The document discusses the development of the Superpave asphalt pavement mix design system. It describes how the Strategic Highway Research Program from 1989-1993 invested $150 million, including $50 million to improve asphalt mix design. The Superpave system introduced a two-level mix design approach involving volumetric mix design specifications at Level 1 and performance testing of rutting, fatigue, and low-temperature cracking at Level 2. Over time, revisions have been made to reduce compaction levels, allow for increased reclaimed asphalt, and incorporate warm mix asphalt and additional performance tests.

2.  Superior Performing Asphalt Pavement
 Product of SHRP –
●Strategic Highway Research Program
 1989 – 1993
 $150 Million
 $50 Million on ASPHALT!

3. Materials Selection
Design Aggregate Structure
Design Binder Content
Moisture Sensitivity

4.  Level 1 (Volumetric) Mix Design
●Materials Selection
►Aggregate consensus properties
►PG asphalt binder specification

5.  Level 1 (Volumetric) Mix Design
●Design Aggregate Structure and Design
Asphalt Binder Content
►Using Superpave Gyratory Compactor
(SGC)

6. 7-Day Maximum Air Temp (°C)
Traffic
(106 ESALs)
< 39 39 – 40 41 - 42 43 - 44
< 0.3 68 74 78 82
0.3 – 1 76 83 88 93
1 – 3 86 95 100 105
3 – 10 96 106 113 119
10 – 30 109 121 128 135
30 – 100 126 139 146 153
> 100 142 158 165 172
7 Traffic Categories x 4 Climate Regimes
= 28 Compaction Levels!

7.  Level 1 (Volumetric) Mix Design
●Moisture Sensitivity Evaluation
►AASHTO T-283 (Modified Lottman)

8.  Superpave Level 2/3 Mix Design
●Performance-Based Mix Tests
►Superpave Shear Tester
▪Rutting & Fatigue
►Indirect Tensile Tester
▪Low temp cracking
●Performance Prediction Models

9.  Observations with implementation
●Reduce Ndesign for base mixes
●Reduce the number of traffic levels
●Ndesign yielding low binder contents
●Constructability problematic
●Reduce Ndesign for low volume roads

10. ESAL
(106) Ninitial Ndesign Nmax
< 0.3 6 50 75
0.3 to <3 7 75 115
3 to <30 8 100 160
≥30 9 125 205
Based on independent work by NCAT and Asphalt Institute
4 Compaction Levels!

11.  Revised Ndesign Table
● Lower compaction
►Higher binder content  better durability
►Aggregate structure (coarse, gap-graded
mixes to finer, dense-graded mixes)
 reduced permeability
 WMA

12.  RAP and RAS
●Increased use in recent years (no
provisions for using RAP in original
Superpave mix designs)
 Moisture Sensitivity
●Still AASHTO T283
●Greater reliance on other tests –
Hamburg Wheel Tracking Test

13.  Performance Testing
● Simple Shear Tester (SST)
● AMPT (Asphalt Mixture Performance Tester)
►Flow Number for Rutting
►Dynamic Modulus for Stiffness
►Cyclic Fatigue
● Flexural Beam Fatigue
 Performance Prediction
● MEPDG? CalME?

14.  Volumetric Mix Design
● Reduced Ndesign Levels
● Coarser to Finer Mixes
● Higher Binder Contents
● AASHTO T283 and/or Hamburg
● RAP, RAS & WMA
 Performance Testing
 Performance Prediction