Dynamic Modulus Testing of Asphalt Mixtures

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Dynamic Modulus Testing of Asphalt Mixtures

Mihai O. Marasteanu Tim Clyne

University of Minnesota

Introduction Superpave mix design procedure 9Product of SHRP Different design levels based on traffic level 9Volumetric mix design ( 107 ESALS)

Introduction Superpave volumetric mix design 9No mechanical test to check performance!!! Marshall method included mechanical test In the past years comprehensive research efforts to develop 9A simple performance test (SPT) 9To provide material parameters for use in pavement design (AASHTO 2002)

Introduction Recent research efforts (NCHRP 9-19, 1-37A) indicate that 9Complex Dynamic Modulus is a strong candidate for both pavement design and SPT

Complex Dynamic Modulus Not a new concept (Papazian, 1962) Different research projects over the years 9Various combinations of frequencies and temperatures 9Compression, tension-compression, tension Most comprehensive in the past years 9Professor Witzack and his research team Compression Uniaxial loading Triaxial loading

Background Based on linear viscoelasticity concepts 9Controlled sinusoidal load applied to cylindrical specimen 9Deformation (strain) measured at different locations on the sample 9Two fundamental parameters determined The absolute value |E*| Phase angle,

Test Setup 2 LVDTs 4 specimens

3 LVDTs 2 specimens

Experimental Data0.1 Hz @ 24.3C 2.5 0.145 Extensometer Displacement, mm 0.140 2.0 0.135 0.130 Force, kN 1.5 0.125 0.120 0.115 0.5 0.110 0.105 0.0 100.2 105.2 110.2 115.2 120.2 125.2 130.2 135.2 140.2 145.2 150.2 155.2 Time, sec 0.100

1.0

Sample Preparation Sample preparation under comprehensive investigation (NCHRP 9-29) Typical gyratory sample not homogeneous 9Density gradients Across diameter (Surface vs. Interior) 9 Top and bottom vs. Interior Coring procedure recommended: 9Prepare tall 6 gyratory specimen 9Obtain 4 by 6 tall test specimen

Sample Preparation

Sample Preparation Coring procedure 9Difficult to perform Possible solution 9Use slender 4 mold

AASHTO 2002 Dynamic modulus of asphalt mixtures 9Critical parameter in the design Difficult to obtain in the laboratory 9Link it to properties of components Components properties easier to determine Witczak predictive equation 9Regression techniques developed from 2750 measurements 205 different asphalt mixtures

Mixture Master Curve

Simple Performance Test W1: SPT for Permanent Deformation Based Upon Static Creep/Flow Time Strength W2: SPT for Permanent Deformation Based Upon Repeated Load Test X1: SPT for Permanent Deformation Based Upon Dynamic Modulus X2: SPT for Fatigue Cracking Based Upon Dynamic Modulus A1: Dynamic Modulus of Asphalt Mixtures and Master Curves

SPT Selection Recent study shows that 9|E*| from unconfined test performed at 54.4C correlates best with rutting Confinement may be required for SMA and open-graded mixtures 9|E*| good indicator of fatigue cracking 9|E*| not a good indicator for thermal cracking Need Fracture Mechanics

Conclusions Dynamic Complex Modulus critical parameter for design and specifications Sample preparation and testing protocol detailed in AASHTO draft test protocols 9Coring vs. slender mold Extensive validation required 9Predictive equation 9Design parameter 9Performance specification

Thank You