Dynamic Modulus Testing of Dynamic Modulus Testing of

Asphalt MixturesAsphalt Mixtures

Mihai O. MarasteanuTim Clyne

University of Minnesota

IntroductionIntroduction

Superpave mix design procedureProduct of SHRP

Different design levels based on traffic levelVolumetric mix design (<106 ESALS)Intermediate analysis (up to 107 ESALS)Complete analysis (> 107 ESALS)

IntroductionIntroduction

Superpave volumetric mix designNo mechanical test to check performance!!!–Marshall method included mechanical test

In the past years comprehensive research efforts to develop

A simple performance test (SPT)To provide material parameters for use in

pavement design (AASHTO 2002)

Introduction Introduction

Recent research efforts (NCHRP 9-19, 1-37A) indicate that

Complex Dynamic Modulus is a strong candidate for both pavement design and SPT

Complex Dynamic ModulusComplex Dynamic Modulus

Not a new concept (Papazian, 1962)Different research projects over the years

Various combinations of frequencies and temperaturesCompression, tension-compression, tension

Most comprehensive in the past yearsProfessor Witzack and his research team–Compression

– Uniaxial loading– Triaxial loading

BackgroundBackground

Based on linear viscoelasticity conceptsControlled sinusoidal load applied to cylindrical

specimenDeformation (strain) measured at different

locations on the sampleTwo fundamental parameters determined–The absolute value |E*|–Phase angle, δ

Test SetupTest Setup

2 LVDT’s4 specimens

3 LVDT’s2 specimens

Experimental DataExperimental Data0.1 Hz @ 24.3°C

0.0

0.5

1.0

1.5

2.0

2.5

100.2 105.2 110.2 115.2 120.2 125.2 130.2 135.2 140.2 145.2 150.2 155.2Time, sec

Forc

e, k

N

0.100

0.105

0.110

0.115

0.120

0.125

0.130

0.135

0.140

0.145

Exte

nsom

eter

Dis

plac

emen

t, m

m

Sample PreparationSample PreparationSample preparation under comprehensive investigation (NCHRP 9-29)Typical gyratory sample not homogeneous

Density gradients–Across diameter (Surface vs. Interior)Top and bottom vs. Interior

Coring procedure recommended:Prepare tall 6” gyratory specimenObtain 4” by 6” tall test specimen

Sample PreparationSample Preparation

Sample PreparationSample PreparationCoring procedure

Difficult to performPossible solution

Use slender 4” mold

AASHTO 2002AASHTO 2002

Dynamic modulus of asphalt mixturesCritical parameter in the design

Difficult to obtain in the laboratoryLink it to properties of components–Components properties easier to determine

Witczak predictive equationRegression techniques developed from–2750 measurements–205 different asphalt mixtures

Mixture Master CurveMixture Master Curve

Simple Performance TestSimple Performance Test

W1: SPT for Permanent Deformation Based Upon Static Creep/Flow Time StrengthW2: SPT for Permanent Deformation Based Upon Repeated Load TestX1: SPT for Permanent Deformation Based Upon Dynamic ModulusX2: SPT for Fatigue Cracking Based Upon Dynamic ModulusA1: Dynamic Modulus of Asphalt Mixtures and Master Curves

SPT SelectionSPT Selection

Recent study shows that|E*| from unconfined test performed at 54.4C

correlates best with rutting–Confinement may be required for SMA and open-graded mixtures|E*| good indicator of fatigue cracking|E*| not a good indicator for thermal cracking–Need Fracture Mechanics

ConclusionsConclusions

Dynamic Complex Modulus critical parameter for design and specificationsSample preparation and testing protocol detailed in AASHTO draft test protocols

Coring vs. slender mold Extensive validation required

Predictive equationDesign parameterPerformance specification

Thank YouThank You