influence of warm mix asphalt on aging of asphalt binders...binders, and atomic force microscopy...
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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
Influence of Warm Mix Asphalt on Aging of Asphalt Binders
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
Influence of Warm Mix Asphalt on Aging of Asphalt Binders
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
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
Mixtures Prepared using PG 70-22 (Reference Temperature of 70oF) .............................. 72
Figure 5.31: Dynamic Modulus Master Curve for STOA and LTOA Foamed WMA
Mixtures Prepared using PG 64-22 (Reference Temperature of 70oF) .............................. 73
Figure 5.32: Dynamic Modulus Master Curve for STOA and LTOA HMA
Mixtures Prepared using PG 64-22 (Reference Temperature of 70oF) .............................. 73
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
Figure 5.34: DSR Test Results for PG 64-22 Binder Recovered from Surface Course
of Project No. 342-08 in Pickaway County ....................................................................... 79
Figure 3.35: DSR Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 352-08 in Summit County .......................................................................... 80
Figure 5.36: DSR Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 386-08 in Portage County ........................................................................... 81
Figure 5.37: FTIR Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 329-08 in Miami County ............................................................................ 82
Figure 5.38: FTIR Test Results for PG 64-22 Binder Recovered from Surface Course
of Project No. 342-08 in Pickaway County ....................................................................... 83
Figure 5.39: FTIR Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 352-08 in Summit County .......................................................................... 84
Figure 5.40: FTIR Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 386-08 in Portage County ........................................................................... 85
Figure 5.41: GPC Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 329-08 in Miami County ............................................................................ 86
Figure 5.42: GPC Test Results for PG 64-22 Binder Recovered from Surface Course
of Project No. 342-08 in Pickaway County ....................................................................... 86
Figure 5.43: GPC Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 352-08 in Summit County .......................................................................... 87
Figure 5.44: GPC Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 386-08 in Portage County ........................................................................... 87
Figure 5.45: AFM Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 329-08 in Miami County ............................................................................ 88
Figure 5.46: AFM Test Results for PG 64-22 Binder Recovered from Surface Course
of Project No. 342-08 in Pickaway County ....................................................................... 89
Figure 5.47: AFM Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 352-08 in Summit County .......................................................................... 90
xi
Figure 5.48: AFM Test Results for PG 70-22 Binder Recovered from Surface Course
of Project No. 386-08 in Portage County ........................................................................... 91
1
Influence of Warm Mix Asphalt on Aging of Asphalt Binders
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
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.
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
)
Radial Frequency (rad/sec)
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
)
Radial Frequency (rad/sec)
PAV
RTFO
Unaged
0.1
10
1000
100000
0.01 0.1 1 10 100 1000
G*
sinδ
at
25
oC
(k
Pa
)
Radial Frequency (rad/sec)
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)
G*/sinat 70oC and 10 rad/sec (kPa)
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)
G*sinat 28oC and 10 rad/sec (kPa)
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)
G*/sinat 64oC and 10 rad/sec (kPa)
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)
G*/sinat 64oC and 10 rad/sec (kPa)
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)
G*sinat 25oC and 10 rad/sec (kPa)
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)
G*sinat 25oC and 10 rad/sec (kPa)
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
for Asphalt Binder and Asphalt Mixture Aging for PG 64-22.
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
for Asphalt Binder and Asphalt Mixture Aging for PG 70-22.
Figure 5.20: Comparison of GPC Test Results
for Asphalt Binder and Asphalt Mixture Aging for PG 64-22.
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
for Asphalt Binder and Asphalt Mixture Aging for PG 70-22.
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
for Asphalt Binder and Asphalt Mixture Aging for PG 64-22.
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).
Figure 5.30: Dynamic Modulus Master Curve for STOA and LTOA
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
Figure 5.31: Dynamic Modulus Master Curve for STOA and LTOA
Foamed WMA Mixtures Prepared using PG 64-22 (Reference Temperature of 70oF).
Figure 5.32: Dynamic Modulus Master Curve for STOA and LTOA
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 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,
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
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,
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
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
at
28
oC
an
d 1
0 r
ad
/sec
(k
Pa
)
79
Figure 5.34: DSR Test Results for PG 64-22 Binder Recovered
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
Unaged RTFO PAV Unaged
+ 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
Unaged RTFO PAV Unaged
+ 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
Figure 3.35: DSR Test Results for PG 70-22 Binder Recovered
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
Unaged RTFO PAV Unaged
+ 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
Unaged RTFO PAV Unaged
+ 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
Figure 5.36: DSR Test Results for PG 70-22 Binder Recovered
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
Unaged RTFO PAV Unaged
+ 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
Unaged RTFO PAV Unaged
+ 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
from Surface Course of Project No. 329-08 in Miami County.
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
Unaged RTFO PAV 329-08
Miami
HMA
329-08
Miami
WMA
I S=
O
83
Figure 5.38: FTIR Test Results for PG 64-22 Binder Recovered
from Surface Course of Project No. 342-08 in Pickaway County.
0.021
0.024
0.032
0.017
0.021
0
0.01
0.02
0.03
0.04
0.05
0.06
Unaged RTFO PAV 342-08
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
Unaged RTFO PAV 342-08
Pickaway
HMA
342-08
Pickaway
WMA
I S=
O
84
Figure 5.39: FTIR Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 352-08 in Summit County.
0.020
0.025
0.036
0.0400.042
0
0.01
0.02
0.03
0.04
0.05
0.06
Unaged RTFO PAV 352-08
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
Unaged RTFO PAV 352-08
Summit
HMA
352-08
Summit
WMA
I S=
O
85
Figure 5.40: FTIR Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 386-08 in Portage County.
0.020
0.025
0.036
0.023
0.032
0
0.01
0.02
0.03
0.04
0.05
0.06
Unaged RTFO PAV 386-08
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
Unaged RTFO PAV 386-08
Portage
HMA
386-08
Portage
WMA
I S=
O
86
Figure 5.41: GPC Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 329-08 in Miami County.
Figure 5.42: GPC Test Results for PG 64-22 Binder Recovered
from Surface Course of Project No. 342-08 in Pickaway County.
4.1%
7.1%
15.1%
23.0% 23.1%
0%
8%
16%
24%
32%
40%
Unaged RTFO PAV 329-08
Miami
HMA
329-08
Miami
WMA
LM
S (
%)
10.7%
19.3%
24.5%
31.0%
24.5%
0%
8%
16%
24%
32%
40%
Unaged RTFO PAV 342-08
Pickaway
HMA
342-08
Pickaway
WMA
LM
S (
%)
87
Figure 5.43: GPC Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 352-08 in Summit County.
Figure 5.44: GPC Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 386-08 in Portage County.
4.1%
7.1%
15.1%
12.9%
16.4%
0%
8%
16%
24%
32%
40%
Unaged RTFO PAV 352-08
Summit
HMA
352-08
Summit
WMA
LM
S (
%)
4.1%
7.1%
15.1%
19.2%
16.0%
0%
8%
16%
24%
32%
40%
Unaged RTFO PAV 386-08
Portage
HMA
386-08
Portage
WMA
LM
S (
%)
88
Figure 5.45: AFM Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 329-08 in Miami County.
11,512
20,858
49,329
22,889
28,855
19,820
23,491
0
10000
20000
30000
40000
50000
60000
70000
Unaged RTFO PAV 329-08
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
Unaged RTFO PAV 329-08
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
Figure 5.46: AFM Test Results for PG 64-22 Binder Recovered
from Surface Course of Project No. 342-08 in Pickaway County.
6,991
10,650
40,606
6,970
10,70813,106 12,598
0
10000
20000
30000
40000
50000
60000
Unaged RTFO PAV 342-08
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
Unaged RTFO PAV 342-08
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
Figure 5.47: AFM Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 352-08 in Summit County.
11,512
20,858
49,329
31,79233,079
28,665
39,175
0
10000
20000
30000
40000
50000
60000
70000
Unaged RTFO PAV 352-08
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
Unaged RTFO PAV 352-08
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
Figure 5.48: AFM Test Results for PG 70-22 Binder Recovered
from Surface Course of Project No. 386-08 in Portage County.
11,512
20,858
49,329
20,552
31,991 31,934 32,072
0
10000
20000
30000
40000
50000
60000
70000
Unaged RTFO PAV 386-08
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
Unaged RTFO PAV 386-08
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
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