influence of warm mix asphalt on aging of asphalt binders...binders, and atomic force microscopy...

Influence of Warm Mix Asphalt on Aging of Asphalt Binders

Ala R. Abbas, Munir Nazzal, Savas Kaya,

Sunday Akinbowale, Bijay Subedi, Lana Abu Qtaish, and Mir Shahnewaz Arefin

for the

Ohio Department of Transportation Office of Statewide Planning and Research,

Research Section

and the U. S. Department of Transportation

Federal Highway Administration

State Job Number 134707

November 2014

1. Report No.

FHWA/OH-2014/13

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and subtitle


5. Report Date

November 2014

6. Performing Organization Code

7. Author(s)

Ala R. Abbas, Munir Nazzal, Savas Kaya, Sunday Akinbowale,

Bijay Subedi, Lana Abu Qtaish, and Mir Shahnewaz Arefin

8. Performing Organization Report No.

10. Work Unit No. (TRAIS)

9. Performing Organization Name and Address

The University of Akron

402 Buchtel Common

Akron, OH 44325-2102

11. Contract or Grant No.

SJN 134707

13. Type of Report and Period

Covered

Final Report

12. Sponsoring Agency Name and Address

Ohio Department of Transportation

1980 West Broad Street, MS 3280

Columbus, OH 43223

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

This study evaluated the short-term and long-term aging characteristics of foamed WMA in comparison to

traditional HMA. Two asphalt binders (PG 70-22 and PG 64-22) and one aggregate (12.5 mm NMAS limestone

aggregate) were used in this study. The short-term and long-term aging of the two asphalt binders was simulated using

the rolling thin film oven (RTFO) and pressure aging vessel (PAV), respectively, while AASHTO R 30 was used to

simulate the short-term and long-term aging of the laboratory-prepared asphalt mixtures. The dynamic shear rheometer

(DSR) was used to characterize the viscoelastic behavior of the unaged and aged asphalt binders, Fourier-transform

infrared (FTIR) spectroscopy was used to identify and quantify the amount of functional groups present in the asphalt

binders, gel permeation chromatography (GPC) was used to determine the molecular size distribution within the asphalt

binders, and atomic force microscopy (AFM) was used to examine the effect of aging on the microstructure and

morphology of the asphalt binders. In addition, the dynamic modulus (E*) test was utilized to examine the effect of

aging on the viscoelastic behavior of foamed WMA and HMA mixtures. The dynamic modulus (E*) test was conducted

according to AASHTO T 342. However, it was performed on short-term aged as well as long-term aged foamed WMA

and HMA specimens.

The laboratory testing plan was also designed to quantify the effect of the extraction and recovery procedures

(AASHTO T 164 and AASHTO T 170, respectively) on the two asphalt binders (PG 70-22 and PG 64-22) that were

used in the laboratory-produced asphalt mixtures. In addition, this study investigated the effect of aging on foamed

WMA and HMA mixtures placed in the field. Field cores were collected from four roadway sections in Ohio that were

constructed using both foamed WMA and HMA mixtures prepared using the same materials (asphalt binder and

aggregates), aggregate gradation, and asphalt binder content. All pavement sections were constructed in 2008 as part of

ODOT’s initial field implementation of foamed WMA in Ohio. The asphalt binder was extracted from the field cores

using AASHTO T 164 and recovered using AASHTO T 170. The recovered binders were examined for the same

physical, chemical, and morphological properties using the same test procedures as the laboratory-produced foamed

WMA and HMA mixtures.

17. Key Words

Warm mix asphalt, Hot mix asphalt, Aging,

Dynamic shear rheometer, Fourier-transform infrared

spectroscopy, Gel permeation chromatography.

18. Distribution Statement

No restrictions. This document is available to the public

through the National Technical Information Service,

Springfield, Virginia 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified 21. No. of Pages

99 22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized

Final Report

State Job No. 134707


Prepared by:

Ala R. Abbas, Ph.D.

Sunday Akinbowale, M.S.

Bijay Subedi, B.S.

Mir Shahnewaz Arefin, B.S.

The University of Akron

Department of Civil Engineering

Akron, Ohio 44325

Munir Nazzal, PhD., P.E.

Lana Abu Qtaish, M.S.

Ohio University

Department of Civil Engineering

Athens, Ohio 45701

Savas Kaya, PhD.

Ohio University

Department of Electrical Engineering and Computer Science

Athens, Ohio 45701

Prepared in Cooperation with

The Ohio Department of Transportation

&

The U. S. Department of Transportation

Federal Highway Administration

November 2014

Disclaimer

The contents of this report reflect the views of the authors who are responsible for the

facts and accuracy of the data presented herein. The contents do not necessarily reflect the

official views or policies of the Ohio Department of Transportation (ODOT) or the Federal

Highway Administration (FHWA). This report does not constitute a standard, specification or

regulation.

Acknowledgements

The researchers would like to thank the Ohio Department of Transportation (ODOT) and

the Federal Highway Administration (FHWA) for sponsoring this study. The researchers would

like to extend their thanks to Mr. David Powers and Mr. Eric Biehl of ODOT Office of Materials

Management for their valuable contributions to this report. Without their assistance, this work

would not have been possible.

iv

Table of Contents

Abstract .................................................................................................................................... 1

Chapter 1: Introduction ............................................................................................................ 3

1.1 Problem Statement ....................................................................................................... 3

1.2 Objectives of the Study ................................................................................................ 3

1.3 Report Organization ..................................................................................................... 4

Chapter 2: Literature Review ................................................................................................... 7

2.1 Introduction .................................................................................................................. 7

2.2 Asphalt Binder Chemistry ............................................................................................ 7

2.3 Asphalt Binder Aging .................................................................................................. 10

2.4 Previous Studies on WMA Aging ............................................................................... 12

2.5 Summary ...................................................................................................................... 16

Chapter 3: Testing Plan ............................................................................................................ 17

3.1 Introduction .................................................................................................................. 17

3.2 Laboratory Binder Aging ............................................................................................. 17

3.3 Effect of Binder Extraction and Recovery ................................................................... 19

3.4 Laboratory Mixture Aging ........................................................................................... 20

3.5 Field Mixture Aging .................................................................................................... 22

Chapter 4: Test Methods .......................................................................................................... 24

4.1 Introduction .................................................................................................................. 24

4.2 Laboratory Asphalt Binder Aging Procedures ............................................................. 24

4.3 Laboratory Asphalt Mixture Aging Procedures ........................................................... 26

4.4 Asphalt Binder Extraction and Recovery .................................................................... 27

4.5 Rheological Behavior of Asphalt Binders ................................................................... 29

4.6 Chemical Properties and Morphology of Asphalt Binders .......................................... 30

4.6.1 Fourier Transform Infrared Spectroscopy (FTIR) .............................................. 31

4.6.2 Gel-Permeation Chromatography (GPC) ............................................................ 32

4.6.3 Atomic Force Microscopy (AFM) ...................................................................... 34

4.6.4 X-Ray Diffraction (XRD) ................................................................................... 39

4.7 Dynamic Modulus Testing of Foamed WMA and HMA Mixtures ............................. 40

Chapter 5: Results and Discussion ........................................................................................... 44

5.1 Introduction .................................................................................................................. 44

5.2 Laboratory Aging of Asphalt Binders .......................................................................... 44

5.3 Effect of Extraction and Recovery ............................................................................... 51

5.4 Laboratory Aging of Asphalt Mixtures ........................................................................ 55

5.4.1 DSR Test Results ................................................................................................ 55

5.4.2 FTIR Test Results ............................................................................................... 59

5.4.3 GPC Test Results ................................................................................................ 62

5.4.4 AFM Test Results ............................................................................................... 64

5.4.5 Dynamic Modulus Test Results .......................................................................... 67

v

5.5 Field Aging of Asphalt Mixtures ................................................................................. 74

5.5.1 DSR Test Results ................................................................................................ 74

5.5.2 FTIR Test Results ............................................................................................... 75

5.5.3 GPC Test Results ................................................................................................ 75

5.5.4 AFM Test Results ............................................................................................... 76

Chapter 6: Conclusions and Recommendations ...................................................................... 92

6.1 Introduction .................................................................................................................. 92

6.2 Conclusions .................................................................................................................. 93

6.3 Recommendations for Implementation ........................................................................ 96

References ................................................................................................................................ 97

vi

List of Tables

Table 2.1: Elemental Analysis of Selected Asphalt Binders (Peterson 1984) ......................... 8

vii

List of Figures

Figure 2.1: Example of Carbon-Carbon Bonds in an Asphalt Molecule

(Jennings et al. 1993) ......................................................................................................... 8

Figure 2.2: Basic Components of Asphalt Binders (Roberts et al. 1996) ................................ 9

Figure 2.3: Asphalt Binder Components ................................................................................. 9

Figure 2.4: Oxidation Reaction in Asphalt Binders ................................................................. 11

Figure 2.5: Chemical Groups in Asphalt Molecules Normally Present or Formed Due

to Oxidation (Peterson 2009) ............................................................................................. 11

Figure 3.1: Laboratory Testing Plan ........................................................................................ 17

Figure 3.2: Laboratory Binder Aging ...................................................................................... 18

Figure 3.3: Effect of Binder Extraction and Recovery ............................................................ 19

Figure 3.4: Laboratory Mixture Aging .................................................................................... 20

Figure 3.5: Aggregate Gradation ............................................................................................. 21

Figure 3.6: Laboratory-Scale Asphalt Binder Foaming Device .............................................. 22

Figure 3.7: Field Mixture Aging .............................................................................................. 23

Figure 4.1: Despatch Rolling Thin Film Oven (RTFO) .......................................................... 25

Figure 4.2: Applied Test System (ATS) Pressure Aging Vessel (PAV) ................................. 25

Figure 4.3: Humboldt 1500 g Centrifuge Extractor ................................................................. 27

Figure 4.4: Humboldt Filterless Centrifuge Extractor ............................................................. 28

Figure 4.5: Abson Recovery Distillation Assembly ................................................................ 28

Figure 4.6: ARES Dynamic Shear Rheometer (DSR) ............................................................. 30

Figure 4.7: Fourier Transform Infrared Spectroscopy Setup (www.thermonicolet.com) ....... 31

Figure 4.8: Digilab Excalibur Series FTIR Spectrometer ........................................................ 32

Figure 4.9: Gel-Permeation Chromatography Setup (Striegel et al. 2009) .............................. 33

Figure 4.10: Malvern Viscotek GPC with Waters 2414 Refractive Index Detector ............... 34

Figure 4.11: Agilent 5500LS Atomic Force Microscope ........................................................ 35

Figure 4.12: Atomic Force Microscopy (AFM) Test Sample .................................................. 36

Figure 4.13: AFM Force Spectroscopy (www.agilent.com) .................................................... 37

Figure 4.14: Typical Force-Distance Curve Obtained in a Force Spectroscopy

Experiment ......................................................................................................................... 38

http://www.thermonicolet.com/

http://www.agilent.com/

viii

Figure 4.15: Estimation of Ebonding from a Force-Distance Curve ........................................... 39

Figure 4.16: Rigaku Miniflex XRD System ............................................................................ 40

Figure 4.17: Wrapping of Dynamic Modulus Specimens with Thin Aluminum Sheets

Prior to Long-Term Aging ................................................................................................. 42

Figure 4.18: Material Test System (MTS) Model 810 ............................................................ 43

Figure 5.1: DSR Test Results for Unaged, RTFO-aged, and PAV-aged PG 70-22

at High and Intermediate Temperatures ............................................................................. 46

Figure 5.2: DSR Test Results for Unaged, RTFO-aged, and PAV-aged PG 64-22

at High and Intermediate Temperatures ............................................................................. 47

Figure 5.3 FTIR Spectra for Unaged, RTFO-aged, and PAV-aged PG 70-22 ........................ 48

Figure 5.4 FTIR Spectra for Unaged, RTFO-aged, and PAV-aged PG 64-22 ........................ 48

Figure 5.5: GPC Chromatograms for Unaged, RTFO-aged, and PAV-aged PG 70-22 .......... 49

Figure 5.6: GPC Chromatograms for Unaged, RTFO-aged, and PAV-aged PG 64-22 .......... 49

Figure 5.7: AFM Force-Distance Curves for Unaged, RTFO-aged, and PAV-aged

PG 70-22 ............................................................................................................................ 50

Figure 5.8: AFM Force-Distance Curves for Unaged, RTFO-aged, and PAV-aged

PG 64-22 ............................................................................................................................ 50

Figure 5.9: Effect of Extraction and Recovery on DSR Test Results for Unaged,

RTFO-aged, and PAV-aged PG 70-22 .............................................................................. 52

Figure 5.10: Effect of Extraction and Recovery on DSR Test Results for Unaged,

RTFO-aged, and PAV-aged PG 64-22 .............................................................................. 53

Figure 5.11 XRD Test Results for Limestone Dust ................................................................. 54

Figure 5.12: XRD Test Results for Unaged, RTFO-aged, and PAV-aged PG 70-22

Binders Recovered from TCE/Binder Solutions without Dust .......................................... 54

Figure 5.13: XRD Test Results for Unaged, RTFO-aged, and PAV-aged PG 70-22

Binders Recovered from TCE/Binder Solutions Containing Dust .................................... 55

Figure 5.14: Comparison of DSR Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 70-22 ........................................................................................................... 57

Figure 5.15: Comparison of DSR Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 64-22 ........................................................................................................... 58

ix

Figure 5.16: Comparison of FTIR Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 70-22 ........................................................................................................... 60

Figure 5.17: Comparison of FTIR Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 64-22 ........................................................................................................... 61

Figure 5.18: Analysis of GPC Data to Obtain Large, Medium, and Small Molecular

Size Fractions ..................................................................................................................... 62

Figure 5.19: Comparison of GPC Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 70-22 ........................................................................................................... 63

Figure 5.20: Comparison of GPC Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 64-22 ........................................................................................................... 63

Figure 5.21: Comparison of AFM Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 70-22 ........................................................................................................... 65

Figure 5.22: Comparison of AFM Test Results for Asphalt Binder and Asphalt Mixture

Aging for PG 64-22 ........................................................................................................... 66

Figure 5.23: |E*| of STOA HMA and Foamed WMA Mixtures Prepared using PG 70-22 .... 69

Figure 5.24: |E*| of LTOA HMA and Foamed WMA Mixtures Prepared using PG 70-22 .... 69

Figure 5.25: |E*| of STOA HMA and Foamed WMA Mixtures Prepared using PG 64-22 .... 70

Figure 5.26: |E*| of LTOA HMA and Foamed WMA Mixtures Prepared using PG 64-22 .... 70

Figure 5.27: |E*|LTOA/|E*|STOA for HMA and Foamed WMA Mixtures Prepared using

PG 70-22 ............................................................................................................................ 71

Figure 5.28: |E*|LTOA/|E*|STOA for HMA and Foamed WMA Mixtures Prepared using

PG 64-22 ............................................................................................................................ 71

Figure 5.29: Dynamic Modulus Master Curve for STOA and LTOA Foamed WMA

Mixtures Prepared using PG 70-22 (Reference Temperature of 70oF) .............................. 72

Figure 5.30: Dynamic Modulus Master Curve for STOA and LTOA HMA


Figure 5.31: Dynamic Modulus Master Curve for STOA and LTOA Foamed WMA


Figure 5.32: Dynamic Modulus Master Curve for STOA and LTOA HMA


x

Figure 5.33: DSR Test Results for PG 70-22 Binder Recovered from Surface Course

of Project No. 329-08 in Miami County ............................................................................ 78


of Project No. 342-08 in Pickaway County ....................................................................... 79


of Project No. 352-08 in Summit County .......................................................................... 80


of Project No. 386-08 in Portage County ........................................................................... 81

Figure 5.37: FTIR Test Results for PG 70-22 Binder Recovered from Surface Course








Figure 5.41: GPC Test Results for PG 70-22 Binder Recovered from Surface Course








Figure 5.45: AFM Test Results for PG 70-22 Binder Recovered from Surface Course






xi



1


Abstract

This study evaluated the short-term and long-term aging characteristics of foamed WMA

in comparison to traditional HMA. Two asphalt binders (PG 70-22 and PG 64-22) and one

aggregate (12.5 mm NMAS limestone aggregate) were used in this study. The short-term and

long-term aging of the two asphalt binders was simulated using the rolling thin film oven

(RTFO) and pressure aging vessel (PAV), respectively, while AASHTO R 30 was used to

simulate the short-term and long-term aging of the laboratory-prepared asphalt mixtures. The

dynamic shear rheometer (DSR) was used to characterize the viscoelastic behavior of the unaged

and aged asphalt binders, Fourier-transform infrared (FTIR) spectroscopy was used to identify

and quantify the amount of functional groups present in the asphalt binders, gel permeation

chromatography (GPC) was used to determine the molecular size distribution within the asphalt

binders, and atomic force microscopy (AFM) was used to examine the effect of aging on the

microstructure and morphology of the asphalt binders. In addition, the dynamic modulus (E*)

test was utilized to examine the effect of aging on the viscoelastic behavior of foamed WMA and

HMA mixtures. The dynamic modulus (E*) test was conducted according to AASHTO T 342

(Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete

Mixtures). However, it was performed on short-term aged as well as long-term aged foamed

WMA and HMA specimens.

The laboratory testing plan was also designed to quantify the effect of the extraction and

recovery procedures (AASHTO T 164 and AASHTO T 170, respectively) on the two asphalt

binders (PG 70-22 and PG 64-22) that were used in the laboratory-produced asphalt mixtures. In

addition, this study investigated the effect of aging on foamed WMA and HMA mixtures placed

in the field. Field cores were collected from four roadway sections in Ohio that were constructed

using both foamed WMA and HMA mixtures prepared using the same materials (asphalt binder

and aggregates), aggregate gradation, and asphalt binder content. All pavement sections were

constructed in 2008 as part of ODOT’s initial field implementation of foamed WMA in Ohio.

The asphalt binder was extracted from the field cores using AASHTO T 164 and recovered using

AASHTO T 170. The recovered binders were examined for the same physical, chemical, and

2

morphological properties using the same test procedures as the laboratory-produced foamed

WMA and HMA mixtures.

The experimental test results showed a slightly lower level of aging for laboratory-

prepared foamed WMA mixtures than for laboratory-prepared traditional HMA mixtures.

However, no consistent differences in the level of aging were observed for foamed WMA and

HMA mixtures placed in the field in 2008. The effect of aging on foamed WMA and HMA

mixtures was observed to be highly influenced by the type of asphalt binder used in the asphalt

mixture more so than the mix type. In this study, foamed WMA and HMA mixtures prepared

using PG 70-22 were found to be more susceptible to aging than foamed WMA and HMA

mixtures prepared using PG 64-22. The asphalt binder extraction and recovery procedures were

also observed to have a significant influence on the rheological properties of the recovered

PG 64-22 asphalt binder and little influence on the rheological properties of the recovered PG

70-22 asphalt binder. Therefore, care should be taken in interpreting the DSR test results for

recovered asphalt binders.

3

Chapter 1

Introduction

1.1 Problem Statement

Warm mix asphalt (WMA) has become more widely adopted in the United States due

to its environmental benefits, energy savings, enhanced compaction, and increased haul

distances. Over the last decade, different types of WMA technologies have been marketed and

used in Ohio. However, foamed WMA produced by water injection has gained popularity among

asphalt mix producers as it allows for the production of WMA with a standard grade asphalt

binder through a one-time mechanical plant modification, eliminating the need for costly

additives associated with other WMA technologies. In recent years, the amount of foamed WMA

used in Ohio has increased from approximately 10,000 tons in 2008 to more than 10,000,000

tons in 2013, which represents nearly 60% of the total amount of asphalt mixtures produced in

the state.

To date, satisfactory performance has been obtained for pavements constructed using

foamed WMA, with minimal issues arising from the reduction of the production temperature.

However, one subject that has not been thoroughly studied that might affect the performance and

durability of foamed WMA is binder aging. Since lower temperatures are used during the

production of foamed WMA, it is generally expected that the asphalt binders in these mixtures

will undergo less aging, leading to lower resistance to permanent deformation but better

resistance to thermal and fatigue cracking than traditional hot mix asphalt (HMA). However, the

difference in aging between foamed WMA and HMA may also be affected by other factors such

as the binder type, aggregate type, aggregate gradation, and air void content within the mix.

Therefore, there is a need to investigate the aging characteristics of foamed WMA mixtures to

better understand their influence on pavement performance.

1.2 Objectives of the Study

The primary objective of this study is to examine the short-term and long-term aging

characteristics of foamed WMA as compared to traditional HMA. The specific objectives

include:

4

Evaluate the rheological, chemical, and morphological properties of unaged and aged asphalt

binders recovered from foamed WMA and HMA mixture at different stages of aging.

Study field aging in foamed WMA and traditional HMA mixtures.

Compare the standard laboratory aging procedures that are used for short-term and long-term

aging of asphalt binders and asphalt mixtures.

Determine the ability of the standard laboratory aging procedures for asphalt binders and

asphalt mixtures to simulate field aging of foamed WMA and HMA mixtures.

1.3 Report Organization

This report is organized into six chapters. Chapter 2 presents an overview of the basic

chemistry of asphalt binders and asphalt binder aging. In addition, it provides a summary of

previous studies on WMA binder and mixture aging. Chapter 3 presents the laboratory testing

plan implemented in this study to examine the short-term and long-term aging characteristics of

foamed WMA as compared to traditional HMA. Chapter 4 provides a discussion of the

experimental test methods included in the laboratory testing plan. It covers the laboratory

simulation of short-term and long-term aging of asphalt binders and asphalt mixtures. This

chapter also discusses the asphalt binder extraction and recovery procedures. In addition, it

presents the experimental test methods that were utilized to characterize the rheological,

chemical, and morphological properties of unaged and aged asphalt binders. Finally, detailed

information is provided in this chapter regarding the dynamic modulus test that was conducted

on short-term and long-term aged foamed WMA and HMA mixtures. Chapter 5 presents the

experimental test results that were obtained as part of the laboratory testing plan. Finally,

Chapter 6 presents the observations and conclusions that were made based on the experimental

test results as well as the recommendations for implementation by ODOT.

7

Chapter 2

Literature Review

2.1 Introduction

A comprehensive literature review was conducted on the subject of asphalt binder and

asphalt mixture aging. Special attention was given to recent studies that examined the aging

characteristics of warm mix asphalt (WMA) binders and mixtures, which is the focus of this

research project. This chapter summarizes the outcome of this literature review. Because the

aging process for asphalt binders and mixtures is dictated by changes in the physical behavior of

asphalt binders, which in turn are a result of changes in the asphalt binders’ chemical and

morphological properties, this chapter also provides an overview of the basic chemistry of

asphalt binders and asphalt binder aging.

2.2 Asphalt Binder Chemistry

Asphalt binder is a highly complex material that results from the distillation of crude oil.

The physical properties of this material are directly related to its chemical composition.

Therefore, to better understand the physical behavior of asphalt binders and predict their

performance, it is necessary to understand their chemical composition and structure.

The chemical composition of an asphalt binder can be characterized at two levels: the

molecular level and the intermolecular level. At the molecular level, the most abundant elements

present are carbon and hydrogen (Table 2.1). As shown in Figure 2.1, the carbon atoms are

linked with each other using three types of bonds: aromatic (stable unsaturated hydrogen-carbon

rings), alicyclic or naphthenic (saturated rings of hydrocarbons), and aliphatic or paraffinic

(straight or branched chains of hydrocarbons). Other elements such as sulfur, nitrogen, and

oxygen are usually present in an asphalt binder molecule in very small amounts. Trace amounts

of heavy metals such as vanadium and nickel can also be present. These additional non-

hydrocarbon elements are called “heteroatoms”. Heteroatoms and other components are attached

to carbon atoms in asphalt molecules in various configurations and in the form of different

compounds. The amount of heteroatoms can vary widely depending on the source of the crude

oil. Although the percentage of heteroatoms in asphalt is very small as compared to that of

hydrocarbons, most of the properties and intermolecular interactions of the asphalt can be

8

attributed to these heteroatoms. Because these configurations contribute to the functionality of

the asphalt molecule, they are commonly referred to as “functional groups.”

Table 2.1: Elemental Analysis of Selected Asphalt Binders (Peterson 1984).

Element B-2959

Mexican Blend

B-3036

Arkansas-Louisiana

B-3051

Boscan

B-3602

California

Carbon, % 83.77 85.78 82.90 86.77

Hydrogen, % 9.91 10.19 10.45 10.93

Nitrogen, % 0.28 0.26 0.78 1.10

Sulfur, % 5.25 3.41 5.43 0.99

Oxygen, % 0.77 0.36 0.29 0.20

Vanadium, ppm 180 7 1380 4

Nickel, ppm 22 0.4 109 6

Figure 2.1: Example of Carbon-Carbon Bonds in an Asphalt Molecule (Jennings et al. 1993).

At the intermolecular level, asphalt is a colloid that contains polar and non-polar

molecules. This colloid has a high-molecular-weight component known as “asphaltene” that is

dispersed within a low-molecular-weight component known as “maltene” (Figures 2.2 and 2.3).

Asphaltene is an insoluble, high-polarity, nonvolatile solid that makes up 5 to 25 % by weight of

an asphalt binder. It plays a major role in building up the hardness and viscosity of asphalt

9

binder. A high asphaltene content generally leads to a high viscosity. Maltene is a soluble, low-

polarity liquid that consists of oil (aromatics and saturates) and resin, which acts as a transition

between the asphaltene and the oil. Research has shown that if the maltene has a high aromatic

content, it disperses the asphaltene better, resulting in high-ductility, low-complexity flows and

lower rates of age hardening. On the other hand, maltene with low aromatic content will result in

the formation of “gel-type” asphalt cement, which has a network-like structure. Gel-type asphalts

have low ductility, increased elasticity, and a higher rate of age hardening.

Figure 2.2: Basic Components of Asphalt Binders (Roberts et al. 1996).

Figure 2.3: Asphalt Binder Components.

Asphalt Binder

Asphaltenes Maltenes

Resins Oils

10

2.3 Asphalt Binder Aging

Asphalt binder aging is a major factor affecting the life span of an asphalt pavement.

Asphalt aging takes place during the production and construction phase (short-term aging) as

well as during the pavement service life (long-term aging). Upon aging, the physical and

chemical properties of the asphalt binder change, causing it to become harder and more prone to

cracking. Any cracks on the pavement surface may accelerate the aging process due to the

increased exposure to air, and may result in further pavement deterioration, leading to premature

pavement failure.

Several processes have been reported to contribute to the age hardening of asphalt

mixtures, including oxidation, volatilization, thixotropy, syneresis, polymerization, and

separation (Roberts et al. 1996). Oxidation is the reaction of asphalt binder with oxygen. It is

believed to be the most important process leading to age hardening. The rate of oxidation

depends on the type of asphalt binder and ambient temperature, with a higher rate of oxidation

taking place during short-term aging than long-term aging. Volatilization is the evaporation of

the lighter constituents of the asphalt binder. It mainly takes place during short-term aging due to

the use of high temperatures in the production of asphalt mixtures. Thixotropy, also referred to as

steric hardening, is caused by the formation of a structure due to hydrophilic suspended particles

within the asphalt binder over a period of time. Thixotropy is generally observed in pavements

with little or no traffic, and can be reversed by reheating and reworking the placed asphalt

mixture. Syneresis is a reaction in which oily liquids are exuded from the asphalt surface,

causing the asphalt binder to become harder. Polymerization is the formation of larger molecules

by combining like molecules, leading to material hardening. This process is not believed to be

significant for asphalt binder aging. Separation is the removal of the oils, resins, or asphaltenes

from the asphalt binder due to the selective absorption by some porous aggregates.

Most of the oxidation in asphalt binders involves changes at the molecular and

intermolecular level. At the molecular level, oxidation causes the formation of organic oxygen

compounds, resulting in an increase in hetero-structures and a decrease in aromatic structures.

The primary compounds that form due to aging are ketones and sulfoxides (Figure 2.4). Extreme

oxidation produces carboxylic anhydrides and a small amount of oxidized species. Figure 2.5

show the natural compounds and oxidized compounds formed in asphalt binders due to aging.

11

Figure 2.4: Oxidation Reaction in Asphalt Binders.

Figure 2.5: Chemical Groups in Asphalt Molecules

Normally Present or Formed Due to Oxidation (Peterson 2009).

As oxygen-containing functional groups are formed in the asphalt molecules during the

process of oxidation, there will be a movement from the nonpolar molecular fractions to the

polar molecular fractions (Peterson 2009). Since the various molecular fractions show different

reactivities toward oxidation, this process will typically result in a net loss of naphthene

aromatics and a possible net loss in polar aromatics, with a corresponding increase in

12

asphaltenes. Therefore, as oxidative aging proceeds, the amount of the larger molecular size

fraction will increase, resulting in an increase in the concentration of solids in the asphalt binder.

From a structural standpoint, the increase in the concentration of solids and the decrease in the

concentration of oils will bring about an increase in the structurization and viscosity of the

asphalt binder. In other words, the change in the viscosity of an asphalt binder due to aging is

caused by an increase in the solid-to-liquid ratio within the asphalt binder, which is directly

related to the asphaltene content.

2.4 Previous Studies on WMA Aging

Over the last three decades, several research studies have been conducted on asphalt

binder and asphalt mixture aging. However, the overwhelming majority of these studies have

focused on hot mix asphalt (HMA). In recent years, the focus has shifted to evaluating the aging

characteristics of warm mix asphalt (WMA) binders and mixtures. The following paragraphs

summarize the outcome of the literature review that was conducted on this subject.

Gandhi and Amirkhanian (2008) evaluated the short-term and long-term aging in two

WMA mixtures prepared using Asphamin and Sasobit in comparison to traditional HMA. The

asphalt mixtures were aged in a forced-draft oven and the asphalt binder was extracted and

recovered for testing. The recovered asphalt binders were tested for viscosity, high and low

temperature properties, and molecular size distribution using gel permeation chromatography. It

was reported that the asphalt binders extracted from the WMA mixtures had a significantly lower

level of aging as compared to those extracted from the control HMA. It was also reported that

that the WMA additives did not have a significant effect on the fatigue cracking parameter

(G*sinδ) or the creep stiffness of the asphalt binders. However, Asphamin was found to

significantly increase the m-value of the asphalt binders.

Gandhi et al. (2009) utilized the rolling thin film oven (RTFO) and the pressure aging

vessel (PAV) to simulate the short-term and long-term aging, respectively, of WMA binders.

Three PG 64-22 asphalt binders and two WMA additives (Asphamin and Sasobit) were used in

this study. The RTFO was performed at the standard 163oC and one additional temperature

(130oC or 140

oC) that was selected based on the mixing and compaction temperatures of the

three asphalt binders. It was reported that the addition of the WMA additives significantly

increased the G*/sinδ values and decreased the m-values of the asphalt binders. It was also

13

reported that reducing the aging temperature resulted in a lower aging index and higher m-

values, but had no significant effect on G*/sinδ, G*sinδ and stiffness of the asphalt binders.

Gandhi et al. (2010) examined the effect of long-term aging on the mechanical behavior

of WMA mixtures in comparison to traditional HMA. Two asphalt binders, two aggregates, and

two WMA additives (Sasobit and Asphamin) were used in the preparation of the WMA

mixtures. Laboratory-prepared asphalt mixtures were artificially aged in a forced-draft oven to

simulate long-term aging, and the mechanical behavior of the unaged and laboratory-aged

asphalt mixtures was characterized using the indirect tensile strength (ITS), resilient modulus

(MR), and asphalt pavement analyzer (APA) tests. It was reported that the WMA additives did

not have a significant effect on the moisture susceptibility or the rutting resistance of the aged

asphalt mixtures, but significantly increased the resilient modulus of the aged asphalt mixtures.

Arega et al. (2011) and Arega and Bhasin (2012) investigated the influence of warm-mix

additives and reduced aging on the rheology of asphalt binders with different natural wax

contents. Four asphalt binders (PG 76-22 and PG 76-28 asphalt binders with high natural wax

content and two PG 64-22 binders with low natural wax content) and five WMA additives

(Evotherm DAT, Evotherm 3G, Sasobit, Rediset WMX, and Cecabase RT 945) were included in

the study. It was reported that the cumulative effect of short-term aging followed by PAV aging

on asphalt binder stiffness depended on the type of the binder and the WMA additive. It was also

found that certain WMA additives may reduce the viscosity of short-term aged binders,

especially those containing higher natural wax content. This difference was more significant

when asphalt binders were subjected to a longer period of short-term aging.

Trujillo (2011) examined the rheological properties of a PG 64-22 asphalt binder blended

with Cecabase RT, Rediset, Evotherm, and Sasobit WMA additives as a function of laboratory

aging. Control asphalt binder samples and binders modified with WMA additives were aged in a

rolling thin film oven (RTFO) at 163°C and 143°C, respectively. All samples were long-term

aged in an environmental chamber maintained at 60°C and subsequently tested over a period of

six months. Dynamic shear rheometer (DSR) testing was performed on the aged samples at

45°C, 60°C, and 76°C using a testing frequency of 0.1 to 25 Hz. Bending beam rheometer (BBR)

and Fourier-transform infrared (FTIR) spectroscopy was also conducted on the aged samples.

The FTIR results were reported to show higher oxidation levels for the control samples than the

14

WMA samples, while the DSR and BBR test results showed similar stiffness for the control and

Sasobit samples and lower stiffness for the Cecabase, Evotherm, and Rediset samples.

Ahmed et al. (2012) evaluated the effect of 15 warm mix additives and dispersants on the

rheological, aging, and failure properties of four asphalt binders. The DSR test was conducted on

the unaged binder and RTFO residue to determine the high temperature grade. The PAV residue

was tested in the DSR to determine the intermediate grade and the BBR to determine the low

temperature grade. In addition, a modified BBR test and the double-edge-notched tension test

were used to evaluate the low strain rheological and high strain failure characteristics of the

asphalt binders. Significant changes in rheological and failure properties as well as asphalt binder

grade span were reported due to the addition of the warm mix additives and dispersants. The

addition of the additives and dispersants was also reported to affect the tendency to undergo

chemical and physical hardening.

Banerjee et al. (2012) evaluated the effect of four warm mix asphalt additives (Sasobit,

Rediset, Cecabase and Evotherm) on the long-term aging characteristics on a PG 64-22 asphalt

binder. Shear testing of the control and WMA binders was conducted in the laboratory at various

levels of aging using the DSR test, and statistical analysis was utilized to model the effect of

temperature, loading rate (or frequency), and aging on the asphalt binder dynamic shear

modulus. All WMA additives were observed to reduce the dynamic shear modulus of the control

asphalt binder. It was reported that the Rediset WMA binder had the lowest shear modulus,

followed by the Evotherm, Cecabase and Sasobit WMA binders. It was also observed that the

control PG 64-22 had the highest rate of aging, while the Rediset WMA binder had the lowest

rate of aging, followed by the Evotherm, Cecabase and Sasobit WMA binders.

Punith et al. (2012) investigated the influence of long-term aging on moisture

susceptibility of foamed warm mix asphalt (WMA) mixtures containing moist aggregate. Weight

loss, indirect tensile strength (ITS) of dry and conditioned specimens, and deformation (flow)

were measured for all mixtures. The experimental design included two aggregate moisture

contents (0 and ~0.5% by weight of the dry mass of the aggregate); two lime contents (1 and 2%

lime by weight of dry aggregate) and one liquid anti-stripping agent; one foaming WMA additive

(Asphamin) and two foaming water contents (2 and 3%); and two aggregate sources (granite and

schist). It was reported that the long-term aging improved the moisture resistance of the WMA

15

mixtures regardless of the anti-stripping agent and moisture conditioning, with the aged WMA

mixtures generally having a greater wet ITS value than the aged control mixtures.

Xiao et al. (2012) conducted a study to examine the influence of short-term aging on the

rheological properties of non-foaming WMA binders. The experimental plan included four

asphalt binders and four non-foaming WMA additives. Viscosity testing, performance grading,

creep and creep recovery, amplitude sweep, and frequency sweep were performed to determine

the influence of the non-foaming WMA additives on the asphalt binders. As expected, it was

observed that the non-foaming WMA additives can reduce the viscosity of the asphalt binder and

thus decrease the mixing and compaction temperatures for the asphalt mixture. A slight increase

in failure temperatures were also reported for the unaged binders and RTFO residues containing

non-foam WMA additives as compared to the virgin asphalt binder. The experimental test results

also showed a slightly higher complex modulus for the unaged binders and RTFO residues

containing Sasobit but lower creep compliance and phase angle than binders containing other

WMA additives.

Kim et al. (2013) evaluated the short-term aging characteristics of polymer-modified

asphalt mixtures that incorporated two WMA additives (Asphamin and Sasobit) using gel

permeation chromatography (GPC). The polymer-modified asphalt binders containing the WMA

additives were aged in the RTFO at 135°C and 163°C for 85 minutes to simulate the short-term

aging of the asphalt binder that takes place during production, transportation, and construction.

Short-term asphalt mixture aging was simulated in the lab by placing the loose asphalt mixture in

a forced-draft oven for 2 and 4 hours at 135°C and for 2 and 4 hours at 154°C. The experimental

test results showed a higher level of aging for the asphalt mixture short-term aging procedures

than for the RTFO method, which can be attributed to the thinner asphalt binder film thickness

on the aggregates than in the RTFO test. It was also reported that the use of WMA additives

resulted in lower binder aging for the polymer-modified asphalt mixtures.

Hossain and Zaman (2013) evaluated the viscoelastic properties of an asphalt binder

containing different percentages of a wax-based WMA additive, and utilized these properties to

estimate the dynamic modulus (E*) of the resulting WMA mixtures using the Witczak and

Hirsch models. The RTFO test was used to simulate the short-term aging of the asphalt binder.

The Witczak model, which is based on the DSR test results, was found to significantly

16

underestimate the dynamic modulus, while the Hirsch model was found to provide better

approximations of the E* values.

2.5 Summary

In summary, a number of research studies have been conducted to evaluate the aging

characteristics of WMA binders and mixtures. However, nearly all these studies focused on

additive-based WMA technologies rather than foamed WMA produced by water injection, which

is the most commonly used WMA technology in Ohio. Therefore, there is a need to investigate

the aging characteristics of foamed WMA mixtures to better understand their influence on

pavement performance.

17

Chapter 3

Testing Plan

3.1 Introduction

A laboratory testing plan was implemented in this study to examine the short-term and

long-term aging characteristics of foamed WMA as compared to traditional HMA (Figure 3.1).

As can be noticed from this figure, the laboratory testing plan included a binder aging study and

a mixture aging study. The binder aging study evaluated the short-term and long-term aging

characteristics of the selected asphalt binders. The mixture aging study was divided into three

components. The first component investigated the effect of the extraction and recovery

procedure on the rheological properties of the two asphalt binders that were used in the

preparation of the laboratory-produced asphalt mixtures. The second component evaluated the

short-term and long-term aging characteristics of binders recovered from laboratory-produced

asphalt mixtures. The third component focused on comparing the long-term aging in binders

recovered from field-placed foamed WMA and HMA mixtures. The following sections provide

detailed information about the asphalt binder and asphalt mixture aging studies. Further

discussion of the experimental test methods that are included in the laboratory testing plan is

provided in Chapter 4.

Figure 3.1: Laboratory Testing Plan.

3.2 Laboratory Binder Aging

Figure 3.2 presents the laboratory testing plan for the asphalt binder aging. As can be

noticed from this figure, two types of asphalt binders (one polymer-modified PG 70-22 asphalt

Laboratory

Testing Plan

Binder

Aging

Mixture

Aging

Effect of Binder

Extraction and Recovery

Laboratory

Mixture Aging

Field

Mixture Aging

18

binder and one neat PG 64-22 asphalt binder) that are typically used in surface mixtures in Ohio

were included in this study. The short-term aging of the two asphalt binders was simulated using

a Despatch rolling thin film oven (RTFO) according to AASHTO T 240, and the long-term aging

of the asphalt binders was simulated using a pressure aging vessel (PAV) from Applied Test

System (Cheswick, Pennsylvania) according to AASHTO R 28. The dynamic shear rheometer

(DSR) was used to characterize the viscoelastic behavior of the unaged, RTFO-aged, and PAV-

aged asphalt binders at intermediate and high service temperatures. Temperature and frequency

sweeps were conducted using a research grade DSR device from Rheometric Scientific

(currently owned by TA Instruments). The dynamic shear modulus, G*, and phase angle, , were

obtained at each loading frequency and testing temperature. In addition, Fourier transform

infrared (FTIR) spectroscopy was used to identify and quantify the amount of functional groups

present in the asphalt binders, gel permeation chromatography (GPC) was used to determine the

molecular size distribution within the unaged, RTFO-aged, and PAV-aged asphalt binders, and

atomic force microscopy (AFM) was utilized to examine the effect of aging on the

microstructure and morphology of the unaged and aged asphalt binders.

Figure 3.2: Laboratory Binder Aging.

Laboratory

Binder Aging

PG 70-22

(A)

Physical

Tests

DSR (G*, δ)

Int. + High Temp.

Unaged

RTFO

PAV

Chemical

Tests

FTIR

Unaged

RTFO

PAV

GPC

Unaged

RTFO

PAV

Analytical

Tests

AFM

Unaged

RTFO

PAV

PG 64-22

(B)

Same

as (A)

19

3.3 Effect of Binder Extraction and Recovery

In order to examine the extent of binder aging in laboratory-prepared and field-placed

mixtures, it is necessary to extract and recover the asphalt binders from these mixtures. The

asphalt binders are generally extracted in accordance with AASHTO T 164 (Quantitative

Extraction of Asphalt Binder from Hot Mix Asphalt) and are recovered in accordance with

AASHTO T 170 (Recovery of Asphalt Binder from Solution by Abson Method). Because these

procedures introduce a solvent during the extraction and heat during the recovery, they are

expected to have some effect on the physical and chemical characteristics of the recovered

asphalt binders.

A laboratory testing plan was designed to quantify the effect of the extraction and

recovery procedures on the two asphalt binders (PG 70-22 and PG 64-22) that were used in the

laboratory-produced asphalt mixtures (Figure 3.3). To determine the sensitivity of these asphalt

binders to extraction and recovery, controlled amounts of trichloroethylene (TCE), the solvent

Figure 3.3: Effect of Binder Extraction and Recovery.

Effect of Binder

Extraction and Recovery

PG 70-22

(A)

DSR and XRD

Original

Binder

Unaged

RTFO

PAV

Recovered from

Binder + TCE

Unaged

RTFO

PAV

Recovered from

Binder + TCE + Dust

Unaged

RTFO

PAV

PG 64-22

(B)

Same

as (A)

20

used in AASHTO T 164, and dust were added to the unaged, RTFO-aged, and PAV-aged binders

of both PG grades. AASHTO T 164 and AASHTO T 170 were then used to recover the asphalt

binders from the resulting solutions. As can be noticed from Figure 3.3, the DSR test was used to

characterize the viscoelastic behavior of the original and recovered unaged, RTFO-aged, and

PAV-aged asphalt binders, and x-ray diffraction (XRD) was used to identify the presence of any

limestone dust remaining in the recovered asphalt binder.

3.4 Laboratory Mixture Aging

Figure 3.4 presents the laboratory testing plan for the asphalt mixture aging. As can be

noticed from this figure, asphalt mixture aging was evaluated by examining the physical,

chemical and morphological properties of asphalt binders recovered from laboratory-produced

foamed WMA and HMA mixtures at different stages of aging (immediately after mixing, short-

term aging, and long-term aging) and by comparing the dynamic modulus, |E*|, of short-term

and long-term aged foamed WMA and HMA asphalt mixtures.

Figure 3.4: Laboratory Mixture Aging.

In this study, two asphalt binders (PG 70-22 and PG 64-22) and one aggregate

(limestone) were used in the preparation of the foamed WMA and HMA asphalt mixtures. The

aggregate gradation met the Ohio Department of Transportation (ODOT) Construction and

Material Specifications (C&MS) requirements for Item 442 (Superpave Asphalt Concrete) Type

Laboratory

Mixture Aging

HMA

(A)

Recovered

Binders

DSR, FTIR, GPC, and AFM

After Mixing Short-Term Long-Term

Mixture

Testing

|E*|

Short-Term Long-Term

Foamed WMA

(B)

Same as

(A)

21

A with a nominal maximum aggregate size (NMAS) of 12.5 mm (Figure 3.5). The aggregate

blend was prepared by mixing 55% #8 limestone aggregate, 30% limestone sand, and 15%

natural sand. An optimum asphalt binder content of 5.7% was used in the preparation of the

asphalt mixtures. None of the asphalt mixtures contained reclaimed asphalt pavement (RAP). It

is noted that ODOT requires using PG 70-22 for Superpave surface mixtures. However, PG 64-

22 was included in this study to allow for determining the effect of the asphalt binder type on

mixture aging.

Figure 3.5: Aggregate Gradation.

A Wirtgen WLB10 laboratory-scale asphalt binder foaming device was utilized to foam

the asphalt binder by injecting cold water into the heated asphalt binder (Figure 3.6). This device

employs a process similar to that used by large-scale foaming systems that are incorporated into

commercial asphalt plants. As shown in Figure 3.6, the WLB10 device consists of an asphalt

binder tank, a water tank, an air tank, an asphalt pump, heating components, a foaming nozzle,

air and water pressure regulators, and a control panel. A foaming water content of 1.8% by

weight of the asphalt binder was used in the production of the foamed asphalt binder. This

quantity represents the maximum water content permitted by ODOT for foamed WMA mixtures.

251912.59.54.752.360.60.0750

10

20

30

40

50

60

70

80

90

100

0 1

Perc

en

t P

ass

ing

(%

)

Sieve Size (mm)

Aggregate Gradation

Control Points

Maximum Density Line

22

In addition, the foamed WMA mixtures were produced at 30oF (16.7

oC) lower mixing and

compaction temperatures than the traditional HMA mixtures. This temperature reduction is

consistent with current ODOT specifications for foamed WMA mixtures that allow using a

compaction temperature 30oF (16.7

oC) lower than that of the HMA. ODOT, however, does not

control the mixing temperature of the foamed WMA. It is up to the contractor to determine the

appropriate mixing temperature for this material.

Figure 3.6: Laboratory-Scale Asphalt Binder Foaming Device.

3.5 Field Mixture Aging

This study also involved investigating the effect of aging on foamed WMA and HMA

mixtures placed in the field (Figure 3.7). As can be noticed from this figure, field cores were

collected from four roadway sections in Ohio (US Route 224 in Portage County, State Route 303

in Summit County, US Route 62 in Pickaway County, and State Route 49 in Miami County) that

were constructed using both foamed WMA and HMA mixtures prepared using the same

materials (asphalt binder and aggregates), aggregate gradation, and asphalt binder content. All

pavement sections were constructed in 2008 as part of ODOT’s initial field implementation of

foamed WMA in Ohio. The asphalt binder was extracted from the field cores using AASHTO T

164 and recovered using AASHTO T 170. The recovered binders were examined for the same

Foaming

Nozzle

Binder

Tank

Air

Tank

Water

Tank

Control

Panel

23

physical, chemical, and morphological properties using the same test procedures as the

laboratory-produced foamed WMA and HMA mixtures.

Figure 3.7: Field Mixture Aging.

Field

Mixture Aging

DSR, FTIR, GPC, and AFM

Project No.: 329-08

County: Darke/Miami

Surface Layer

Thickness: 1.5"

Binder: PG 70-22

Project No.: 342-08

County: Pickaway

Surface Layer

Thickness: 1.5"

Binder: PG 64-22

Project No.: 352-08

County: Summit

Surface Layer

Thickness: 1.5"

Binder: PG 70-22

Project No.: 386-08

County: Portage

Surface Layer

Thickness: 1.25"

Binder: PG 70-22

24

Chapter 4

Test Methods

4.1 Introduction

This chapter presents an overview of the experimental test methods that were included in

the laboratory testing plan. It covers the laboratory simulation of short-term and long-term aging

of asphalt binders and asphalt mixtures. This chapter also discusses the asphalt binder extraction

and recovery procedures. In addition, it presents the experimental test methods that were utilized

to characterize the rheological, chemical, and morphological properties of unaged and aged

asphalt binders. Finally, detailed information is provided in this chapter regarding the dynamic

modulus test that was conducted on short-term and long-term aged foamed WMA and HMA

mixtures.

4.2 Laboratory Asphalt Binder Aging Procedures

Two standard laboratory test procedures were used in this study to simulate asphalt

binder aging. AASHTO T 240 (Standard Method of Test for Effect of Heat and Air on a Moving

Film of Asphalt Binder) was used to simulate short-term aging, and AASHTO R 28 (Standard

Practice for Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel) was used to

simulate long-term aging. A Despatch rolling thin-film oven (RTFO) was used for the short-term

aging (Figure 4.1). In this test, 1.2 ounces (35 g) of asphalt binder were heated and poured into

cylindrical glass bottles. The asphalt was allowed to cool for 60 minutes. After cooling, the

bottles were placed in the rotating carriage within the RTFO. The RTFO was operated at a rate of

15 rpm for 85 minutes. During this time, the temperature of the oven was maintained at 325°F

(163°C), and the rate of airflow into the bottle was kept at 244 in3/min (4000 ml/min). After 85

minutes, the bottles were removed from the oven one at a time, and the residue was scraped from

the bottles and stored for later use.

A portion of the residue from the RTFO test was used to prepare the long-term aged

binders. A pressure aging vessel (PAV) from Applied Test Systems (ATS) was used for this test

(Figure 4.2). A total of 1.76 ounces (50 g) of RTFO-aged asphalt binder was poured into

preheated thin film oven pans. The pans were placed in a pan holder and loaded into a preheated

PAV. The PAV was sealed and allowed to return to the aging temperature. Once the PAV had

25

reached the desired temperature (212°F or 100°C), the chamber was pressurized to 300 psi (2.07

MPa) and the samples were kept at this condition for 20 hours. At the end of the aging period,

the pressure was released gradually, and the pans were transferred from the PAV to an oven set

at 325°F (163°C). After 15 minutes, the pans were removed from the oven and the residue was

scraped into a container and stored for later testing.

Figure 4.1: Despatch Rolling Thin Film Oven (RTFO).

Figure 4.2: Applied Test System (ATS) Pressure Aging Vessel (PAV).

26

4.3 Laboratory Asphalt Mixture Aging Procedures

Short-term and long-term aging of foamed WMA and HMA mixtures was simulated in

the laboratory using AASHTO R 30 (Standard Practice for Mixture Conditioning of Hot Mix

Asphalt). It is noted that this test method was originally developed for traditional HMA.

However, the same procedure was used in this study to simulate the aging of foamed WMA in

order to facilitate the comparison with traditional HMA.

To simulate short-term aging, the aggregates were heated to the mixing temperature for a

minimum of 2 hours before being mixed with the asphalt binder for approximately 3 minutes.

The loose asphalt mixture was then placed in a pan and was spread to an even thickness of 1 to 2

inches (25 to 50 mm). The loose mixture was then conditioned in a forced-draft oven for a total

of 4 hours at 275°F (135°C), with the mixture being stirred every 60 minutes to maintain uniform

conditioning. After 4 hours, the mixture was removed from the oven and retained for later use.

To simulate long-term aging, the loose short-term aged asphalt mixture was heated to the

compaction temperature for 2 hours and compacted into cylindrical specimens using the

Superpave gyratory compactor according to AASHTO T 312 (Preparing and Determining the

Density of Hot-Mix Asphalt). The compacted specimens were then extracted from the Superpave

gyratory molds and allowed to cool overnight before being placed in a forced-draft oven for 5

days at 185°F (85oC).

Two sets of long-term aged specimens were used in this study. The first set was used for

asphalt binder recovery to determine the effect of mixture aging on asphalt binder properties,

while the second set was used to examine the effect of asphalt mixture aging on the dynamic

modulus of foamed WMA and HMA mixtures. The first set of specimens measured 6 inch (15

cm) in diameter by 4 inch (10 cm) in height with a target air void level of 7 ± 0.5%. These

specimens were cored using a 4-inch (10-cm) coring bit and the outer shell was used for asphalt

binder recovery to simulate long-term aging in surface mixtures. The second set of specimens

measured 6 inch (15 cm) in diameter by approximately 6.7 inch (17 cm) in height. These

specimens were subsequently cored to 4-inch (10-cm) cylindrical samples and trimmed to a

height of 6 inches (15 cm) with a target air void level of 7 ± 0.5% before being used in the

dynamic modulus test.

27

4.4 Asphalt Binder Extraction and Recovery

Asphalt binder extraction was performed according to AASHTO T 164 (Quantitative

Extraction of Asphalt Binder from Hot Mix Asphalt) and asphalt binder recovery was conducted

in accordance with AASHTO T 170 (Recovery of Asphalt Binder from Solution by Abson

Method). A Humboldt 1500 g centrifuge was used for the asphalt binder extraction (Figure 4.3).

In this procedure, the asphalt mixture sample was placed in a bowl and covered with 17 ounces

(500 ml) of trichloroethylene. The bowl was then placed in the centrifuge, with a filter ring fitted

to the edge and a cover plate clamped to the top of the bowl. After a 5-minute waiting period, the

speed of the centrifuge was gradually increased to 3600 rpm and the centrifuge was operated

until the solvent stopped flowing from the drain. At that point, 6.7 ounces (200 ml) or more of

trichloroethylene was added to the bowl, and the same procedure was repeated at least three

times until the extract was clear and had a light straw color.

Figure 4.3: Humboldt 1500 g Centrifuge Extractor.

After extraction, a second centrifuge was used to remove any fine particles from the

extract. A continuous centrifuge was used for this purpose. The centrifuge exerted a centrifugal

force equal to 3000 times gravity for a minimum of 30 minutes (Figure 4.4). The resulting

solution was then poured into a distillation flask to recover the asphalt binder. The distillation

assembly consisted of a heating mantel, condenser, aeration tube, thermometer, and CO2 flow

28

tube and meter (Figure 4.5). Heat was applied and a low CO2 flow rate of 3.4 ounces/min (100

ml/min) was introduced until the temperature of the flask reached 315°F to 320°F (157°C to

160°C). Once that temperature was reached, the flow of CO2 was increased to 34 ounces/min

(1000 ml/min). The temperature and CO2 flow rate were maintained the same until the

condensed solvent stopped dripping from the condenser, which lasted for approximately 10 to 15

minutes. At the end of the distillation, the recovered asphalt binder was stored in air-tight

containers for later testing.

Figure 4.4: Humboldt Filterless Centrifuge Extractor.

Figure 4.5: Abson Recovery Distillation Assembly.

29

4.5 Rheological Behavior of Asphalt Binders

The dynamic shear rheometer (DSR) test was used to characterize the rheological

behavior of asphalt binders at high and intermediate service temperatures. The DSR measures the

dynamic shear modulus (G*) and phase angle (δ) of the asphalt binder at the specified testing

temperature and loading frequency. The dynamic shear modulus is a measure of the total

resistance of the binder to deformation when repeatedly sheared. The phase angle represents the

immediate elastic and the delayed viscous responses of the binder, obtained from the lag between

the measured shear stresses and the induced strains in a strain-controlled device.

The G* and δ are generally used to evaluate the resistance of the asphalt mixtures to

permanent deformation (rutting) and fatigue cracking. The Superpave asphalt binder

specifications use G*/sinδ of unaged and RTFO-aged asphalt binders measured at high service

temperatures to determine the rutting potential of asphalt mixtures, and G*sinδ of PAV-aged

asphalt binders measured at intermediate service temperatures to determine the susceptibility of

asphalt mixtures to fatigue cracking. To resist rutting, an asphalt binder needs to be stiff and

elastic at high temperatures. Therefore in the Superpave asphalt binder performance grading

(PG) system, a minimum G*/sinδ value of 0.15 psi (1.0 kPa) is specified for unaged asphalt

binders and a minimum G*/sinδ value of 0.32 psi (2.2 kPa) is specified for RTFO-aged binders.

Later in the life of asphalt mixtures, fatigue cracking becomes more of a concern as the asphalt

binder stiffens and gets more brittle. Therefore, to ensure that the asphalt binder provides

satisfactory long-term performance, the Superpave grading system specifies a maximum G*sinδ

value of 725 psi (5000 kPa) for PAV-aged binders. Both rutting and fatigue cracking parameters

are measured at a standard loading frequency of 10 rad/sec (1.59 Hz) to imitate the shearing

action of a vehicle travelling at 55 mph (89 km/h).

The DSR test was conducted according to AASHTO T 315 (Determining the Rheological

Properties of Asphalt Binder Using a Dynamic Shear Rheometer). An ARES DSR from

Rheometric Scientific (currently owned by TA Instruments) was used in this study to measure

G* and δ of the asphalt binders (Figure 4.6). DSR testing was carried out by placing the asphalt

binder samples between two parallel plates, a fixed bottom plate and an oscillating top plate.

A specimen measuring 25 mm in diameter and 1 mm in thickness was used for the high

temperature tests, and a specimen measuring 8 mm in diameter and 2 mm in thickness was used

for the intermediate temperature tests. A 600-second delay was used for each sample prior to the

30

beginning of the test, with an additional soak time of 300 seconds for every temperature change.

Three test replicates were used for all asphalt binders tested in this study.

The DSR test was performed over a wide range of temperatures (55°F to 77°F with 5.4°F

intervals or 13°C to 25°C with 3°C intervals representing the intermediate service temperatures

and 126°F to 180°F with 10.8°F intervals or 52°C to 82°C with 6°C intervals representing

the high service temperatures) and frequencies (0.1 to 100 rad/sec). As mentioned earlier, the

DSR test is typically performed on unaged and RTFO-aged asphalt binders at high service

temperatures and on PAV-aged asphalt binders at intermediate service temperatures. However,

in order to compare the rheological behavior of the unaged and aged asphalt binders, the DSR

test was performed on all asphalt binders at both intermediate and high service temperatures.

For the non-standard DSR tests, the applied shear strain level was varied in order to remain

within the linear viscoelastic range and the device load detection and tolerance limits.

Figure 4.6: ARES Dynamic Shear Rheometer (DSR).

4.6 Chemical Properties and Morphology of Asphalt Binders

Several tests have been used in this study to characterize the chemical properties and

morphology of asphalt binders including Fourier transform infrared spectroscopy (FTIR), gel-

permeation chromatography (GPC), atomic force microscopy (AFM), and X-ray diffraction

31

(XRD). The following subsections present an overview of each of these techniques along with a

discussion of the test procedure and equipment.

4.6.1 Fourier Transform Infrared Spectroscopy (FTIR)

FTIR spectroscopy is a technique that can be used to characterize the chemical

composition of a material and identify the dominant functional groups. In this test, a sample is

subjected to infrared light of varying frequencies to determine how well it absorbs the light at

each wavelength (Figure 4.7). The raw data is converted into an FTIR spectrum through the use

of a mathematical algorithm. The resulting spectrum will be unique, as it represents a sum of the

individual infrared absorbencies for all components present in the sample. By comparing the

sample’s spectrum with reference spectra in the FTIR library, chemical bonding and

characterization of the sample can be determined.

Figure 4.7: Fourier Transform Infrared Spectroscopy Setup (www.thermonicolet.com).

A Digilab Excalibur Series FTIR spectrometer with Win-IR Pro software was used in

this study to identify and quantify the amount of functional groups present in the unaged and

aged asphalt binders (Figure 4.8). The asphalt binder samples were dissolved in tetrahydrofuran

(THF) to prepare a solution with a concentration of 30 mg/ml. The resulting solution was

http://www.thermonicolet.com/

32

allowed to sit for 1 hour in order for the asphalt binder to fully dissolve in THF. The solution was

then pipetted and applied to a potassium bromide (KBr) crystal. The solution on the crystal was

allowed to dry for at least 30 minutes before the crystal was placed in the FTIR device for

scanning. The background spectra and sample spectra were scanned using a wavelength range of

400 to 4000 cm-1

and a scan resolution of 4 cm-1

. To reduce the variability of the test results, an

asphalt binder sample of 100 to 200 mg was used in the preparation of the asphalt binder/THF

solution. Three replicates were tested using the same solution for all asphalt binders included in

this study.

Figure 4.8: Digilab Excalibur Series FTIR Spectrometer.

4.6.2 Gel-Permeation Chromatography (GPC)

The GPC test is a technique that separates the components in a solution based on their

molecular size. As illustrated in Figure 4.9, the GPC equipment consists of a solution injection

unit that pumps the sample solution through columns packed with porous beads. Larger

molecules of a sample will spend less time in the bead pores and will flow through the column

more quickly, thus reaching a differential refractometer detector ahead of the smaller molecules,

which can enter the pores more easily and will be retained by the beads for a longer period of

time. The detector continuously measures the amount of molecules flowing through as a function

33

of time. The system is connected to a recorder, which produces a continuous tracing of time

versus amount of flowing molecules. The resulting chromatogram can be used to obtain the

molecular size distribution within the sample.

Figure 4.9: Gel-Permeation Chromatography Setup (Striegel et al. 2009).

In this study, a Malvern VE 2001 Viscotek GPC device with Waters 2414 refractive

index detector (Figure 4.10) was used to separate the asphalt constituents by molecular size as

the sample passed through a series of three columns (Styragel HR 1, Styragel HR 4E, and

Styragel HR 5E with an effective molecular weight of 100 to 5,000, 50 to 100,000, and 2,000 to

4,000,000, respectively). The instrument was calibrated using a series of polystyrene standards

prior to testing. In this test, the asphalt binder samples were dissolved in THF to prepare a

solution with a concentration of 1 mg/ml. An asphalt binder sample of approximately 30 to 50

mg was used in the preparation of the asphalt binder/THF solution. The resulting solutions were

allowed to rest for approximately 1 hour at room temperature. The samples were then filtered

using a 0.2 micron Teflon syringe filter and injected into the GPC unit. The solution was drained

through the columns and allowed to flow at a rate of 1 ml/min. The columns were maintained at

a temperature of 95°F (35°C) during the test. The components’ concentration in the eluent was

recorded using a differential refractometer, and the resulting chromatogram was analyzed to

34

obtain the molecular size distribution. Three GPC test replicates were used for all asphalt binders

included in this study.

Figure 4.10: Malvern Viscotek GPC with Waters 2414 Refractive Index Detector.

4.6.3 Atomic Force Microscopy (AFM)

AFM is a high-resolution scanning technique that uses a laser-tracked cantilever with a

sharp underside tip (probe) to raster over a sample while interacting with the surface. It can

accurately map a particular force in various imaging modes with nanometer resolution or track

the dependence of different components as a function of tip-surface distance with sub-nanometer

resolution. This method can be used to evaluate the material structure and mechanical properties

at the nano-scale and micro-scale levels.

An Agilent 5500LS atomic force microscope was utilized in this study to evaluate the

morphological characteristics of the unaged and aged asphalt binders (Figure 4.11). This device

has a large, motorized stage that enables fast and accurate probe positioning for imaging and

mapping large samples at nanometer-scale resolution. This stage is ideal for imaging large

samples in air and fluids providing a versatile tool for characterizing a wide range of materials.

Samples up to 6 inch in diameter can be easily scanned without rotation or repositioning. Agilent

5500 LS AFM can be operated with many different contact and non-contact imaging modes

35

allowing elastic (contact), viscoelastic (FMM), magnetic (MFM), electrostatic (EFM), lateral-

force (LFM) and friction (FFM) forces to be mapped. All aspects of this AFM including

alignment, imaging, and calibration are controlled by PicoView software. This software can be

also used for post processing of AFM images and data.

Figure 4.11: Agilent 5500LS Atomic Force Microscope.

Dual Screens

AFM Controllers

Temperature

Controller Dynamic Vibration

Isolation

36

The AFM sample preparation method employed in this study is similar to that used in a

previous ODOT research project (Nazzal et al. 2013) with minor modifications. The AFM

samples were prepared by placing two strips of a heat-resistant tape approximately 1 inch apart

on a pre-cleaned glass slide. A syringe was used to place 0.25 ml of asphalt binder on the slide

between the two strips. The glass slide was then placed in an oven to allow the asphalt binder to

spread to a uniform thickness. After approximately 8 minutes, the slide was removed from the

oven and allowed to cool to room temperature (Figure 4.12). The slides were then placed in an

airtight container, which was placed in a Ziploc vacuum bag and stored for later testing. The

heat-resistant tape was removed from the slide prior to AFM testing. This approach was found to

provide uniform sample surfaces resulting in consistent AFM test results.

Figure 4.12: Atomic Force Microscopy (AFM) Test Sample.

Force spectroscopy experiments were conducted at a temperature of 25C to measure the

micro-scale stiffness and adhesive properties of the unaged and aged asphalt binders. As shown

in Figure 4.13, the force spectroscopy experiments were performed by forcing the tip into the

asphalt binder sample to a preselected indentation depth, followed by retracting the tip from the

binder sample until the tip separates from the sample. These experiments were conducted

according the guidelines presented in (Oliver and Pharr 2004; Tranchida et al. 2006). The

37

indentation depth was chosen deep enough to minimize the surface effect, but not more than 10%

of the asphalt binder film thickness to avoid any effect from the glass substrate. An indentation

speed of 350 nm/s was used for all experiments. The force spectroscopy experiments consisted

of at least 24 indentations with a minimum spacing of 9 m between any two indentations. This

spacing was selected to reduce the effect of the interaction between adjacent indents. A sharp

tetrahedron pyramidal tip with an inclination angle of 20° was used in this study. The cantilever

supporting the tip had a resonance frequency of 126 kHz and a spring constant of 5 N/m.

Figure 4.13: AFM Force Spectroscopy (www.agilent.com).

The outcome of a single indentation in a force spectroscopy experiment is a force-

distance curve similar to that presented in Figure 4.14. As can be noticed from this figure, this

curve can be divided into two main regions: the approaching region and the retracting region. In

the approaching region, the tip is brought closer to the asphalt sample until contact is made with

the sample and continues to a pre-specified indentation depth. An increase in force is observed in

this region once the tip makes contact with the sample. In the retracting region, the tip is pulled

away from the asphalt sample until it completely separates from the sample. A rapid drop in

force is observed as the tip is retracted from the asphalt sample. The force continues to drop

beyond the point of initial contact due to the adhesion between the tip and the asphalt sample.

Once it separates from the sample, the tip springs back to its original position and the force

measured by the tip goes down to zero.

http://www.agilent.com/

38

Figure 4.14: Typical Force-Distance Curve Obtained in a Force Spectroscopy Experiment.

The force spectroscopy test results were analyzed to determine the reduced elastic

modulus of the asphalt binder and the total energy needed to separate the tip from the asphalt

sample. The reduced elastic modulus, E reduced, was calculated using Equation 4.1, which is based

on Sneddon’s modification of the Hertzian model for the indentation of a flat, soft sample by a

stiff tip (Fischer-Cripps 2006):

2

δ2 tan ( )

(4.1)

= z – d (4.2)

where F is the measured force, is the indentation depth, is the half-opening angle of the AFM

tip, d is the cantilever deflection, and z is the piezo-driver displacement.

The total energy needed to separate the tip from the asphalt sample, Ebonding, was

estimated using Equation 4.3 (Pauli et al. 2013). This equation represents the area under the

force-distance curve in the retraction region where the force is less than zero, as indicated by the

Fo

rce,

F

Distance, z

Approaching

Retracting

39

shaded portion of Figure 4.15. This area was approximated using the trapezoidal rule, as shown

in the right-hand side of Equation 4.3.

∫

2 ∑ [ ( ) ( )] (4.3)

Figure 4.15: Estimation of Ebonding from a Force-Distance Curve.

4.6.4 X-Ray Diffraction (XRD)

XRD is a non-destructive structural analysis technique for solid crystalline materials. It is

based on the angular dependency of the amplitude of x-ray beams reflected off from basal planes

in the crystals, which can produce sharp resonances when the half wavelength of the x-ray beam

matches the separation between crystal layers. The reflected beam is unique for a given crystal’s

geometry as well as its arrangement and number of atoms, hence providing a unique insight into

the long-range order and the nature of the crystal. Using the calculated or recorded references of

diffraction patterns, it is possible to obtain a quantitative match for the crystal’s physical

structure and chemical composition, even though the latter is limited in accuracy.

Forc

e, F

Distance, z

Approaching

Retracting

Ebonding

40

In this study, the XRD method was used to detect changes in atomic and molecular

structure as well as the arrangement of the asphalt binder due to aging. In addition, XRD was

used to identify the presence of any limestone dust remaining in the recovered asphalt binders.

All XRD experiments were conducted using the Rigaku Miniflex XRD system shown in Figure

4.16.

Figure 4.16: Rigaku Miniflex XRD System.

4.7 Dynamic Modulus Testing of Foamed WMA and HMA Mixtures

The dynamic modulus is a fundamental material property commonly used to describe the

mechanical behavior of viscoelastic materials such as asphalt mixtures. It relates stresses to

strains induced under different loading rates and temperature conditions. In recent years, the

dynamic modulus has been incorporated into the Mechanistic-Empirical Pavement Design Guide

(MEPDG) to describe the response of asphaltic layers, and to subsequently predict the

performance of asphalt pavements. Asphalt mixtures with higher dynamic moduli are expected

to result in less permanent deformation (or rutting), as predicted using the MEPDG.

41

The dynamic modulus (E*) test was also used in this study to examine the effect of aging

on the viscoelastic behavior of asphalt mixtures. The dynamic modulus (E*) test was conducted

according to AASHTO T 342 (Standard Method of Test for Determining Dynamic Modulus of

Hot-Mix Asphalt Concrete Mixtures). However, it was performed on short-term aged as well as

long-term aged foamed WMA and HMA specimens.

The dynamic modulus test was performed on cylindrical specimens cored from

Superpave gyratory compacted mixtures. An air void content of 7±0.5% was targeted in the

preparation of the dynamic modulus specimens. A trial and error procedure was followed in

determining the weight of mixture required to achieve the target air void level. Before

compaction, the loose mixture was short-term aged for a period of 4 hours at 275oF (135

oC),

during which the mixture was stirred every hour. The temperature was then raised to the

compaction temperature and the mixture was heated for 30 minutes. The compacted samples

were then cored and trimmed to obtain cylindrical specimens measuring 4 inch (100 mm) in

diameter and 6 inch (150 mm) in height.

As mentioned earlier, the dynamic modulus test (E*) was also conducted on long-term

aged foamed WMA and HMA specimens. The long-term aged specimens were prepared by

wrapping the short-term aged specimens in thin aluminum sheets (Figure 4.17) and placing them

in a forced-draft oven for 5 days at 185°F (85oC). The research team initially tried to perform

long-term aging without wrapping the specimens. However, some distortion in the specimen

shape was observed due to material flow. Therefore, it was decided to wrap the dynamic

modulus specimens with the thin aluminum sheets to preserve the shape of the specimens during

long-term aging. A small amount of dust was applied to the dynamic modulus samples prior to

wrapping to prevent the samples from sticking to the aluminum sheets.

42

Figure 4.17: Wrapping of Dynamic Modulus Specimens

with Thin Aluminum Sheets Prior to Long-Term Aging.

A servo-hydraulic Material Test System (MTS) Model 810 was used to conduct the

dynamic modulus test (Figure 4.18). This system is operated using a personal computer and a

digital controller called MTS TestStar II. It is capable of applying various types of loading

including cyclic, monotonic, and creep. The system is also equipped with an environmental

chamber capable of controlling the testing temperature, and a self-leveling loading platen that

helps in alleviating any shear stresses that might arise due to imperfections caused by trimming

the top and bottom of the specimens. Load measurements are obtained using an external load cell

located underneath the bottom loading platen. Two extensometers were used in this study to

measure the vertical deformation in the specimens as the load was applied. The use of

extensometers was preferred over using Linear Variable Differential Transducers (LVDTs),

since the former provides higher accuracy and can be easily installed on the specimen.

43

Figure 4.18: Material Test System (MTS) Model 810.

The dynamic modulus test was conducted at four testing temperatures (40, 70, 100, and

130oF or 4.4, 21.1, 37.8, and 54.4

oC) and six loading frequencies (25, 10, 5, 1, 0.5, and 0.1 Hz).

Testing was conducted from the lowest to the highest temperature starting with the highest

frequency. A rest period of 2 minutes was used between successive frequencies. At each

temperature and frequency, a repeated sinusoidal load was applied on the specimen and the

resulting deformation was recorded. The applied load level was determined as the load that will

result in 75 to 125 microstrain. The dynamic modulus, |E*|, was calculated as the ratio between

the applied stress level and the recoverable strain level, where the applied stress level is equal to

the applied load level divided by the specimen cross-sectional area and the applied strain level is

equal to the average recoverable deformation level in the two extensometers divided by the

extensometer length. At the end of testing, the specimen was discarded if excessive deformation

(greater than 1500 micro strain) was accumulated.

Piston Rod

Extensometer

Environmental

ChamberSelf-Leveling

Loading Platen

44

Chapter 5

Results and Discussion

5.1 Introduction

The laboratory testing plan was designed to allow for a comparison between the standard

laboratory procedures that are used for short-term aging and long-term aging of asphalt binders

and asphalt mixtures. The testing plan was also devised to examine the ability of the standard

laboratory aging procedures for asphalt binders and asphalt mixtures to simulate field aging of

foamed WMA and HMA mixtures. A separate component of the testing plan was conducted in

order to quantify the effect of the extraction and recovery procedures on the asphalt binders that

were used in the laboratory-produced asphalt mixtures so that the effect of extraction and

recovery is taken into consideration in the comparisons. This chapter presents the experimental

test results that were obtained as part of the laboratory testing plan.

5.2 Laboratory Aging of Asphalt Binders

Figures 5.1 and 5.2 present the effect of the laboratory asphalt binder aging on the DSR

test results for PG 70-22 and PG 64-22, respectively. Figures 5.1a and 5.2a show the effect of

aging on G*/sinδ (rutting parameter) obtained at the high temperature grade, and Figures 5.1b

and 5.2b show the effect of aging on G*sinδ (fatigue parameter) obtained at the intermediate

temperature. As can be noticed from these figures, the G*/sinδ and G*sinδ values for the PAV-

aged residue are higher than the RTFO-aged residue, which in turn are higher than the unaged

asphalt binder. It can also be noticed that the G*/sinδ and G*sinδ values for the RTFO-aged

residue are closer to the unaged asphalt binder than the PAV-aged residue.

Figures 5.3 and 5.4 present the FTIR spectra for the unaged, RTFO-aged, and PAV-aged

PG 70-22 and PG 64-22 asphalt binders, respectively. This figure shows an increase in the 1700

cm-1

peak corresponding to the carbonyl group (C=O) and the 1030 cm-1

peak corresponding to

the sulfoxide group (S=O) due to aging in the RTFO and PAV tests. The increase in the carbonyl

and sulfoxide groups indicates an increase in the number of large molecules in the asphalt binder,

resulting in higher stiffness and more solid-like behavior.

45

Figures 5.5 and 5.6 show the GPC chromatograms for the unaged, RTFO-aged, and

PAV-aged PG 70-22 and PG 64-22 asphalt binders. As expected, the chromatograms for the

RTFO-aged and PAV-aged binders are slightly shifted to the left because of the increase in the

larger molecular fraction in the asphalt binder due to aging. In addition, the chromatograms for

the RTFO-aged and PAV-aged binders are slightly narrower than those for the unaged asphalt

binders because of the presence of a smaller portion of the small molecules.

Figures 5.7 and 5.8 present example AFM force-distance curves obtained for unaged,

RTFO-aged, and PAV-aged PG 70-22 and PG 64-22 asphalt binders, respectively. As mentioned

earlier, a minimum of 24 indentations were utilized in each force spectroscopy test resulting in

24 force-distance curves for each asphalt binder. Figures 5.7 and 5.8 show the force-distance

curves obtained from one indentation at each level of aging. As can be noticed from these

figures, higher forces were needed to indent the PAV-aged binders than the RTFO-aged binders

to the same indentation depth and higher forces were needed to indent the RTFO-aged binders

than the unaged binders. This indicates that the PAV-aged binders are stiffer than the

corresponding RTFO-aged binders, which in turn are stiffer than the corresponding unaged

asphalt binders. It can also be noticed from Figures 5.7 and 5.8 that the area under the force-

distance curve in the retraction region where the force is less than zero (i.e., total energy needed

to separate the tip from the asphalt sample or Ebonding) is larger for the unaged asphalt binders

than the RTFO-aged and PAV-aged binders. This indicates that aging reduces the bonding

energy and subsequently the adhesive properties of the asphalt binders.

46

Figure 5.1: DSR Test Results for Unaged, RTFO-aged, and PAV-aged

PG 70-22 at High and Intermediate Temperatures.

0.001

0.1

10

1000

0.01 0.1 1 10 100 1000

G*

/sinδ

at

70

oC

(k

Pa

)

Radial Frequency (rad/sec)

Unaged

RTFO

PAV

0.1

10

1000

100000

0.01 0.1 1 10 100 1000

G*

sinδ

at

28

oC

(k

Pa

)


Unaged

RTFO

PAV

47

Figure 5.2: DSR Test Results for Unaged, RTFO-aged, and PAV-aged

PG 64-22 at High and Intermediate Temperatures.

0.001

0.1

10

1000

0.01 0.1 1 10 100 1000

G*

/sinδ

at

64

oC

(k

Pa

)


PAV

RTFO

Unaged

0.1

10

1000

100000

0.01 0.1 1 10 100 1000

G*

sinδ

at

25

oC

(k

Pa

)


PAV

RTFO

Unaged

48

Figure 5.3 FTIR Spectra for Unaged, RTFO-aged, and PAV-aged PG 70-22.

Figure 5.4 FTIR Spectra for Unaged, RTFO-aged, and PAV-aged PG 64-22.

0

0.06

0.12

0.18

0.24

0.3

500 750 1000 1250 1500 1750 2000

Ab

sorb

an

ce

Wavenumber (cm-1)

PAV

RTFO

Unaged

C=OS=O

0

0.1

0.2

0.3

0.4

0.5

500 750 1000 1250 1500 1750 2000

Ab

sorb

an

ce

Wavenumber (cm-1)

PAV

RTFO

Unaged

S=OC=O

49

Figure 5.5: GPC Chromatograms for Unaged, RTFO-aged, and PAV-aged PG 70-22.

Figure 5.6: GPC Chromatograms for Unaged, RTFO-aged, and PAV-aged PG 64-22.

0

5

10

15

20

25

0 4 8 12 16 20

Ref

ract

ive

Ind

ex (

RI)

Retention Volume (mL)

PAV

RTFO

Unaged

0

5

10

15

20

25

0 4 8 12 16 20

Ref

ract

ive

Ind

ex (

RI)

Retention Volume (mL)

PAV

RTFO

Unaged

50

Figure 5.7: AFM Force-Distance Curves for Unaged, RTFO-aged, and PAV-aged PG 70-22.

Figure 5.8: AFM Force-Distance Curves for Unaged, RTFO-aged, and PAV-aged PG 64-22.

-800

-600

-400

-200

0

200

400

600

800

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Forc

e (n

N)

Distance (m)

Unaged

RTFO

PAV

-400

-300

-200

-100

0

100

200

300

400

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Forc

e (n

N)

Distance (m)

Unaged

RTFO

PAV

51

5.3 Effect of Extraction and Recovery

Figures 5.9 and 5.10 present the effect of the extraction and recovery procedures on the

DSR test results for the unaged, RTFO-aged, and PAV-aged PG 70-22 and PG 64-22 asphalt

binders, respectively. The error bars in these figures represent one standard deviation from the

mean. As can be noticed from Figure 5.9, little effect was observed for the unaged and RTFO-

aged PG 70-22 asphalt binders due to the extraction and recovery. However, a slight decrease in

G*/sin and G*sin was noticed for the PAV-aged PG 70-22 asphalt binder. In addition, by

comparing the DSR test results obtained for the asphalt binders recovered from the binder/TCE

solutions with and without dust, it appears that the extraction procedure was able to remove most

of the dust that was introduced into the binder/TCE solutions. Figure 5.10 shows that the effect

of the extraction and recovery procedures was more pronounced on the rheological properties of

PG 64-22 especially at the intermediate temperature. This was the case for the unaged, RTFO-

aged, and PAV-aged asphalt binders. This implies that PG 64-22 is more sensitive to the

extraction and recovery procedures using TCE than PG 70-22.

As mentioned earlier, XRD testing was performed to examine the presence of any dust

remaining in the recovered unaged, RTFO-aged, and PAV-aged asphalt binders. Figure 5.11

presents the XRD test results for limestone dust, and Figures 5.12 and 5.13 present the XRD test

results for unaged, RTFO-aged, and PAV-aged PG 70-22 asphalt binders recovered from

TCE/binder and from TCE/binder/dust solutions, respectively. As can be noticed from these

figures, the same dominant peaks for the limestone dust were observed in the recovered asphalt

binders that were obtained from the binder/TCE solutions containing dust, but not in the asphalt

binders recovered from the binder/TCE solutions that did not contain any dust. This indicates

that some traces of dust remained in the asphalt binders after recovery from the binder/TCE/dust

solutions even though the effect was minimal on the DSR test results. Similar results were

obtained for PG 64-22 asphalt binder. Therefore, they were not included in this section.

52

Figure 5.9: Effect of Extraction and Recovery on DSR

Test Results for Unaged, RTFO-aged, and PAV-aged PG 70-22.

1.5 1.71.4

3.73.3

3.8

11.0

9.3

7.8

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Unaged Unaged

+ TCE

Unaged

+ TCE

+ Dust

RTFO RTFO

+ TCE

RTFO

+ TCE

+ Dust

PAV PAV

+ TCE

PAV

+ TCE

+ Dust

G*

/sin

a

t 7

0oC

an

d 1

0 r

ad

/sec

(k

Pa)

487 545

308

948 9721082

2269

17601761

0

1000

2000

3000

4000

5000

Unaged Unaged

+ TCE

Unaged

+ TCE

+ Dust

RTFO RTFO

+ TCE

RTFO

+ TCE

+ Dust

PAV PAV

+ TCE

PAV

+ TCE

+ Dust

G*

sin

at

28

oC

an

d 1

0 r

ad

/sec

(k

Pa)

53

Figure 5.10: Effect of Extraction and Recovery on DSR

Test Results for Unaged, RTFO-aged, and PAV-aged PG 64-22.

1.2

0.5 0.5

2.8

1.41.0

8.7

6.1

3.8

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Unaged Unaged

+ TCE

Unaged

+ TCE

+ Dust

RTFO RTFO

+ TCE

RTFO

+ TCE

+ Dust

PAV PAV

+ TCE

PAV

+ TCE

+ Dust

G*

/sin

a

t 6

4oC

an

d 1

0 r

ad

/sec

(k

Pa)

833

176 187

1843

272327

3032

936 941

0

1000

2000

3000

4000

5000

Unaged Unaged

+ TCE

Unaged

+ TCE

+ Dust

RTFO RTFO

+ TCE

RTFO

+ TCE

+ Dust

PAV PAV

+ TCE

PAV

+ TCE

+ Dust

G*

sin

at

25

oC

an

d 1

0 r

ad

/sec

(k

Pa)

54

Figure 5.11 XRD Test Results for Limestone Dust.

Figure 5.12: XRD Test Results for Unaged, RTFO-aged, and PAV-aged

PG 70-22 Binders Recovered from TCE/Binder Solutions without Dust.

0

5000

10000

15000

20000

25000

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty

2q (degrees)

Dust

0

1000

2000

3000

4000

5000

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty

2q (degrees)

Binder Recovered from Unaged+TCE

Binder Recovered from RTFO+TCE

Binder Recovered from PAV+TCE

55

Figure 5.13: XRD Test Results for Unaged, RTFO-aged, and PAV-aged

PG 70-22 Binders Recovered from TCE/Binder Solutions Containing Dust.

5.4 Laboratory Aging of Asphalt Mixtures

5.4.1 DSR Test Results

Figures 5.14 and 5.15 present the effect of asphalt binder and mixture aging on the DSR

test results for PG 70-22 and PG 64-22, respectively. The error bars in these figures represent

one standard deviation from the mean. The DSR test was performed on two foamed WMA and

HMA blends to facilitate the interpretation of the test results. As can be noticed from these

figures, comparable or slightly higher G*/sin and G*sin values were obtained for the asphalt

binders recovered from the HMA mixtures than those recovered from the foamed WMA

mixtures. This was the case for both short-term and long-term oven aging.

Figure 5.14 shows that the G*/sin and G*sin values obtained for PG 70-22 asphalt

binder recovered from foamed WMA and HMA mixtures immediately after mixing are slightly

higher than those obtained for the unaged asphalt binder. This indicates that the asphalt binder

undergoes a slight increase in stiffness after mixing with the aggregates, which can be attributed

to the reduced asphalt binder film thickness and increased exposure to air. It can also be noticed

0

1000

2000

3000

4000

5000

0 10 20 30 40 50 60 70 80 90

Inte

nsi

ty

2q (degrees)

Binder Recovered from Unaged+TCE+Dust

Binder Recovered from RTFO+TCE+Dust

Binder Recovered from PAV+TCE+Dust

56

from this figure that the G*/sin and G*sin values obtained for PG 70-22 asphalt binder

recovered from short-term oven aged (STOA) foamed WMA and HMA mixtures are slightly

higher than those obtained for the RTFO-aged residue, while the G*/sin and G*sin values

obtained for PG 70-22 asphalt binder recovered from long-term oven aged (LTOA) foamed

WMA and HMA mixtures are slightly lower than the PAV-aged residue except for the asphalt

binder recovered from the LTOA HMA mixture tested at 70oC. This indicates that the RTFO test

results in less aging than the short-term oven aging procedure in AASHTO R30, while the PAV

test results in not consistently higher or lower aging than the long-term oven aging procedure in

AASHTO R30.

The effect of the extraction and recovery procedures on the rheological properties of

PG 64-22 is obvious in Figure 5.15 in that the G*/sin and G*sin values for the asphalt binders

recovered from foamed WMA and HMA mixtures immediately after mixing are lower than the

unaged PG 64-22 asphalt binder. It can be noticed, however, that the G*/sin and G*sin values

obtained for the PG 64-22 asphalt binder recovered after mixing in Figure 5.15 are close to those

obtained for the PG 64-22 asphalt binder recovered from the unaged binder/TCE solutions with

and without dust in Figure 5.10.

Similar comparisons between Figure 5.15 and Figure 5.10 show that the short-term oven

aging of PG 64-22 asphalt mixtures results in higher levels of binder aging than the RTFO

procedure, and that the long-term oven aging of traditional HMA mixtures prepared using PG

64-22 results in higher levels of binder aging than the PAV procedure, while the long-term oven

aging of foamed WMA mixtures prepared using PG 64-22 results in lower levels of binder aging

than the PAV procedure. Similar to PG 70-22 asphalt binder, this indicates that the RTFO test

results in less aging than the short-term oven aging procedure in AASHTO R30, while the PAV

test results in not consistently higher or lower aging than the long-term oven aging procedure in

AASHTO R30.

57

Fig

ure

5.1

4:

Com

par

ison

of

DS

R T

est

Res

ult

s fo

r A

sphal

t B

inder

and A

sph

alt

Mix

ture

Agin

g f

or

PG

70

-22.

1.5

2.1

2.4

3.7

5.3

4.4

11

.0

13

.0

8.0

0.0

3.0

6.0

9.0

12

.0

15

.0

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

1)

WM

A

Aft

er

Mix

ing

(Ble

nd

1)

RT

FO

HM

A

ST

OA

(Ble

nd

1)

WM

A

ST

OA

(Ble

nd

1)

PA

VH

MA

LT

OA

(Ble

nd

1)

WM

A

LT

OA

(Ble

nd

1)

G*/sinat 70oC and 10 rad/sec (kPa)

1.5

2.5

2.3

3.7

5.2

5.1

11

.0

13

.1

9.0

0.0

3.0

6.0

9.0

12

.0

15

.0

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

2)

WM

A

Aft

er

Mix

ing

(Ble

nd

2)

RT

FO

HM

A

ST

OA

(Ble

nd

2)

WM

A

ST

OA

(Ble

nd

2)

PA

VH

MA

LT

OA

(Ble

nd

2)

WM

A

LT

OA

(Ble

nd

2)


48

76

50

66

7

94

8

13

87

12

92

22

69

22

33

17

98

0

10

00

20

00

30

00

40

00

50

00

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

1)

WM

A

Aft

er

Mix

ing

(Ble

nd

1)

RT

FO

HM

A

ST

OA

(Ble

nd

1)

WM

A

ST

OA

(Ble

nd

1)

PA

VH

MA

LT

OA

(Ble

nd

1)

WM

A

LT

OA

(Ble

nd

1)

G*sinat 28oC and 10 rad/sec (kPa)

48

75

96

.87

29

.1

94

8

13

72

.51

30

0.3

22

69

17

85

.8

21

36

.4

0

10

00

20

00

30

00

40

00

50

00

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

2)

WM

A

Aft

er

Mix

ing

(Ble

nd

2)

RT

FO

HM

A

ST

OA

(Ble

nd

2)

WM

A

ST

OA

(Ble

nd

2)

PA

VH

MA

LT

OA

(Ble

nd

2)

WM

A

LT

OA

(Ble

nd

2)


58

Fig

ure

5.1

5:

Com

par

ison

of

DS

R T

est

Res

ult

s fo

r A

sphal

t B

inder

and A

sph

alt

Mix

ture

Agin

g f

or

PG

64

-22.

1.2

0.7

0.4

2.8

2.3

1.5

8.7

5.7

2.7

0.0

3.0

6.0

9.0

12

.0

15

.0

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

1)

WM

A

Aft

er

Mix

ing

(Ble

nd

1)

RT

FO

HM

A

ST

OA

(Ble

nd

1)

WM

A

ST

OA

(Ble

nd

1)

PA

VH

MA

LT

OA

(Ble

nd

1)

WM

A

LT

OA

(Ble

nd

1)


1.2

0.6

0.8

2.8

2.2

1.8

8.7

4.8

3.1

0.0

3.0

6.0

9.0

12

.0

15

.0

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

2)

WM

A

Aft

er

Mix

ing

(Ble

nd

2)

RT

FO

HM

A

ST

OA

(Ble

nd

2)

WM

A

ST

OA

(Ble

nd

2)

PA

VH

MA

LT

OA

(Ble

nd

2)

WM

A

LT

OA

(Ble

nd

2)


83

3

23

51

04

18

43

67

25

50

30

32

11

83

70

1

0

10

00

20

00

30

00

40

00

50

00

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

1)

WM

A

Aft

er

Mix

ing

(Ble

nd

1)

RT

FO

HM

A

ST

OA

(Ble

nd

1)

WM

A

ST

OA

(Ble

nd

1)

PA

VH

MA

LT

OA

(Ble

nd

1)

WM

A

LT

OA

(Ble

nd

1)


83

3

11

32

34

18

43

83

6

59

9

30

32

99

79

10

0

10

00

20

00

30

00

40

00

50

00

Un

aged

HM

A

Aft

er

Mix

ing

(Ble

nd

2)

WM

A

Aft

er

Mix

ing

(Ble

nd

2)

RT

FO

HM

A

ST

OA

(Ble

nd

2)

WM

A

ST

OA

(Ble

nd

2)

PA

VH

MA

LT

OA

(Ble

nd

2)

WM

A

LT

OA

(Ble

nd

2)


59

5.4.2 FTIR Test Results

The carbonyl and sulfoxide indices suggested by Lamontagne et al. (2001) were utilized

to quantify the asphalt binder aging from the FTIR spectra:

C O Area of the carbonyl band centered around 00 cm-

Area of the spectral bands between 2000 and 500 cm- (5.1)

S O Area of the sulfoxide band centered around 030 cm-

Area of the spectral bands between 2000 and 500 cm- (5.2)

Spectral normalization was performed by bringing the same absorbent series at the same

point to avoid the variation of binder film thickness on the KBr plate. This normalization was

performed to compare the test results using the same scale.

Figures 5.16 and 5.17 present the carbonyl and sulfoxide indices obtained from the FTIR

spectra for PG 70-22 and PG 64-22 asphalt binders, respectively. The error bars in these figures

represent one standard deviation from the mean. As can be noticed from these figures, the

carbonyl and sulfoxide indices for asphalt binders recovered from foamed WMA mixtures are

generally lower than those recovered from traditional HMA mixtures. It can also be noticed from

these figures that the increase in the carbonyl indices is more consistent than the increase in the

sulfoxide indices. Therefore, the change in the carbonyl index might be a better indicator of the

effect of aging.

As can be noticed from Figure 5.16, the carbonyl indices for PG 70-22 asphalt binder

recovered from STOA foamed WMA and HMA mixtures are slightly higher than those obtained

for the RTFO-aged residue, while the carbonyl indices for PG 70-22 asphalt binder recovered

from LTOA foamed WMA and HMA mixtures are slightly lower than those obtained for the

PAV-aged residue. A similar observation can be made for PG 64-22 in Figure 5.17. However,

little difference in carbonyl indices is observed between LTOA and STOA asphalt mixtures,

especially for foamed WMA. This indicates that laboratory-prepared foamed WMA and

HMA mixtures prepared using PG 64-22 are less susceptible to aging than those prepared using

PG 70-22.

60

Figure 5.16: Comparison of FTIR Test Results

for Asphalt Binder and Asphalt Mixture Aging for PG 70-22.

0.0200.020 0.019

0.025

0.027

0.026

0.0360.035

0.030

0.00

0.01

0.02

0.03

0.04

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

I C=

O

0.035

0.0410.039

0.035

0.0410.039

0.0450.046

0.043

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

I S=

O

61

Figure 5.17: Comparison of FTIR Test Results


0.021 0.021

0.018

0.024 0.024 0.025

0.032

0.027

0.025

0.00

0.01

0.02

0.03

0.04

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

I C=

O

0.039 0.040

0.044

0.0350.037

0.035

0.0440.045

0.041

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

I S=

O

62

5.4.3 GPC Test Results

The GPC data was analyzed by dividing the chromatogram into 13 slices of equal

retention volumes (or elution times) and classifying the slices into three groups: Slices 1-5 for

the large molecular size (LMS), Slices 6-9 for the medium molecular size (MMS), and Slices 10-

13 for the small molecular size (SMS), as shown in Figure 5.18. Previous research studies have

reported high correlation between asphalt binder properties upon aging and the percentage of

LMS within the asphalt binder. Therefore, only the percentage of LMS was used in this study to

evaluate aging. The percentage of LMS was calculated as the cumulative molecular weight

fraction obtained for the first five slices.

Figure 5.18: Analysis of GPC Data to Obtain

Large, Medium, and Small Molecular Size Fractions.

Figures 5.19 and 5.20 present the percentage of LMS obtained from the GPC

chromatograms for PG 70-22 and PG 64-22 asphalt binders, respectively. The error bars in these

figures represent one standard deviation from the mean. As can be noticed from these figures, the

percentage of LMS increased with the increase in the level of aging for both asphalt binders,

with the percentage of LMS being slightly higher for the traditional HMA mixtures than the

foamed WMA mixtures. Similar to the FTIR test results, little difference is observed in the

percentage of LMS between STOA and LTOA asphalt mixtures prepared using PG 64-22 as

compared to STOA and LTOA asphalt mixtures prepared using PG 70-22.

63

Figure 5.19: Comparison of GPC Test Results


Figure 5.20: Comparison of GPC Test Results


4.1%

7.5% 7.7%7.1%

11.4%10.5%

15.1%

18.1%

14.9%

0%

5%

10%

15%

20%

25%

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

LM

S (

%)

10.7%

15.4%14.4%

19.3%

25.4%

22.8%24.5%

27.4%26.6%

0%

7%

14%

21%

28%

35%

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

LM

S (

%)

64

5.4.4 AFM Test Results

Figures 5.21 and 5.22 present the effect of asphalt binder and mixture aging on the AFM

test results for PG 70-22 and PG 64-22, respectively. The reduced modulus, Ereduced, was

calculated using Equation 4.1, and the total energy needed to separate the AFM tip from the

asphalt sample, Ebonding, was calculated using Equation 4.3. The error bars in these figures

represent one standard deviation from the mean.

As can be noticed from Figures 5.21a and 5.22a, the reduced modulus of PG 70-22 and

PG 64-22 asphalt binders increased with the increase in the level of aging, with lower stiffness

values obtained for PG 64-22. It can also be noticed from these figures that asphalt binders

recovered from traditional HMA mixtures had slightly higher moduli than those recovered from

foamed WMA mixtures. In addition, it can be noticed that the reduced moduli of the RTFO-aged

binders were close to or less than the reduced moduli of the asphalt binders recovered from

STOA HMA and foamed WMA mixtures. Furthermore, the reduced moduli of the PAV-aged

binders were close to or less than the reduced moduli of the asphalt binders recovered from

LTOA HMA and foamed WMA mixtures. Interestingly, the effect of the extraction and recovery

procedures was not as obvious on the AFM test results as it was on the DSR test results for PG

64-22.

As can be noticed from Figures 5.21b and 5.22b, the total bonding energy of PG 70-22

and PG 64-22 asphalt binders decreased with the increase in the level of aging, with higher

bonding energy values obtained for PG 64-22. It can also be noticed from these figures that

asphalt binders recovered from traditional HMA mixtures had slightly lower bonding energy

values than those recovered from foamed WMA mixtures. In addition, it can be noticed that the

bonding energy values obtained for the asphalt binders recovered from the STOA HMA and

foamed WMA mixtures were close to or higher than that obtained for the RTFO-aged binder for

PG 70-22 and close to or lower than that obtained for the RTFO-aged binder for PG 64-22.

Furthermore, the bonding energy values obtained for the asphalt binders recovered from the

LTOA HMA and foamed WMA mixtures were close to or higher than that obtained for the

PAV-aged binder for PG 70-22 and close to or lower than that obtained for the PAV-aged binder

for PG 64-22. However, in general, the bonding energy values obtained for the asphalt binders

recovered from short-term and long-term aged asphalt mixtures were similar to those obtained

for short-term and long-term aged binders.

65

Figure 5.21: Comparison of AFM Test Results


11,512

16,294

13,343

20,858 19,85220,459

49,329

61,090

44,427

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

Ere

du

ced

(kP

a)

(a)

152,751

136,858135,345

86,39191,712

115,706

84,035

88,441102,370

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

Eb

on

din

g(n

N.n

m)

(b)

66

Figure 5.22: Comparison of AFM Test Results


6,991 5,762 5,620

10,650

18,45818,099

40,606

46,113 43,596

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

Ere

du

ced

(kP

a)

(a)

249,350

201,130 209,397

220,806

175,134

176,605

122,814

116,808131,521

0

40,000

80,000

120,000

160,000

200,000

240,000

280,000

320,000

360,000

Unaged HMA

After

Mixing

(Blend 1)

WMA

After

Mixing

(Blend 1)

RTFO HMA

STOA

(Blend 1)

WMA

STOA

(Blend 1)

PAV HMA

LTOA

(Blend 1)

WMA

LTOA

(Blend 1)

Eb

on

din

g(n

N.n

m)

(b)

67

5.4.5 Dynamic Modulus Test Results

Figures 5.23 to 5.26 present the dynamic modulus test results for the STOA and

LTOA foamed WMA and HMA mixtures prepared using PG 70-22 and PG 64-22. As can be

noticed from these figures, the dynamic modulus decreased with the increase in testing

temperature and increased with the increase in loading frequency for all asphalt mixtures. It can

also be noticed from these figures that the dynamic modulus of the foamed WMA mixtures was

slightly lower than that of the HMA mixtures. This was the case for both STOA and LTOA

asphalt mixtures.

In order to quantify the effect of aging on the dynamic modulus of the foamed WMA and

HMA asphalt mixtures, the dynamic modulus of the LTOA specimens (Figures 5.24 and 5.26)

was divided by the dynamic modulus of the STOA specimens (Figures 5.23 and 5.25). The

resulting |E*|LTOA/|E*|STOA ratios for asphalt mixtures prepared using PG 70-22 and PG 64-22

are presented in Figures 5.27 and 5.28, respectively. As can be noticed from these figures,

the |E*|LTOA/|E*|STOA ratios obtained for asphalt mixtures prepared using PG 70-22 ranged

between 1.2 and 2.4, while the |E*|LTOA/|E*|STOA ratios obtained for asphalt mixtures prepared

using PG 64-22 ranged between 1.1 and 1.5. This indicates that aging had a more pronounced

effect on the dynamic modulus of asphalt mixtures prepared using PG 70-22 than the dynamic

modulus of asphalt mixtures prepared using PG 64-22.

To further examine the effect of aging on the dynamic modulus of the foamed WMA and

HMA mixtures, dynamic modulus master curves were developed for the STOA and LTOA

asphalt mixtures and compared over a wide range of frequencies that cannot be achieved using

traditional testing equipment. The dynamic modulus master curves were developed according to

the procedure described in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The

dynamic moduli obtained at various testing temperatures were plotted against loading frequency.

The dynamic moduli for each temperature were parallel-shifted to a reference temperature to

form a single continuous curve using the following equation:

(5.3)

where,

aT = frequency temperature shift factor for temperature, T;

= reduced frequency at reference temperature, To; and

fT = frequency at test temperature, T.

68

The sigmoidal function suggested by the MEPDG was used in this study to fit the

dynamic modulus master curve:

| |

( ) (5.4)

where,

E* = dynamic modulus;

fr = reduced frequency of loading at reference temperature; and

, δ, , = sigmoidal model parameters.

The Solver option in Microsoft Excel was used to determine the temperature shift factors

and sigmoidal model parameters.

Figures 5.29 and 5.32 present the dynamic modulus master curves for the STOA and

LTOA foamed WMA and HMA mixtures prepared using PG 70-22 and PG 64-22. A reference

temperature of 70oF (21

oC) was used in the development of these master curves. As can be

noticed from these figures, the effect of aging on the dynamic modulus of foamed WMA and

traditional HMA mixtures prepared using PG 70-22 was different than that observed for foamed

WMA and traditional HMA mixtures prepared using PG 64-22. As shown in Figures 5.29 and

5.30, aging had a pronounced effect on the dynamic modulus of foamed WMA and HMA

mixtures prepared using PG 70-22 at low frequencies (or high temperatures) and a relatively

small effect at high frequencies (or low temperatures). As for asphalt mixtures prepared using

PG 64-22, little difference in dynamic modulus is observed between the LTOA and STOA

foamed WMA mixtures at low and high frequencies, while a small increase in dynamic modulus

is noticed between the LTOA and STOA HMA mixtures at low and high frequencies (Figures

5.31 and 5.32). This implies that out of these four asphalt mixtures, foamed WMA mixtures

prepared using PG 64-22 are the least susceptible to aging.

69

Figure 5.23: |E*| of STOA HMA and Foamed WMA Mixtures Prepared using PG 70-22.

Figure 5.24: |E*| of LTOA HMA and Foamed WMA Mixtures Prepared using PG 70-22.

0

500

1000

1500

2000

2500

3000

3500

4000

25 10 5 1 0.5 0.1

Dy

na

mic

Mo

du

lus,

|E

*|(k

si)

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

0

500

1000

1500

2000

2500

3000

3500

4000

25 10 5 1 0.5 0.1

Dy

na

mic

Mo

du

lus,

|E

*|(k

si)

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

70

Figure 5.25: |E*| of STOA HMA and Foamed WMA Mixtures Prepared using PG 64-22.

Figure 5.26: |E*| of LTOA HMA and Foamed WMA Mixtures Prepared using PG 64-22.

0

500

1000

1500

2000

2500

3000

3500

4000

25 10 5 1 0.5 0.1

Dy

na

mic

Mo

du

lus,

|E

*|(k

si)

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

0

500

1000

1500

2000

2500

3000

3500

4000

25 10 5 1 0.5 0.1

Dy

na

mic

Mo

du

lus,

|E

*|(k

si)

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

71

Figure 5.27: |E*|LTOA/|E*|STOA for HMA and Foamed WMA Mixtures Prepared using PG 70-22.

Figure 5.28: |E*|LTOA/|E*|STOA for HMA and Foamed WMA Mixtures Prepared using PG 64-22.

0

0.5

1

1.5

2

2.5

3

25 10 5 1 0.5 0.1

|E*

| LT

OA

/ |E

*| S

TO

A

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

0

0.5

1

1.5

2

2.5

3

25 10 5 1 0.5 0.1

|E*

| LT

OA

/ |E

*| S

TO

A

Frequency, f (Hz)

WMA 40F

HMA 40F

WMA 70F

HMA 70F

WMA 100F

HMA 100F

WMA 130F

HMA 130F

72

Figure 5.29: Dynamic Modulus Master Curve for STOA and LTOA

Foamed WMA Mixtures Prepared using PG 70-22 (Reference Temperature of 70oF).


HMA Mixtures Prepared using PG 70-22 (Reference Temperature of 70oF).

1

10

100

1000

10000

0.000001 0.0001 0.01 1 100 10000 1000000

Dy

na

mic

Mo

du

lus,

|E

*| (k

si)

Frequency, f (Hz)

WMA LTOA

WMA STOA

1

10

100

1000

10000

0.000001 0.0001 0.01 1 100 10000 1000000

Dy

na

mic

Mo

du

lus,

|E

*| (k

si)

Frequency, f (Hz)

HMA LTOA

HMA STOA

73


Foamed WMA Mixtures Prepared using PG 64-22 (Reference Temperature of 70oF).


HMA Mixtures Prepared using PG 64-22 (Reference Temperature of 70oF).

1

10

100

1000

10000

0.000001 0.0001 0.01 1 100 10000 1000000

Dy

na

mic

Mo

du

lus,

|E

*| (k

si)

Frequency, f (Hz)

WMA LTOA

WMA STOA

1

10

100

1000

10000

0.000001 0.0001 0.01 1 100 10000 1000000

Dy

na

mic

Mo

du

lus,

|E

*| (k

si)

Frequency, f (Hz)

HMA LTOA

HMA STOA

74

5.5 Field Aging of Asphalt Mixtures

As mentioned earlier, this study investigated the effect of aging on foamed WMA and

HMA mixtures placed in the field. Field cores were collected from four roadway sections in

Ohio (US Route 224 in Portage County, State Route 303 in Summit County, US Route 62 in

Pickaway County, and State Route 49 in Miami County) that were constructed using both

foamed WMA and HMA mixtures prepared using the same materials (asphalt binder and

aggregates), aggregate gradation, and asphalt binder content. All pavement sections were

constructed in 2008 as part of ODOT’s initial field implementation of foamed WMA in Ohio.

The asphalt binder recovered from each field core was examined for the same physical,

chemical, and morphological properties using the same test procedures as the laboratory-

produced foamed WMA and HMA mixtures.

5.5.1 DSR Test Results

Figures 5.33 to 5.36 present the DSR test results for the asphalt binders recovered from

the surface course of the four roadway sections mentioned earlier. Each figure is divided into

three parts. The first part shows the DSR test results for the unaged, RTFO-aged, and PAV-aged

binders. The second part shows the effect of the extraction and recovery procedures on the

unaged and aged asphalt binders. The third part shows the DSR test results for the asphalt

binders recovered from the surface course of each project. For comparison purposes, two field

cores were used for each mix type in each project. As can be noticed from these figures, PG 70-

22 asphalt binder was used in all surface courses with the exception of Project No. 342-08 in

Pickaway County. It is noted, however, that the PG 70-22 and PG 64-22 asphalt binders used in

the laboratory were not identical to the asphalt binders used in the field even though they had the

same performance grade. Therefore, care should be taken in interpreting the laboratory and field

test results.

By comparing the DSR test results in Figures 5.33 to 5.36 for the asphalt binders

recovered from foamed WMA and HMA field cores, it can be seen that there are no consistent

differences between the two mix types. This was the case for both PG 70-22 and PG 64-22

asphalt binders. Furthermore, it can be noticed that there was high variability between cores A

and B even though they were obtained from the same roadway section.

75

In general, the DSR test results obtained for the asphalt binders recovered from the

foamed WMA and HMA field cores fell within the range obtained for the RTFO-aged and PAV-

aged binders recovered from binder/TCE solutions containing dust, with the DSR test results for

the asphalt binders recovered from the field cores being closer to those obtained for the RTFO-

aged binders. This was not unexpected since the PAV test was designed to simulate asphalt

binder aging after 7 to 10 years of service, while the field cores were obtained 6 years after

placement of the surface course.

5.5.2 FTIR Test Results

Figures 5.37 to 5.40 present the FTIR test results for the asphalt binders recovered from

the four roadway sections as well as the unaged, RTFO-aged, and PAV-aged PG 70-22 and PG

64-22 asphalt binders used in the laboratory investigation. As can be noticed from these figures,

similar results were obtained for the asphalt binders recovered from foamed WMA and HMA

field cores, without one mix type showing consistently higher carbonyl and sulfoxide indices

than the other. This implies that both mix types had comparable levels of aging with no mix type

showing significantly higher levels of aging than the other.

As mentioned earlier, the asphalt binders used in the laboratory were different than those

used in the field even though they had the same performance grade. This difference is obvious in

Figures 5.37 to 5.40 in that widely varying carbonyl and sulfoxide indices were obtained for the

laboratory and field asphalt binders, which is likely due to the difference in chemical

composition of laboratory and field asphalt binders. This was particularly the case for the

sulfoxide indices where asphalt binders recovered from field cores showed higher indices than

unaged and laboratory aged asphalt binders.

5.5.3 GPC Test Results

Figures 5.41 to 5.44 present the GPC test results for the asphalt binders recovered from



the percentage of LMS was almost the same for asphalt binders recovered from foamed WMA

and HMA field cores obtained from State Route 49 (Project No. 329-08) in Miami County. For

field cores obtained from US Route 62 (Project No. 342-08) in Pickaway County and US Route

76

224 (Project No. 386-08) in Portage County, the percentage of LMS was higher for asphalt

binders recovered from HMA than those recovered from foamed WMA mixtures, while for field

cores obtained from State Route 303 (Project No. 352-08) in Summit County, the percentage of

LMS was higher for asphalt binders recovered from foamed WMA than those recovered from

HMA mixtures. This implies that no one mix type showed consistently higher levels of aging.

By comparing the percentage of LMS for the asphalt binders recovered from the field

cores to the unaged, RTFO-aged, and PAV-aged PG 70-22 and PG 64-22 asphalt binders, it can

be noticed that the percentage of LMS obtained for the asphalt binders recovered from the field

cores were generally higher than those obtained for the PAV-aged asphalt binders. However,

given that the asphalt binders used in the laboratory were different than those used in the field,

no direct comparison can be made between the laboratory and field asphalt binders.

5.5.4 AFM Test Results

Figures 5.45 to 5.48 present the AFM test results for the asphalt binders recovered from



there are no consistent differences between foamed WMA and HMA mixtures placed in the field

based on Ereduced and Ebonding. This implies that there are no consistent differences in the level of

aging between the two mix types.

By comparing the Ereduced values obtained for the asphalt binders recovered from the field

cores to the unaged, RTFO-aged, and PAV-aged PG 70-22 and PG 64-22 asphalt binders in

Figures 5.45a to 5.48a, it can be noticed that the Ereduced values obtained for the PG 70-22 asphalt

binders recovered from the field cores were generally higher than those obtained for the RTFO-

aged PG 70-22 binder, but lower than those obtained for the PAV-aged PG 70-22 binder, while

the Ereduced values obtained for the PG 64-22 asphalt binders recovered from the field cores were

generally close to or lower than those obtained for the RTFO-aged PG 64-22 binder.

By comparing the Ebonding values obtained for the asphalt binders recovered from the field

cores to the unaged, RTFO-aged, and PAV-aged PG 70-22 and PG 64-22 asphalt binders in

Figures 5.45b to 5.48b, it can be noticed that the Ebonding values obtained for the asphalt binders

recovered from the field cores were significantly higher than those obtained for the PAV-aged

asphalt binders. This was the case for both PG 70-22 and PG 64-22 binders. This can be

77

attributed to the differences in the crude oil source, chemical composition and properties of the

asphalt binders used in the field and those evaluated in the laboratory study.

78

Figure 5.33: DSR Test Results for PG 70-22 Binder Recovered

from Surface Course of Project No. 329-08 in Miami County.

1.5

3.7

11.0

1.4

3.8

7.8

3.5 3.3 3.4

4.8

0.0

3.0

6.0

9.0

12.0

15.0

Unaged RTFO PAV Unaged

+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

329-08

Miami

HMA

Core A

329-08

Miami

HMA

Core B

329-08

Miami

WMA

Core A

329-08

Miami

WMA

Core B

G*

/sin

a

t 7

0oC

an

d 1

0 r

ad

/sec

(k

Pa

)

487

948

2269

308

1082

1761

1286

1079

951

1477

0

600

1200

1800

2400

3000


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

329-08

Miami

HMA

Core A

329-08

Miami

HMA

Core B

329-08

Miami

WMA

Core A

329-08

Miami

WMA

Core B

G*

sin

at

28

oC

an

d 1

0 r

ad

/sec

(k

Pa

)

79


from Surface Course of Project No. 342-08 in Pickaway County.

1.2

2.8

8.7

0.51.0

3.8

2.0

3.4

1.1

2.1

0.0

3.0

6.0

9.0

12.0

15.0


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

342-08

Pickaway

HMA

Core A

342-08

Pickaway

HMA

Core B

342-08

Pickaway

WMA

Core A

342-08

Pickaway

WMA

Core B

G*

/sin

a

t 6

4oC

an

d 1

0 r

ad

/sec

(k

Pa

)

833

1843

3032

187

327

941854

1760

278

703

0

700

1400

2100

2800

3500


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

342-08

Pickaway

HMA

Core A

342-08

Pickaway

HMA

Core B

342-08

Pickaway

WMA

Core A

342-08

Pickaway

WMA

Core B

G*

sin

at

25

oC

an

d 1

0 r

ad

/sec

(k

Pa

)

80


from Surface Course of Project No. 352-08 in Summit County.

1.5

3.7

11.0

1.4

3.8

7.8

6.2

3.2

7.7

3.4

0.0

3.0

6.0

9.0

12.0

15.0


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

352-08

Summit

HMA

Core A

352-08

Summit

HMA

Core B

352-08

Summit

WMA

Core A

352-08

Summit

WMA

Core B

G*

/sin

a

t 7

0oC

an

d 1

0 r

ad

/sec

(k

Pa

)

487

948

2269

308

1082

1761

2269

872

2010

777

0

600

1200

1800

2400

3000


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

352-08

Summit

HMA

Core A

352-08

Summit

HMA

Core B

352-08

Summit

WMA

Core A

352-08

Summit

WMA

Core B

G*

sin

at

28

oC

an

d 1

0 r

ad

/sec

(k

Pa

)

81


from Surface Course of Project No. 386-08 in Portage County.

1.5

3.7

11.0

1.4

3.8

7.8

4.0

2.4 2.2

5.0

0.0

3.0

6.0

9.0

12.0

15.0


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

386-08

Portage

HMA

Core A

386-08

Portage

HMA

Core B

386-08

Portage

WMA

Core A

386-08

Portage

WMA

Core B

G*

/sin

a

t 7

0oC

an

d 1

0 r

ad

/sec

(k

Pa

)

487

948

2269

308

1082

1761

890

561 525 525

0

600

1200

1800

2400

3000


+ TCE

+ Dust

RTFO

+ TCE

+ Dust

PAV

+ TCE

+ Dust

386-08

Portage

HMA

Core A

386-08

Portage

HMA

Core B

386-08

Portage

WMA

Core A

386-08

Portage

WMA

Core B

G*

sin

at

28

oC

an

d 1

0 r

ad

/sec

(k

Pa

)

82

Figure 5.37: FTIR Test Results for PG 70-22 Binder Recovered


0.020

0.025

0.036

0.025

0.047

0

0.01

0.02

0.03

0.04

0.05

0.06

Unaged RTFO PAV 329-08

Miami

HMA

329-08

Miami

WMA

I C=

O

0.035 0.035

0.045

0.051

0.042

0

0.01

0.02

0.03

0.04

0.05

0.06


Miami

HMA

329-08

Miami

WMA

I S=

O

83



0.021

0.024

0.032

0.017

0.021

0

0.01

0.02

0.03

0.04

0.05

0.06


Pickaway

HMA

342-08

Pickaway

WMA

I C=

O

0.0390.035

0.044

0.095

0.083

0

0.02

0.04

0.06

0.08

0.1

0.12


Pickaway

HMA

342-08

Pickaway

WMA

I S=

O

84



0.020

0.025

0.036

0.0400.042

0

0.01

0.02

0.03

0.04

0.05

0.06


Summit

HMA

352-08

Summit

WMA

I C=

O

0.035 0.035

0.045

0.069

0.066

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08


Summit

HMA

352-08

Summit

WMA

I S=

O

85



0.020

0.025

0.036

0.023

0.032

0

0.01

0.02

0.03

0.04

0.05

0.06


Portage

HMA

386-08

Portage

WMA

I C=

O

0.035 0.035

0.045

0.0890.086

0

0.02

0.04

0.06

0.08

0.1


Portage

HMA

386-08

Portage

WMA

I S=

O

86

Figure 5.41: GPC Test Results for PG 70-22 Binder Recovered




4.1%

7.1%

15.1%

23.0% 23.1%

0%

8%

16%

24%

32%

40%


Miami

HMA

329-08

Miami

WMA

LM

S (

%)

10.7%

19.3%

24.5%

31.0%

24.5%

0%

8%

16%

24%

32%

40%


Pickaway

HMA

342-08

Pickaway

WMA

LM

S (

%)

87





4.1%

7.1%

15.1%

12.9%

16.4%

0%

8%

16%

24%

32%

40%


Summit

HMA

352-08

Summit

WMA

LM

S (

%)

4.1%

7.1%

15.1%

19.2%

16.0%

0%

8%

16%

24%

32%

40%


Portage

HMA

386-08

Portage

WMA

LM

S (

%)

88

Figure 5.45: AFM Test Results for PG 70-22 Binder Recovered


11,512

20,858

49,329

22,889

28,855

19,820

23,491

0

10000

20000

30000

40000

50000

60000

70000


Miami

HMA

Core A

329-08

Miami

HMA

Core B

329-08

Miami

WMA

Core A

329-08

Miami

WMA

Core B

Ere

du

ced

(kP

a)

(a)

152,751

86,39184,035

126,834

162,133

122,201

210,878

0

50000

100000

150000

200000

250000

300000

350000

400000


Miami

HMA

Core A

329-08

Miami

HMA

Core B

329-08

Miami

WMA

Core A

329-08

Miami

WMA

Core B

Eb

on

din

g(n

N.n

m)

(b)

89



6,991

10,650

40,606

6,970

10,70813,106 12,598

0

10000

20000

30000

40000

50000

60000


Pickaway

HMA

Core A

342-08

Pickaway

HMA

Core B

342-08

Pickaway

WMA

Core A

342-08

Pickaway

WMA

Core B

Ere

du

ced

(kP

a)

(a)

249,350 220,806

122,814

235,148

92,671

199,779

169,225

0

50000

100000

150000

200000

250000

300000

350000

400000


Pickaway

HMA

Core A

342-08

Pickaway

HMA

Core B

342-08

Pickaway

WMA

Core A

342-08

Pickaway

WMA

Core B

Eb

on

din

g(n

N.n

m)

(b)

90



11,512

20,858

49,329

31,79233,079

28,665

39,175

0

10000

20000

30000

40000

50000

60000

70000


Summit

HMA

Core A

352-08

Summit

HMA

Core B

352-08

Summit

WMA

Core A

352-08

Summit

WMA

Core A

Ere

du

ced

(kP

a)

(a)

152,751

86,39184,035

220,828

183,410

127,731

220,537

0

50000

100000

150000

200000

250000

300000

350000

400000


Summit

HMA

Core A

352-08

Summit

HMA

Core B

352-08

Summit

WMA

Core A

352-08

Summit

WMA

Core A

Eb

on

din

g(n

N.n

m)

(b)

91



11,512

20,858

49,329

20,552

31,991 31,934 32,072

0

10000

20000

30000

40000

50000

60000

70000


Portage

HMA

Core A

386-08

Portage

HMA

Core B

386-08

Portage

WMA

Core A

386-08

Portage

WMA

Core B

Ere

du

ced

(kP

a)

(a)

152,751

86,39184,035

175,825

275,175

233,538

141,969

0

50000

100000

150000

200000

250000

300000

350000

400000


Portage

HMA

Core A

386-08

Portage

HMA

Core B

386-08

Portage

WMA

Core A

386-08

Portage

WMA

Core B

Eb

on

din

g(n

N.n

m)

(b)

92

Chapter 6

Conclusions and Recommendations

6.1 Introduction

This study evaluated the short-term and long-term aging characteristics of foamed WMA

in comparison to traditional HMA. Two asphalt binders (PG 70-22 and PG 64-22) and one

aggregate (12.5 mm NMAS limestone aggregate) were used in this study. The short-term and

long-term aging of the two asphalt binders was simulated using the rolling thin film oven

(RTFO) and pressure aging vessel (PAV), respectively, while AASHTO R 30 was used to

simulate the short-term and long-term aging of the laboratory-prepared asphalt mixtures. The

dynamic shear rheometer (DSR) was used to characterize the viscoelastic behavior of the unaged

and aged asphalt binders, Fourier-transform infrared (FTIR) spectroscopy was used to identify

and quantify the amount of functional groups present in the asphalt binders, gel permeation

chromatography (GPC) was used to determine the molecular size distribution within the asphalt

binders, and atomic force microscopy (AFM) was used to examine the effect of aging on the

microstructure and morphology of the asphalt binders. In addition, the dynamic modulus (E*)

test was utilized to examine the effect of aging on the viscoelastic behavior of foamed WMA and

HMA mixtures. The dynamic modulus (E*) test was conducted according to AASHTO T 342

(Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete

Mixtures). However, it was performed on short-term aged as well as long-term aged foamed

WMA and HMA specimens.

The laboratory testing plan was also designed to quantify the effect of the extraction and

recovery procedures (AASHTO T 164 and AASHTO T 170, respectively) on the two asphalt

binders (PG 70-22 and PG 64-22) that were used in the laboratory-produced asphalt mixtures.

To determine the sensitivity of these asphalt binders to extraction and recovery, controlled

amounts of trichloroethylene (TCE), the solvent used in AASHTO T 164, and dust were added to

the unaged, RTFO-aged, and PAV-aged binders of both PG grades. AASHTO T 164 and

AASHTO T 170 were then used to recover the asphalt binders from the resulting solutions. The

DSR test was used to characterize the viscoelastic behavior of the original and recovered unaged,

RTFO-aged, and PAV-aged asphalt binders, and x-ray diffraction (XRD) was used to identify

the presence of any limestone dust remaining in the recovered asphalt binder.

93

This study also involved investigating the effect of aging on foamed WMA and HMA

mixtures placed in the field. Field cores were collected from four roadway sections in Ohio (US

Route 224 in Portage County, State Route 303 in Summit County, US Route 62 in Pickaway

County, and State Route 49 in Miami County) that were constructed using both foamed WMA

and HMA mixtures prepared using the same materials (asphalt binder and aggregates), aggregate

gradation, and asphalt binder content. All pavement sections were constructed in 2008 as part of

ODOT’s initial field implementation of foamed WMA in Ohio. The asphalt binder was extracted

from the field cores using AASHTO T 164 and recovered using AASHTO T 170. The recovered

binders were examined for the same physical, chemical, and morphological properties using the

same test procedures as the laboratory-produced foamed WMA and HMA mixtures.

6.2 Conclusions

Based on the experimental test results, the following observations and conclusions were

made:

Laboratory aging of foamed WMA and HMA mixtures:

- n general, comparable or slightly higher G*/sinδ and G*sinδ values were obtained using

the DSR test for asphalt binders recovered from laboratory-prepared HMA mixtures than

those recovered from laboratory-prepared foamed WMA mixtures. This was the case for

both short-term and long-term aged mixtures. This indicates that laboratory-prepared

foamed WMA mixtures undergo comparable or slightly lower levels of aging than

traditional HMA mixtures.

- The conventional DSR test results were consistent with the FTIR, GPC, and AFM test

results in that the carbonyl and sulfoxide indices from the FTIR, the percentage of large

molecular size (LMS) from the GPC, and the reduced modulus (Ereduced) from the AFM

indicated a slightly higher level of aging for the laboratory-prepared HMA mixtures than

the laboratory-prepared foamed WMA mixtures.

- The laboratory-prepared foamed WMA mixtures also exhibited a slightly lower dynamic

modulus than the traditional HMA mixtures. This was the case for both short-term and

long-term oven aged asphalt mixtures.

- Aging had a pronounced effect on the dynamic modulus of foamed WMA and HMA

mixtures prepared using PG 70-22 and little effect on the dynamic modulus of foamed

94

WMA and HMA mixtures prepared using PG 64-22. This indicates that the effect of

aging on the dynamic modulus is highly influenced by the type of asphalt binder used in

the asphalt mixture.

Effect of asphalt binder extraction and recovery:

- Little effect was observed for the extraction and recovery procedures on the rheological

properties of PG 70-22 especially for the unaged and RTFO-aged asphalt binders.

However, significantly lower G*/sinδ and G*sinδ values were obtained for the recovered

PG 64-22 asphalt binder. This implies that the PG 64-22 asphalt binder is more sensitive

to the extraction and recovery procedures using TCE than PG 70-22.

- Little difference in G*/sinδ and G*sinδ was observed for asphalt binders recovered from

binder/TCE solutions with and without dust. This suggests that the undertaken extraction

procedure was able to remove most of the dust that was introduced into the binder/TCE

solutions.

- The same dominant peaks for limestone dust were observed in the XRD test results for

recovered asphalt binders obtained from binder/TCE solutions containing dust. This

indicates that some traces of dust remained in the recovered asphalt binders even though

the effect was minimal on the DSR test results.

Comparison of laboratory binder and laboratory mixture aging:

- n general, the G*/sinδ and G*sinδ values obtained for asphalt binders recovered from

short-term oven aged foamed WMA and HMA mixtures were slightly higher than those

obtained for the corresponding RTFO-aged binders, while the G*/sinδ and G*sinδ values

obtained for asphalt binders recovered from long-term oven aged foamed WMA and

HMA mixtures were not consistently higher or lower than those obtained for the

corresponding PAV-aged binders. This indicates that the RTFO test procedure results in

less aging than the short-term oven aging procedure specified in AASHTO R30, while

the PAV test procedure results in comparable aging to the long-term oven aging

procedure specified in AASHTO R30. Similar results were also obtained from the FTIR,

GPC, and AFM tests.

Field aging of foamed WMA and HMA mixtures:

- No consistent differences were observed in the DSR test results for asphalt binders

recovered from field-placed foamed WMA and HMA mixtures. This was the case for

95

both PG 70-22 and PG 64-22 asphalt binders. This finding was likely due to the high

variability between the field cores even though a small standard deviation was obtained

for each core.

- In general, the DSR test results obtained for the asphalt binders recovered from the

foamed WMA and HMA field cores fell within the range obtained for the RTFO-aged

and PAV-aged binders recovered from binder/TCE solutions containing dust, with the

DSR test results for the asphalt binders recovered from the field cores being closer to

those obtained for the RTFO-aged binders. This was not unexpected since the PAV test

was designed to simulate asphalt binder aging after 7 to 10 years of service, while the

field cores were obtained 6 years after placement of the surface course.

- Similar results were obtained using the FTIR test for asphalt binders recovered from

foamed WMA and HMA field cores, without one mix type showing consistently higher

carbonyl and sulfoxide indices than the other. This implies that both mix types had

comparable levels of aging with no mix type showing significantly higher levels of aging

than the other.

- The percentage of LMS obtained using the GPC test was almost the same for asphalt

binders recovered from foamed WMA and HMA field cores obtained from State Route

49 (Project No. 329-08) in Miami County. For field cores obtained from US Route 62

(Project No. 342-08) in Pickaway County and US Route 224 (Project No. 386-08) in

Portage County, the percentage of LMS was higher for asphalt binders recovered from

HMA than those recovered from foamed WMA mixtures, while for field cores obtained

from State Route 303 (Project No. 352-08) in Summit County, the percentage of LMS

was higher for asphalt binders recovered from foamed WMA than those recovered from

HMA mixtures. This implies that no one mix type showed consistently higher levels of

aging.

- Given that the asphalt binders used in the laboratory were different than those used in the

field, no direct comparison can be made between the laboratory and field asphalt binders

using the FTIR and GPC tests.

- Comparable results were obtained for asphalt binders recovered from field-placed foamed

WMA and HMA mixtures using the AFM test, which is consistent with the previous test

results.

96

6.3 Recommendations for Implementation

This study investigated the short-term and long-term aging characteristics of foamed

WMA mixtures in comparison to traditional HMA mixtures. The experimental test results

showed a slightly lower level of aging for laboratory-prepared foamed WMA mixtures than for

laboratory-prepared traditional HMA mixtures. However, no consistent differences in the level

of aging were observed for foamed WMA and HMA mixtures placed in the field in 2008.

Consequently, there is no need to modify the asphalt binder and/or asphalt mixture laboratory

aging procedures to simulate the short-term and long-term aging of foamed WMA mixtures.

The extraction and recovery procedures were observed to have a significant influence on

the rheological properties of the recovered PG 64-22 asphalt binder and little influence on the

rheological properties of the recovered PG 70-22 asphalt binder. It is recommended to expand

this study to evaluate the effect of the extraction and recovery procedures using trichloroethylene

(TCE) on additional asphalt binders. Further research can also be conducted to determine if

alternative solvents can be used instead of TCE for asphalt binder extraction.

The effect of aging on foamed WMA and HMA mixtures was highly influenced by the

type of asphalt binder used in the asphalt mixture more so than the mix type. In this study,

foamed WMA and HMA mixtures prepared using PG 70-22 were found to be more susceptible

to aging than foamed WMA and HMA mixtures prepared using PG 64-22. Because field placed

asphalt mixtures may eventually be used as reclaimed asphalt pavement (RAP) in future

construction projects, the difference in binder aging shall be taken into consideration in the mix

design of new asphalt mixtures.

97

References

- Ahmed, E. I., S. A. M. Hesp, S. K. P. Samy, S. D. Rubab, and G. Warburton (2012). Effect of

Warm Mix Additives and Dispersants on Asphalt Rheological, Aging, and Failure Properties.

Construction and Building Materials, Vol. 37, pp. 493-498.

- Arega, Z., A. Bhasin, A. Motamed, and F. Turner (2011). Influence of Warm-Mix Additives

and Reduced Aging on the Rheology of Asphalt Binders with Different Natural Wax

Contents. Journal of Materials in Civil Engineering, Vol. 23, pp. 1453-1459.

- Arega, Z. and A. Bhasin (2012). Binder Rheology and Performance in Warm Mix Asphalt.

Texas Department of Transportation, Austin, TX. Report No. FHWA/TX-12/0-6591-2.

- Banerjee, A., A. de Fortier Smit, and J. A. Prozzi (2012). The Effect of Long-Term Aging on

the Rheology of Warm Mix Asphalt Binders. Fuel, Vol. 97, pp. 603-611.

- Fischer-Cripps, A. C. (2006). Critical Review of Analysis and Interpretation of Nano-

indentation Test Data. Surface and Coatings Technology, Vol. 200, Issues 14-15, pp. 4153-

4165.

- Gandhi, T. and S. Amirkhanian (2008). Laboratory Simulation of Warm Mix Asphalt (WMA)

Binder Aging Characteristics. Airfield and Highway Pavements, pp. 195-204.

- Gandhi, T., C. Akisetty, and S. Amirkhanian (2009). Laboratory Evaluation of Warm Asphalt

Binder Aging Characteristics. International Journal of Pavement Engineering, Vol. 10,

pp. 353-359.

- Gandhi, T., W. Rogers, and S. Amirkhanian (2010). Laboratory Evaluation of Warm Mix

Asphalt Ageing Characteristics. International Journal of Pavement Engineering, Vo. 11, pp.

133-142.

- Hossain, Z. and M. Zaman (2013). Behavior of Selected Warm Mix Asphalt Additive

Modified Binders and Prediction of Dynamic Modulus of the Mixes. Journal of Testing and

Evaluation, Vol. 41, pp. 159-170.

- Jennings, P. W., J. A. Pribanic, M. A. Desando, M. F. Raub, F. Stewart, J. Hoberg, R. Moats,

J. A. Smith, T. M. Mendes, M. McGrane, B. Fanconi, D. L. VanderHart, and W. F. Manders

(1993). Binder Characterization and Evaluation by Nuclear Magnetic Resonance

Spectroscopy. Strategic Highway Research Program, SHRP-A-335.

98

- Kim. H., S.-J. Lee, S. N. Amirkhanian, and K.-D. Jeong (2013). Quantification of Oxidative

Aging of Polymer-Modified Asphalt Mixes Made with Warm Mix Technologies. Journal of

Materials in Civil Engineering, Vol. 25, pp. 1-8.

- Lamontagne, J., P. Dumas, V. Mouillet, and J. Kister (2001). Comparison by Fourier

Transform Infrared (FTIR) Spectroscopy of Different Ageing Techniques: Application to

Road Bitumens. Fuel, Vol. 80(4), pp. 483-488.

- Nazzal, M. D. and L. Abu Qtaish (2013). The Use of Atomic Force Microscopy to Evaluate

Warm Mix Asphalt, Ohio Department of Transportation (ODOT), Report No. FHWA/OH-

2012/19.

- Oliver, W. C and G. M. Pharr (2004). Measurement of Hardness and Elastic Modulus by

Instrumented Indentation: Advances in Understanding and Refinements to Methodology.

Journal of Materials Research, Vol. 19(1), pp. 3-20.

- Pauli, T., W. Grimes, A. Cookman, and S. Huang (20 3). “Adherence Energy of Asphalt

Thin Films Measured by Force-Displacement Atomic Force Microscopy.” Journal of

Materials in Civil Engineering, 10.1061/(ASCE)MT.1943-5533.0001003 , 04014089.

- Petersen, J. C. ( 984). “Chemical Composition of Asphalt as Related to Asphalt Durability:

State of the Art,” Journal of the Transportation Research Board, Research Record 999, pp.

13-30.

- Petersen, J. C. (2009). A Review of the Fundamentals of Asphalt Oxidation: Chemical,

Physicochemical, Physical Property, and Durability Relationships. Transportation Research

E-Circular, E-C140, Transportation Research Board.

- Punith, V. S., F. Xiao, B. Putman, and S. N. Amirkhanian (2012). Effects of Long-Term

Aging on Moisture Sensitivity of Foamed WMA Mixtures Containing Moist Aggregates.

Materials and Structures, Vol. 45, pp. 251-264.

- Roberts, F. L., P. S. Kandhal, E. R. Brown, D. Lee, and T. Kennedy (1996). Hot Mix Asphalt

Materials, Mixture Design and Construction. National Asphalt Pavement Association

(NAPA), Lanham, MD, 2nd

Edition.

- Striegel, A. M., W. W. Yau, J. J. Kirkland, and D. D. Bly (2009). Modern Size-Exclusion

Liquid Chromatography-Practice of Gel Permeation and Gel Filtration Chromatography.

Wiley, Hoboken, NJ, 2nd

Edition.

99

- Tranchida, D., S. Piccarolo, J. Loos, and A. Alexeev (2006). Accurately Evaluating Young’s

Modulus of Polymers through Nanoindentations: A Phenomenological Correction Factor to

the Oliver and Pharr Procedure. Applied Physics Letters, Vol. 89(17).

- Trujillo, P. (2011). Long Term Aging Study of WMA Binder. The University of Texas at

Austin, Master’s Thesis.

- Xiao, F., S. N. Amirkhanian, and R. Zhang (2012). Influence of Short-Term Aging on

Rheological Characteristics of Non-Foaming WMA Binders. Journal of Performance of

Constructed Facilities, Vol. 26, pp. 145-152.

influence of warm mix asphalt on aging of asphalt binders...binders, and atomic force microscopy...

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