03 rita leahy

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