03 rita leahy
DESCRIPTION
Presentation delivered by Rita Leahy of CalAPA at the California Asphalt Pavement Association Spring Conference April 25, 2013 in Ontario, CA.TRANSCRIPT
Superpave – Historical Perspective
Rita B Leahy, PhD, PETechnical ConsultantCalAPA
Superpave
Superior Performing Asphalt PavementProduct of SHRP –
●Strategic Highway Research Program1989 – 1993$150 Million$50 Million on ASPHALT!
Superpave 1993
Materials Selection Design Aggregate Structure
Design Binder ContentMoisture Sensitivity
Superpave 1993
Level 1 (Volumetric) Mix Design
●Materials Selection►Aggregate consensus properties►PG asphalt binder specification
Superpave 1993
Level 1 (Volumetric) Mix Design
●Design Aggregate Structure and Design Asphalt Binder Content►Using Superpave Gyratory Compactor (SGC)
Original Ndesign Table
7-Day Maximum Air Temp (°C)
Traffic(106 ESALs)
< 39 39 – 40 41 - 42 43 - 44
< 0.3 68 74 78 820.3 – 1 76 83 88 931 – 3 86 95 100 1053 – 10 96 106 113 11910 – 30 109 121 128 13530 – 100 126 139 146 153
> 100 142 158 165 172
7 Traffic Categories x 4 Climate Regimes = 28 Compaction Levels!
Superpave 1993
Level 1 (Volumetric) Mix Design
●Moisture Sensitivity Evaluation►AASHTO T-283 (Modified Lottman)
Superpave 1993
Superpave Level 2/3 Mix Design
●Performance-Based Mix Tests►Superpave Shear Tester
▪Rutting & Fatigue►Indirect Tensile Tester
▪Low temp cracking
●Performance Prediction Models
Superpave 1993
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
Superpave 2013 – Ndesign Table
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!
Superpave 2013
Revised Ndesign Table
●Lower compaction
►Higher binder content better durability
►Aggregate structure (coarse, gap-graded mixes to finer, dense-graded mixes)
reduced permeability
WMA
Superpave 2013
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
Superpave 2013
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?
Superpave – 1993 to 2013
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