix A) is 

unique in that it is performance based and that binders are selected on the basis of the 

climate in which they are intended to serve. The physical property (eg, creep stiffness, 

G*/sin 6, etc.) requirements are constant among all grades of binders. 

What differentiates the various binder grades is the temperature at which the requirements 

must be met. For example, a binder classified as a PG 64-22 means that the binder must 

meet high temperature physical property requirements at least up to a temperature of 64" 

C and low temperature physical property requirements at least down to -2Z0 C. 

Table 111-1 shows the current binder grades in the SHRP binder specification. In this 

table, the PG 76 and 82 grades are used only to accommodate slow transient or standing 

loads, 

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or excessive truck traffic. 
111. Materials Selection 

A module in the Superpave software assists users in selecting binder grades. Superpave 

contains three methods by which the user can select an asphalt binder grade: 

By Geographic Area: An Agency would develop a map showing binder grade 

to be used by the designer based on weather andlor policy decisions. 

By Pavement Temperature: The designer would need to know design 

pavement temperature. 

By Air Temperature: The designer determines design air temperatures, which 

are converted to design pavement temperatures. 

Superpave Weather Database 

Superpave software contains a database of weather information for 6500 reporting 

stations in the US and Canada, which allows users to select binder grades for the climate 

specific to project location. For each year a weather station has been in operation the 

hottest seven-day period is determined and the average maximum air temperature for 

those seven consecutive days is calculated. For all the years of record (stations with less 

than 20 years of records were not used) a mean and standard deviation are calculated. 

Likewise the coldest day of each year is identified and the mean and standard deviation 

are calculated. 

Reliability 

As used in Superpave, reliability is the percent probability in a single year that the actual 

temperature will not exceed the design temperature. SHRP binder selection is very 

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III. Materials Selection 

flexible in that a different level of reliability can be assigned to high and low temperature 

grades. Consider summer air temperatures in Topeka, Kansas, which has a mean sevenday maximum of 36" C and a standard deviation of 2" C. Figure 111-1 shows the 

frequency distribution for this data. In an average year there is a 50 percent chance the 

seven-day maximum air temperature will exceed 36" C. However, only a two percent 

chance exists that the temperature will exceed 40" C; hence, a design air temperature of 

40" C will provide 98 percent reliability. 

50 % reliability 

36 40 

7-Day Maximum Air Temperature 

Figure 111-1. Distribution of Annual Seven-Day Maximum Air 

Temperature for Topeka, KS 

Start with Air Temperature 

To see how the binder selection works assume that an asphalt mixture is designed for 

Topeka. Figure 111-2 shows frequency distributions for high and low design air 

temperatures. In a normal summer, the average seven-day maximum air temperature is 

36" C with a standard deviation of 2" C. In a normal winter, the average coldest 

temperature is -23" C. For a very cold winter the temperature is -31" C, with a standard 

deviation of 4" C. 

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IZI. Materials Selection 

Figure 111-2. Distribution of High and Low Design Air Temperatures 

for Topeka, KS 

Convert to Pavement Temperature 

Superpave software calculates high pavement temperature 20 rnm below the pavement 

surface and low temperature at the pavement surface. For a wearing course at the top of a 

pavement section, the pavement temperatures in Topeka are 56" and -23" C for 50 

percent reliability and 60" (56" + 2 standard deviations) and -3 1" C for 98 percent 

reliability (Figure 111-3). 

Figure In-3. Distribution of High and Low Design Pavement 

Temperatures for Topeka, KS 

In Superpave, the high pavement design temperature at a depth of 20 mm is computed by 

the following formula: 

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III. Materials Selection 

where, Tzo,, = pavement temperature at a depth of 20 rnrn in "C, 

Td, = maximum average high air temperature during the hottest seven-day period 

in "C, and 

lat = project latitude in degrees. 

There are two possible ways to determine the low pavement design temperature in 

Superpave. First, the low pavement design temperature simply can be assumed to be the 

same as the low air temperature. This method was originally recommended by SHRP 

researchers. This is a very conservative assumption because pavement temperature is 

almost always warmer than air temperature in cold weather. The Topeka, Kansas 

example above used this approach. The second method utilizes the following formula, 

which was developed by Canadian SHRP researchers: 

where, Tmi, = minimum pavement design temperature in "C, 

Tair = minimum air temperature in average year in "C. 

Using this approach for the Topeka example, the minimum pavement design temperature 

would be 0.859 x -23" + 1.7" or 18" C. This method of computing minimum pavement 

design temperature is gaining favor among asphalt technologists in North America. 

However, the first method is still used by Superpave. 

Select Binder Grade 

For a reliability of at least 50 percent, the high temperature grade must be PG 58 for 

Topeka. Selecting a PG 58 would actually result in a higher level of reliability, about 85 

percent, because of the "rounding up" to the next standard grade. The next lower grade 

only protects to 52" C, less than 50 percent reliability. The low temperature grade must 

be a PG XX-28. As with high temperature grade, rounding to this standard low 

temperature grade results in almost 90 percent reliability. For 98 percent reliability, the 

needed high temperature grade is PG 64; the low temperature grade is PG XX-34. 

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111. Materials Selection 

Both of these low temperature grades utilize the Superpave approach that assumes low air 

and low pavement temperatures are the same. Had the alternative approach been used, 

the binder grades selected would have been PG 58-22 for minimum 50 percent reliability 

and PG 58-28 for minimum 98 percent reIiability. The method of converting low air to 

low pavement temperature has a profound effect on the binder selection process. 

b 

PG 64-34 (98 % minimum reliability) 

Figure 111-4. Various Binder Grades for Topeka, KS 

Manipulating temperature frequency distributions is not a task that the designer need 

worry about. Superpave software handles the calculations. For any site, the user can 

enter a minimum reliability and Superpave will calculate the required asphalt binder 

grade. Alternately the user can specify a desired asphalt binder grade and Superpave will 

calculate the reliability obtained. 

Effect of Loading Rate on Binder Selection 

SHRP binder selection by climate only assumes that a binder will be used in a mixture 

subjected to fast moving loads. The loading rate used by the dynamic shear rheometer is 

10 radians per second, which corresponds to a traffic speed of approximately 90 

kilometers per hour. Much slower loading rates are experienced by pavements near 

intersections, toll booths, etc. In some cases, loads are not moving but rather are 

stationary. In these cases, a binder would have to exhibit a higher stiffness to overcome 

the slower loading rate. 

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III. Materials Selection 

To accommodate these situations, Superpave requires that the high temperature grade be 

increased by at least one or as many as two grades. For example, if a temperature based 

selection resulted in a desired binder grade of PG 64-22, to account for slow transient 

loads, the designer would select one grade higher binder, a PG 70-22. If standing loads 

were anticipated, the designer would select a PG 76-22. Loading rate has no effect on the 

selected low temperature grade. Pavement design temperatures of 76" or 82" C do not 

correspond to any climate zone in North America. Specifying this grade is simply a 

means of ensuring that the binder will have higher stiffness at 64" C, the actual high 

pavement design temperature. Because the highest possible pavement temperature in 

North America is about 70" C, two additional high temperature grades, PG 76 and PG 82, 

were necessary to accommodate slow loading rates. 

Effect of Traffic Level on Binder Selection 

Superpave recommends that traffic level be considered when selecting binders. When the 

design traffic level exceeds 10 million equivalent single axle loads (ESALs), the designer 

is encouraged to "consider" increasing the high temperature grade by one grade. When 

the design traffic level exceeds 30 million ESALs, the designer is required to increase the 

high temperature grade by one grade. As with loading rate, there is no effect of traffic 

level on low temperature grade. For the Topeka example where the temperature based 

selection required a PG 58-28, a project with a very high number of ESALs would require 

a PG 64-28. 

MINERAL AGGREGATE 

During SHRP, pavement experts were surveyed to ascertain which aggregate properties 

were most important. There was general agreement that aggregate properties played a 

central role in overcoming permanent deformation. Fatigue cracking and low temperature 

cracking were less affected by aggregate characteristics. SHRP researchers relied on the 

experience of these experts and their own to identify two categories of aggregate 

properties that needed to be used in the Superpave system: consensus properties and 

source properties. In addition, a new way of specifying aggregate gradation was 

developed. It is 

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called the design aggregate structure. 
III. Materials Selection 

Consensus Properties 

It was the consensus of the pavement experts that certain aggregate characteristics were 

critical and needed to be achieved in all cases to arrive at well performing HMA. These 

characteristics were called "consensus properties" because there was wide agreement in 

their use and specified values. Those properties are: 

coarse aggregate angularity, 

fine aggregate angularity, 

flat, elongated particles, and 

. clay content. 

There are required standards for these aggregate properties. The consensus standards are 

not uniform. They are based on traffic level and position within the pavement structure. 

Materials near the pavement surface subjected to high traffic levels require more stringent 

consensus standards. They are intended to be applied to a proposed aggregate blend 

rather than individual components. However, many agencies currently apply such 

requirements to individual aggregates so that undesirable components can be identified. 

Coarse Aggregate Angularity 

This property ensures a high degree of aggregate internal friction and rutting resistance. It 

is defined as the percent by weight of aggregates larger than 4.75 mm with one or more 

fractured faces. 

Many state DOTS have protocols to measure coarse aggregate angularity. These usually 

involve manually counting particles to determine fractured faces. A fractured face is 

defined as any fractured surface that occupies more than 25 percent of the area of the 

outline of the aggregate particle visible in that orientation. One test method example is 

the Pennsylvania DOT'S Test Method No. 62 1, "Determining the Percentage of Crushed 

Fragments in Gravel." 

Table 111-2 outlines the required minimum values for coarse aggregate angularity as a 

function of 

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traffic level and position within the pavement. 
III. Materials Selection 

Table 111-2. Superpave Coarse Aggregate Angularity Requirements 

I Traffic, million I Depth from Surface I 

Fine Aggregate Angularity 

< 1 

< 3 

< 10 

< 30 

< 100 

> 100 

This property ensures a high degree of fine aggregate internal friction and rutting 

resistance. It is defined as the percent air voids present in loosely compacted aggregates 

smaller than 2.36 rnm. Higher void contents mean more fractured faces. 

A test procedure currently promulgated by the National Aggregates Association is used to 

measure this property. In the test, a sample of fine aggregate is poured into a small 

calibrated cylinder by flowing through a standard funnel (Figure 111-5). 

Note: "85180" means that 85 % of the coarse aggregate has one 

fractured face and 80 % has two fractured faces. 

651- 

751- 

85/80 

95190 

1001100 

100/100 

funnel 

-1- 

501- 

601- 

80175 

95/90 

1001100 

fine aggr sample 

cylinder of known volume (V) 

uncompacted voids = 

v -WIG,, 

v 

Figure 111-5. Fine Aggregate Angularity Apparatus 

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III. Materials Selection 

By determining the weight of fine aggregate (W) in the filled cylinder of known volume 

(V), void content can be calculated as the difference between the cylinder volume and 

fine aggregate volume collected in the cylinder. The fine aggregate bulk specific gravity 

(Gs,) is used to compute fine aggregate volume. 

Table HI-3 outlines the required minimum values for fine aggregate angularity as a 

function of traffic level and position within pavement. 

Table 111-3. Superpave Fine Aggregate Angularity Requirements 

Note: Criteria are presented as percent air voids in loosely 

compacted fine aggregate. 

Traffic, million 

ESALs 

< 0.3 

Flat, Elongated Particles 

This characteristic is the percentage by weight of coarse aggregates that have a maximum 

to minimum dimension of greater than five. Elongated particles are undesirable because 

Depth from Surface 

they have a tendency to break during construction and under traffic. The test procedure 

used is ASTM D 4791, "Flat or Elongated Particles in Coarse Aggregate" and it is 

< 100mm 

- 

performed on coarse aggregate larger than 4.75 mrn. 

> 100 mm 

- 

The procedure uses a proportional caliper device (Figure 111-6) to measure the 

dimensional ratio of a representative sample of aggregate particles. In Figure 111-6, the 

aggregate particle is first placed with its largest dimension between the swinging arm and 

fixed post at position A. The swinging arm then remains stationary while the aggregate is 

placed between the swinging arm and fixed post at position B. If the aggregate passes 

through this gap, then it is counted as a flat or elongated particle. 

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III. Materials Selection 

1 :5 pivot point fixed post (B) 

Figure 1114. Proportional Caliper Device to Measure Flat and 

Elongated Particles 

Two values are measured: percentage of flat particles and percentage of elongated 

particles. Table 111-4 outlines the required maximum values for flat, elongated particles 

in coarse aggregate. 

Table 111-4. Superpave Flat, Elongated Particle Requirements 

I Traffic, million I Percent 

1 particles. I 

< 3 

< 10 

< 30 

< 100 

- > 100 

10 

10 

10 

10 

10 

Note: Criteria are presented as maximum 

Archived

percent by weight of flat and elongated 
IZI. Materials Selection 

Clay Content 

Clay content is the percentage of clay material contained in the aggregate fraction that is 

finer than a 4.75 mm sieve. It is measured by AASHTO T 176, "Plastic Fines in Graded 

Aggregates and Soils by Use of the Sand Equivalent Test." 

In this test, a sample of fine aggregate is placed in a graduated cylinder with a 

flocculating solution and agitated to loosen clayey fines present in and coating the 

aggregate. The flocculating solution forces the clayey material into suspension above the 

granular aggregate. After a period that allows sedimentation, the cylinder height of 

suspended clay and sedimented sand is measured (Figure 111-7). The sand equivalent 

value is computed as a ratio of the sand to clay height readings expressed as a percentage. 

/- graduated 

d cylinder 

flocculating 

solution 

suspended clay / 

sedimented aggregatereading 

reading 

Figure 111-7. Sand Equivalent Test 

Table III-5 

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outlines the required clay content values for fine aggregate. 
III. Materials Selection 

Table 111-5. Superpave Clay Content Requirements 

Source Properties 

In addition to the consensus aggregate properties, pavement experts believed that certain 

other aggregate characteristics were critical. However, critical values of these properties 

could not be reached by consensus because needed values were source specific. 

Consequently, a set of "source properties" were recommended. Specified values are 

established by local agencies. While these properties are relevant during the mix design 

process, they may also be used as source acceptance control. Those properties are: 

toughness, 

soundness, and 

deleterious materials. 

Toughness 

Toughness is the percent loss of materials from an aggregate blend during the Los 

Angeles Abrasion test. The procedure is stated in AASHTO T 96, "Resistance to 

Abrasion of Small Size Coarse Aggregate by Use of the Eos Angeles Machine." This test 

estimates the resistance of coarse aggregate to abrasion and mechanical degradation 

during handling, construction, and in-service. It is performed by subjecting the coarse 

aggregate, usually larger than 2.36 mm, to impact and grinding by steel spheres. The test 

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IZI. Materials Selection 

result is percent loss, which is the weight percentage of coarse material lost during the 

test as a result of the mechanical degradation. Maximum loss values typically range from 

approximately 35 to 45 percent. 

Soundness 

Soundness is the percent loss of materials from an aggregate blend during the sodium or 

magnesium sulfate soundness test. The procedure is stated in AASHTO T 104, 

"Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate." This test 

estimates the resistance of aggregate to weathering while in-service. It can be performed 

on both coarse and fine aggregate. The test is performed by alternately exposing an 

aggregate sample to repeated immersions in saturated solutions of sodium or magnesium 

sulfate each followed by oven drying. One immersion and drying is considered one 

soundness cycle. During the drying phase, salts precipitate in the permeable void space 

of the aggregate. Upon re-immersion the salt re-hydrates and exerts internal expansive 

forces that simulate the expansive forces of freezing water. The test result is total percent 

loss over various sieve intervals for a required number of cycles, Maximum loss values 

range from approximately 10 to 20 percent for five'cycles. 

Deleterious Materials 

Deleterious materials are defined as the weight percentage of contaminants such as shale, 

wood, mica, and coal in the blended aggregate. This property is measured by AASHTO 

T 112, "Clay Lumps and Friable Particles in Aggregates." It can be performed on both 

coarse and fine aggregate. The test is performed by wet sieving aggregate size fractions 

over prescribed sieves. The weight percentage of material lost as a result of wet sieving 

is reported as the percent of clay lumps and friable particles. A wide range of maximum 

permissible percentage of clay lumps and friable particles is evident. Values range from 

as little as 0.2 percent to as high as 10 percent, depending on the exact composition of the 

contaminant. 

Gradation 

To specify gradation, Superpave uses a modification of an approach already used by some 

agencies. It uses the 0.45 power gradation chart to define a permissible gradation. This 

chart uses a unique graphing technique to judge the cumulative particle size distribution 

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III. Materials Selection 

of a blend of aggregate. The ordinate of the chart is percent passing. The abscissa is an 

arithmetic scale of sieve size in millimeters, raised to the 0.45 power. Figure III-8 

illustrates how the abscissa is scaled. In this example, the 4.75 rnm sieve is plotted at 

2.02 units to the right of the origin, This number, 2.02, is the sieve size, 4.75 rnm, raised 

to 0.45 power. Normal 0.45 power charts do not show arithmetic abscissa labels such as 

those in Figure 111-8. Instead, the scale is annotated with the actual sieve size as shown in 

Figure 111-9. 

Percent Passing 

loo T 

6o I Example: 

4.75 mm sieve plots at (4.75)0-45 = 2.02 

20 / 

Figure 111-8. Graphical Basis for 0.45 Power Chart 

An important feature of this chart is the maximum density gradation. This gradation plots 

as a straight line from the maximum aggregate size through the origin. Superpave uses a 

standard set of ASTM sieves and the following definitions with respect to aggregate size 

(Appendix B shows sieve sizes used by Superpave): 

Maximum Size: One sieve size larger than the nominal maximum size. 

Nominal Maximum Size: One sieve size larger than the first sieve to retain 

more than 10 percent. 

The maximum density gradation (Figure 111-9) represents a gradation in which the 

aggregate particles fit together in their densest possible arrangement. Clearly this is a 

gradation to avoid because there would be very little aggregate space within which to 

develop sufficiently thick asphalt films for a durable mixture. Figure III-9 shows a 0.45 

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ZIZ. Materials Selection 

power gradation chart with a maximum density gradation for a 19 mm maximum 

aggregate size and 12.5 rnm nominal maximum size. 

( Percent Passing 

I Sieve Size, mm Raised to 0.45 Power 

Figure 111-9. Maximum Density Gradation for 19 mm Maximum Size 

To specify aggregate gradation, two additional features are added to the 0.45 power chart: 

control points and a restricted zone. Control points function as master ranges through 

which gradations must pass. They are placed on the nominal maximum size, an 

intermediate size (2.36 mm), and the dust size (0.075 mm). 

The restricted zone resides along the maximum density gradation between the 

intermediate size (either 4.75 or 2.36 mm) and the 0.3 mm size. It forms a band through 

which gradations are not permitted to pass. Gradations that pass through the restricted 

zone have often been called "humped gradations" because of the characteristic hump in 

the grading curve that passes through the restricted zone. In most cases, a humped 

gradation indicates a mixture that possesses too much fine sand in relation to total sand. 

This gradation practically always results in tender mix behavior, which is manifested by 

a mixture that is difficult to compact during construction and offers reduced resistance to 

permanent deformation during its performance life. Gradations that violate the restricted 

zone possess weak aggregate skeletons that depend too much on asphalt binder stiffness 

to achieve mixture shear strength. These mixtures are also very sensitive to asphalt 

content and 

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can easily become plastic. 
111. Materials Selection 

The term used to describe the cumulative frequency distribution of aggregate particle 

sizes is the design aggregate structure. A design aggregate structure that lies between the 

control points and avoids the restricted zone meets the requirements of Superpave with 

respect to gradation. Superpave defines six mixture types (Table 111-6) as defined by their 

nominal maximum aggregate size: 

Table 111-6. Superpave Mixture Designations 

I Superpave I Nominal Maximum I Maximum I 

I 

Figure III- 10 illustrates the control points and restricted zone for a 12.5 mrn Superpave 

mixture. Appendix B shows numerical gradation limits and gradation charts for the six 

Designation 

25 mm 

19 mm 

12.5 rnrn 

9.5 rnm 

Superpave mixtures. 

Size, mm I Size, mm 

I Percent Passing 

I I 

25 

19 

12.5 

9.5 

.075 .3 2.36 4.75 9.5 12.5 19.0 

Sieve Size, mrn (raised to 0.45 power) 

37.5 

25 

19 

12.5 

Figure 

Archived

111-10. Superpave Gradation Limits, 12.5 mm Mixture 
III. Materials Selection 

Superpave recommends, but does not require, mixtures to be graded below the restricted 

zone. It also recommends that as project traffic level increases, gradations move closer to 

the coarse control points. Furthermore, the Superpave gradation control requirements 

were not intended to be applied to special purpose mix types such as stone matrix asphalt 

or open graded mixtures. 

ASPHALT MIXTURES 

Asphalt mixture design requirements in Superpave consist of: 

mixture volumetric requirements, 

dust proportion, and 

moisture susceptibility. 

Specified values for these parameters are applied during the Level 1 mixture design 

phase. 

Mixture Volumetric Requirements 

Mixture volumetric requirements consist of air voids, voids in the mineral aggregate and 

voids filled with asphalt. Air void content is an important property because it is used as 

the basis for asphalt binder content selection. In Superpave, the design air void content is 

four percent. 

Superpave defines voids in the mineral aggregate (VMA) as the sum of the volume of air 

voids and effective (i.e., unabsorbed) binder in a compacted sample. It represents the 

void space between aggregate particles. Specified minimum values for VMA at the 

design air void content of four percent are a function of nominal maximum aggregate 

size. Table 

Archived

111-7 shows Superpave VMA requirements. 
III. Materials Selection 

Table 111-7. Superpave VMA Requirements 

I Nominal Maximum I I 

Voids filled with asphalt (VFA or Pf,) is defined as the percentage of the VMA 

containing asphalt binder. Consequently, VFA is the volume of effective asphalt binder 

expressed as a percentage of the VMA. The acceptable range of design VFA at four 

percent air voids is a function of traffic level as shown in Table 111-8. 

Aggregate Size 

Table 111-8. Superpave VFA Requirements 

Minimum VMA, % 

I I 

Dust Proportion 

Another mixture requirement is the dust proportion. This is computed as the ratio of the 

percentage by weight of aggregate finer than the 0.075 mm sieve to the effective asphalt 

content expressed as a percent by weight of total mix. Effective asphalt content is the 

total asphalt used in the mixture less the percentage of absorbed asphalt. Dust proportion 

is used during the mixture design phase as a design criterion. An acceptable dust 

proportion is in the range from 0.6 to 1.2, inclusive for all mixtures. 

Traffic, ESALs 

< 3 x 105 

< 1 x 106 

<3x 106 

< 1 107 

Design VFA, % 

70 - 80 

65 - 78 

65 - 78 

65 - 75 

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III. Materials Selection 

Moisture Susceptibility 

The moisture susceptibility test used to evaluate HMA for stripping is AASHTO T 283, 

"Resistance of Compacted Bituminous Mixtures to Moisture Induced Damage." This test 

is not a performance based test but serves two purposes. First, it identifies whether a 

combination of asphalt binder and aggregate is moisture susceptible. Second, it measures 

the effectiveness of anti-stripping additives. 

In the test, two subsets of test specimens are produced. Specimens are compacted to 

achieve an air void content in the range from six to eight percent with a target value of 

seven percent. Test specimens should be sorted so that each subset has the same air void 

content. One subset is moisture conditioned by vacuum saturation to a constant degree of 

saturation in the range from 55 to 80 percent. This is followed by an optional freeze 

cycle. The final conditioning step is a hot water soak. After conditioning both subsets 

are tested for indirect tensile strength. The test result reported is the ratio of tensile 

strength of the conditioned subset to that of the unconditioned subset. This ratio is called 

the "tensile strength ratio" or TSR. Superpave requires a minimum TSR of 80 percent. 

Table 111-9 outlines the current test parameters in AASHTO T 283. 

Table 111-9. Test Parameters for AASHTO T283 

Test Parameter 

Short-Term Aging 

Sample Grouping 

Test Requirement 

Loose mix1: 16 hrs at 60" C 

Air Voids Compacted Specimens 

Average air voids of two subsets should be I eoual I 

Compacted mix: 72-96 hrs at 25' C 

6 to 8 % 

precision Statement I None 

Short-term aging protocol of AASHTO T 283 does not match short-term aging 

Saturation 

Swell Determination 

Freeze 

Hot Water Soak 

Strength Property 

Loading Rate 

protocol of Superpave. Suggest using T283 procedure of 16 hours at 

60" C. 

55 to 80 % 

None 

Minimum 16 hrs at - 18" C (optional) 

24 hrs at 60" C 

Indirect tensile strength 

Archived

5 1 mdmin at 25" C 
IV. 

ASPHALT MIXTURE VOLUMETRICS 

INTRODUCTION 

A factor that must be taken into account when considering asphalt mixture behavior is the 

volumetric proportions of asphalt binder and aggregate components, or more simply, 

asphalt mixture volumetrics. The developers of Superpave felt that the volumetric 

properties of asphalt mixtures were so important that a volumetric mixture design 

protocol was developed. The following section describes volumetric analysis of HMA, 

which plays a significant role in most mixture design procedures, including the Superpave 

system. 

COMPONENT DIAGRAM APPROACH 

The model used to describe HMA mass and volume properties is the component diagram. 

It considers a compacted sample of HMA with its constituent air voids, asphalt cement, 

and mineral aggregate shown as discrete components (Fig IV-I). The compacted sample 

is assumed to consist of a unit volume (e.g., one cubic meter, one cubic centimeter, etc.) 

with known mass (e.g., kilograms or grams). The component diagram is particularly 

suited to metric units because in this system, density and specific gravity are numerically 

the same since the density of water is very nearly 1.000 gram per cubic centimeter and its 

specific gravity is 1.000 at 25' C. It is a tool commonly used for many civil engineering 

applications because it represents a convenient model to track distinct masses and 

volumes in non-homogeneous construction materials. 

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ZV. Asphalt Mixture Volumetrics 

VOLUME MASS 

Unit 

Volume 

VMI 

- 

Bulk 

rol aggr 

air 

-- I Mass air = 0 

rota1 

Mass 

Figure IV-1. Component Diagram of Compacted Sample of HMA 

The component diagram provides a clear definition of density, that is, the mass of a unit 

volume of compacted material. Since the model consists of several distinct materials, the 

density of the entire sample is often called its bulk density. It is determined by dividing 

the total mass of the sample by its total volume. 

For a given asphalt content, the maximum theoretical density is the mass of aggregate 

and asphalt divided by the volume of only these two components. In other words, the 

volume of air voids is not included. Maximum theoretical density (or specific gravity) is 

an extremely useful property because it can be used as a reference to calculate several 

other important properties such as air void content. 

AsphaZt content is the mass concentration of asphalt binder. It is expressed as percent by 

total mass of mixture or percent by total mass of aggregate. Most agencies use percent by 

mass of mixture. Effective asphalt content is the mass concentration of asphalt binder 

that is not lost to absorption. Absorbed asphalt content is the mass concentration of 

asphalt binder absorbed by the aggregate. It is normally reported as a percentage of the 

mass of aggregate. 

The volume concentration of air within the compacted sample is the air void content. Air 

voids are always expressed as a percentage of total volume of mixture. 

Archived
IV. As~halt Mixture Volumetrics 

The intergranular space occupied by asphalt and air in a compacted mixture is called the 

voids in the mineral aggregate or VMA. In the component diagram, the sum of the 

volume of air and volume of effective asphalt, expressed as a percent of total volume, is 

the VMA. The volume of absorbed asphalt is usually not considered to be part of the 

VMA. 

Not shown on the diagram is the percentage of voidsfilled with asphalt or VFA. This 

property is the percentage of the VMA that contains asphalt. While it could be computed 

by dividing the volume of asphalt by the volume of the VMA, it is normally computed by 

the following formula. 

VFA = [(VMA - Volume of Air)NMA] x 100 % 

Although contrary to physical laws, the model shows mass and volume on the same 

diagram, with the same scale. Another deceptive feature of the component diagram is 

that it is not well suited for considering secondary weights and volumes such as absorbed 

asphalt. Furthermore, narrow reliance on the physical model sometimes inhibits a more 

fundamental understanding of volumetric properties such as VMA. Even with these 

flaws, the component diagram is still the best way to define and illustrate determination 

of the properties of compacted HMA. 

Note that when calculating HMA properties during mix design, engineers seldom work 

from a sketch of a component diagram. They normally use well established formulas, 

originally derived from a component diagram, to arrive at the various properties of 

interest. Appendix D contains a list of all the formulas used to compute compacted mix 

properties. 

SPECIFIC GRAVITY 

In order to use the component diagram, it is necessary to be able to convert between mass 

and volume. Specific gravity is the tool employed for this purpose. Specific gravity is 

the ratio of the mass of a given volume of a substance to the mass of an equal volume of 

water, both at the same temperature. It is a unique material property that allows for two 

important determinations. 

Archived
IV. Asphalt Mixture Volumetrics 

First, specific gravity is used to determine density by: 

D=Gx 1.000 

where, D = density of material in grams per cubic centimeter (g/cm3), 

G = specific gravity of material, and 

1.000 = density of water in grams per cubic centimeter. 

The terms "density" and "specific gravity" are often interchanged, which suggests they 

have the same meaning. In fact, in metric units, they have the same numerical value. 

While this usage is technically incorrect, context most often conveys the intended 

meaning. This equation offers the most precise meaning of each. 

Second, knowing the mass and specific gravity of a material, the volume of the material 

can be determined by: 

where, V = volume of material, 

M = mass of material, and 

G = specific gravity of material, and 

1.000 = density of water (1.000 g/cm3). 

Use of this equation is best understood by the following example. 

Consider an object placed on a scale and found to weigh 75 kilograms. This object is 

known to have a specific gravity very nearly that of water, or 1.000. Using these values 

in the above equation indicates the object has a volume of about 75,000 cubic centimeters 

(i.e., 175 kg x 1,000g/kg]/[1.000 x 1.000 g/cm3] = 75,000 cm3). 

This example is also useful to illustrate the fact that different specific gravities must often 

be considered. The conditions of the example were somewhat obscure with respect to the 

precise meaning 

Archived

of the specific gravity used. 
IV. Asphalt Mixture Volumetrics 

While the object may be a homogeneous material, it is more likely a composite of several 

materials. Consequently, the conditions of the example needed to be more precise and 

should have specified bulk specific gravity. Bulk specific gravity is least determinate 

since it considers the object in whole or "bulk" form and is blind to the contributions of 

the object's individual components. A volume determined from a bulk specific gravity 

must be assumed to include the total volume and not unique component volumes. 

In the case of mineral aggregate, bulk, effective, and apparent specific gravities are 

usually determined. Bulk specific gravity (AASHTO T84 and T85) is determined by 

measuring the dry weight and bulk volume of an aggregate sample (Figure IV-2). The 

bulk volume includes the solid aggregate volume plus the volume of surface pores 

holding water. The bulk volume is measured on the aggregate in a saturated surface dry 

(SSD) condition. 

Bulk Vol 

Bulk Volume = solid volume + 

water permeable pore volume 

"SSD Level 

water permeable pore volume 

Figure IV-2. Bulk Specific Gravity of Aggregate 

Apparent specific gravity (also measured using AASHTO T84 and T85) is determined by 

measuring the dry weight and apparent volume of an aggregate sample (Figure IV-3). 

The apparent volume only includes the volume of the solid aggregate and does not 

include 

Archived

the volume of any surface pores. 
ZV. Asphalt Mixture Volumetrics 

-.--- C "" - App Vol 

volume of surface pores 

Figure IV-3. Apparent Specific Gravity of Aggregate 

Effective specific gravity is measured on asphalt mixtures (AASHTO T209) of known 

asphalt content. It the context of bulk and apparent specific gravity, it is computed using 

the dry weight of aggregate and the effective volume of the aggregate. The aggregate 

effective volume includes the volume of the solid aggregate and the volume of surface 

pores filled with water but not asphalt (Figure IV-4). Aggregate effective specific gravity 

is not directly measured in the same manner as bulk and apparent specific gravity. 

Instead, it is calculated by knowing the maximum theoretical specific gravity of a mixture 

and the asphalt content. 

+ volume of water permeable pores not r[9&!\ k~,cri&~ filled with asphalt 

f@$j volume of water permeable pores not 

filled with asphalt 

6 $4~ asphalt coating 

Archived

Figure IV-4. Effective Specific Gravity of Aggregate 
IV. Asphalt Mixture Volumetrics 

Only bulk and effective specific gravities are used during mix design volumetric 

calculations. Volumes calculated with each of these would have different meanings and 

thus, numeric values. The wide array of asphalt, aggregate, and mixture specific gravities 

are often confusing to those new to asphalt technology. Careful attention to the meaning 

of each, and the desired HMA property will clarify the analysis. 

EXAMPLE CALCULATIONS 

A sample of compacted HMA is known to have the following properties at 25" C: 

Mix Bulk Specific Gravity = 2.329 

Aggregate Bulk Specific Gravity = 2.705 

Aggregate Effective Specific Gravity = 2.73 1 

Asphalt Binder Specific Gravity = 1.015 

Asphalt Content = 5.0 percent by mass of total mix 

The air void content, VMA, VFA, maximum theoretical specific gravity, absorbed asphalt 

content, and effective asphalt content should be determined. Figure IV-5 shows these 

known items on a component diagram. The required calculations are with the following 

steps. 

G,, = 2.329 

P, = 5.0 % 

by total mass of mix 

Figure IV-5. Known Items for Example 

Archived
IV. Asphalt Mixture Volumetrics 

Step 1 : Determine Density 

Thus, the sample in the component diagram is assumed to have a mass of 2.329 grams 

and occupy one cubic centimeter. Note that an alternate approach could use 2,329 

kilograms and one cubic meter. 

Steu 2: Determine Mass 

Thus, in the component diagram, the asphalt binder has a mass of 0.1 16 g and the 

aggregate 2.213 g. The air was assumed to be without mass. 

Stev 3: Determine Volumes 

Vtotal-,ph = MaMhlGasph x 1 .OW g1cm3 = 0.1 16 gl(1.015 x 1.000 g/cm3) = 0.1 14 cm3 

Vbulk-aggr = Maggi%ulk-aggr X 1.000 gl~m3 = 2.2 13 gf(2.705 X 1 .ooO g/~m3) = 0.8 18 cm3 

Veffmaggr = Maggr/Geff-, x 1.000 glcm3 = 2.21 3 gl(2.73 1 x 1.000 glcm3) = 0.810 cm3 

Vabsqasph = Vt,ulk-aggr - Veffmaggr = 0.818 cm3 - 0.810 cm3 = 0.008 cm3 

Vefgasph = Vtotal-asph - Vabs-asph = 0.114 cm3 - 0.008 cm3 = 0.106 cm3 

Vair = Vtotal - (Veff-asph + Vbulk-aggr) = 1.000 cm" (0.106 cm3 + 0.8 18 cm3) = 0.076 cm3 

VMA = V,ir + Veff-asph = 0.076 cm3 + 0.106 cm3 = 0.182 cm3 

Archived
IV. Amhalt Mixture Volurnetrics 

Percent volume concentration by total mix of each component is calculated by: 

Percent volume air voids = (0.076 cm3/1.000 cm3) x 100 % = 7.6 % 

Percent volume of total asphalt = (0.1 14 cm3/1.000 cm3) x 100 % = 11.4 % 

Percent volume of effective asphalt = (0.106 cm3/1.000 cm3) x 100 % = 10.6 % 

Percent volume of bulk aggregate = (0.818 cm3/1.000 cm3) x 100 % = 81.8 % 

Percent VMA = (0.182 cm3/1.000 cm3) x 100 % = 18.2 % 

An alternative procedure to compute VMA is: 

Percent VMA = 100 % - % volume of bulk aggregate = 100 % - 8 1.8 % = 18.2 % 

Step 4: Calculate Effective Asphalt Content and Absorbed Asphalt Content 

Mass of effective asphalt = Vefi-asph x Gmph x 1.000 &m3 = 0.106 cm3 x 1.015 x 1.000 glcm3 = 0,108 g 

Mass of absorbed asphalt = Vabs-asph x Gaqh x 1 .OOO g/cm3 = 0.008 em3 x 1 .Ol5 x 1,000 &m3 = 0.008 g 

Effective Asphalt Content = (Meffmasph / Mtotal ) x 100 % = (0.108 g / 2.329) x 100 % = 4.6 % 

Absorbed Asphalt Content = (Mabs-asph / Maggr ) x 100 % = (0.008 g / 2.213 g) x 100 % = 0.4 % 

Step 5: Calculate VFA 

Percent VFA = Veff-asph / Volume of VMA x I 00 % = (0.106 cm3/0.182 cm3) x LOO % = 58.2 % 

Step 6: Calculate Maximum Theoretical Specific Gravity 

Grnax-theo = [(Masph + Maggr)l(Veff-asph + Vbulk-aggr)l/l-oOO gtcm3 

= [(0.116 g + 2.213 g)/(0.106 cm3 + 0.818cm3)]/l.000g/cm3 = 2.521 

Archived
N. Asphalt Mixture Volumetrics 

Answer: Air Void Content = 7.6 % 

VMA = 18.2 % 

VFA = 58.2 % 

Absorbed Asphalt Content = 0.4 % 

Effective Asphalt Content = 4.6 % 

Max. theo. sp. grav. = 2.521 

All of the computed masses and volumes are shown on a component diagram in Figure 

IV-6. 

VOL (cm3) 

Figure IV-6. Computed Masses and Volumes for Example 

The conditions of this example stated that the asphalt content was five percent by mass of 

total mix." Although this is the most common method of expressing asphalt content, 

some agencies express asphalt content as percent by mass of aggregate. Had asphalt 

content been expressed in this way, the weight of asphalt and aggregate would have been 

calculated by: 

5/100 = Masph / Maggr and 2.329 = Masph + Maggr 

Solving these equations simultaneously yields: 

Archived
N. Asphalt Mixture Volumetrics 

The analysis would continue from this point as before. This illustrates the importance of 

clearly stating the basis for asphalt content. 

The example used the volume of effective asphalt and air voids to compute VMA. In 

effect, the aggregate bulk specific gravity was used to compute VMA. This is the 

approach currently used by most agencies. Superpave also uses this convention. In the 

Superpave mix design procedure, VMA criteria are based on aggregate bulk specific 

gravity. Use of other aggregate specific gravities to compute VMA means that the VMA 

criteria no longer apply and the mixture does not meet the requirements of Superpave. 

Archived
Archived
SUPERPAVE GYRATORY COMPACTION 

INTRODUCTION 

In selecting a method of laboratory compaction, SHRP researchers had several goals. 

Most important, they desired a device that would realistically compact trial mix 

specimens to densities achieved under actual pavement climate and loading conditions. 

The device needed to be capable of accommodating large aggregates. Furthermore, it was 

desired that the device afford a measure of compactibility so that potential tender mixture 

behavior and similar compaction problems could be identified. A high priority for SHRP 

researchers was a device that was well suited to mixing facility quality control and quality 

assurance operations. No compactor in current use achieved all these goals. 

Consequently, a new compactor was developed, the Superpave Gyratory Compactor 

(SGC). 

The basis for the SGC was a large Texas gyratory compactor modified to use the 

compaction principles of a French gyratory compactor. The Texas device accomplished 

the goals of achieving realistic specimen densification and it was reasonably portable. Its 

6-inch sample diameter (ultimately 150 mm on an SGC) could accommodate mixtures 

containing aggregate up to 50 mm maximum (37.5 nominal) size. SHRP researchers 

modified the Texas device by lowering its angle and speed of gyration and adding real 

time specimen height recordation. In fact, a considerable amount of this phase of SHRP 

mixture research was conducted on a modified Texas gyratory compactor loaned to SHRP 

by the Texas DOT. 

TEST EQUIPMENT 

The SGC is an mechanical device comprised of the following system of components: 

reaction frame, rotating base, and motor, 

Archived
V. Superpave Gyratoiy Compaction 

loading system, loading ram, and pressure gauge, 

height measuring and recordation system, and 

mold and base plate. 

Figure V-1 shows a generic SGC. 

reaction 

frame 

rotating 

base 

control and data 

acquisition pane1 

loading 

/ ram 

mold 

Figure V-1. Superpave Gyratory Compactor 

The reaction frame provides a non-compliant structure against which the loading ram can 

push when compacting specimens. The base of the SGC rotates and is affixed to the 

loading frame. It supports the mold while compaction occurs. Reaction bearings are 

used to position the mold at an angle of 1.25 degrees, which is the compaction angle of 

the SGC. The electric motor drives the rotating base at a constant speed of 30 revolutions 

per minute. 

A hydraulic or mechanical system applies a load to the loading ram, which imparts 600 

kPa compaction pressure to the specimen. The loading ram diameter nominally matches 

the inside diameter of the mold, which is 150 rnm. A pressure gauge with digital signal 

conditioning measures the ram pressure during compaction, As the specimen densifies 

during compaction, the pressure gauge signals the loading system to adjust the position of 

the loading ram so that a constant compaction pressure is maintained throughout the 

compaction process. 

Specimen height measurement is an important function of the SGC. By knowing the 

mass of material placed in the mold, the diameter of the mold, and the specimen height, 

Archived
V. Superpave Gyratory Compaction 

an estimate of specimen density can be made at any time throughout the compaction 

process. Specimen density is computed by dividing the mass by the volume of the 

specimen. The specimen volume is calculated as the volume of a smooth-sided cylinder 

with a diameter of 150 rnrn and the measured height. Height recordation is variously 

accomplished by measuring the position of the ram before and during the test. The 

vertical change in ram position identically equals the change in specimen height. The 

specimen height signal is processed through a serial port connection which is connected 

to a personal computer, printer, or other device to record height (i.e., density) 

measurements throughout the compaction process. By this method, a compaction 

characteristic is developed as the specimen is compacted (Figure V-2). 

Percent of Maximum 

Theoretical Density 

10 100 1000 - 

Log Gyrations 

Figure V-2. Compaction Characteristic of SGC 

The SGC uses a mold (Figure V-3) with an inside diameter of 150 mrn and a nominal 

height of 250 m. A base plate fits in the bottom of the mold to afford specimen 

confinement during compaction. 

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V. Superpave Gyratory Compaction 

ram pressure 

0.6 MPa 

Figure V-3. SGC Mold Configuration and Compaction Parameters 

SPECIMEN PREPARATION 

Compaction specimens are required to be mixed and compacted under equiviscous 

temperature conditions corresponding to 0.170 Paas and 0.280 Pa-s, respectively. Figure 

V-4 shows a typical temperature-viscosity chart for an asphalt binder. Mixing is 

accomplished by a mechanical mixer. After mixing, loose test specimens are subjected to 

four hours of short term aging in a forced draft oven maintained at a constant 135' C. 

During short term aging, loose mix specimens are required to be spread into a thickness 

resulting in 21 to 22 kg per cubic meter and stirred every hour to ensure uniform aging. 

The compaction molds and base plates should also be placed in an oven at 135O C for at 

least 30 to 45 minutes prior to use. 

Viscosity, Paws 

Temperature, C 

Archived

Figure V-4. Temperature-Viscosity Relationship 
V. Superpave Gyratory Compaction 

Three specimen sizes are used. If specimens are to be used for volumetric determinations 

only, use sufficient mix to arrive at a specimen 150 mm in diameter by approximately 115 

mm height. This requires approximately 4500 grams of aggregate. In this case, the test 

specimen produced is tested without trimming, Alternatively, to produce specimens for 

performance testing, approximately 5500 grams of aggregate is used to fabricate a 

specimen that is 150 mm in diameter by approximately 135 mm height. In this case, 

specimens will have to be trimmed to 50 mm before testing in the SST or IDT. At least 

one loose sample should remain uncompacted to obtain a maximum theoretical specific 

gravity using AASHTO T 209. For performing AASHTO T283, test specimens are 

fabricated to a height of 95 rnm, which requires approximately 3500 grams of aggregate. 

OVERVIEW OF PROCEDURE 

After short term aging the loose test specimens are ready for compacting. The compactor 

is initiated by turning on its main power. The vertical pressure should be set at 600 kPa 

(+ 18 kPa). The gyration counter should be zeroed and set to stop when the desired 

number of gyrations is achieved. Three gyration levels are of interest: 

design number of gyrations (Ndesign), 

initial number of gyrations (Niitial), and 

maximum number of gyrations (N,,,imu,). 

Test specimens are compacted using Nmaximum gyrations. The relationship between Nbiw, 

Nmaximum, and Ninitial are: 

The design number of gyrations (Ndesign) ranges from 68 to 172 and is a function of the 

climate in which the mix will be placed and the traffic level. The average design high air 

temperature is provided by Superpave software and represents the average seven-day 

maximum air temperature for project conditions. The range of values for Ndesign, 

Nmaxlmum, 

Archived

and Ninitid is shown in Table V-1. 
V. Superpave Gyratory Compaction 

Table V-1. Superpave Gyratory Compaction Effort 

Average Design High Air Temperatur 

39 - 40°C 41 - 42°C 

Design 

ESALs 

(millions) 

< 0.3 

0.3 - 1 

1-3 

3 - 10 

10-30 

30 - 100 

> 100 

I Nini Ndes Nmax I Nini Ndes Nmax 

<3g°C 

N,,, Ndes Nmax 

7 68 104 

7 76 117 

7 86 134 

8 96 152 

8 109 174 

9 126 204 

9 142 233 

43 - 44°C 

Nini Ndes Nmax 

7 82 127 

8 93 146 

8 105 167 

9 119 192 

9 135 220 

10 153 253 

10 172 288 

After the base plate is in place, a paper disk is placed on top of the plate and the mold is 

charged in a single lift. The top of the uncompacted specimen should be slightly rounded. 

A paper disk is placed on top of the mixture. 

The mold is placed in the compactor and centered under the ram. The ram is then 

lowered until it contacts the mixture and the resisting pressure is 600 kPa (+ 18 kPa). 

The angle of gyration (1.25" k 0.02") is then applied and the compaction process begins. 

When NmXi,,, has been reached, the compactor should automatically cease. After the 

angle and pressure are released, the mold containing the compacted specimen is then 

removed. After a suitable cooling period, the specimen is extruded from the mold. 

The bulk specific gravity of test specimens should be measured using AASHTO T 166. 

Maximum theoretical specific gravity should be measured using AASHTO T 209. 

DATA ANALYSIS AND PRESENTATION 

Superpave gyratory compaction data should be analyzed by computing the estimated bulk 

specific gravity, corrected bulk specific gravity, and percentage of maximum theoretical 

specific gravity for each desired gyration. The example specimen compaction 

information in Table V-2 illustrates 

Archived

this analysis. 
V. Superpave Gyratory Compaction 

Table V-2. Example Specimen Compaction Information 

Project conditions for this mixture are such that N, = 174, Ndes = 109, and Nini = 8 

gyrations. During compaction, the height was measured after each gyration and recorded 

for the number of gyrations shown in the first column. The Gmb (estimated) values were 

determined by: 

Specimen No. 1: Total Mass = 4869 g 

G, (measured) = 2.563 

where, V,,, = volume of specimen in mold during compaction (cm3), 

d = diameter of mold (150 mrn), and 

h, = height of specimen in mold during compaction (mm). 

G,, (estimated) = K, 1 vm 

1.000~ / cm3 

No. of Gyrations 

8 (Nmi) 

50 

100 

109 WdeJ 

150 

174 (Nrnad 

Gmb (measured) 

where, Gmb(estimated) = estimated bulk sp grav of specimen during compaction, 

W, = mass of specimen (g). 

Gnb 

(estimated) 

2.170 

2.334 

2.391 

2.398 

2.425 

2.436 

2.489 

Height, mm 

127.0 

118.0 

115.2 

114.9 

113.6 

113.1 

To illustrate this determination, consider the specimen conditions at 50 gyrations. The 

specimen height is measured as 118.0 mm. The estimated volume of the specimen at 50 

gyrations is: 

Gmb 

(corrected) 

2.218 

2.385 

2.444 

2.45 1 

2.478 

2.489 

- 

% Gm, 

86.5 

93.1 

95.4 

95.6 

96.7 

97.1 

- 

Archived
V. Superpave Gyratory Compaction 

Thus, the Gmb(estimated) at 50 gyrations is: 

G,, (estimated) = 

4867.8g / 2085.2cm3 = 2.334 

1. OOOg I cm3 

This calculation assumes that the specimen is a smooth-sided cylinder, which of course, it 

is not. The volume of the specimen is slightly less than the volume of a smooth-sided 

cylinder because of surface irregularities. That is why the final estimated Gmb at 174 

gyrations, 2.436, is different than the measured Gmb after 174 gyrations, 2.489. To correct 

for this difference, the estimated Gmb at any given number of gyrations is corrected by a 

ratio of the measured to estimated bulk specific gravity at Nmimum using the following 

formula. 

G, (measured) C= 

G, (estimated) 

where, C = correction factor, 

Gmb(measured) = measured bulk specific gravity after Nmimum, and 

Gmb(estimated) = estimated bulk specific gravity at Nma,imum. 

The estimated Gmb at all other number of gyrations can then be corrected by using the 

correction factor in the following formula. 

G,, (corrected) = C x G,, (estimated) 

where, Gmb(corrected) = corrected bulk sp grav of specimen at any gyration, N, 

C = correction factor, and 

Gmb(estimated) = estimated bulk sp grav at any gyration, N. 

In this example, this ratio is 2.48912.436 or 1.022. Percent G, is computed as the ratio 

Gmb (corrected) to G, (measured). 

Archived
V. Superpave Gyratory Compaction 

If this example had been for the purpose of mix design, a companion specimen would 

have been compacted and average percent G,, values resulting from the two specimens 

would have been used for further analysis. A densification plot for this example showing 

two specimens and an average is shown in Figure V-5. 

I 

I 

II I I I 

10 100 1000 

Number of Gyrations 

Figure V-5. Densification Plot for Example Specimens 

Design parameters are established on the basis of air void content at Ndesign, Ninitial, and 

Nm,im,,. The following table shows the criteria and observed average values considering 

the average of the two specimens in the example. 

Table V-3. Densification Values and Criteria 

No. of gyrations 

Nini (8) 

Criterion for %Gmm 

< 89.0 

Observed %Gmm 

Archived

87.1 
V. Superpave Gyratory Compaction 

CALIBRATION AND STANDARDIZATION 

A critical calibration item is the height measurement system. This is normally 

accomplished by means of a dummy specimen of known dimensions. The loading ram 

can be calibrated by means of a proving ring or load cell of suitable accuracy. The speed 

of gyration can be checked by accurately timing the rotation over a known number of 

rotating base revolutions. 

Calibration of the angle of gyration is another critical calibration item. This is 

accomplished by various means that are compactor dependent. One method of calibrating 

the angle involves the use of a digital protractor that directly reports angular deviation 

from a fixed datum. Another method uses precise dial gauge measurements collected 

with the mold at various orientations. The measurements are used to calculate the angle 

of gyration. In any case, the angle should be checked while the mold contains a specimen 

under loaded conditions. 

Archived
VI. 

VOLUMETRIC MIX DESIGN 

INTRODUCTION 

Volumetric mix design plays a central role in Superpave mixture design. The best way of 

illustrating its steps is by means of an example. This section provides the Superpave 

Level 1 mixture design test results for a project that was constructed in 1992 by the 

Wisconsin Department of Transportation on IH-43 in Milwaukee. The information 

presented follows the logical progression of testing and data analysis involved in a Level 

1 mixture design and encompasses the concepts outlined in previous sections. There are 

four major steps (see Appendix E for an outline of the major steps in Level 1 mix design) 

in the testing and analysis process: 

1. selection of materials (aggregates, binders, modifiers, etc.), 

2. selection of a design aggregate structure, 

3. selection of a design asphalt binder content, 

4. evaluation of moisture sensitivity of the design mixture. 

Selection of materials consists of determining the traffic and environmental factors for the 

paving project. From that, the performance grade of asphalt binder required for the 

project is selected. Aggregate requirements are determined based on traffic level and 

layer depth. Materials are selected based on their ability to meet or exceed the established 

criteria. 

Selection of the design aggregate structure is a trial-and-error process. This step consists 

of blending available aggregate stockpiles at different percentages to arrive at aggregate 

gradations that meet Superpave requirements. Three trial blends are normally employed 

for this purpose. A trial blend is considered acceptable if it possesses suitable volumetric 

properties (based on traffic and environmental conditions) at a predicted design binder 

content. Once selected, the trial blend becomes the design aggregate structure. 

Archived
VZ. Volumetric Mix Design 

Selection of a design asphalt binder content consists of varying the amount of asphalt 

binder with the design aggregate structure to obtain acceptable volumetric and 

compaction properties when compared to the mixture criteria, which are based on traffic 

and environmental conditions. This step is a verification of the results obtained from the 

previous step. This step also allows the designer to observe the sensitivity of volumetric 

and compaction properties of the design aggregate structure to asphalt content. The 

design aggregate structure at the design asphalt binder content becomes the job-mix 

formula. 

Evaluation of moisture sensitivity consists of testing the designed mixture by AASHTO 

T283 to determine if the mix will be susceptible to moisture damage. 

MATERIAL SELECTION 

For the IH-43 project, design ESALs are determined to be 18 million in the design lane. 

This places the design in the traffic category from 10 to 30 million ESALs. Traffic level 

is used to determine design requirements such as number of design gyrations for 

compaction, aggregate physical property requirements, and mixture volumetric 

requirements. The traffic level also determines the level of mixture design required. For 

18 million ESALs and higher, a Superpave Level 3 design is required. Consequently, the 

design process requires a Level 1 design to determine mixture volumetric properties, 

followed by performance testing and analysis required by Level 3. 

The mixture in this example is an intermediate course mixture. It will have a nominal 

maximum particle size of 19.0 mm. It will be placed at a depth less than 100 rnm from 

the surface of the pavement. 

Binder Selection 

Environmental conditions are determined from weather station data stored in the 

Superpave weather database. The project is near Milwaukee, which has 2 weather 

stations: 

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VI. Volumetric Mix Design 

Table VI-1. Project Environmental Conditions and Binder Grades 

Low and high reliability level binders are shown. Reliability is the percent probability 

that the actual temperature will not exceed the design pavement temperatures listed in the 

binder grade. In this example, the designer chooses high reliability for all conditions. 

Thus, a PG 58-34 binder is needed. The average Design High Air Temperature is 35OC. 

Having determined the need for a PG 58-34 binder, the binder is selected and tested for 

specification compliance. Test results are indicated in Table VI-2. 

Table VI-2. Binder Specification Test Results 

. 

Weather Station Min. Pvmt. Max. Pvmt. Binder Design Air 

Temp. ("C) Temp. ("C) Grade Temp. ("C) 

Dynamic Shear Rheometer G*/sin 6 @ 58°C 11 1.42 kPa 11 1.00 kPa minimum 

RTFO-aged Binder 

1 

Test Property 1) Test Result 11 Criteria 

Original Binder 

Low Reliability (50%) 

Flash Point n/a 

Rotational Viscosity 135°C 

Rotational Viscosity 175°C 

High Reliability (98%) 

Milwaukee Mt. Mary -32 5 5 PG 58-34 36 

Milwaukee WSO AP -33 54 PG 58-34 34 1 

Paving Location 

(Assumed) -33 5 5 PG 58-34 35 

Milwaukee Mt. Mary 

Milwaukee WSO AP 

Paving Location 

(Assumed) 

" 

-26 5 1 PG 52-28 32 

-25 5 1 PG 52-28 3 1 

-26 5 1 PG 52-28 32 

304°C 

0.575 Pas 

0.142 Pa+s 

Mass Loss nla 

Dynamic Shear Rheometer G*/sin 6 @ 58°C 

230°C minimum 

3 Pass maximum 

n/a 

0.14% 

2.41 kPa 

1.00% maximum 

2.20 kPa minimum 

PAV-aged Binder 

Dynamic Shear Rheometer G*sin 6 @ 16°C 

Bending Beam Rheometer Stiffness @ -24°C 

Bending Beam Rheometer m-value @ -24°C 

1543 kPa 

172.0 MPa 

0.321 

5000 kPa maximum 

300.0 MPa 

maximum 

0.300 minimum 

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VI. Volumetric Mix Design 

Comparing the test results to specifications, the designer verifies that the asphalt binder 

meets the requirements of a PG 58-34 grade. Specification testing requires only that 

rotational viscosity be performed at 135°C. Additional testing was performed at 175°C to 

establish laboratory mixing and compaction temperatures. Figure VI-1 illustrates the 

temperature-viscosity relationship for this binder. Based on these test results, the mixing 

temperature range is selected between 165°C and 172°C. The compaction temperature 

range is selected between 15 1°C and 157°C. 

PG 58-34 Binder 

Figure VI-1. Temperature-Viscosity Relationship for Project Binder 

Aggregate Selection 

Next, the designer selects the aggregates to use in the mixture. For this example, there 

are 5 stockpiles of materials consisting of three coarse materials and two fine materials. 

It is assumed that the mixing facility will have at least 5 cold feed bins. If fewer cold feed 

bins are available, fewer stockpiles will be used. The materials are split into 

Archived
VI. Volumetric Mix Design 

representative samples, and a washed sieve analysis is performed for each aggregate. 

These test results are shown in the section on selecting design aggregate structure. 

The bulk and apparent specific gravities are determined for each aggregate. These 

specific gravities are used in trial binder content and VMA calculations. Test results are 

indicated in Table VI-3. 

Table VI-3. Aggregate Specific Gravities 

Aggregate 

#1 Stone 

112" Chip 

318" Chiz, 

In addition to sieve analysis and specific gravity determination, Superpave requires that 

consensus aggregate tests be performed to assure that the aggregates selected for the mix 

design are acceptable. The four tests required are: coarse aggregate angularity, fine 

aggregate angularity, thin and elongated particles, and clay content. In addition, the 

specifying agency can select any other aggregate tests deemed important. These tests can 

include items such as soundness, toughness, and deleterious materials among others. 

Manuf. Sand 

Screen Sand 

Superpave consensus aggregate criteria are intended to be applied to combined aggregate 

Bulk Sp. Gravity 

2.703 

2.689 

2.723 

gradations rather than individual aggregate components. However, some designers find it 

Apparent Sp. Gravity 

2.785 

2.776 

2.797 

2.694 

2.679 

useful to perform the aggregate tests on the individual aggregate components. This step 

allows the designer to use the test results in narrowing the acceptable range of blend 

2.744 

2.73 1 

percentages for the aggregates. It also allows for greater flexibility if nlultiple trial blends 

are attempted. The test results from the components can be used to estimate the results 

for a given combination of materials. The drawback to this procedure is that it takes 

more time to perform this additional testing. For this example, the aggregate properties 

are measured for each stockpile as well as for the aggregate trial blends. 

Archived
VI. Volumetric Mix Design 

Coarse Aggregate Angularity 

This test is performed on the coarse aggregate particles of the aggregate stockpiles. The 

coarse aggregate particles are defined as particles larger than 4.75 mm. Test results are 

indicated in Table VI-4. 

Table VI-4. Coarse Aggregate Angularity 

Note that this test is not performed on the two fine aggregates, even though they have 

some small percentage retained on the 4.75 mm sieve. The manufactured sand has 4.5% 

retained and the Screen Sand has 10.5% retained on the 4.75 mm sieve. 

Table VI-4 also indicates criteria for fractured faces based on traffic (18 million ESALs) 

and depth from the surface (< 100 mm). The criteria change as the traffic level and layer 

position (relative to the surface) change. The criteria are also based on the test results 

from the aggregate blend rather than individual materials. Thus, even though the #1 

Stone appears to be below the minimum criteria, it can be used as long as the selected 

blend of aggregates meets the criteria in Table VI-4. 

Fine Aggregate Angularity 

This test is performed on the fine aggregate particles of the aggregate stockpiles. The fine 

aggregate particles are defined as particles smaller than 2.36 mm. Test results are 

indicated in 

Archived

Table VI-5. 
VI. Volumetric Mix Design 

Table VI-5. Fine Aggregate Angularity 

I Screen Sand I 36% I I 

Aggregate 

Manufactured Sand 

Note that this test is not performed on the three coarse aggregates, even though they have 

a small percentage passing the 2.36 millimeter sieve. The #1 Stone has 1.9% passing, the 

112" Chip has 2.6% passing, and the 318" Chip has 3.0% passing the 2.36 rnm sieve. 

Table VI-5 also indicates criterion for fine aggregate angularity based on traffic and depth 

from the surface. Even though the Screen Sand appears to be below the minimum 

criterion, it can be used as long as the selected blend of aggregates meets the criterion in 

Table VI-5. 

% Air Voids (Loose) 

62% 

Flat and Elongated Particles 

Criterion 

45% min 

This test is performed on the coarse aggregate particles of the aggregate stockpiles. The 

coarse aggregate particles are defined as particles larger than 4.75 mrn. Test results are 

indicated in Table VI-6. 

Table VI-6. Plat and Elongated Particles 

Aggregate I %Thin/Elongated I Criterion 

I 3/8" Chip I 0% I 1 

#1 Stone 

112" Chiu 

Note that this test is not performed on the two fine aggregates, even though they have 

some small percentage retained on the 4.75 mm sieve. The manufactured sand has 4.5% 

retained and the Screen Sand has 10.5% retained on the 4.75 mm sieve. Table VI-6 also 

indicates the criterion for percentage of flat and elongated particles, which is based on 

0% 

0% 10% max I 

Archived
VI. Volumetric Mix Design 

traffic only. The criterion changes as the traffic level changes. In this case, the 

aggregates are cubical and not in danger of failing the criterion. 

Clay Content (Sand Equivalent) 

This test is performed on the fine aggregate particles of the aggregate stockpiles. The fine 

aggregate particles are defined as particles smaller than 4.75 mm. Test results are 

indicated in Table VI-7 

Table VI-7. Clay Content (Sand Equivalent) 

I Ageregate I Sand Eauivalent I Criterion 1 

( Manufactured Sand I 47 1 45 rnin I 

L Screen Sand 1 70 I I 

14ote that this test is not performed on the three coarse aggregates, even though they have 

some small percentage passing the 4.75 mm sieve. The #1 Stone has 2.1 % passing, the 

112" Chip has 3.1% passing, and the 318" Chip has 4.8% passing the 4.75 mm sieve. 

Table VI-7 also indicates the criterion for clay content (sand equivalent) based on traffic 

only. The criterion changes as the traffic level changes. The criterion is also based on the 

test results from the aggregate blend rather than individual materials. Both fine 

aggregates are above the minimum requirement, so there is reasonable expectation that 

the blend will also meet the clay content requirement. Once all of the aggregate testing is 

complete, the material selection process is complete. The next step is to select the design 

aggregate structure. 

SELECT DESIGN AGGREGATE STRUCTURE 

To select the design aggregate structure, the designer establishes trial blends by 

mathematically combining the gradations of the individual materials into a single 

gradation. The 

Archived

blend gradation is then compared to the specification requirements for the 
VI. Volumetric Mix Design 

appropriate sieves. Gradation control is based on four control sieves: the maximum 

sieve, the nominal maximum sieve, the 2.36 mm sieve, and the 75 micron sieve. 

The nominal maximum sieve is one sieve size larger than the first sieve to retain more 

than ten percent of combined aggregate. The maximum sieve size is one sieve size 

greater than the nominal maximum sieve. 

The restricted zone is an area on either side of the maximum density line. For a 19.0 mm 

nominal mixture, it starts at the 2.36 mm sieve and extends to the 300 micron sieve. 

The minimum and maximum values required for the control sieves change (as does the 

restricted zone) as the nominal size of the mixture changes. Table VI-8 indicates the 

gradation requirements for this example. 

Table VI-8. Gradation Criteria for 19.0 mm Nominal Mixture 

Gradation I Sieve Size, I Minimum, Maximum, 1 

I Control Item I mm I % % I 

I Control 1 19.0 1 90.0 100.0 I I Points I 2.36 I 23.0 49.0 I 

Any proposed trial blend gradation has to pass between the control points established on 

the four sieves. In addition, it has to be outside of the area bounded by the limits set for 

the restricted zone. 

Restricted 

Zone 

Figure VI-2 indicates the gradation requirements for a 19.0 mm nominal mixture. 

0.075 

2.36 

1.18 

0.600 

2.0 8.0 

34.6 34.6 

22.3 28.3 

16.7 20.7 

Archived
VI. Volumetric Mix Design 

Superpave 19.0 mm Nominal Gradation 

Sieve Size (mm) Raised to 0.45 Power) 

Figure VI-2. Gradation Requirements for 19.0 mm Nominal Mixture 

Any number of trial blends can be attempted, but three is the standard number of blends. 

Trial blending consists of varying stockpile percentages of each aggregate to obtain blend 

gradations meeting the gradation requirements for that particular mixture. For this 

example, three trial blends are used: an intermediate blend, a coarse blend, and a fine 

blend. The intermediate blend is combined to produce a gradation that is not close to 

either the gradation limits for the control sieves, or the restricted zone. The stockpile 

percentages and combined gradation for Trial Blend 1 are indicated in Table VI-9 and 

Figure VI-3. The coarse blend is combined to produce a gradation that is close to the 

minimum criteria for the nominal maximum sieve, the 2.36 mm sieve, and the 75 micron 

sieve. The stockpile percentages and combined gradation for Trial Blend 2 are indicated 

in Table VI-10 and Figure VI-4. The fine blend is combined to produce a gradation that is 

close to the maximum criteria for the nominal maximum sieve, and the restricted zone. 

The stockpile percentages and combined gradation for Trial Blend 3 are indicated in 

Table VIArchived

1 1 and Figure VI-5. 
VI. Volumetric Mix Design 

Table VI-9. Trial Gradation for Intermediate Blend 

#l 1/2" 3/8" Mfg Scr. 

Stone chip chip sand sand 

Blend 1 25.0% 15.0% 22.0% 18.0% 20.0% 

Blend 2 30.0% 25.0% 13.0% 17.0% 15.0% 

Blend 3 10.0% 15.0% 30.0% 31.0% 14.0% 

Sieve 

Blend 1 Blend 2 Blend 3 

Gradation Gradation Gradation 

IH-43 Trial Blend 1- Intermediate Blend 

19.0 mm Nominal Mixture 

0.075 0.300 2.36 19.0 25.0 

Sieve Size (mm) Raised to 0.45 Power) 

Archived

Figure VI-3. Trial Blend 1 - Intermediate Blend 
VZ. Volumetric Mix Design 

Table VI-10. Trial Gradation for Coarse Blend 

#1 1 3/8" Mfg Scr. 

Stone chip chip sand sand 

Blend 1 25.0% 15.0% 22.0% 18.0% 20.0% 

Blend 2 30.0% 25.0% 13.0% 17.0% 15.0% 

Blend 3 10.0% 15.0% 30.0% 31.0% 14.0% 

Blend 1 Blend 2 Blend 3 

Sieve Gradation Gradation Gradation 

25.4mm 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 

IH-43 Trial Blend 2 - Coarse Blend 

19.0 mm Nominal Mixture 

V 

0.075 0.300 2.36 19.0 25.0 

Sieve Size (mm) Raised to 0.45 Power) 

Archived

Figure VI-4. Trial Blend 2 - Coarse Blend 
VI. Volumetric Mix Design 

Table VI-11. Trial Gradation for Fine Blend 

#I 1/2 " 3/8 " Mfg Scr. 

Stone chip chip sand sad 

Blend 1 25.0% 15.0% 22.0% 18.0% 20.0% 

Blend 2 30.0% 25.0% 13.0% 17.0% 15.0% 

Blend 3 10.0% 15.0% 30.0% 31.0% 14.0% 

Sieve 

25.4 mm 

19.0 mm 

12.5 mm 

9.5 mm 

4.75 mm 

2.36 mm 

1.18 mm 

600 pm 

300 pm 

150 pm 

75 pm 

Blend 1 Blend 2 ~l~~d 3 

Gradation Gradation &adation 

IH-43 Trial Blend 3 - Fine Blend 

19.0 mm Nominal Mixture 

0.075 0.300 2.36 19.0 25.0 

Sieve Size (mm) Raised to 0.45 Power 

Figure VI-5. Trial Bknd 3 - Fine Blend 

Archived
VI. Volumetric Mix Design 

All three of the trial blends are shown graphically in Figure VI-6. Note that all three trial 

blends pass below the restricted zone. This is not a requirement. Superpave allows but 

does not recommend blends that plot above the restricted zone. 

IH-43 Trial Gradations 

19.0 mm Nominal Mixture 

.- 

0.075 0.300 2.36 19.0 25.0 

Sieve Size (mm) Raised to 0.45 Power 

Figure VI-6. IH-43 Trial Blends 

Once the trial blends are selected, a preliminary determination of the blended aggregate 

properties is necessary. This can be estimated mathematically from the aggregate 

properties (Tables VI-3 to VI-7). Estimated values are indicated in Table VI-12. 

Tablc 

Property 

Coarse Ang. 

Fine hg. 

ThinlElongated 

Sand Equivalent 

Combined G,b 

Combined G,, 

VI-12. Estimated Aggregate Blend Properties 

Criteria Trial Blend 1 Trial Blend 2 Trial Blend 3 

95%190% rnin. 96%/92% 95%/92% 97%/93% 

45% min. 

45 min. 

n/a 2.699 2.697 2.701 

Archived

nla 2.768 2.769 2.767 
VI. Volumetric Mix Design 

Values for coarse aggregate angularity are shown as percentage of one or more fractured 

faces followed by percentage of two or more fractured faces. Based on the estimates, all 

three trial blends are acceptable. When the design aggregate structure is selected, the 

blend aggregate properties will need to be verified by testing. 

The next step is to evaluate the trial blends by compacting specimens and determining the 

volumetric properties of each trial blend. For each blend, a minimum of two specimens 

will be compacted using the SGC. The trial asphalt binder content is determined for each 

trial blend by estimating the effective specific gravity of the blend and using the 

calc:ulations shown below. The effective specific gravity (G,) of the blend is estimated 

by: 

The: factor, 0.8, can be adjusted at the discretion of the designer. Absorptive aggregates 

ma!y require values closer to 0.6 or 0.5. The blend calculations are shown below: 

Blend 1: Gse = 2.699 + 0.8~(2.768 - 2.699) = 2.754 

Blend 2: Gse = 2.697 + O.gx(2.769 - 2.697) = 2.755 

Blend 3: Gse = 2.701 + 0.8~(2.767 - 2.701) = 2.754 

The: volume of asphalt binder (Vba) absorbed into the aggregate is estimated using the 

following equation: 

Ps x (1 - Va) 1 1 Vbn = Pb Ps x(---) 

Gsb Gse (-+-I Gb Gse 

where Vba = volume of absorbed binder, cm3/cm3 of mix 

pb = percent of binder (assumed 0.05), 

Archived
VI. Volumetric Mix Design 

PS = percent of aggregate (assumed 0.95), 

Gb = specific gravity of binder (assumed 1.02), 

v, = volume of air voids (assumed 0.04 crnVcm3 of mix) 

Blend 1 : 0.95 x (1 - 0.04) - 

1 1 - -1 = 0.01 7 1 cm3/cm3 of mix 

vba = 0.05 0.95 X(2.699 2.754 (-+-I 1.02 2.754 

Blend 2: Vba = 0.95 x (1 - 0.04) 1 1 x (- - -1 = 0.01 8 1 cm3/cm3 of mix 

(=+El 2.697 2.755 1.02 2.755 

Blend 3: 0.95 x (1 - 0.04) Vba = 

1 1 ) = 0,0165 cm3km3 of mix 

0.0s 0.95 X(~-~ (-+-) 1.02 2.754 

The volume of the effective binder (Vbe) can be determined from the equation below: 

where S, = the nominal maximum sieve size of the aggregate blend (in inches) 

Blend 1-3: Vbe = 0.08 1 - 0.0293 1x [ln(0.75)] = 0.089 cm3/cm3 of mix 

Finally, the initial trial asphalt binder (Phi) content is calculated from the following 

equation: 

CTb x (Vbe + Vba) 

Pbi = x 100 

(Gb x (Vbe + Vba)) + Ws 

where Phi = percent (by weight of mix) of binder 

W, = weight of aggregate, grams 

Archived
VI. Volumetric Mix Design 

(-+-) 

Gb Gse 

Blend 1 : Ws = 0.95 x (1 - 0.04) 

,0.05 0.95 . = 2.315 

Pbi = (0.0g9 + 0.0171) x 100 = 4.46% (by mass of mix) (1.02 x (0.089 + 0.0171)) + 2.3 15 

Blend 2: 0.95 x (1 - 0.04) Ws = ,0.05 0.95 , 

= 2.316 

pbl = (Oaog9 + O.Olgl) x 100 = 4.46% (by mass of mix) (1.02 x (0.089 + 0.0171)) + 2.316 

Blend 3: 0.95 x (1 - 0.04) Ws = ,0.05 0.95 . = 2.315 

Pbi = (Oeog9 + 0.0165) x 100 = 4.46% (by mass of mix) (1.02 x (0.089 + 0.0171)) + 2.315 

Next, a minimum of two specimens for each trial blend are compacted using the SGC. 

Two specimens are also prepared for determination of the mixture's maximum theoretical 

specific gravity (G,,). An aggregate weight of 4500 grams is usually sufficient for the 

compacted specimens. An aggregate weight of 2000 grams is usually sufficient for the 

specimens used to determine maximum theoretical specific gravity (G,,). AASHTO 

T 209 should be consulted to determine the minimum sample size required for various 

mixtures. 

Archived
VI. Volumetric Mix Desinn 

Specimens are mixed at the appropriate mixing temperature, which is 165°C to 172°C for 

the selected PG 58-34 binder. The specimens are then short-term aged by placing the 

loose mix in a flat pan, in a forced draft oven at 135OC, for 4 hours. Next, the specimens 

are brought to compaction temperature range (151°C to 157°C) by placing them in 

another oven for a short time (generally less than 30 minutes). Finally, the specimens are 

then removed and either compacted or allowed to cool loose (for G, determination). 

The number of gyrations used for compaction is determined based on the design high air 

temperature of the paving location (35°C) and the traffic level. Table VI- 13 indicates the 

number of gyrations required. 

Table VI-13. Gyratory Compactive Effort 

Design 

ESALs 

(millions) 

c 0.3 

0.3 - 1 

1-3 

3- 10 

10 - 30 

30 - 100 

> 100 

Nini Ndes 

iverage Design Hi 

39" - 40°C 

Ntnt Ndes Nmax 

7 74 114 

7 83 129 

8 95 150 

8 106 169 

9 121 195 

9 139 228 

10 158 262 

h Air Temperatur 

41" - 42°C 

Nini Nde, Nmax 

7 78 121 

7 88 138 

8 100 158 

8 113 181 

9 128 208 

9 146 240 

10 165 275 

43" - 44°C 

Nini Ndes Nmax 

7 82 127 

8 93 146 

8 105 167 

9 119 192 

9 135 220 

10 153 253 

10 172 288 

From Table VI-13, the number of gyrations for initial compaction, design 

compaction, and maximum compaction are determined: 

Ninitial = 8 gyrations 

NdeSign = 109 gyrations 

Nmaximum = 174 gyrations 

The equations used to develop the information in Table VI-13, which describes the 

relationship among 

Archived

Ndesign, Ninitial, and Nmaximum areshown below: 
VI, Volumetric Mix Design 

Each specimen will be compacted to the maximum number of gyrations, with specimen 

height data collected during the compaction process. This is illustrated for Trial Blend 1 

in Table VI-14. SGC compaction data reduction is accomplished as follows. 

During compaction, the height of the specimen is continuously monitored. Knowing the 

mass of the mix, the fixed diameter of the mold (150 mm), and the measured height at 

any gyration, the specimen specific gravity can be estimated [Gmb(est) in Table VI-141 at 

any gyration throughout the compaction process. This is accomplished by dividing the 

mass of the specimen by volume of the specimen, which is represented by the volume of 

a smooth-sided cylinder of known diameter and (measured) height. 

After compaction is complete, the specimen is extruded from the mold and allowed to 

cool. Next, the measured bulk specific gravity [Gmb(meas) in Table IV- 141 of the 

specimen is determined by AASHTO T166. The G, of each blend is also determined 

by AASHTO T209 [G,,(meas) in Table VI-141. 

A comparison of the specimen's estimated bulk specific gravity [Gmb(est)] and measured 

bulk specific gravity [Gmb(meas)] at itm, shows a difference between these two 

parameters. In Table VI-14, these two values are 2.436 and 2.489, respectively. The 

assumption that was used to estimate the bulk specific gravity was that during 

compaction, the volume of the specimen could be represented by a smooth-sided cylinder, 

which of course, it is not. The actual volume of the specimen is slightly smaller due to 

the presence of surface voids surrounding the perimeter of the specimen. Thus, the 

estimated bulk specific gravity of the specimen at any given gyration must be corrected 

by a factor that is the ratio of the measured to estimated bulk specific gravity of the 

specimen at N,. In Table VI-14, this ratio is 2.48912.436 or 1.022. This corrective step 

is indicated in Table VI-14 in the column labeled Gmb(cOrr). In this step, each value in 

Archived
VI. Volumetric Mix Design 

the column labeled Gmb(est) is multiplied by the correction factor, 1.022, to arrive at the 

values in the column labeled Gmb(cOrr). 

Coarser aggregate mixtures, or mixtures lean in asphalt binder, tend to have larger 

differences between estimated and measured bulk specific gravity at NmaXimum. Finer 

aggregate mixtures, or mixtures rich in asphalt binder, tend to have smaller differences 

between these two parameters. That is because fine, high asphalt content mixtures more 

closely approximate the "smooth-sided cylinder" assumption. 

The final step is to report %Gmm for each specimen. This is computed by dividing the 

corrected bulk specific gravity of the specimen by the measured value for G,. The 

average %G,, for the duplicate specimens is also reported. The average %G,, is used 

as the basis for comparison among the trial mixtures. 

The SGC data reduction for the three trial blends is shown in Tables VI-14, VI-15, and 

VI-16. The most important points of comparison are %Gm at Ninitial, Ndesign, and 

Nmaximm which are highlighted in these tables. Figures VI-7 to VI-9 illustrate the 

compaction plots for data generated in these tables. The figures show %Gmm versus the 

logarithm of the number of gyrations. 

Archived
VI. Volumetric Mix Design 

Table VI-14. Densification Data for Trial Blend 1 

3,, 

I 

(meas) = 2.563 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

125 

150 

174 

Gmb(meas) 

Ht, mm Gmb(est) Gmb(corr) %Gm 

Specimen 2 

Ht, mm Gmb(est) Gmb (con) %G,, 

130.3 2.154 2.209 86.2 

AVG 

IH-43, 19.0 mm Nominal, 4.4% AC, Trial Blend 1 

Specimen 2 I A,,,, 

75 1 1 

1 10 loo 1000 

Number of Gyrations 

Archived

Figure VI-7. Densification Curves for Trial Blend 1 
VI. Volumetric Mix Design 

Table VI-15. Densification Data for Trial Blend 2 

G,,,,,, (meas) = 2.565 

I 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

125 

150 

174 

Gmb(meas) 

Specimen 1 

Ht, mrn Gmb(est) Gmb(corr) %G,, 

131.7 2.090 2.158 84.2 

Specimen 2 

Ht, mm G,b(est) G,b (corr) %G,, 

132.3 2.098 2.159 

- AVG 

- %G, 

84.2 

88.1 

89.2 

90.7 

91.9 

92.7 

93.4 

94.5 

95.4 

IH-43, 19.0 mm Nominal, 4.4% AC, Trial Blend 2 

75 1 1 

1 10 100 1000 

Number of Gyrations I 

Archived

Figure VI-8. Densification Curves for Trial Blend 2 
VI. Volumetric Mix Design 

Table VI-16. Densification Data for Trial Blend 3 

3- 

1 

(meas) = 2.568 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

1 09 

125 

150 

174 

GmbWas) 

Swecimen 1 Specimen 2 

Kt, mm Gmb(est) Gmb (corr) %G,, 

129.5 2.136 2.188 85.2 

AVG 

IH-43, 19.0 mm Nominal, 4.4% AC, Trial Blend 3 1 

Number of Gyrations 

Archived

Figure VI-9. Densification Curves for Trial Blend 3 
VI. Volumetric Mix Design 

The average %Gmm is determined for Ni,itial (8 gyrations), Ndesign (109 gyrations), and 

NmaXi,,, (174 gyrations) for each trial blend. This data is extracted directly from Tables 

VI- 14 to VI-16. Table VI- 17 indicates these values for Trial Blends 1,2, and 3. 

Table VI-17. Determination of %Gm at Nini, Ndesr and N,, for Trial Blends 

The percent of air voids and voids in the mineral aggregate (VMA) are determined at 

Nksign. The percent air voids is calculated as follows: 

%Air Voids = 100 - %Gmm @ Ndesign 

% Gmm @ N97.6 

97 -4 

96.5 

Blend 1: %Air Voids = 100 - 96.2 = 3.8% 

Blend 2: %Air Voids = 100 - 95.7 = 4.3% 

Blend 3: %Air Voids = 100 - 95.2 = 4.8% 

% Gmm @ Ndes 

96.2 

95.7 

95.2 

Trial Blend 

1 

2 

3 

The percent voids in the mineral aggregate is calculated as follows: 

% G- @ Nini 

87.1 

85.6 

86.3 

%Gmm @ Ndes x Gmm x Ps 

%VMA= 100 - ( 

Gsb 

1 

96.2% x 2.563 x 0.956) - 12m74 Blend 1: %VMA = 100 - ( - 

2.699 

Blend 2: %VMA = 100 - ( 95.7% x 2.565 x 0.956 ) = 13.0% 

2.697 

Blend 3: 95.2% x 2.568 x 0.956 %VMA = 100-( ) = 13.5% 

2.701 

Archived
VI. Volumetric Mix Design 

Table VI-18. Compaction Summary of Trial Blends 

Blend %AC %Gm, @ N=8 %G,, @ %G,, @ %Air %VMA 

N=174 N= 109 Voids 

1 4.4% 87.1% 97.6% 96.2% 3.8% 12.7% 

2 4.4% 85.6% 97.4% 95.7% 4.3% 13.0% 

3 4.4% 86.3% 96.5% 95.2% 4.8% 13.5% 

Table VI-18 indicates the compaction summary of the trial blends. The central premise in 

Superpave Level 1 mix design is that the correct amount of asphalt binder is used in each 

trial blend so that each blend achieves exactly 96% of G, or 4% air void content at 

Ndesign. Clearly, this did not happen for any of the three IH-43 trial blends. Because the 

trial blends exhibit different air void contents at Ndesign, their other volumetric and 

compaction properties cannot be properly compared. For example, Trial Blend 1 

contained slightly too much asphalt to achieve 4 % air voids at Ndesign. Instead, it had 

only 3.8% air voids. The VMA of Trial Blend 1 is also too low. The designer must ask 

the question, "If I had used less asphalt in Trial Blend 1 to achieve 4% air voids at Ndesignr 

would the VMA and other required properties improve to acceptable levels?' 

Providing an answer to this question is an important step in Level 1 mix design. To 

answer this question, an estimated asphalt binder content to achieve 4% air voids (96% 

G, at Ndesign) isdetermined for each trial blend using the following empirical formula. 

where Pb,estimated = estimated percent binder 

Phi = initial (trial) percent binder 

V, = percent air voids at Ndesign 

Blend 1: Pb,estimated = 4.4 - (0.4~(4 - 3.8)) = 4.3% 

Blend 2: Pb,estimated = 4.4 - (0.4~(4 - 4.3)) = 4.5% 

Archived
VZ. Volumetric Mix Design 

Blend 3: Pb,estimated = 4.4 - (0.4~(4 - 4.8)) = 4.7% 

The volumetric (VMA and VFA) and mixture compaction properties are then estimated at 

this asphalt binder content using the equations that follow. These steps are solely aimed 

at answering the question, "What would have been the trial blend properties if I had used 

the right amount of asphalt to achieve 4% air voids at Ndesign?' It is by these steps that a 

proper comparison among trial blends can be accomplished. 

For VMA: 

where: %VMAinitial = %VMA from trial asphalt binder content 

C = constant (either 0.1 or 0.2) 

Note: C = 0.1 if V, is less than 4.0% 

C = 0.2 if V, is greater than 4.0% 

Blend 1 : %VMLstimated = 12.7 + (O.lx(4.0 - 3.8)) = 12.7% 

Blend 2: %VMAestimakd = 13.0 + (0.2~(4.0 - 4.3)) = 13.0% 

Blend 3: %VMLStimakd = 13.5 + (0.2~(4.0 - 4.8)) = 13.3% 

For VFA: 

(12.7 - 4.0) Blend 1: %VFAestirnated = 100% X = 68.5% 

12.7 

(13.0 - 4.0) Blend 2: %VFAestirnated = 100% X = 69.2% 

13.0 

Blend 3: 

Archived
VZ. Volumetric Mix Design 

Blend 1: %Gmm estimated @ Nini = 87.1 - (4.0 - 3.8) = 86.9% 

Blend 2: %Gmmestimated @ Nini = 85.6 - (4.0 - 4.3) = 85.9% 

Blend 3: %Gmmestimatea @ Nini = 86.3 - (4.0 - 4.8) = 87.1% 

Blend 1 : %Gmm estimated @ Nmax = 97.6 - (4.0 - 3.8) = 97.4% 

Blend 2: %Gmm estimated @ Nmax = 97.4 - (4.0 - 4.3) = 97.7% 

Blend 3: %Gmm,,tim,d @ N, = 96.5 - (4.0 - 4.8) = 97.3% 

Tables VI- 19 and VI-20 indicate the estimated volumetric and mixture compaction 

properties for the trial blends at the asphalt binder content that should result in 4.0% air 

voids at Ndesign. 

Table VI-19. Estimated Mixture Volumetric Properties @ Naesig, 

Blend Trial %AC Est. %AC %Air Voids %VMA %VFA 

1 4.4% 4.3% 4.0% 12.7% 68.5% 

2 4.4% 4.5% 4.0% 13.0% 69.2% 

3 4.4% 4.7% 4.0% 13.3% 70.1% 

Estimated properties are compared against the mixture criteria. For the design traffic and 

nominal maximum particle 

Archived

size, the volumetric and densification criteria are as follows: 
VI. Volumetric Mix Design 

% Air Voids 4.0% 

% VMA 13.0% (1 9.0 rnrn nominal mixture) 

% VFA 65% - 75% (10-30 x lo7 ESALs) 

% Gmm @ Ninitial less than 89% 

%G,, @ Nmaximum less than 98% 

Table VI-20. Estimated Mixture Compaction Properties 

Blend Trial %AC Est. %AC %G,, @ N=8 %G,, @ N=174 

1 4.4% 4.3% 86.9% 97.4% 

Finally, there is a required range on the dust proportion. This criteria is constant for all 

levels of traffic. It is calculated as the percent by mass of the material passing the 0.075 

rnrn sieve (by wet sieve analysis) divided by the effective asphalt binder content 

(expressed as percent by mass of mix). The effective asphalt binder content is calculated 

as follows: 

Gse - Gsb Pbe, estimated = -(Ps x Gb) X ( ) + Pb, estimated 

Gse x Gsb 

Blend 1 : Pbe,estimated = -(95,7 X 1.02) X ( 2.754 - 2.699 ) + 4.3 = 3.6% 

2.754 x 2.699 

Blend 2: Pbe,estimated = 495.5 X 1.02) X ( 2.755 - 2.697 ) + 4.5 = 3.7% 

2.755 x 2.697 

Blend 3 : 

2.754 - 2.701 Pbe, estimated = 495.3 X 1.02) X ( ) + 4.7 = 4.0% 

2,754 x 2.701 

Dust Proportion is calculated as follows: 

DP = p.075 

Archived

Pbe, estimated 
VI. Volumetric Mix Design 

Blend 1: 

Blend 2: 

Blend 3: 

The dust proportion must be between 0.6 and 1.2. Table VI-2 1 indicates the results. 

Table VI-21. Dust Proportion of Trial Blends 

I Blend I Dust Proportion I Criterion I 

After establishing all the estimated mixture properties, the designer can observe the 

values for the trial blends and decide if one or more are acceptable, or if further trial 

blends need to be evaluated. 

Trial Blend 1 

Trial Blend 2 

Trial Blend 3 

Blend 1 is unacceptable based on a failure to meet the minimum VMA criteria. Blend 2 

is acceptable, but the VMA is at the minimum. Blend 3 has acceptable VMA as well as 

meeting the criteria for VFA, dust proportion, and the densification criteria. From this 

data, Trial Blend 3 is selected as the design aggregate structure. 

SELECT DESIGN ASPHALT BINDER CONTENT 

0.86 

0.78 

0.88 

Once the design aggregate structure is selected, Trial Blend 3 in this case, specimens are 

0.6 - 1.2 

compacted at varying asphalt binder contents. The mixture properties are then evaluated 

to determine a design asphalt binder content. 

A minimum 

Archived

of two specimens are compacted at each of the following asphalt contents: 
VI. Volumetric Mix Design 

estimated binder content 

estimated binder content k 0.5%, and 

estimated binder content + 1.0%. 

For Trial Blend 3, the binder contents for the mix design are 4.2%, 4.7%, 5.2%, and 

5.7%. Four asphalt binder contents are a minimum in Superpave Level 1 analyses. 

A minimum of two specimens are also prepared for determination of maximum 

theoretical specific gravity at the estimated binder content. Specimens are prepared and 

tested in the same manner as the specimens from the "Select Design Aggregate Structure" 

section. 

Tables VI-22 to VI-25 indicate the test results in tabular form for each trial asphalt binder 

content. Figures VI- 10 to VI- 13 illustrate the densification curves for each trial asphalt 

binder content. Figure VI-14 illustrates the average densification curves for each trial 

asphalt binder content. 

Archived
VI. Volumetric Mix Design 

Table VI-22. Densification Data for Blend 3,4.2% Asphalt Binder 

;,, (meas) = 2.582 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

125 

150 

174 

Gmb(meas) 

Specimen 1 AVG 

3, mm Gmb(est) Gmb(corr) %Gm 

131.3 2.116 2.167 83.9 

Specimen 2 

Ht, mm Gmb(est) G* (corr) %G,, 

131.0 2.136 2.186 84.7 

128.8 2.172 2.223 86.1 

127.4 2.196 2.248 87.1 

125.5 2.229 2.281 88.4 

124.2 2.253 2.306 89.3 

122.4 2.286 2.340 90.6 

121.1 2.310 2.364 91.6 

120.1 2.330 2.385 92.4 

119.4 2.342 2.397 92.9 

118.3 2.365 2.421 93.8 

117.4 2.383 2.439 94.5 

117.1 2.389 2.445 94.7 

116.6 2.400 2.456 95.1 

115.9 2.413 2.470 95.7 

115.4 2.424 2.481 96.1 

2.481 

IH-43, 19.0 mm Nominal, Blend 3,4.2% AC 

I Average 1 

10 100 

Number of Gyrations 

Figure 

Archived

VI-10. Densification Curves for Blend 3,4.2% Asphalt Binder 
VI. Volumetric Mix Design 

Table VI-23. Densification Data for Blend 3,4.7% Asphalt Binder 

3- (meas) = 2.562 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

1 25 

150 

174 

Gmb(meas1 

Specimen 2 AVG 

Ht, mm Gmb(est) Gmb(corr) %Gmm 

130.4 2.152 2.199 85.8 

Ht, mm Gmb(est) G,,b (corr) %G,, 

IH-43, 19.0 mm Nominal, Blend 3,4.7% AC 

I - Specimen 2 ( I Average I 

75 1 

1 10 100 1000 

Number of Gyrations 

Figure 

Archived

VI-11. Densification Curves for Blend 3,4.7% Asphalt Binder 
VI. Volumetric Mh Design 

Table VI-24. Densification Data for Blend 3,5.2% Asphalt Binder 

f ,, (meas) = 2.542 

I Specimen 1 Specimen 2 AVG 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

125 

150 

174 

Gmb(meas) 

Ht, mm Gmb(est) Gmb(corr) %G,, 

132.0 2.148 2.187 86.0 

It, mm Gmb(est) Gmb (corr) %Gm %Gmm 

132.6 2.142 2.183 85.8 85.9 

I IH-43, 19.0 mm Nominal, Blend 3,5.2% AC 

75 

1 10 100 1000 

Number of Gyrations 

Figure 

Archived

VI-12. Densification Curves for Blend 3,5.2% Asphalt Binder 
VZ. Volumetric Mix Design 

Table VI-25. Densification Data for Blend 3,5.7% Asphalt Binder 

3- (meas) = 2.523 

Gyrations 

5 

8 

10 

15 

20 

30 

40 

50 

60 

80 

100 

109 

125 

150 

174 

Gmb(meas) 

Specimen 1 AVG 

Ht, mm Gmb(est) G,b(corr) %Gm 

130.4 2.170 2.204 87.4 

128.6 2.201 2.236 88.7 

127.4 2.222 2.257 89.5 

125.4 2.256 2.292 90.8 

124.0 2.282 2.318 91.9 

122.4 2.313 2.349 93.1 

120.5 2.349 2.386 94.6 

119.4 2.371 2.408 95.5 

118.9 2.381 2.419 95.9 

117.6 2.406 2.444 96.9 

116.7 2.426 2.464 97.7 

116.2 2.453 2.474 98.1 

115.4 2.452 2.491 98.7 

114.9 2.463 2.502 99.2 

114.3 2.476 2.515 99.7 

2.515 

Saecimen 2 

Ht, mm G,b(est) G,b (corr) %G,, 

IH-43, 19.0 mm Nominal, Blend 3, 5.7% AC 

- 

Figure VI-13. Densification Curves for Blend 3,5.7% Asphalt Binder 

10 100 

Archived

Number of Gyrations 
VI. Volumetric Mix Design 

IH-43, 19.0 mm Nominal, Blend 3 

10 100 

Number of Gyrations 

Figure VI-14. Average Densification Curves for Blend 3, Varying 

Asphalt Binder Content 

Mixture properties are evaluated for the selected blend at the different asphalt binder 

contents, by using the densification data at Ninitid (8 gyrations), Ndesign (109 gyrations), 

and Nmmimum (174 gyrations). Tables VI-26 and VI-27 indicate the response of the 

mixture's compaction and volumetric properties with varying asphalt binder contents. 

Table VI-26. Summary of Blend 3 - Mix Compaction Properties 

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VI. Volumetric Mix Design 

Table VI-27. Summary of Blend 3 - Mix Volumetric Properties at Ndesign 

%AC %Air Voids %VMA %VFA Density (kg/m3) 

4.2% 5.5% 13.4% 59.3% 244 1 

4.7% 3.9% 13.2% 70.1% 246 1 

5.2% 3 .O% 13.4% 77.9% 2467 

5.7% 1.9% 13.6% 86.2% 2476 

The volumetric properties are calculated at the design number of gyrations (Ndesign) for 

each trial asphalt binder content. From these data points, the designer can generate 

graphs of air voids, VMA, and VFA versus asphalt binder content. 

The design asphalt binder content is established at 4.0% air voids. In this example, the 

design asphalt binder content is 4.7% - the value that corresponds to 4.0% air voids at 

Ndesign = 109 gyrations. All other mixture properties are checked at the design asphalt 

binder content to verify that they meet criteria. The design values for the 19.0 mm 

nominal mixture (Trial Blend 3) are indicated in Table VI-28. 

IH-43 Intermediate Course, Blend 3 

I % Asphalt Binder 1 

Archived

Figure VI-15. Air Voids versus Asphalt Binder Content 
VI. Volumetric Mix Design 

IH-43 Intermediate Course, Blend 3 

14.5 

14.3 

14.1 

13.9 

13.7 

13.5 

13.3 

13.1 

12.9 

12.75 

3.7 

1 

4.2 4.7 5.2 5.7 6.2 

% Asphalt Binder 

Figure VI-16. VMA versus Asphalt Binder Content 

IH-43 Intermediate Course, Blend 3 

3.7 

c 

4.2 4.7 5.2 5.7 6.2 

% Asphalt Binder 

Archived

Figure VI-17. VFA versus Asphalt Binder Content 
VI. Volumetric Mix Design 

Table VI-28. Design Mixture Properties at 4.7% Binder Content 

I Mix Pro~ertv I Result I Criteria 1 

% Air Voids 

%VMA 

%VFA 

Dust Pro~ortion 

EVALUATE MOISTURE SENSITIVITY 

4.0% 

13.2% 

%Gmm @ Ninitial = 8 

%Gm, @ Nmwimum = 174 

The final step in the Level 1 mix design process is to evaluate the moisture sensitivity of 

the design mixture. This step is accomplished by performing AASHTO T 283 testing on 

the design aggregate blend at the design asphalt binder content. Specimens are 

compacted to approximately 7% air voids. One subset of three specimens are considered 

4.0% 

13.0%min. 

70.0% 

0.88 

control specimens. The other subset of three specimens is the conditioned subset. The 

conditioned subset is subjected to vacuum saturation followed by an optional freeze 

cycle, followed by a 24 hour thaw cycle at 60' C. All specimens are tested to determine 

their indirect tensile strengths. The moisture sensitivity is determined as a ratio of the 

tensile strengths of the conditioned subset divided by the tensile strengths of the control 

subset. Table VI-29 indicates the moisture sensitivity data for the mixture at the design 

asphalt binder content. 

65% - 75% 

0.6 - 1.2 

87.1% 

97.5% 

less than 89% 

less than 98% 

Archived
VI. Volumetric Mix: Design 

Table VI-29. Moisture Sensitivity Data for Blend 3 at 4.7% Design 

SAMPLE 

Diameter, rnrn D 

Thickness, mm t 

Dry mass, g A 

SSD mass, g B 

Mass in Water, g C 

Volume, cc (B-C) E 

Bulk Sp Gravity (AIE) F 

Max Sp Gravity G 

% Air Voids(lOO(G-F)/G) H 

Vol Air Voids (HEI100) I 

Saturated ll 

SSD mass, g B' 

Mass in water, g C ' 

Volume, cc (B1-C') E' 

Vol Abs Water, cc (B1-A) J' 

% Saturation (lOOJ1/I) 

% Swell (lOO(E1-E)/E) . Conditioned 

Thickness, mm t" 

SSD mass, g B" 

Mass in water, g C" 

Volume, cc (B1'-C") E" 

Vol Abs Water, cc (B"-A) J" 

% Saturation (100J"A) 

% Swell (100(E"-E)E) 

Load, N ky Str. (2OOOP/(tDn)) iii 

Wet Str. (2000P"/(t"Dn;)) St, 

Average Dry Strength (kPa) 

Average Wet Strength (kPa) 

%TSR 

ialt B lder Content 

The minimum criteria for tensile strength ratio 80%. The design blend (82.6%) exceeded 

the minimum requirement. The Superpave Level 1 Mix Design is now complete for the 

intermediate mixture for M-43. Additional performance prediction testing is required as 

described 

Archived

under the Level 3 testing process. 
Archived
VII. 

PERFORMANCE TESTING (LEVELS 2 AND 3) 

INTRODUCTION 

In the Superpave mixture design and analysis system, performance tests are used only in 

situations involving moderate to high traffic. This means that they are required only for 

Levels 2 and 3 mixture designs. Performance testing utilizes new equipment and 

procedures to ensure that Superpave mixtures exhibit acceptable amounts of the distress 

types that were considered by SHRP researchers: permanent deformation, fatigue 

cracking, and low temperature cracking. Two performance test devices were developed: 

the Superpave Shear Tester (SST) and the Indirect Tensile Tester (IDT). The extent of 

use of performance testing for Levels 2 and 3 mix design are shown in Table VII- 1 for a 

new two layer HMA system, which is the most new layers considered by Superpave. 

Table VII-1, Performance Tests, Levels 2 and 3 (New Construction) 

Design 

Level 

2 

To check 

Performance Distress Mode I I 

Indirect tensile creep compl 

at 0°, -lo0, -20' C. 

Indirect tensile strength at 

-10" C. 

Binder creep stiffness (S) 

and creep rate (m). 

Permanent ~eformation' 

Simple shear test at constant 

height at Tefl(PD). 

Frequency sweep test at 

constant height at TEff(PD). 

Indirect, tensile creep 

compliance and strength at 

00, -to0, -zoo C. 

Fatigue Cracking 

Simple shear test at constant 

height at Teff(FC). 

Frequency sweep test at 

constant height at Teff(FC). 

Indirect tensile strength at 

Teff(FC). 

r tertiary flow, Level 2 and 3 require repeated shear test at constant stress ratio at T, 

Uniaxial strain test at 4O, 

20°, 40" C. 

40' C. - lo0, 4O, and 20" C. 

Simple shear test at constant 

Archived

height at 4O, 20°, 40" C. 
VZI. Perfomance Testing 

If an overlay is being designed, Superpave does not attempt to predict fatigue cracking or 

low temperature cracking. Only permanent deformation is considered. Consequently, the 

extent of use of performance testing for asphalt mixtures used for overlays is shown in 

Table VII-2, 

Table VII-2. Performance Tests, Levels 2 and 3 (Overlay Construction) 

I I Frequency sweep test at constant height at 4O, 20°, and 40°C I 

Design Level 

2 

I 3 I Uniaxial strain test at 4', 20°, and 40' C I 

Permanent ~eformation' 

Simple shear test at constant height at T,ff(PD) 

Frequency sweep test at constant height at T,dPD) 

I I Volumetric test at 4O, 20°, and 40° C I I I Simple shear test at constant height at 4O, 20°, and 40" C I I ' To check for tertiary flow, Level 2 and 3 require repeated shear test at constant stress I ratio at T, I 

PERFORMANCE MODELS 

While much attention was focused in SHRP on the new test equipment and testing 

protocols, a key component of performance testing are performance models. These are 

prediction algorithms that accept performance test results and output predicted pavement 

performance. The models account not only for the new asphalt mixture being designed, 

but also the characteristics of the in-place pavement. The use of performance testing and 

performance prediction models represents an important new tool for engineers in 

designing and managing pavements. 

Performance prediction is accomplished by the Superpave software using four 

components : 

material property model, 

environmental effects model, 

pavement response model, and 

Archived

pavement distress model. 
VII. Per$ormance Testing 

Performance test results (i.e., SST and IDT) are used as input to the material property 

model to determine non-linear elastic, viscoelastic, plastic, and fracture properties. The 

environmental effects model calculates pavement temperature as a function of depth and 

material thermal characteristics. The pavement response model uses a two-dimensional, 

axisymmetric finite element approach to predict stresses and strains within the layered 

system. It uses output from the material property and environmental effects models to 

predict these responses of the pavement system to traffic and environmental loads. 

Output from the pavement response and material property models are used by the distress 

models to estimate rutting and fatigue and low temperature cracking. Figure IV-1 shows 

the performance prediction approach of Superpave. 

Project Data: layer info, traffic, climate 

I Material Property Model I II 

Environmental 

Effects Model 

1 Performance Test Results I 

Rutting 

.Fatigue Cracking 

Thermal 

Figure VII-1. Superpave Performance Prediction System 

TEST PARAMETERS 

Test Temperatures 

Level 3 testing provides a more reliable prediction of pavement performance because it 

involves performance testing over a wider range of temperatures (i.e., 4*, 20°, and 40" C). 

This allows use of the environmental effects model to more accurately predict pavement 

performance. 

Level 2 testing involves performing tests at an effective temperature (Teff). While a less 

accurate performance prediction results in Level 2 testing, the testing is greatly 

Archived
VII. Performance Testinn 

simplified. Because permanent deformation and fatigue cracking occur at different 

temperatures, two effective temperatures are used: T,ff(PD) and Teff(FC). Teff(PD) is the 

single temperature at which the predicted permanent deformation would be identical to 

that predicted by a multiple temperature analysis. Teff(FC) is the single temperature at 

which an equal amount of fatigue damage would occur to that measured by considering 

each season separately throughout the year. Both temperatures are computed by 

Superpave software and are a function of project mean annual air temperature, layer 

depth, and user selected reliability. 

While tertiary flow is a permanent deformation type of distress, it is treated separately by 

Superpave. Tertiary flow occurs when an asphalt mixture densifies to a very low air void 

content, normally less than about two to three percent air voids. In this condition, the 

mixture exhibits extreme plastic flow with very few load applications. Figure VII-2 

illustrates the concept of tertiary flow. 

Log Plastic Strain 

ary Flow 

-- - 

Log Number of Load Applictions 

Figure VII-2. Tertiary Rutting 

The tertiary flow analysis using the repeated shear test at constant stress ratio is 

conducted at a control temperature (T,). The control temperature is computed by 

Superpave software and depends on project weather and traffic conditions. 

Asphalt Binder Contents 

Superpave performance testing requires that specimens be tested at multiple asphalt 

binder contents. For tests concerned with permanent deformation, fatigue cracking, and 

Archived
VII. Performance Testing 

low temperature cracking, these consist of binder contents that result in three, four, and 

six percent air voids at Ndesign. However, performance test specimens are fabricated using 

less gyrations than Ndesign in order to achieve test specimens containing approximately 

seven percent air voids. 

For the tertiary flow analysis, only the binder content resulting in three percent air voids 

is used. Two test specimens are required for a given test condition (i.e., test temperature 

and binder content). They are fabricated to achieve three percent air voids. Appendix F 

shows a visual representation of specimen requirements for Levels 1,2, and 3 testing. 

SUPERPAVE SHEAR TESTER 

The SST (Figure VII-3) is a closed-loop feedback, servo hydraulic system that consists of 

four major components: the testing apparatus, the test control unit and data acquisition 

system, the environmental control chamber, and the hydraulic system. 

environmental n 

control chamber \ 

control and 

data acquisition 

testing 

apparatus 

hydraulic system 

Figure VII-3. Superpave Shear Tester Components 

Testing Apparatus 

The testing apparatus includes a reaction frame and shear table. It also serves to house 

the various coniponents that are driven by other system components such as 

temperaturelpressure control, hydraulic actuators, and input and output transducers. The 

reaction frame is extremely rigid so that precise specimen displacement measurements 

Archived
VII. Performance Testing 

can 'be achieved without worrying about displacements from frame compliance. The 

shear table holds specimens during testing and can be actuated to impart shear loads. 

Test Control Unit 

The test control unit consists of the system hardware and software. The hardware 

interfaces with the testing apparatus through input and output transducers, and it consists 

of controllers, signal conditioners, and a computer and its peripherals. The software 

consists of the algorithms required to control the testing apparatus and to acquire data 

during a test. 

Linear variable differential transducers (LVDTs) are affixed to specimens and measure 

the response of specimens to applied testing loads. The LVDTs make it possible for the 

system to operate in a closed loop feedback mode, which means that LVDT signals are 

used to control applied testing loads. 

Environmental Control Unit 

The environmental control unit is required to control the temperature and air pressure 

inside the testing chamber at a constant level. The unit is capable of providing 

temperatures within a wide range from lo to 80' C. Air pressure and the rate of pressure 

change within the chamber is precisely controlled. Air pressure is normally applied at a 

rate of 70 kPa per second up to a maximum value of 840 kPa. This is achieved by storing 

compressed air in separate storage tanks that can be emptied into the testing chamber at 

the required rate. Air pressure provides specimen confinement for two of the six tests. 

Hydraulic System 

The hydraulic system provides the required force to load specimens for different testing 

conditions. A hydraulic motor powers two actuators, each with a capacity of 

approximately 32 MV. The vertical actuator applies an axial force to test specimens. The 

horizontal actuator 

Archived

drives the shear table, which imparts shear loads to the specimen. 
VII. Performance Testinn 

Specimen Preparation and Instrumentation 

The first step in specimen preparation is to trim test specimens to a thickness of 50 mm. 

For the three tests that require no confining pressure, the specimen is glued between two 

platens. 

A gluing device (Figure VII-4) is used to squeeze the specimen between the platens while 

the glue cures. An epoxy-type glue such as Devcon Plastic Steel is employed for this 

purpose. The gluing device rigidly holds the platens and specimen to ensure that the 

platen faces are parallel. 

After the glue has cured, four screws are affixed to the side of the specimen using a gap 

filling variety of cyanoacrylate glue. These screws are used to affix the bracket that holds 

the horizontal LVDT (Figures VII-5 and VII-6). Axial LVDTs are affixed to the platens. 

platens 

Archived

Figure VII-4. SST Gluing Device 
VII. Peq4ormance Testing 

screws affixed 

to specimens 

scre& affixed 

to specimens 

Figure VIM. Specimen Instrumentation for Unconfined SST Tests 

(Side View) 

screws 

affixed to 

specimen 

horizontal 

LVDT 

axial 

LVDT 

Figure VII-6. Specimen Instrumentation for Unconfined SST Tests 

(Front View) 

A different specimen configuration is used for confined tests. Test specimens are still 

placed between platens, however, no glue is used. A rubber membrane surrounds the 

specimen. A radkd LVDT is affixed by a collar that surrounds the perimeter of the 

specimen (Figure 

Archived

VII-7). Axial LVDTs are affixed to the platens. 
VII. Pe$ormance Testing 

radial LVDT rubber membrane 

axial 

LVDT 

Figure VII-7. Specimen Instrumentation for Confined SST Tests 

(Front View) 

Test Procedures 

Six tests are performed using the SST: 

volumetric test, 

uniaxial strain test, 

repeated shear test at constant stress ratio, 

repeated shear test at constant height (not required by Superpave), 

simple shear test at constant height, and 

frequency sweep test at constant height. 

The volumetric and uniaxial strain tests use confining pressure in their protocol. These 

two tests are performed only for a Level 3 mixture design. Levels 2 and 3 design use 

repeated shear at constant stress ratio, simple shear at constant height, and frequency 

sweep at constant height tests. The repeated shear test at constant height is a stand-alone 

test that can be used for rut depth estimation and it is not a part of the Superpave mixture 

design and analysis system. A brief description of each test follows. 

Volumetric Test 

The volumetric test is one of two tests that uses confining pressure. It is performed at 

three temperatures and pressures as indicated below. 

Archived
VII. Per$ormance Testing 

Table VII-3. Volumetric Test Parameters 

The test is performed by increasing the confining stress at a rate of 70 kPa per second up 

to the values shown and measuring the circumferential strain by means of the radial 

LVDT, Figure VII-8 shows the change in confining pressure versus time during the 

Temperature, "C 

4 

20 

40 

volumetric test at 20° C. 

Pressure, kPa 

830 

690 

550 

Air Pres, kPa 

30 sec 

0 10 20 30 40 50 60 70 80 

Time, sec 

Figure VII-8. Co&ning Pressure in Volumetric Test at 20" C 

Uniaxial Strain Test 

The uniaxial strain test also uses confining pressure. In this test, axial stress is applied to 

the test specimen and the specimen tries to increase its circumference. The radial LVDT 

senses this change in circumference and air pressure is applied so that the circumference 

remains constant. This approach uses the signal from the radial LVDT as feedback for 

the purpose of applying confining pressure to prevent radial deformation. Three axid 

stress levels are 

Archived

used depending on the test temperature as shown in Table VII-4. 
VII. PerJomance Testing 

Table VII-4. Uniaxial Strain Test Parameters 

Confining pressure is measured throughout the test. Axial deformation is measured on 

both sides of the specimen by the vertical LVDTs. Axial load is also measured. Radial 

deformation is also measured although it should be relatively small. Figure VII-9 shows 

Temperature, "C 

4 

20 

40 

the application of axial stress during the test. 

Axial Stress, kPa 

655 

550 

345 

I Axial Stress, kPa 

Confining Stress, kPa variable magnitude 

circumference constant 

10 20 

Time, sec 

Figure VII-9. Stress Applications in Uniaxial Strain Test at 20" C 

Repeated Shear Test at Constant Stress Ratio 

The repeated shear test at constant stress ratio is performed for either Level 2 or 3 mix 

design. It is a screening test to delineate an asphalt mixture that is subject to tertiary 

rutting. This form of rutting occurs at low air void contents and is the result of bulk 

mixture 

Archived

instability. 
VIZ. Pe$ormance Testing 

In this test, repeated synchronized haversine shear and axial load pulses are applied to the 

specimen. A load cycle consists of 0.7-second, which is comprised of 0.1-second load 

application followed by 0.6-second rest period. Test specimens are subjected to a varying 

number of load cycles in the range from 5000 to 120,000, depending on the traffic level 

and climate conditions or until accumulated permanent strain reaches five percent. The 

ratio of axial to shear stress is maintained constant in the range from 1.2 to 1.5. The 

magnitude of stresses are selected to simulate actual in-place stresses that will be 

encountered by the mixture. Suggested stress values are shown in Table VII-5. 

Table VII-5. Suggested Stress Values for Repeated Shear Test at 

Constant Stress Ratio 

Base 

Condition 

Weak 

In Table VII-5, a weak base is considered any unstabilized granular material while a 

strong base is considered an existing pavement or stabilized layer. The test temperature 

used is called the control temperature (T,) for permanent deformation. It is computed by 

Superpave as a function of the project traffic conditions and climate. The test is typically 

performed at high asphalt contents corresponding to three percent air voids, which is the 

extreme condition for tertiary rutting. 

Asphalt Content 

I I 

During the test axial and shear loads and deformations are measured and recorded. 

Figure VII-10 shows typical stress pulses in the test. 

High 

Shear Stress, I Axial Stress, 

kPa 

84 

Medium 

Shear Stress, I Axial Stress, 

Pa 

119 

I 1 05 5 6 

Low 

Shear Stress, I Axial Stress, 

84 91 

kPa 

63 

Strong 9 8 175 

kPa 

98 

kPa 

49 

kPa 

56 

Archived
VII. Performance Testing 

1 Shear yss, kPa 

I Axial SFss, kPa variable milgni tide 

to keep axiaVshear 

r\ stress between 1.2-1.5 

I Time, sec 

Figure VII-10. Stress Pulses in Repeated Shear Test 

at Constant Stress Ratio 

Repeated Shear Test at Constant Height 

This test is performed as an option to Levels 2 or 3 design to estimate rut depth and is not 

a required by Superpave. A haversine shear load is applied to achieve a controlled shear 

stress level of 68 kPa. When the repeated shear load is applied, the test specimen seeks to 

dilate. The signal from the axial LVDT is used as feedback by the vertical actuator to 

apply sufficient axial load to keep the specimen from dilating. 

A load cycle consists of 0.7-second, which is comprised of 0. l-second shear load 

application followed by 0.6-second rest period. Test specimens are subjected to 5000 

load cycles or until the permanent shear strain reaches five percent. 

The test temperature used is T,, which is the seven-day maximum pavement 

temperature at 50 mm depth. During the test, axial and shear loads and deformations are 

measured 

Archived

and recorded. Figure VII- 1 1 shows typical stress pulses in the test. 
VZZ. Pe$ormance Testing 

( Shear Stress, kPa 

Axial Stress, kPa variable magnitude 

height constant 

0.1 0.7 1.4 

I Time, sec 

Figure VII-11. Stress Pulses in Repeated Shear Test at Constant Height 

Simple Shear Test at Constant Height 

This test is performed in Levels 2 or 3 design. A controlled shearing stress is applied to a 

test specimen. As the test specimen is sheared, it seeks to dilate, which increases its 

height. The vertical actuator uses the signal from the axial LVDT to apply sufficient axial 

stress to keep the specimen height constant. The test is performed at different stress 

levels and temperatures depending on whether a Level 2 or 3 design is being performed. 

The following tables outline test parameters. 

Table VII-6. Simple Shear Test Parameters 

In this table, Teff(FC) is the effective pavement temperature for fatigue cracking. It is 

computed by Superpave as a function of climate, depth of mixture in pavement, and 

designer selected reliability level in the same manner as TCE(PD). Figure VII-12 shows 

Mix Design Level Temperature, "C Shear Stress, kPa 

Archived
VII. Per$ormance Testing 

the application of stresses during the test. During the test axial and shear loads and 

deformations are measured and recorded. 

Shear Stress, kPa 

Axial Stress, kPa variable magnitude 

10 20 30 

Time, sec 

Figure VII-12. Stress Applications in Simple Shear Test at 20° C 

Frequency Sweep Test at Constant Height 

This test is performed in Levels 2 or 3 design. A repeated sinusoidal shearing load is 

applied to the specimen to achieve a controlled shearing strain of 0.005 percent. One 

hundred cycles are used for the test at each of the following loading frequencies: 10,5,2, 

1,0.5,0.2,0.1,0.05,0.02, and 0.01 Hz. 

As the test specimen is sheared, it seeks to dilate, which increases its height. The vertical 

actuator uses the signal from the axial LVDT to apply sufficient axial stress to keep the 

specimen height constant. The test is performed at different temperatures depending on 

whether a Level 2 or 3 design is being performed. The following table outlines test 

parameters. 

Archived
VII. Performance Testing -- 

Table VII-6. Frequency Sweep Test Parameters 

I Mix Design Level I Temperature, OC I 

During the test axial and shear loads and deformations are measured and recorded. 

Figure VII-13 illustrates the application of shearing strains and axial stresses during the 

test. 

Shear Strain, % 100 cycles 

Axial Stress, kPa , variable magnitude 

Time 

Figure VII-13. Shear Strain and Axial Stress Applications in 

Frequency Sweep Test at Constant Height 

INDIRECT TENSILE TESTER 

The IDT is a device that measures the creep compliance and strength of asphalt mixtures 

using indirect tensile loading techniques at intermediate to low temperatures (< 20" C). 

Indirect tensile testing involves applying a compressive load across the 

Archived

diametrical axis of 
VII. Performance Testing 

a cylindrical specimen (Figure VII-14). The mechanics of the test are such that a nearly 

uniform state of tensile stress is achieved across the diametrical plane. 

load 

test \ compression tension 

load 

stress distribution across 

diametral plane 

Figure VII-14. Indirect Tensile Test 

The IDT device has four components: the testing apparatus, the test control unit and data 

acquisition system, load measuring device, and the environmental control chamber. 

Testing Apparatus 

The testing apparatus consists of a closed-loop electrohydraulic, servohydraulic, or 

mechanical screw system capable of resolving static loads as low as 5 N. A rigid loading 

frame is also necessary so that precise displacement measurements can be made without 

frame compliance contributing to displacement measurements. 

Control Unit and Data Acquisition System 

The reaction of specimens to load can be captured by means of a multi-channel strip chart 

recorder 

Archived

or an analog to digital data acquisition device. 
VIZ. Performance Testing 

Load Measuring Device 

Applied loads are measured and controlled by means of an electronic load cell. The load 

cell resides between the loading piston and loading platen. It accurately measures the 

load applied to the test specimen. 

Environmental Control Chamber 

The environmental chamber controls test specimen temperature during the test. It must 

be able to accurately control temperature in the range from -20" to 20" C and have 

sufficient room to accommodate at least three test specimens and the loading frame. 

Specimen Preparation and Instrumentation 

The first step in specimen preparation is to trim test specimens to a thickness such that 

their thickness to diameter ratio is greater than 0.33. For a 150 mm diameter specimen, 

the minimum specimen thickness is 50 mm. Specimens must also be trimmed so that 

they posses smooth, parallel surfaces onto which measurement gauges can be mounted. 

The response of test specimens to load is measured by LVDTs mounted to the face of the 

specimen (Figure VII- 15). Two LVDTs are mounted at right angles on each side of the 

specimen for a total of four mounted LVDTs. The LVDTs are mounted very close to the 

surface of the specimen, in no case greater than 6 mm. 

, test specimen \ 6 mm max 

' LVDTs / 

Front View Side View 

Figure VII-15. Specimen Instrumentation for IDT 

Archived
VII. Performance Testing 

Test Procedures 

Two tests are performed using the IDT: 

IDT Creep Compliance and Strength at Low Temperatures and 

0 IDT Strength at Intermediate Temperatures. 

A brief description of each test follows. 

IDT Creep Compliance and Strength (Low Temperature Cracking Analysis) 

This test is used to analyze mixtures for low temperature cracking. It is performed at 

three temperatures for both levels of mixture design. These temperatures are 0°, -lo0, 

and -20" C. 

In the first phase of the test, a static creep load of fixed magnitude is placed on the 

specimen (Figure VII-16). The magnitude of the load should be that which produces 

between 50 and 750 horizontal microstrain in the test specimen during the 100 seconds, 

which is the duration of the creep phase of the test. Vertical and horizontal deformations 

are measured on both sides of the specimen throughout the test. 

0 

Deformation, microstrains 

1 00 

Time, sec 

Figure VII-16. Load Controlled Creep Portion of IDT Test 

Archived
VIZ. Peq4ormance Testing 

At the conclusion of the creep loading period, the specimen is loaded until failure (peak 

load) by applying additional load at a rate of 12.5 mrn per minute. Vertical and horizontal 

movements and load are measured. Measurements are taken until the load has decreased 

to a value of at least 10 percent less than peak load. Figure VII-17 shows the controlled 

deformation portion of the test. 

Vertical Load 

100 

Deformation 

A 

Time. sec 

Figure VII-17. Deformation Controlled Failure Portion of IDT Test 

In Level 2 mixture design, test specimens are tested for creep compliance at 0°, -lo0, and 

-20" C with tensile strength measured only at -10" C. Level 3 mixture design requires 

that creep compliance and tensile strength be measured at all three temperatures. 

IDT Strength (Fatigue Cracking Analysis) 

This test is used to analyze mixtures for fatigue cracking resistance. It is performed at 

various temperatures ranging from -10" to 20" C. Levels 2 and 3 use different 

temperatures 

Archived

at which to acquire data as shown in Table VII-7. 
VII. Pet$ormance Testing 

Table VII-7. Indirect Tensile Strength Test P rrameters 

In this test, the specimen is loaded at a constant deformation rate of 50 mm per minute of 

vertical ram movement. The specimen is loaded until failure, which is the peak load. 

Load and deformation are measured throughout the test. Figure VII-18 shows the load 

and deformation characteristics of this test. 

Mix Design Level 

2 

3 

Vertical Load 

Temperature, "C 

TedFC) 

- 10,4,20 

Deformation 

0 

Time, sec 

Figure VII-18. Load and Deformation Characteristics of IDT Fatigue 

Cracking Test 

DATA ANALYSIS AND INTERPRETATION 

The data collected from performance testing is used by the performance prediction 

models in Superpave to predict pavement performance for various combinations of 

asphalt binder and mineral aggregate. Performance plots such as those shown in Figures 

VII-19, 20, and 21 are used to select a mixture that offers the desired level of 

performance. In these figures, Materials A, B, and C might be three entirely different 

materials. If so, the performance prediction would be considered part of an analysis 

Archived
VII. Per$ormance Testing 

procedure. This methodology is suited to evaluating the performance effects of aggregate 

types and proportions, asphalt and mixture modifiers, or any other potentially innovative 

HMA ingredient. 

For the materials represented in Figures VII- 19,20, and 2 1, no material meets all the 

distress criteria at the design number of ESALs. However, if distress such as fatigue and 

low temperature cracking were of most concern, Material C would be a clear choice since 

it meets the specified performance values. Unfortunately, Material C would exhibit 

significant rutting after relatively few load applications. Both Materials A and B meet the 

rutting criterion but they fail the cracking criteria. Because fatigue life is greatly affected 

by pavement thickness, it may be possible to slightly increase the layer thickness and so 

that Material B would meet the fatigue cracking criterion. 

Alternatively, Materials A, B, and C might be the same aggregate blend with varying 

asphalt content. Material A has the lowest asphalt content while Material C has the 

highest asphalt content. Material B has a median value of asphalt content. In that case, 

the performance prediction would be considered a design procedure and three additional 

design plots would be useful (Figures VII-22). These design plots would define the range 

of asphalt contents meeting performance standards. In this example, an asphalt content 

approximately two-thirds between B and C would optimize pavement performance. 

This type of information would also be useful in establishing job control tolerances. 

Rut Depth, mm 

Design ESALs 

10 20 30 

ESALs x lo6 

Figure VII-19. Predicted Performance - Permanent Deformation 

Archived
VII. Pe$ormance Testing 

I percent Area (Fatigue Cracking) 

Design ESALs A 

i 

Figure VII-20. Predicted Performance - Fatigue Cracking 

1 crack Spacing, m ti 

Design Life 

L 

5 10 

Years 

Figure 

Archived

VII-21. Predicted Performance - Low Temperature Cracking 
VII. Per$ormance Testing 

Rut Depth, mm 

I 

ABc 

% Asphalt 

Fatigue Low Temp 

Cracking, % Crack Spacing, m 

I 

ABC 

% Asphalt 

ABC 

% Asphalt 

Figure VII-22. Design Chart 

Archived
APPENDIX A: SUPERPAVE ASPHALT BINDER 

SPECIFICATION 

Archived
Performance Graded Binder Specification 

Average 7-day Maximum Pavement 42 

Design Temperature, "C a 

Performance Grade PG 52 

Minimum Pavement Design 

Temperature, "C a 

Pressure Aging Vessel Residue (PP1) 

Original Binder 

PAV Aging Temperature, "cd I 90 I 100 I 100 

PG 58 

Hash Point Temp, T48: Minimum "C 

Viscosity, ASTM D 4402: b 

Maximum, 3 Pas (3000 cP), 

Test Temp, OC 

Dynamic Shear, TP5: 

G*/sin 6, Minimum, 1.00 kPa 

Test Temperature @ 10 radh, "C 

>-lo 

I 

( 

Notes: 

PG 64 

230 

135 

Dynamic Shear, TP5: 

G*sin6~Maximum*5000kPa 

Test Temp @ 10 radlsec, "C 

PG 70 

>-I6 >-I6 

52 

Rolling Thin Film Oven (T24O) or Thin Film Oven (T179) Residue 

a. Pavement temperatures can be estimated from air temperatures using an algorithm contained in the SUPERPAVE software program or may be provided by 

the specifying agency, or by following the procedures as outlined in PPX. 

Mass Loss, Maximum, % 

Dynamic Shear, TP5: 

G*/sin 8, Minimum, 2.20 kPa 

Test Temp @ 10 radlsec, "C 

Physical Hardening 

Creep Stiffness, TPI: 

S, Maximum, 300 MPa 

m-value, Minimum, 0.300 

Test Temp, @ 60 sec, "C 

Direct Tension, TP3: 

Failure Strain, Minimum, 1.0% 

Test Temp @ 1.0 mmlmin, OC 

b. This requirement may be waived at the discretion of the specifying agency if the supplier warrants that the asphalt binder can be adequately pumped and 

mixed at temperatures that meet all applicable safety standards. 

>-22 >-22 >-I6 

58 

0 

c. For quality control of unmodified asphalt cement production, measurement of the viscosity of the original asphalt cement may be substituted for dynamic 

shear measurmeents of G*/sin 6 at test temperatures where the asphalt is a Newtonian fluid. Any suitable standard means of viscosity measurement may be 

used, including capillary or rotational viscometry (AASHTO T 201 or T 202). 

>-lo 

1 .OO 

25 

d. The PAV aging temperature is based on simulated climatic conditions and is one of three temperatures 90" C, 100" C or 110" C. The PAV aging 

temperature is 100" C for PG 58- and above, except in desert climates, where it is 110" C. 

>-28 2-28 >-22 

64 

52 

13 25 

e. Physical Hardening - TP 1 is performed on a set of asphalt beams according to Section 13.1, except the conditioning time is extended to 24 hrs + 10 

minutes at 10' C above the minimum performance temperature. The 24-hour stiffness and m-value are reported for information purposes only. 

>-I6 

70 

22 

f. If the creep stiffness is below 300 MPa, the direct tension test is not required. If the creep stiffness between 300 and 600 MPa the direct tension failure 

strain requirement can be used in lieu of the creep stiffness requirement. The m-value requirement must be satisfied in both cases. 

>-34 >-34 >-28 

58 

10 22 28 

2-40 >-22 

19 7 34 

2-40 >-34 2-21 

64 

16 19 25 

>-46 >-40 

70 

16 13 22 19 16 31 28 25 

Archived
APPENDIX B: SUPERPAVE ASPHALT MIXTURE 

GRADATION REQUIREMENTS 

37.5 MM NOMINAL SIZE 

I 1 I Restricted Zone 

Sieve Size (mm) Raised to 0.45 Power 

Sieve, mm 

50 

Control Points 

1 100.0 

Boundary 

Minimum Maximum 

Archived
Appendix B: Superpave Asphalt Mixture Gradation Requirements 

25 MM NOMINAL SIZE 

I I I Restricted Zone I 

Sieve, mm 

100 

90 

80 

ba 70 

'1 60 2 

5 50 

a 

* 40-- B 

30 

20 

10 

0 

Control Points 

- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

I 

Boundary 

Minimum I Maximum 

.075 .3 2.36 4.75 25 37.5 

Archived

Sieve Size Raised to 0.45 Power 
Appendix B: Superpave Asphalt Mixture Gradation Requirements 

19 MM NOMINAL SIZE 

Restricted Zone 

Boundary 

Sieve, mm Control Points Minimum I Maximum 

0' .075 . .3 2.36 19 25 

Archived

Sieve Size Raised to 0.45 Power 
Appendix B: Superpave Asphalt Mixture Gradation Requirements 

12.5 MM NOMINAL SIZE 

Restricted Zone 

Sieve. mm Control Points 

Archived

Sieve Size Raised to 0.45 Power 
Appendix B: Superpave Asphalt Mixture Gradation Requirements 

9.5 MM NOMINAL SIZE 

I Restricted Zone I I I Boundary I Sieve, mm I Control Points I Minimum ( Maximum 

Archived

Sieve Size Raised to 0.45 Power 
Archived
APPENDIX C: SUPERPAVE CONSENSUS 

AGGREGATE REQUIREMENTS 

COARSE AGGREGATE ANGULARITY 

Coarse Aggregate Angularity: 

I fractured face and 80 % has two fractured faces. I 

Traffic, million 

ESALs 

< 0.3 

- >100 I 100/1 00 

FINE AGGREGATE ANGULARITY 

1001100 

Depth from Surface 

Note: "85180 denotes that 85 % of the coarse aggregate has one 

< 100 rnrn 

5 51- 

Fine Aggregate Angularity: 

compacted fine aggregate. 

,> 100 mm 

-ITraffic million, 

ESALs 

< 0.3 

< 1 

< 3 

< 10 

< 30 

< 100 

- > 100 

Depth from Surface 

Note: Criteria are presented as percent air voids in loosely 

45 

45 

45 

45 

< 100 mm 

- 

40 

40 

40 

40 

45 

45 

> 100 mm 

- 

- 

40 

Archived
Appendix C: Superpave Consensus Aggregate Requirements 

FLAT AND ELONGATED PARTICLES 

Flat. Elongated Particles 

I Traffic, million I Percent 

CLAY CONTENT 

ESALs 

< 0.3 

I Clay Content I 

- 

I Traffic, million 

I ESALs I 

Sand Equivalent, minimum 

Archived
APPENDIX D: VOLUMETRIC ANALYSIS OF 

COMPACTED HOT MIX ASPHALT (HMA) 

DESCRIPTION OF TERMS 

Term 

Air Voids 

Voids in the 

Mineral Aggregate 

Effective Asphalt 

Content 

Voids Filled with 

Asphalt 

Aggregate Bulk 

Specific Gravity 

Aggregate Effective 

Specific Gravity 

Asphalt Binder 

Specific Gravity 

Identifier 

Pa or V, 

VMA 

Pbe 

Pfa or VFA 

Description 

total volume of the small air pockets 

between coated aggregate particles; 

expressed as a percentage of the bulk 

volume of the compacted paving mixture 

the volume of inter granular void space 

between the aggregate particles of a 

compacted paving mixture that includes 

the air voids and effective asphalt content; 

expressed as a percentage of the total 

volume of the compacted paving mixture 

the total asphalt content of the paving 

mixture less the portion of asphalt binder 

that is absorbed by the aggregate particles; 

expressed as a percentage of the total 

weight of the compacted paving mixture 

the portion of the VMA that contains 

asphalt binder; expressed as a percentage 

of the total volume of mix or VMA 

the ratio of the mass in air of a unit 

volume of aggregate, including permeable 

and impermeable voids, to the mass of an 

equal volume of water, both at the same 

temperature 

the ratio of the mass in air of a unit 

volume of aggregate, excluding voids 

permeable to asphalt, to the mass of an 

equal volume of water, both at the same 

temuerature 

the ratio of the mass in air of a given 

volume of asphalt binder to the mass of an 

equal volume of water, both at the same 

temuerature 

Archived
Appendix D: Volumetric Analysis of Compacted HMA 

Specific Gravity 

Maximum Specific 

Gravity of the Mix 

the ratio of the mass in air of a given 

volume of compacted HMA to the mass of 

an equal volume of water, both at the 

same temperature 

the ratio of the mass of a given volume of 

HMA with no air voids to the mass of an 

equal volume of water, both at the same 

temperature 

the volume of asphalt binder that has been 

STANDARD CONVENTIONS 

The following conventions are used to abbreviate binder, aggregate, and mixture 

characteristics. 

Specific Gravity (GI Gxy 

x - b =binder 

s = aggregate (i.e., stone) 

m = mixture 

y - b = bulk 

e = effective 

a = _apparent 

m = maximum theoretical 

Mass (P) or Volume (V) Concentration: P,, or Vx, 

x - b = binder 

s = aggregate (i.e., stone) 

a = _air 

y - e = effective 

a = absorbed 

(note: standard conventions 

Archived

do not apply to Vba and Pf,) 
Appendix D: Volumetric Analysis of Compacted HMA 

CALCULATIONS 

The following equations are necessary to compute the volumetric properties of 

compacted HMA: 

Bulk Specific Gravity of the combined aggregate (Gsb): 

where, Pi = percent by mass of each component aggregate in blend 

(note: PI + P2 + Pg = 100) 

Gi = Gsh of each component aggregate in blend 

Effective Specific Gravity (Gse): 

where, Ph = percent by mass total mix of asphalt binder in mix, 

Gh = specific gravity of asphalt binder, and 

G, = maximum theoretical specific gravity of mixture at Pb. 

Maximum Theoretical Specific Gravity (G-): 

Percent Absorbed Asphalt (Pba): 

where 

Archived

Pba = percent absorbed asphalt by total mass of aggregate 
Appendix D: Volumetric Analysis of Compacted HMA 

Percent Effective Asphalt Content (Pbe): 

where, Pb, = percent effective asphalt by total mass of mix, 

Pb = percent asphalt content in mix by mass of total mix, and 

P, = percent aggregate content in mix by mass of total mix. 

Voids in the Mineral Aggregate (VMA): 

where, Gmb = bulk specific gravity of compacted mix. 

Percent Air Voids (Pa): 

(Note: Pa is sometimes abbreviated V,) 

Percent Voids Filled with Asphalt (Pf,): 

VMA - P, 

VMA 

(Note: Pf, is often called VFA) 

Dust Proportion: 

where, P.075 = percent by mass of total aggregate passing 0.075 mm sieve, and 

Pbe = percent effective asphalt content by mass total mix. 

(Note: The 

Archived

0.075 rnm sieve is often called the 75 micron sieve). 
APPENDIX E: OUTLINE OF STEPS IN 

SUPERPAVE LEVEL 1 MIX DESIGN 

I. SELECTION OF MATERIALS 

A. Selection of Asphalt Binder 

1. Determine project weather conditions using weather database 

2. Select reliability 

3. Determine design temperatures 

4. Verify asphalt binder grade 

5. Temperature-viscosity relationship for lab mixing and compaction 

B. Selection of Aggregates 

1. Consensus properties 

a. Combined gradation 

b. Coarse aggregate angularity 

c. Fine aggregate angularity 

d. Flat and elongated particles 

e. Clay content 

2. Agency and Other properties 

a. Specific gravity 

b. Toughness 

c. Soundness 

d. Deleterious materials 

e. Other 

C. Selection of Modifiers 

11. SELECTION OF DESIGN AGGREGATE STRUCTURE 

A. Establish Trial Blends 

1. Develop three blends 

2. Evaluate combined aggregate properties 

B. Compact Trial Blend Specimens 

1. Establish trial asphalt binder content 

a. Superpave method 

b. Engineering judgment method 

2. Establish trial blend specimen size 

3. Determine Ninitial & Ndesign & Nmnximum 

4. Batch trial blend specimens 

5. Compact specimens and generate densification tables 

6. Determine mixture properties (Gmm & Gmb) 

Archived
Appendix E: Outline of Steps in Superpave Level I Mix Design 

C. Evaluate Trial Blends 

Determine %Gmm @ Ninitlal & Ndesip & Nmaximum 

Determine %Air Voids and %VMA 

Estimate asphalt binder content to achieve 4% air voids 

Estimate mix properties @ estimated asphalt binder content 

Determine dust-asphalt ratio 

Compare mixture properties to criteria 

D. Select Most Promising Design Aggregate Structure for Further Analysis 

111. SELECTION OF DESIGN ASPHALT BINDER CONTENT 

A. Compact Design Aggr Structure Specimens Multiple Binder Contents 

1. Batch design aggregate structure specimens 

2. Compact specimens and generate densification tables 

B. Determine Mixture Properties versus Asphalt Binder Content 

1. Determine %Gmm @ Ninitial & Ndesign & Nmaximum 

2. Determine volumetric properties 

3. Determine dust-asphalt ratio 

4. Graph mixture properties versus asphalt binder content 

C. Select Design Asphalt Binder Content 

1. Determine asphalt binder content at 4% air voids 

2. Determine mixture properties at selected asphalt binder content 

3. Compare mixture properties to criteria 

IV. EVALUATION OF MOISTURE SENSITIVITY OF DESIGN 

ASPHALT MIXTURE USING AASHTO T283 

Archived
APPENDIX F: TESTING REQUIREMENTS FOR 

SUPERPAVE 

SUPERPAVE LEVEL 1 

Design Aggregate Structure 

I Blend 1 Blend 2 Blend 3 

Rep 1 

Rep 2 

x 1 

Design Binder Content I 

I - 0.5% Est. Optimum +0.5% +1.0% 

Rep 1 

Rep 2 

x 1 

AASHTO T283 

Wet 

x 1 

Total Specimens = 20 

Archived
Appendix F: Testing Requirements for Superpave 

SUPERPAVE LEVEL 2 

I 

Simple Shear & Frequency Sweep 

at T,(PD) and Teff(FC) 

I high - a/c medium a/c low a/c 

Rep 1 

Rep 2 x 1 

Repeated Shear Constant 

Stress Ratio at T, 

I high a/c 

Rep 1 

Rep 2 

x 1 

Indirect Tensile Strength at T,&C) 

high a/c medium a/c low a/c 

Rep 1 

Rep 2 

x 1 

Indirect Tensile Creep Compliance 

and Strength at 0, -10, and -20 C / 

I high - a/c medium a/c low a/c 

Rep 1 

Rep 2 

Rep 3 

x 1 

test strength at -1 0 C only 

Total Specimens = 23 

Archived
Appendix F: Testing Requirements for Superpave 

SUPERPAVE LEVEL 3 I Simple Shear & Frequency Sweep at 4,20,40 C 

I high a/c medium a/c low a/c 

Rep 1 

k 

Rep 2 \ use same specimen 

at each of three temps 

I high a/c medium a/c low a/c r 

Rep 1 

Rep 2 

x I 

I high a/c 

Rep 1 

Rep 2 

x l 

Indirect Tensile Strength at -10,4,20 C 

I high a/c medium a/c low a/c 

Indirect Tensile Creep Compliance 

and Strength at 0, -10, and -20 C - 

I high - a/c medium a/c low a/c 

Rep 1 

use different specimens 

at each of three temps 

Archived

Total Specimens = 59 
Archived
1. R. J. Cominsky, G. A. Huber, T. W. Kennedy, and R. M. Anderson, "The Superpave 

Mix Design Manual for New Construction and Overlays," Strategic Highway 

Research Program, SHRP-A-407, 1994. This is an important manual that describes 

the details of Superpave mix design and analysis, It is essential for those who are 

interested in or will be intimately involved in mix designs of the future. 

2. T. W. Kennedy, G. A. Huber, E. T. Harrigan, R. J. Cominsky, C. S. Hughes, H. L. 

Von Quintus, and J. S. Moulthrop, "Superior Performing Asphalt Pavements 

(Superpave): The Product of the SHRP Asphalt Research Program," Strategic 

Highway Research Program, SHRP-A-410, 1994. This report provides a broad 

overview of the Superpave system including binder and mixture analysis. It explains 

special approaches necessary in Superpave for handling modified binder and mixture 

systems. 

3. G. A. Huber, "Weather Database for the Superpave Mix Design System," Strategic 

Highway Research Program, SHRP-A-648A, 19%. This report describes how 

weather station data is used for the purpose of Superpave binder selection. It lists 

binder selection weather database parameters for 531 3 United States and 151 5 

Canadian weather stations. This is an important information source for those 

interested in understanding weather based Superpave binder selection. 

4. R. J. Cominsky, R. B. Leahy, and E. T. Harrigan, "Level One Mix Design: Materials 

Selection, Compaction, and Conditioning," Strategic Highway Research Program, 

SHRP-A-408, 1994. This report describes the background of many features found in 

Superpave Level 1 mix design. It relates important information pertaining to 

aggregate selection, gyratory compaction, aging, and moisture sensitivity. 

5. J. D'Angelo, J. R. Bukowski, and T. Harman, "Superpave Level 1 Mixture Design 

Workshop, Illinois #9402B," Federal Highway Administration, Office of Technology 

Applications, Demonstration Project No. 90, July 1994. This report, developed by 

FHWADTA, provides very useful, practical Level 1 mix design information. It also 

provides a good list of standard AASHTO and ASTM test procedures forpe$orming 

Superpave mix design. It is available through FHWmTA. 

6. D. A. Anderson, D. W. Christensen, H. U. Bahia, R. Dongre, M. G. Sharma, C. E. 

Antle, and J. Button, "Binder Characterization and Evaluation, Volume 3: Physical 

Characterization," Strategic Highway Research Program, SHRP-A-369, 1994. This 

report explains the science and engineering behind the Superpave method of binder 

characterization. It is a very important resource for those who are interested in 

understanding more about asphalt binder rheology, particularly as generalized by the 

Superpave system. 

Archived
Bibliography 

7. R. L. Lytton, J. Uzan, E. G. Fernando, R. Roque, D. Hiltunen, and S. M. Stoffels, 

"Development and Validation of Performance Prediction Models and Specifications 

for Asphalt Binders and Paving Mixes," Strategic Highway Research Program, 

SHRP-A-357, 1993. This report explains the methodology and theory of the 

pavement per3cormance prediction algorithms in Superpave Levels 2 and 3 mix design. 

It is a must for those who intend to use this important new tool for asphalt mix design 

and analysis. 

8. R. B. Leahy and H. L. Von Quintus, "Validation of Relationships Between 

Specification Properties and Performance," Strategic Highway Research Program, 

SHRP-A-409, 1994. This report outlines the two-stage process and results used to 

validate Superpave binder and mixture tests and specifications. 

9. E. T. Harrigan, R. B. Leahy, and J. S. Youcheff, "The Superpave Mix Design System 

Manual of Specifications, Test Methods, and Practices," Strategic Highway Research 

Program, SHRP-A-379, 1994. This report lists the Superpave binder and mixture 

tests as produced by SHRP researchers. It is a valuable tool for practitioners who 

desire to know the exact protocols recommended by SHRP researchers. However, 

users are cautioned that many changes have occurred to these test procedures as they 

have been adopted by AASHTO. 

10. The Asphalt Institute, "Mix Design Methods for Asphalt Concrete and Other Hot-Mix 

Types," Manual Series No. 2 (MS-2), Sixth Edition, 1993. While this manual is 

mostly devoted to Marshall and Hveem methods of mix design, its chapter on 

volumetric properties of compactedpaving mixes remains one of the best available 

sources on this important subject. 

SHRP publications are available through the Transportation Research Board, 

Archived
Archived
Printed By 

Federal Highway Administration 

Office of Technology Applications 

US. Department of Transportation 

400 Seventh Street, SW 

Washington, D.C. 20590 

Archived