COMPARISON BETWEEN THE ROLLING THIN FILM OVEN TEST AND THE
PRESSURE AGING VESSEL AGING SIMULATION TESTS
AHMED MOFTAH SALEH
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Engineering (Civil - Transportation and Highway)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
JUNE 2008
iii
“Dedicated to my beloved father and mother for their support and love and for my
honest friend Hamed Algass and my classmate Rosmawati”
iv
ACKNOWLEDGEMENT
In the name of Allah (S.W.T), I would like to express my gratefulness for giving me
strength to finish my project.
I wish to express my sincere appreciation to my main project supervisor, Associate
Professor Dr.Mohd Rosli bin Hainin, for encouragement, guidance and critics.
My special thanks must be extended to technical staff members at the highway and
transportation engineering laboratory at UTM for their collaboration. In particular, En.
Suhaimi, for his steadfast assistance while carrying out my laboratory work.
Last but not least, thanks for Malaysia especially my beloved Johor state and I will be
forever loving Joh.
v
ABSTRACT
Three samples of fresh bitumen of 80/100 pen, 60/70, and PG70 were tested to
determine whether pressure Aging Vessel (PAV) test for 25 hours would provide
similar results to the protocol of Strategic Highway Research program (SHRP) coupled
aging procedure, Rolling Thin Film Oven Test (RTFOT) and PAV. Bitumen conducted
by both procedures (a) PAV only for 5 and 25 hours (b) RTFOT only and
RTFOT+PAV 20 hours. Two procedures compared on the basis of the bitumen
conventional properties, penetration at 25ºC, softening point, and viscosity at 135ºC
tests. This study was intended to simulate the aging process by using Rolling Thin Film
Oven Test to compare with Pressure Aging Vessel. The results show that there is
equivalence between the effects of using RTFOT and PAV for 5 h at temperature of
100ºC under pressure 2.1MPa for the unmodified bitumen 80/100 and 60/70
penetration. It appears that the modified bitumen binder PG70 has significant difference
in the results.
vi
ABSTRAK
Tiga bahan daripada bitumen yang terdiri daripada 80/100 PEN, 60/70, dan PG70 di uji
melalui ujian Pressure Aging Vessel (PAV) selama 25 jam untuk mendapatkan
keputusan yang sama berdasarkan teknik yang ditetapkan oleh Strategic Highway
Research program (SHRP) dengan ujian Rolling Thin Film Oven Test (RTFOT) dan
PAV. Proses bitumen berdasarkan dua jenis iaitu (a) Ujian PAV untuk 5 dan 25 jam (b)
hanya menggunakan RTFOT sahaja dan RTFOT+PAV untuk 20 jam. Dua proses di
bandingkan dengan proses kaedah yang asal. Kajian ini perlu bagi membuat simulasi
proses jangka hayat dengan menjalankan ujian Rolling Thin Film Oven untuk membuat
perbandingan dengan ujian Pressure Aging Vessel. Keputusan menunjukkan ia adalah
sama di antara kesan ujian RTFOT dan PAV untuk 5 jam pada suhu 100 ºC di bawah
2.1MPa
bagi bitumen yang biasa iaitu 80/100 dan 60/70 PEN. Bagi PG70
menunjukkan perbezaan yang ketara boleh berlaku berdasarkan prinsip ujian RTFOT.
vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLES OF CONTENTS
vii
LIST OF FIGURES
x
LIST OF TABLES
xi.
LIST OF ABREVIATIONS
xii.
LIST OF APPENDIX
xiii.
INTRODUCTION
1
1.1 Introduction
1
1.2 Problem Statement
2
1.3 Objective
3
1.4 Scope of Work
3
LITERATURE REVIEW
3
2.1 General Introduction
2.2 Effects of Binder aging on HMA
4
2.3 Bitumen Physical Properties
6
5
2.3.1 Consistency
6
2.3.1.1 Dynamic Shear Modulus (DSM)
7
viii
2.3.1.2 Viscosity
8
2.3.1.3 Penetration
8
2.3.1.4 Softening Point
9
2.3.2
Purity
9
2.3.3
Safety
9
2.4 Relationship between Chemical and Physical
Properties
2.5 Factors affecting age hardening
2.5.1 Plant Hot Mix and Laydown Operation
2.6 Aging simulation
10
11
11
13
2.6.1
Short-term aging
14
2.6.2
Long-Term Aging
15
17
3
METHODOLOGY
17
3.1 Introduction
17
3.2 Laboratory Test Procedure
17
3.3 Rolling Thin Film Oven Test
19
3.3.1
Parameters Measured
3.4 Pressure aging vessel test
3.4.1 Basic Procedure
21
22
25
26
4
RESULTS AND DATA ANALAYSIS
27
4.1 Introduction
27
4.2 Bitumen properties
27
4.2.1 Fresh Bitumen properties
28
4.2.2 Bitumen properties after RTFOT
28
4.2.3 Bitumen properties after PAV (5 Hours)
4.2.4 Bitumen properties after RTFOT+PAV
(20 Hours)
29
29
4.2.5 Bitumen properties after PAV (25 Hours)
30
4.3 Data analysis
30
4.4 Discussion
37
ix
5
CONCLUSION AND
RECOMMENDATIONS
37
REFERENCES
38
Appendices A-C
39-48
x
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
3.1
Laboratory Test Flow chart
18
3.2
Rolling thin-film oven test
19
3.3
Pouring hot asphalt binder into the RTFO bottle
20
3.4
Pressure Aging Vessel (PAV)
23
3.6
PAV pan (with a quarter for scale).
25
4.1
30
4.4
Bitumen 80/100 Variation of logarithm of penetration at
25ºC vs. softening point
Bitumen 60/70 Variation of logarithm of penetration at 25
ºC vs. softening point
PG70 Variation of logarithm of penetration at 25 ºC vs.
softening point
Bitumen 60/70 by the two procedures
4.5
Bitumen 60/70 softening point by the two procedures
32
4.6
Bitumen 60/70 viscosity by the two procedures
33
4.7
Bitumen 80/100 penetration of the two procedures
33
4.8
Bitumen 80/100 softening point of the two procedures
34
4.9
Bitumen 80/100 Viscosity of the two procedures
34
4.10
Bitumen PG70 Penetration of the two procedures
35
4.11
Bitumen PG70 Softening point of the two procedures
35
4.12
Bitumen PG70 Viscosity of the two procedures
36
4.2
4.3
31
31
32
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
11
4.1
Elemental Analysis of Representative Petroleum
Asphalts
Fresh Bitumen properties
4.2
Bitumen properties after RTFOT
29
4.3
Bitumen properties after PAV (5h)
29
4.4
Bitumen properties after RTFOT+PAV (20h)
30
4.5
Bitumen properties after PAV (25h)
30
1
28
xii
LIST OF ABBREVIATIONS
PAV
RTFOR
Pressure Aging Vessel
Rolling Thin Film Oven Test
TFOT
Thin Film Oven Test
SHRP
Strategic Highway program
R@B
Ring and Ball test (Softening Point)
JKR
Department of Public Works
HMA
Hot Mix Asphalt
DSM
Dynamic Shear Modulus
AASHTO
ASTM
American Association of State Highway and
Transportation Officials
American Society for Testing and Materials
xiii
LIST OF APPENDIX
APPENDIX
TITLE
PAGE
A
Bitumen 80/100 Tests
40
B
Bitumen 60/70 Properties
43
C
Bitumen PG70 Properties
45
CHAPTER 1
INTRODUCTION
1.1 Introduction
It is generally agreed that one of the most important factor that causes asphalt
pavements to crack and disintegrate is binder aging, because of hardening phenomena.
Hardening of the binder occurs in two different stages. The first stage is short-term
aging, because of loss of binder volatile components during mixing. The second stage is
long-term aging, because of oxidative hardening during service life. The hardening that
results from loss of volatile components has recognized as the significant and the
highest aging stage. The hardening that results from oxidation may be strong function of
the source or the chemical composition of the original binders. The fact has been proven
by early studies on binder aging Anderson (1994).
In the last decades, a significant amount of research has been focused on the use
and behavior of asphalt cements within pavement applications. It is well documented
that environment plays a significant role in characterizing the paving material properties
as a function of time, which in turn affects the pavement performance. The major
environmental factors that affect material properties include temperature and moisture
changes with time. The original Superpave performance system developed through the
Strategic Highway Research Program (SHRP) incorporated mixing and environmental
2
effects as integral components. This has provided the capability to predict temperature
and moisture conditions in the structure of the pavement throughout its service life and
thus account for specific, short-term and long-term effects of mixing and climate on
material properties and pavement performance.
An exclusive of laboratory studying attempted to evaluate neat bitumen physical
properties. Bitumen are according to the specification that given by Malaysia
Department of Public Works (JKR). This procedure will reflect the binder aging during
first stage that mentioned above and binder will compare with short-term aging
simulation. The second stage of binder hardening during service life will simulate by
pressurized aging vessel (PAV) according to (SHRP) research where it is available in
American society of Testing Materials (ASTM). This simulation attends to predict
aging during service life between 7 to 10 years as proven recently by Strategic Research
Highway Program (SHRP). Aging tests predict binder aging and thus predict its effect
on pavement performance.
1.2 Problem statement
Typically, most aging binder specifications conducted by advanced tests such as
dynamic shear rheometer where it can be considered to be one of the most complex and
powerful instruments for characterizing the flow properties of bitumen. SHRP research
has improved binder experimental procedures, specifications and evaluation. Local
specification is normally based on conventional properties such as penetration,
viscosity, and softening point. There are no items to predict these elements and to be
specifically related to the local conditions.
Thus there is a need for detail study the effect of aging using Rolling Thin Film
Oven Test (RTFOT), and the pressure aging vessel (PAV).
3
1.3 Objectives
This study was intended to simulate the aging process by using Rolling Thin
Film Oven Test to compare with Pressure Aging Vessel by using two procedures in
term of short and long-term aging. Three types of bitumen was used according to JKR
bitumen. This study also looked into the properties of the bitumen after each process
bitumen aging.
1.4 Scope of the Study
This study involves laboratory experiments where this study focus on three
samples of fresh bitumen 80/100, 60/70, and PG70 which obtained from mix plants and
were tested to find their conventional properties based on penetration, softening point,
and viscosity tests. All tests were conducted at Transportation laboratory Universiti
Teknoligi, Skudi Johor.
CHAPTER 2
LITRATURE REVIEW
2.1 General Introduction
In the last decades, a significant amount of research has been focused on the use
and behavior of asphalt cements within pavement applications. It is well documented
that environment plays a significant role in determining the properties of hot mix
asphalt (HMA) as a function of time, which in turn affects the performance of HMA
pavements. The major environmental factors that affect HMA material properties
include the changes of temperature and moisture over time.
In case of asphalt mixes, research conducted in Strategic Highway Research
Program, SHRP A-005 clearly showed the environmental effect (temperature) on the
age hardening characteristics of asphalt binders. The study concluded that higher mean
annual air temperatures result in relatively higher rate of aging compared to the cooler
climates. The study also showed the effect of other parameters such as volumetric
properties and the location of the asphalt layer in the pavement system on asphalt mix
aging. Higher air voids results in higher oxidation and hence more stiffening of the
asphalt mix. Asphalt layers that are located deeper in the pavement system do not come
in direct contact with air; as a result, the oxidation of the binder in these layers is
reduced. Therefore, the stiffening of the asphalt mix is inversely proportional to the
5
depth at which it is located in the pavement system. On the other hand, moisture does
not have any significant effect on the aging properties of asphalt mixes. However,
moisture may result in stripping phenomenon, which will eventually affect the
durability.
Hardening or aging of the original asphalt binder, due to the plant mix process
(short-term aging) and normal in-situ aging (long-term aging) are extremely complex
phenomena because of the numerous factors that influence the rate of aging. While the
mechanism of aging is complex, its impact on pavement performance is generally
understood. The short and long term aging processes result in the hardening of the
asphalt binder with time. Thus, overall response i.e., dynamic modulus of the asphalt
mixture also gradually increases in rigidity with time.
2.2 Effects of Binder aging on HMA
In general, it is essential that short-term aging of mixtures in the field be
controlled and that long-term aging is not excessive. While it is important to note that
short-term aging in the field can be controlled through mixture specifications and by
appropriate quality assurance, long-term aging is more uncertain. As the asphalt mix
becomes more rigid with the aging process, an increased susceptibility to cracking and
fracture occurs. This hardening of the asphalt cements (mixture) aids in the
development of several distress types, which may ultimately lead to the failure of the
pavement system. However, binder properties are not the only cause of the development
of the distress, they are considered to be the very important to the overall performance
of any flexible pavement system.
6
2.3 Bitumen Physical Properties
For most engineering and construction purposes, the physical characteristics of
asphalt cements are usually used in specifications. Physical characteristics are related to
the chemical composition and any change in chemical properties is reflected on the
physical properties. The main physical measures used are by the paving industry are:
1. Consistency (flow properties)
2. Purity
3. Safety
2.3.1 Consistency
Consistency is used to describe the viscosity or the degree of fluidity of asphalt
at a specific temperature. It is important to use a specific temperature when comparing
the consistencies for different asphalts. This is because asphalt is a thermo-plastic
material and its flow properties highly depend upon the temperature. At cold
temperatures it is hard and behaves like an elastic material, whereas at high
temperatures it is more viscous and flows under the action of gravity. The following are
common, standard tests for measuring the consistency of asphalt.
•
Dynamic Shear Modulus (G*)
•
Viscosity
•
Penetration
•
Softening point
7
2.3.1.1 Dynamic Shear Modulus (DSM)
The DSM is determining the linear visco-elastic properties of asphalt binders
required for specification testing and is not intended as a comprehensive procedure for
the full characterization of the visco-elastic properties of asphalt binder. The Dynamic
Shear Rheometer (DSR) is the standard test method (AASHTO TP5-98) for
determining the DSM and is applicable both to un-aged and aged asphalt binders.
The two properties obtained using the DSR are the complex shear modulus, G*
and the phase angle. The G* is defined as the ratio calculated by dividing the absolute
value of the peak-to-peak shear stress, τ, by the absolute value of the peak-to-peak shear
strain, γ. The phase angle, δ, is the angle in radian between a sinusoidally applied strain
and the resultant sinusoidal stress in a controlled strain testing mode or between applied
stress and resultant strain in a controlled stress testing mode.
The test can be carried out at various temperatures and frequencies. Oscillatory
loading frequencies using this standard can range from 1 to 100 rad/s using a sinusoidal
waveform. Specification testing is performed at a test frequency of 10 rad/s. The test
temperatures for this test is related to the temperature experienced by the pavement in
the geographical area for which the asphalt binder is intended. The complex shear
modulus obtained at a specific frequency and temperature is an indicator of the stiffness
or resistance of asphalt binder to deformation under load. The complex shear modulus
and the phase angle define the resistance to shear deformation of asphalt binder in the
linear visco-elastic region. Other linear visco-elastic properties such as the storage
modulus (G’), or the loss modulus (G”), can be calculated from the complex modulus
and the phase angle. The loss modulus (G”) is a measure of the energy dissipated during
each loading cycle.
8
2.3.1.2 Viscosity
Standard viscosity measurements are generally conducted at two major
temperatures: 60°C and 135°C for most specifications. The 60°C temperature typifies
the maximum asphalt pavement temperature in service, whereas 135°C is generally
represents mixing and lay-down temperatures for hot asphalt.
The viscosity test at 60°C is generally carried out by capillary tube viscometers
(ASTM D2171). Two commonly used viscometers are the Asphalt Institute Vacuum
Viscometer and the Cannon-Manning Vacuum Viscometer. However, viscosity at
135°C is commonly estimated by Zeitfuchs cross arm viscometer.
2.3.1.3 Penetration
The penetration test (ASTM D5) is an empirical measure of asphalt consistency. In this
test, a needle with a standard weight is allowed to bear on the surface of asphalt cement
for a given specified time. The distance, in units of 0.1 mm, which the needle penetrates
into the asphalt cement, is the penetration measurement. The test can be carried out over
a wide range of temperatures. However, if the test temperature is not specifically
mentioned, the ASTM recommends the test to be done at 25°C with 100 grams of load
for 5 seconds. Other conditions may be used for special testing, such as the following:
Temperature, °C
Load, gms
Time, sec.
0
200
60
4
200
60
46.1
50
5
9
2.3.1.4 Softening Point
A softening point test is used to determine the temperature at which the fluidity
of asphalt begins (ASTM D36). The softening point is sometimes called the Ring and
Ball test.
Temperature is important because it denotes an equi-viscous point for all asphalt
materials. Samples of asphalt loaded with steel balls are confined in brass rings
suspended in a beaker of water, glycerin or ethylene glycol at 25 mm (1 inch) above the
metal plate. The liquid is then heated at a prescribed rate. As the asphalt softens, the
balls and the asphalt gradually sink towards the plate. At a moment the asphalt touches
the plate, the temperature of water is determined and this is designated as the ring and
ball softening point of asphalt.
2.3.2 Purity
The solubility test (ASTM D2042) is a measure of the purity of asphalt. Bitumen
is a major constituent of asphalt and is 99.5 percent soluble in carbon disulfide (CS2).
Thus the percent of asphalt dissolved in carbon disulfide determines the purity of the
asphalt cement in question.
2.3.3 Safety
The temperature at which asphalt fumes ignite generally defines the safety
aspects of asphalt. Combustible fumes are produced by asphalt upon heating and
specifications usually require that asphalt fumes produced upon heating should not
catch fire up to at least 175°C (374°F). The Flash Point test (ASTM D92) is normally
10
used to check the combustibility of asphalt as a function of temperature. In this test,
asphalt is heated gradually. The temperature at which the fumes released from the
asphalt ignite is defined as the flash point.
2.4 Relationship between Chemical and Physical Properties
A brief overview of the chemical and physical properties of asphalt cement is
presented in the previous sections. Both of these properties are used to characterize the
behavior of asphalt cement, however, for specification purposes, physical properties are
commonly used. This is because of the ease of measuring the physical properties and
interdependence of physical properties on the chemical composition. The dependence
occurs because each chemical fraction does possess a unique set of physical
characteristics. Table 1 shows the physical characteristics of the chemical fractions
considered in Corbett-Swarbrick procedure (Selective Adsorption-Desorption). The
relative percentage of each fraction then defines the physical characteristics of the
overall asphalt.
Table 1 shows that both saturates and naphthene-aromatic are liquid and have
lowviscosities compared to solid polar aromatic and asphaltene. It is important to note
thatall asphalts will have consistencies between the extremes defined by these fractions,
in which the saturates and naphthene-aromatic are liquids acting as plasticizers for the
solid polar aromatic and asphaltenes. No viscosity data for asphaltenes are reported in
Table 1 because they have extremely large viscosities and cannot be determined with
currently available equipment.
11
Table 1 Elemental Analysis of Representative Petroleum Asphalts
2.5 Factors affecting age hardening
The hardening of asphalt binders occurs in two major stages. These stages are:
1. Plant hot mix and laydown operation
2. Long term in-service hardening
The basic cause of the hardening during the first stage (Short Term Aging STA) is mainly due to volatilization and oxidation, whereas, oxidation is the major
factor for the second stage (Long Term Aging - LTA). Several factors are responsible
for the change in binder properties during these two stages. Some of these factors are
controllable while others are uncontrollable. A brief discussion of the effect of these
factors on the aging hardening characteristics of as asphalt binders is discussed below.
2.5.1 Plant Hot Mix and Laydown Operation
It is a generally accepted fact that a considerable amount of hardening occurs in
the mixing and laydown operation in a relatively short period of time. This may amount
12
to10 to 30% of the total ultimate hardening of asphalt cement. The major factors
responsible for hardening during the mixing operation are:
1. Plant Operation
a. Mixing temperature
b. Mixing time
c. Mix composition
d. Asphalt type
e. Plant type
2. Laydown Operation
a. Delay incurred in compaction after laydown
b. Rate of cooling
Of all the factors mentioned above, the mixing temperature and the type of
asphalt cement are considered to be most important elements responsible for the short
term hardening of asphalt cement. Plant mixing temperatures typically range from 135
to 177°C. Higher temperatures usually result in higher loss of volatile material in the
binder and also accelerate the oxidation phenomena.
In addition to the mixing temperature, the type of asphalt (ie. asphalt grade) is
critical to the hardening phenomenon. Softer (low viscosity) asphalts are more prone to
change compared to harder (high viscosity) grade asphalts. However, it is important to
realize that higher temperatures during mixing and laydown are usually required for
harder grade asphalts. Thus, this shows a direct link between the asphalt grade and the
mixing temperature. This is also evident from Asphalt Institute specifications for
mixing asphalt. The Asphalt Institute criteria requires that the mixing should be done
between 150 to 190 centistokes and compaction is accomplished between 250-310
centistokes for all asphalt cement types. Thus higher temperatures are required to
achieve these consistency limits for higher-grade asphalts.
13
Mixing time refers to the time it takes to mix the aggregate with asphalt cement.
Longer mixing time will result in greater hardening of the asphalt cement if all other
variables are kept constant. Greater hardening is due to the fact that asphalt is exposed
to a high temperature (135-177°C) for a longer time period, which results in more loss
of volatile material and also more oxidation. In contrast to long-term aging, mix
composition does not have a significant effect upon the hardening of asphalt cement.
This was also concluded by Bright (1962) based upon three different types of mixes
used in the plant mix operation.
In summary, all the factors discussed do have some effect on the hardening
phenomenon during the mix/laydown process. Unfortunately, not enough knowledge is
currently available to quantitatively evaluate the impact of each parameter upon the
consistency temperature shift from the original asphalt cement properties to those
obtained at the mix/laydown conditions.
2.6 aging simulation
Procedure on age hardening properties was carried out under the Strategic
Highway Research Program, SHRP A-003A to simulate short and long term aging in
the laboratory. As a result of the conduct in SHRP, laboratory procedures were
developed to simulate the hardening potential of asphalt binders and mixes. The two
procedures
developed
were:
American
Association
of
State
Highway
and
Transportation Officials, AASHTO Designation: PP1-98, Standard Practice for
Accelerated Aging of Asphalt Binder Using Rolling Thin Film Oven Test (RTFOT) and
Pressurized Aging Vessel, PAV for the asphalt binders. The approaches followed in
these procedures are of great value for the ongoing research on pavement aging;
however, due to the limited resources and time constraints under the SHRP program,
these provisional procedures developed have certain limitations.
14
NCHRP 9-23, Environmental Effects in Pavement Mix and Structural Design
Systems, research study was initiated to verify the work done under SHRP and to
provide conclusions on the significance of limitations associated with the existing
protocol.
Overcoming these limitations would involve the validation of these procedures
with respect to their capability of predicting the age hardening characteristics of asphalt
binders and mixes. To achieve this objective, laboratory tests were conducted on the
binders and their mixes.
2.6.1 Short-term aging
Changes in asphalt binder characteristics that occur during the mixing, lay
down, and compaction processes were associated with short-term aging. Early In 1940,
Lewis and Welborn introduced the TFO test for differentiating volatility and hardening
characteristics of asphalts. In 1963 Hveem, Zube, and Skog introduced the RTFO test in
specifications for the CALTRANS). Bell, 1989, summarized the test methods that have
been used to simulate the short-term aging on asphalt binders. He identified six test
methods:
1. Thin film oven test
2. Shell microfilm test
3. Rolling thin film oven test
4. Rolling microfilm oven test
5. Tilt-oven durability test and
6. Thin film accelerated aging test
Initially, the Rolling Thin Film Oven (ASTM D 2872) and Thin Film Oven
(ASTM D1754) tests were both being utilized for short-term aging in the Superpave
15
asphalt binder specifications. The same authors stated that further investigation of these
test methods were discontinued and “attention was given to long-term field aging which
is not addressed in the current specifications”. In the final version of the PG
specification, the RTFO test was selected to approximate short-term aging. Film Oven
Test (TFOT) ASTM D 1754 and Rolling Thin Film Oven Test (RTFOT) ASTM D
2872, were reviewed and questions were raised with regard to the calibration of these
methods for different plants, operating conditions, asphalt sources, and aggregate types.
An in-depth study to validate and cross-correlate the two test methods was considered,
however, a comprehensive evaluation of TFOT test and RTFOT test methods would
have consumed a disproportionate amount of the available resources. Therefore, further
study of the two methods was discounted and attention was given to long-term field
aging, which is not addressed in the current specifications. In order to simplify the
specification, the rolling thin film oven test was chosen as the single test for the new
Superpave asphalt binder specification.
The RTFOT test can be completed more rapidly than TFOT test, the RTFOT test
is preferable for polymer-modified binders, and there is less between-laboratory
variability for the RTFOT test than for TFOT test. Hence the RTFOT test was chosen in
preference to the TFOT test. If both the RTFOT and TFOT tests were retained in the
Superpave asphalt binder specification the net effect would have been to double the
number of grades because different asphalt cements and different asphalt binders
respond differently to the two tests.
2.6.2 Long-Term Aging
Asphalt binders age due to two major mechanisms: volatilization or short-term
aging and oxidation or long-term aging. The in-service or long-term aging of asphalt
binder represents slow, longer term oxidation. Due to relatively moderate in-service
temperatures, long-term volatilization is slow. Thus, the in-service aging or long-term
16
aging is mainly related to oxidation of asphalt binders. In the Superpave asphalt binder
specifications, long-term aging is represented by the PAV test, which reflects both the
chemical and physical changes of asphalt binders in-service.
The PAV test is intended to approximate five to ten years of in-service aging.
However, several factors affect in-service aging, which could influence this
approximation. These factors are: local climatic conditions, aggregate type, absorption,
mixture type, asphalt film thickness, air-void content, traffic loading, and asphalt
chemical composition.
In reviewing previous efforts to select a long-term aging test, the PAV test was
adopted for Superpave because it is a relatively fast and simple procedure.
CHAPTER 3
METHODOLOGY
3.1 Introduction
The purpose of this study is to evaluate bitumen and aging simulation to find
relation between short-term aging simulation from RTFOT and PAV. These mixes and neat
bitumen are according to the specification given by Malaysia Department of Public Works
(JKR).
Three types of bitumen of penetration grade 80/100, 60/70, and PG70 available in
the laboratory were used. Samples were tested in laboratory according to SHRP procedure.
3.2 Laboratory Test Procedure
The laboratory tests are divided into several stages begin with samples obtaining
from plant. Neat bitumen is used to simulate short-term aging by Rolling Thin Film
Oven Test (RTFOT). Penetration, softening point, and viscosity tests are conducted.
Pressurized aging vessel (PAV) is followed to simulate long-term aging. Figure 3.1
shows the laboratory test flow chart.
18
Obtain Plant
Fresh bitumen:
1- 80/100
2- 60/70
3- PG 70
RTFOT
Penetration
Softening point
Viscosity
RTFOT+PAV 20
Penetration
Softening point
Viscosity
Comparison
Comparison
Analysis
Conclusion
Recommendation
Figure 3.1: Laboratory Test Flow chart
PAV 5h
Penetration
Softening point
Viscosity
PAV 25h
Penetration
Softening point
Viscosity
19
3.3 Rolling Thin Film Oven Test
The Rolling Thin-Film Oven test (RTFOT) procedure (Figure 3.2) provides
simulated short term aged asphalt binder for physical property testing. Asphalt binder is
exposed to elevated temperatures to simulate manufacturing and placement aging. The
RTFO also provides a quantitative measure of the volatiles lost during the aging
process.
Figure 3.2 Rolling thin-film oven test.
1. Heat a sample of asphalt binder until it is fluid to pour. Stir sample to ensure
homogeneity and remove air bubbles.
2. If a determination of mass change is desired, label two RTFO bottles and weigh them
empty. These are designated as the "mass change" bottles. Record the weights.
3. Pour 1.23 oz (35 g) of asphalt binder into each bottle. Immediately after pouring each
bottle, turn the bottles on their side without rotating or twisting and place them on a
cooling rack.
20
Figure 3.3 Pouring hot asphalt binder into the RTFO bottle
4. Allow all bottles to cool 60 to 180 minutes.
5. After cooling, weigh the two mass change bottles again. Record the weights.
6. Place the bottles in the RTFO oven carousel, close the door, and rotate carousel at 15
RPM for 85 minutes. During this time, maintain the oven temperature at 325°F (163°C)
and the airflow into the bottles at 244 in3/min (4000 ml/min).
7. Remove the bottles one at a time from the carousel, setting the mass change bottles
aside. Residue from the remaining bottles should be transferred to a single container.
Remove residue from each bottle by first pouring as much material as possible, then
scraping the sides of the bottle to remove any remaining residue. There is no standard
21
scraping utensil but at least 90 percent of the asphalt binder should be removed from the
bottle. RTFO residue should be tested within 72 hours of aging
8. After cooling the two mass change bottles for 60 - 180 minutes, weigh them and
discard their residue. Record the weights.
3.3.1 Parameters Measured
Mass change of a sample as a percent of initial mass. The RTFO is primarily
used to simulate short term asphalt binder aging for use in other tests. Performance
Graded Asphalt Binder RTFO Specification is as follows:
Material
Value
Specification
Unaged binder
Mass loss1
≤ 1.0%
Property of
Concern
None
Note 1 Although some samples can gain weight due to the oxidative products formed
during the test (Roberts et al., 1996), there is currently no limit on mass gain. Where
Typical mass loss is in the range of 0.05 to 0.5 percent. Calculations can be done for the
mass change bottles in the following form:
Mass change= (B-A)/A*100
A=Wbi-Wo
Where:
22
•
Wbi = bottle + binder weight before aging
•
Wbf = bottle + binder weight after aging
•
Wo = empty bottle weight
•
A = initial sample weight
•
B = final sample weight
3.4 Pressure aging vessel test
The Pressure Aging Vessel (PAV) (Figure 3.4) provides simulated long term
aged asphalt binder for physical property testing. Asphalt binder is exposed to heat and
pressure to simulate in-service aging over a 7 to 10 year period.
The basic PAV procedure takes RTFOT aged asphalt binder samples, places
them in stainless steel pans and then ages them for 20 hours in a heated vessel
pressurized to 305 psi (2.10 MPa or 20.7 atmospheres). Samples are then stored for use
in physical property tests.
The standard Pressure Aging Vessel procedure is found in:
•
AASHTO R 28: Accelerated Aging of Asphalt Binder Using a Pressurized
Aging Vessel (PAV)
23
Figure 3.4 Pressure Aging Vessel (PAV)
Pressure tests. This approach, although originally less popular than oven tests,
has been around for over 40 years. Pressure tests work by using high pressure to
increase the diffusion rate of oxygen into an asphalt binder sample. In general, this
approach limits the loss of volatiles while aging the asphalt binder sample.
Based on the preceding descriptions, a pressure test was desired for simulating long
term asphalt binder aging because (Bahia and Anderson, 1995):
24
•
Volatile loss is minimized.
•
Aging can be accomplished without high temperatures.
•
Large enough sample sizes can be accommodated.
•
Field climate conditions can be approximated.
•
Laboratory use is practical.
The standard asphalt binder PAV was developed at Iowa State University for
long term aging of asphalt cements and is also a standard method for aging rubber
products (as in ASTM D 454 and ASTM D 572) (Roberts et al., 1996).
The PAV process is typically conducted for 20 hours at either 194, 212 or 230°F (90,
100 or 110°C). These were chosen for practical, rather than theoretical reasons.
Original PAV experiments were conducted at 300 psi (2.07 MPa) and 60°C for 6
days.Results showed insufficient aging and the test period was deemed too long.
Therefore, in order to increasing the aging rate (producing a shorter test) the test
temperature was raised. Originally, a test temperature of 212°F (100°C) was chosen but,
during field validation, it was found to be overly harsh for cold climates and too mild
for hot climates. Therefore, three elevated temperatures are used, each one to simulate a
different general environmental condition:
Temperature 212°F (100°C)
Simulation
194°F (90°C)
Cold climate
230°F (110°C)
Moderate climate
230°F (110°C)
Hot climate
25
3.4.1 Basic Procedure
1. Heat RTFO aged asphalt binder until fluid enough to pour. Stir sample and pour 50 g
into a preheated thin film oven pan (Video 1). Pour as many pans as needed for
intermediate and cold temperature testing (usually 1 – 3 pans will suffice).
2. Place pans (Figure 3.6) in a pan holder and place inside preheated PAV
Figure 3.6 PAV pan (with a quarter for scale).
3. Seal the PAV and allow it to return to the aging temperature.
Aging temperature is based on the climate where the material is expected to be
used. For climates where a PG 52 or lower is specified, the PAV is performed at 194°F
(90°C). For climates where a PG 58 or higher is specified, the PAV is performed at
212°F (100°C). For desert climates, it is recommended to perform the PAV at 230°F
(110°C).
26
4. Once the PAV has reached the desired temperature, pressurize the PAV to 300 psi
(2.07 MPa) and maintained the pressure for for 20 hours. 5. At the end of the aging
period, gradually release the pressure and remove the pans from the PAV. 6. Place the
pans in an oven set at 325°F (163°C) for 15 minutes, then scrape into a single container
sized so that the depth of the residue in the container is between 0.55 and 1.57 inches
(14 and 40 mm). 7. Place the container in a vacuum oven (Figure 9) at 338°F (170°C)
and degas the sample for 30 minutes to remove entrapped air. If not degassed, entrapped
air bubbles may cause premature breaking in the DTT test
CHAPTER 4
RESULTS AND DATA ANALAYSIS
4.1 Introduction
This chapter includes the results and data analysis of all the laboratory tests. The
aim of this study was to compare the Pressure Aging Vessel and the Rolling Thin Film
Oven Test by using three types of bitumen, 80/100 pen, 60/70 pen, and PG 70. These results
were obtained based on the conventional properties tests, penetration, softening point, and
viscosity tests.
4.2 Bitumen properties
Bitumen properties divided in three stages, fresh, short-term, and long-term
aging properties.
28
4.2.1 Fresh Bitumen properties
As preliminary stage the three types of bitumen were tested based on their
conventional properties. These tests were conducted to reflect the original bitumen
properties. According to ASTM standards tables show the data obtained for each type.
Table 4.1 Fresh Bitumen properties
Properties
Penetration ASTM
D5 (pen)
Softening point
ASTM D36°C
Viscosity at 135 C˚
ASTM D4402
cP.s
80/100
60/70
PG70
88
68
60
41
39
46
100
350
700
4.2.2 Bitumen properties after RTFOT
These properties after simulation of short-term aging by using Rolling Thin Film
Oven Test. Each type of bitumen where has been tested for 85 minutes in the oven and
then properties can be obtained. Tables below show the properties of each type.
29
Table 4.2 Bitumen properties after RTFOT
Properties
80/100
60/70
PG70
Penetration ASTM
D5 (pen)
Softening point
ASTM D36°C
Viscosity at 135 C˚
ASTM D4402
cP.s
32
37
31
48.5
45
62
400
800
2400
4.2.3 Bitumen properties after PAV (5 Hours)
Aging simulation conducts for 5 hours to find the properties that can be compare to the
properties of RTFOT. Tables below show the properties of each type of bitumen.
Table 4.3 Bitumen properties after PAV (5h)
Properties
80/100
60/70
PG70
Penetration ASTM
D5 (pen)
Softening point
ASTM D36°C
Viscosity at 135 C˚
ASTM D4402
cP.s
36
37
42
45
43.5
52.5
300
800
1100
4.2.4 Bitumen properties after RTFOT+PAV (20 Hours)
To simulate long-term aging by conducting Rolling Thin Film Oven Test plus Pressure
Aging Vessel for 20 hours. Tables followed show the result that been observed from the
conventional properties for each type used.
30
Table 4.4 Bitumen properties after RTFOT+PAV (20h)
Properties
80/100
60/70
PG70
Penetration ASTM
D5 (pen)
Softening point
ASTM D36°C
Viscosity at 135 C˚
ASTM D4402
cP.s
24
25
22
55
53
71
800
1400
2900
4.2.5 Bitumen properties after PAV (25 Hours)
Test result by using the Pressure Aging Vessel for 25 hours
Table 4.5 Bitumen properties after PAV (25h)
Properties
80/100
60/70
PG70
Penetration ASTM
D5 (pen)
Softening point
ASTM D36°C
Viscosity at 135 C˚
ASTM D4402
cP.s
25
26
25
54
51
68
900
1200
2500
4.3 Data analysis
Figures below show the correlation between penetration and softening point at each
stage. Figure 4.1 shows the relationship between penetration and softening point for
bitumen type 80/100. The figure shows that the relationship is strong with R 2 of 0.81
and as the softening increases the penetration decreases.
31
100
Fresh
PAV 5h
log pen 25C
RTFOT
RTFOT+PAV
20 h
25 PAV
10
y = -3.8506x + 228.75
R2 = 0.81
1
0
20
40
60
R&BC
Figure 4.1 Bitumen 80/100 Variation of logarithm of penetration at 25°C vs. softening
Point
Figure 4.2 shows the relationship between penetration and softening point for
bitumen type 60/70. The figure shows that the relationship is strong with R 2 of 0.857
and as the softening increases the penetration decreases.
100
Fresh
lo g p en 25C
PAV 5h
RTFOT
PAV 25 h
RTFOT+PAV
20h
10
y = -3.084x + 182.53
R2 = 0.8569
1
0
10
20
30
40
50
60
R&B C
Figure 4.2 Bitumen 60/70 Variation of logarithm of penetration at 25C vs. softening
point
Figure 4.3 shows the relationship between penetration and softening point for
bitumen type 60/70. The figure shows that the relationship is strong with R 2 of 0.881
and as the softening increases the penetration decreases.
32
100
fresh
PAV 5h
RTFOT+PAV
20h
RTFOT
log pen 25C
PAV 25h
10
y = -0.6353x + 82.995
R2 = 0.961
1
0
20
40
60
80
R&B C
Figure 4.3 Bitumen PG70 Variation of logarithm of penetration at 25C vs. softening
point
Figures 4.4 to 4.12 show the differences of each procedure, where the best case is
Bitumen 60/70 where the difference is insignificant.
Bitumen 60/70 penetration
pen (1/100 mm)
80
68 68
60
37 37
40
RTFOT+PAV
25 26
PAV
20
0
1
2
3
1. fresh 2. short-term aging 3. longterm aging
Figure 4.4 Bitumen 60/70 by the two procedures
33
Bitumen 60/70 viscosity
1500
cP.s
1000
500
0
RTFOT+PAV
PAV
1
2
3
350
800
1400
350
800
1200
1. fresh 2. short-term aging 3.long-term aging
Figure 4.5 Bitumen 60/70 softening point by the two procedures
Bitumen 60/70 viscosity
1500
cP.s
1000
500
0
1
2
3
RTFOT+PAV
350
800
1400
PAV
350
800
1200
1. fresh 2. short-term aging 3.long-term aging
Figure 4.6 Bitumen 60/70 viscosity by the two procedures
34
pen (1/100 mm)
Bitumen 80/100 pentration
90
80
70
60
50
40
30
20
10
0
80 80
32
1
RTFOT+PAV
PAV
36
24 25
2
3
1. fresh 2. short-term aging
3. long-term aging
Figure 4.7 Bitumen 80/100 penetration of the two procedures
Bitumen 80/100 softening point
Temperature C
60
40
RTFOT+PAV
PAV
20
0
1
2
3
RTFOT+PAV
41
48.5
55
PAV
41
45
54
1. fresh 2. short-term aging
term aging
3. long-
Figure 4.8 Bitumen 80/100 softening point of the two procedures
35
Bitumen 80/100 viscosity
1000
800
cP.s
600
400
200
0
1
2
3
RTFOT+PAV
100
400
800
PAV
100
300
900
1. fresh 2. short-term aging 3. lomg-term aging
Figure 4.9 Bitumen 80/100 Viscosity of the two procedures
pen (1/100 mm)
Bitumen PG70 penetration
70
60
50
40
30
20
10
0
60 60
42
RTFOT+PAV
31
1
22 25
2
PAV
3
1. fresh 2. short-term aging 3. long-term
aging
Figure 4.10 Bitumen PG70 Penetration of the two procedures
36
Bitumen PG70 softening point
Temperature C
80
60
40
20
0
RTFOT+PAV
PAV
1
2
3
46
62
71
46
52.5
68
1. fresh 2. short-term aging 3. lon-term aging
Figure 4.11 Bitumen PG70 Softening point of the two procedures
Bitumen PG70 viscosity
3500
3000
2500
cP.s
2000
1500
1000
500
0
1
2
3
RTFOT+PAV
700
2400
2900
PAV
700
1100
2500
1. fresh 2. short-term aging 3. long-term aging
Figure 4.12 Bitumen PG70 Viscosity of the two procedures
37
4.4 Discussion
The results of each bitumen types in the different stages show mixed results in
term of bitumen properties.
Bitumen 80/100 pen are stable binders in term of losing its volatile materials.
Short-term and long-term aging of the both procedure has showed significant hardening
in the short-term aging. The two procedure give similar results, however unmodified
bitumen such as 80/100 and 60/70 can be conducted by the two procedure with no
significant differences in their properties.
Unlike bitumen type 80/100 and 60/70, the PG70 shows significant difference
when comparing the two procedures for both short and long-term aging. The rheology
of the modified bitumen would have been the contributors to the differences.
CHAPTER 5
CONCLUSION AND RECOMMENDATIONS
This study attempts to simulate the aging and evaluate the standard test
practiced. The standard test procedure for short-term aging is ASTM D 2872 using
RTFOT and simulation was attempted by using PAV for 5 hrs. The results show that
both test procedures are acceptable for bitumen 80/100 and 60/70 penetration grade and
not acceptable for PG70.
An attempt was also made to simulate the current procedure for long-term aging
ASTM D 6521 with using only PAV for 25 hrs. Like the short-term aging similar
results were obtained for the simulation.
It appears that the modified bitumen PG70 has significant difference in the
results where the rheology of the modified binder would contribute to the differences.
It is recommended that the short-term aging test use the PAV equipment for the
unmodified binder. Further tests for more different samples are recommended to
validate the results.
38
REFRENCES
Bahia, H. U. and Anderson, D.A (1994). "The Pressure Aging Vessel (PAV): A Test to
Simulate Rheological Changes Due to Field Aging," Physical Properties of Asphalt
Cement Binders: ASTM STP 1241, John C. Harden, Ed. American Society for Testing
and Materials, (pp. 52-67).
Bright, R. and Reynolds (1962). E.T. "Effect of Mixing Temperature on Hardening of
Asphalt binder in Hot Bituminous Concrete", Highway Research Board, Bulletin
No. 333.
Galal, K. A., White, T. D. and Hand, A. J (2000). Second Phase Study of Changes in InService Asphalt. Joint Transportation Research Program. Purdue University,
Indiana.
Migliori, F, and J.C. Molinengo (2007). Comparative study of RTFOT and PAV Aging
Simulation Laboratory Tests. Paper no.98-0850.
NCHRP 9-23 (2001). Environmental Effects in Pavement Mix and Structural Design
Systems. Interim Report, August
Strategic Highway program SHRP (1994). Project A-003 to Simulate the Hardening
Potential of Asphalt Binders.
APPENDICES
40
APPENDIX A
Bitumen 80/100 Tests
1. Fresh bitumen
Test
1
Penetration
2
3
Sample1
85
86
88
91
89
Sample2
80
79
81
80
80
Sample3
87
89
88
88
90
Softening Point
Sample Sample
Ball
1
2
A
41
41.5
B
40
40.5
4
5
41
2. Bitumen after RTFOT
Test
1
Penetration
2
3
4
5
Sample1
32
32
30
33
34
Sample2
31
32
32
33
32
Sample3
32
34
33
31
32
4
5
Softening Point
Sample Sample
Ball
1
2
A
48.5
48
B
49
48
3. Bitumen after PAV 5h
Test
1
Penetration
2
3
Sample1
36
34
37
37
34
Sample2
34
36
37
36
36
Sample3
32
34
36
37
37
Softening Point
Sample Sample
Ball
1
2
A
45
45.5
B
45
46
42
4. Bitumen after RTFOT+PAV
Test
1
Penetration
2
3
4
5
Sample1
21
22
25
27
26
Sample2
24
24
25
24
24
Sample3
25
25
24
25
24
4
5
Softening Point
Sample Sample
Ball
1
2
A
54.5
55
B
55
55
5. Bitumen after PAV 25 h
Test
1
Penetration
2
3
Sample1
23
23
24
25
25
Sample2
24
24
25
25
26
Sample3
25
25
24
25
26
Softening Point
Sample Sample
Ball
1
2
A
54.5
55
B
54
54
43
APPENDIX B
Bitumen 60/70 Properties
1. Fresh bitumen
Test
1
Penetration
2
3
4
5
Sample1
71
78
73
65
68
Sample2
63
71
70
67
62
Sample3
69
70
64
66
67
Softening Point
Sample Sample
Ball
1
2
A
37
38
B
40
40.5
44
2. Bitumen after RTFOT
Test
1
Penetration
2
3
4
5
Sample1
41
42
43
43
44
Sample2
36
36
37
38
38
Sample3
37
41
41
42
38
4
5
Softening Point
Sample Sample
Ball
1
2
A
44
45
B
45
45.5
3. Bitumen after PAV 5h
Test
1
Penetration
2
3
Sample1
36
40
42
40
45
Sample2
36
37
37
36
38
Sample3
37
41
43
37
42
Softening Point
Sample Sample
Ball
1
2
A
43
43
B
44
44
45
4. Bitumen after RTFOT+PAV
Test
1
Penetration
2
3
4
5
Sample1
21
23
25
27
26
Sample2
24
24
25
26
27
Sample3
25
26
25
25
26
4
5
Softening Point
Sample Sample
Ball
1
2
A
53
53
B
53.5
53
5. Bitumen after PAV 25 h
Test
1
Penetration
2
3
Sample1
24
24
25.5
31
28
Sample2
26
26
25
27
26
Sample3
26
26
27
23
26
Softening Point
Sample Sample
Ball
1
2
A
51
50
B
51
51
46
APPENDIX C
Bitumen PG70 Properties
1. Fresh bitumen
Test
1
Penetration
2
3
4
5
Sample1
63
62
60
61
62
Sample2
61
62
60
55
58
Sample3
56
57
57
61
58
Softening Point
Sample Sample
Ball
1
2
A
46
45
B
47
46
47
2. Bitumen after RTFOT
Test
1
Penetration
2
3
4
5
Sample1
27
28
32
33
33
Sample2
30
31
31
32
32
Sample3
27
33
33
33
33
4
5
Softening Point
Sample Sample
Ball
1
2
A
62
62
B
62
63
3. Bitumen after PAV 5h
Test
1
Penetration
2
3
Sample1
41
42
42
42
37
Sample2
42
43
41
42
43
Sample3
40
40
44
45
46
Softening Point
Sample Sample
Ball
1
2
A
52
52
B
53
53
48
4. Bitumen after RTFOT+PAV
Test
1
Penetration
2
3
4
5
Sample1
21
23
22
27
22
Sample2
20
23
22
21
22
Sample3
24
24
21
22
21
4
5
Softening Point
Sample Sample
Ball
1
2
A
70
71
B
70.5
71.5
5. Bitumen after PAV 25 h
Test
1
Penetration
2
3
Sample1
24
27
22
30
24
Sample2
26
25
25
27
24
Sample3
22.5
26
27
22
23
Softening Point
Sample Sample
Ball
1
2
A
68
67.5
B
68
68