THE EFFECTS OF NOMINAL MAXIMUM AGGREGATE SIZE ON THE
PROPERTIES OF HOT MIX ASPHALT USING GYRATORY COMPACTOR
ELIZABETH CHONG EU MEE
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
NOVEMBER 2006
iii
Dedicated to...
My beloved dad and mum,
Paul Chong and Agatha Lee,
who has so much faith in me.
Love you always.
GIFT members of
past, present, and future.
Life has been wonderfully coloured by you.
iv
ACKNOWLDGEMENTS
Praise be to Almighty God for the graces and abundant blessings to complete
this report. Thy will be done on earth, as it is in Heaven. In doing this report, I had
crossed path with many individuals in whom I am indebted to.
I wish to express my gratitude to my supervisor, Dr. Mohd. Rosli bin Hainin,
for his guidance and constructive critics, as I pen down my thoughts and words for
this report. To my co-supervisor, Tn. Hj. Che Ros bin Ismail, for believing and
trusting in me throughout thick and thin moments. Both of them are my mentor and
friend.
To my parents, I owe them a life-long gratitude for nurturing me with love,
care, and support to be who I am today. Not forgetting my second family, I also
wish to record a word of thanks to the family of GIFT and CMT. Thanks for all of
your prayers, moral support and jokes to lighten up my day.
Appreciation also goes to Mr. Suhaimi, Mr Abdul Rahman, Mr. Mohd. Adin,
and Mr. Azman of the Transportation and Highway Laboratory, UTM, for rendering
their help, both time and energy. A special word of thanks is also reserved for my
laboratory partners, Norliza, Zanariah, Naeem, and Mukhtar for their help.
Last, but not the least, I would like to acknowledge each and every person
who have contributed to the success of this report, whether directly or indirectly.
May God bless you in your life journey.
v
ABSTRACT
The introduction of Superpave mix design in 1993 in the United States has
categorized mixes based on the nominal maximum aggregate size (NMAS). The
centerpiece of the mix design is the Superpave Gyratory Compactor (SGC).
Properties of hot mix asphalt (HMA) have always been associated with pavement
deformations. This study looks into the effects of NMAS on the properties of
Malaysian HMA mixtures, which includes optimum bitumen content (OBC), bulk
specific gravity (Gmb), theoretical maximum density (TMD), water absorption (WA),
voids in mineral aggregate (VMA), voids filled with bitumen (VFB), and dust to
binder ratio (D:B). Thus, a better understanding of the properties can reduce the
pavement deformations. A total of four asphaltic concrete mix designs with different
NMAS were prepared in accordance with the JKR Specification, namely AC10,
AC14, AC20, and AC28. Specimens of each mix design with varying bitumen
content were compacted to 75 and 100 gyrations using SGC to obtain 4±1% air
voids. It was observed that as the NMAS increased, the OBC and VMA decreased.
The Gmb, TMD, WA, and D:B showed opposite trend of the earlier properties. Ttests indicated that all properties except VMA were affected by NMAS. VMA for
AC20 failed the minimum requirement initially but when calculated using the
average asphalt film thickness method, it was acceptable. Different compaction
efforts showed the same pattern on the properties except VFB while t-tests revealed
that OBC, TMD, VMA, and D:B were significantly affected.
Investigation also
showed that AC20 is the best mix from the economic and durability point of views.
vi
ABSTRAK
Pengenalan rekabentuk campuran Superpave pada tahun 1993 di Amerika
Syarikat telah mengkategorikan campuran berdasarkan saiz nominal maksimum
agregat (NMAS). Hasil utama rekabentuk campuran ini ialah Pemadat Legaran
Superpave (SGC).
Sifat-sifat campuran panas berasfalt (HMA) selalu dikaitkan
dengan ubahbentuk turapan. Kajian ini melihat kepada kesan NMAS terhadap sifatsifat campuran HMA Malaysia yang merangkumi kandungan bitumen optimum
(OBC), graviti tentu pukal (Gmb), ketumpatan maksimum teori (TMD), penyerapan
air (WA), lompang dalam agregat mineral (VMA), lompang terisi bitumen (VFB),
dan nisbah debu kepada pengikat (D:B). Oleh itu, pemahaman yang lebih lanjut
mengenai sifat-sifat ini dapat mengurangkan ubahbentukturapan. Sejumlah empat
rekabentuk campuran konkrit berasfalt dengan NMAS yang berbeza telah disediakan
mengikut Spesifikasi JKR, iaitu AC10, AC14, AC20, dan AC28. Spesimen daripada
setiap rekabentuk campuran dengan kandungan bitumen yang berbeza telah
dipadatkan ke 75 dan 100 legaran dengan menggunakan SGC untuk mendapatkan
4±1% kandungan udara. Apabila NMAS meningkat, dapat diperhatikan bahawa
OBC dan VMA menurun. Gmb, TMD, WA, dan D:B menunjukkan corak yang
bertentangan dengan sifat-sifat terdahulu. Keputusan ujian-t menunjukkan bahawa
kesemua sifat dipengaruhi oleh NMAS kecula VMA.
VMA untuk AC20 pada
mulanya gagal untuk memenuhi keperluan minimum tetapi apabila dihitung dengan
menggunakan kaedah ketebalan purata selaput asfalt, ianya dapat diterimapakai.
Usaha pemadatan yang berbeza menunjukkan corak yang sama untuk kesemua sifat
kecuali VFB manakala ujian-t menunjukkan bahawa OBC, TMD, VMA, dan D:B
amat dipengaruhi. Kajian menunjukkan AC20 adalah campuran yang terbaik dari
segi ekonomi dan ketahanlasakan.
vii
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
DECLARATION OF THE STATUS OF THESIS
SUPERVISOR’S DECLARATION
TITLE PAGE
1
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF ABBREVIATIONS
xiv
LIST OF APPENDICES
xvi
INTRODUCTION
1
1.1
Preamble
1
1.2
Problem Statement
3
1.3
Aim
5
1.4
Objectives
5
1.5
Scope of the Study
5
1.6
Importance of the Study
6
1.7
Summary
7
viii
2
3
LITERATURE REVIEW
8
2.1
Introduction
8
2.2
Superior Performing Asphalt Pavement
9
2.2.1
Background of Superpave
9
2.2.2
Superpave Mix Design
10
2.2.3
Superpave Gyratory Compactor
12
2.2.4 Superpave in Malaysian Scenario
16
2.3
Comparison of Superpave and Malaysian Mixes
19
2.4
Measurements of Compaction
21
2.4.1
26
Voids in Mineral Aggregates
2.5
Relation of NMAS to Pavement Deformations
27
2.6
Field Performance
28
2.7
Summary
29
METHODOLOGY
31
3.1
Introduction
31
3.2
Operational Framework
32
3.3
Preparation of Materials for Mix
34
3.3.1
Aggregates
34
3.3.2 Bituminous Binder
35
3.3.3
35
3.4
Mineral Filler
Sieve Analysis
35
3.4.1
Dry Sieve Analysis
35
3.4.2
Wash Sieve Analysis
36
3.5
Aggregate Blending
37
3.6
Determination of Specific Gravity for Aggregate
38
3.6.1 Coarse Aggregate
38
3.6.2 Fine Aggregate
39
Superpave Mix Design
40
3.7.1
41
3.7
3.8
Procedures
3.7.2 Apparatus
41
3.7.3
42
Specimen Preparation
Measurement of Density
43
3.8.1
43
Bulk Specific Gravity
ix
3.8.2
4
Theoretical Maximum Density
44
3.9
Determination of Optimum Bitumen Content
46
3.10
Determination of Other Properties
46
3.11
Summary
47
RESULTS AND DISCUSSIONS
48
4.1
Introduction
48
4.2
Results of Tests Conducted on the Materials
48
4.2.1 Sieve Analyses
49
4.2.2
Determination of Bulk Specific Gravity
of Aggregate
49
4.2.2.1 Specific Gravity of Coarse
Aggregate
49
4.2.2.2 Specific Gravity of Fine
Aggregate
50
4.2.2.3 Specific Gravity of Mineral
Filler
50
4.2.2.4 Bulk Specific Gravity of Aggregate 50
4.2.2.5 Specific Gravity of Bitumen
5
51
4.3
Aggregate Gradation
51
4.4
Results and Discussions of the Properties
53
4.4.1 Optimum Bitumen Content
54
4.4.2
Bulk Specific Gravity
57
4.4.3
Theoretical Maximum Density
58
4.4.4
Water Absorption
59
4.4.5 Voids in Mineral Aggregate
60
4.4.6
Voids Filled with Bitumen
61
4.4.7
Dust to Binder Ratio
62
4.5
Statistical Analysis
62
4.6
Summary
63
CONCLUSIONS AND RECOMMENDATIONS
65
5.1
Conclusions
65
5.2
Recommendations
66
x
REFERENCES
Appendices A – I
67
72 - 82
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Main factors evaluated n ruggedness experiment
15
2.2
Examples of design requirements for asphalt wearing
courses
18
2.3
20
Difference in Superpave and Malaysian sieve sizes
2.4
25
Density requirements
2.5
Comparison of observed critical VMA values with
Superpave requirements
3.1
26
37
Gradation limits for asphaltic concrete
3.2
42
Superpave gyratory compactive effort
3.3
Minimum sample size requriement for theoretical
maximum density
3.4
45
46
Design bitumen content
4.1
51
Values of bulk specific gravity of aggregate
4.2
Summary of results from samples compacted to 4±1% air
voids
4.3
54
63
Summary of statistical analysis, t-tests
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
External and internal gyration angles versus Gmb
14
2.2
Mixture compaction characteristics with varation in angle
15
2.3
Aggregate gradation for projects in Brunei, Indonesia,
Malaysia, and Singapore
18
2.4
Volumetric diagram
21
2.5
Relatioship of air voids and rut depth in Arkansas
28
3.1
Flow diagram for laboratory analysis process
33
4.1
Gradation limits and design curve for AC10
52
4.2
Gradation limits and design curve for AC14
52
4.3
Gradation limits and design curve for AC20
53
4.4
Gradation limits and design curve for AC28
53
4.5
Determination of optimum bitumen content for 75
gyrations
55
4.6
55
4.7
Determination of optimum bitumen content for 100
gyrations
4.8
Optimum bitumen content versus nominal maximum
aggregate size
57
Bulk specific gravity versus nominal maximum aggregate
size
58
56
4.9
4.10
Theoretical maximum density versus nominal maximum
aggregate size
4.11
Water absorption versus nominal maximum aggregate size
59
60
xiii
4.12
4.13
Voids in mineral aggregate versus nominal maximum
aggregate size
Voids filled with bitumen versus nominal maximum
aggregate size
Dust to binder ration versus nominal maximum aggregate
size
61
62
xiv
LIST OF ABBREVIATIONS
AASHTO
-
American Association of State Highway and Transport
Officials
AC10
-
asphaltic concretewith NMAS of 10mm
AC14
-
asphaltic concretewith NMAS of 14mm
AC20
-
asphaltic concretewith NMAS of 20mm
AC28
-
asphaltic concretewith NMAS of 28mm
ASTM
-
American Society for Testing and Materials
D:B
-
dust to binder ratio
ESAL
-
Equivalent Standard Axle Load
Gmb
-
bulk specific gravity
GTM
-
Gyratory Testing Machine
HMA
-
hot mix asphalt
JKR
-
Jabatan Kerja Raya (Public Works Department)
KLIA
-
Kuala Lumpur International Airport
MDL
-
maximum density line
NAPA
-
National Asphalt Paving Association
Ndes
-
design number of gyrations
Ninitial
-
initial number of gyrations
NMAS
-
Nominal Maximum Aggregate Size
Nmaximum
-
maximum number of gyrations
OBC
-
optimum bitumen content
PG
-
Performance Grade
Ps
-
percent by weight of the total amount of aggregate in the mix
SGaggblend
-
bulk specific gravity of the combined aggregate
SGC
-
Superpave Gyratory Compactor
SGcoarse
-
bulk specific gravity of coarse aggregate
xv
SGfiller
-
bulk specific gravity of mineral filler
SGfine
-
bulk specific gravity of fine aggregate
SHRP
-
Strategic Highway Research Program
Superpave
-
Superior Performing Asphalt Pavement
TMD
-
theoretical maximum density
VFB
-
voids filled with bitumen
VMA
-
voids in mineral aggregate
VTM
-
voids in total mix
WA
-
water absorption
xvi
LIST OF APPENDICES
APPENDIX
A
Wash sieve analysis
B
Specific gravity of coarse aggregate
73
C
Specific gravity of fine aggregate
74
D
Aggregate gradation
75
E
Results of theoretical maximum density
76
F1
Results of properties – 75 Gyrations
77
F2
Results of properties – 100 Gyrations
78
G
Sample calculation of surface area
79
H
Sample calculation of VMA based on average asphalt
film thickness method
80
Photos of laboratory works
81
I
TITLE
PAGE
72
CHAPTER 1
INTRODUCTION
1.1
Preamble
With the rapid growth in development and population, Malaysians are
certainly heading towards a better lifestyle. The Ninth Malaysia Plan, with a bulk of
the budget going to the development of infrastructure, sees a need to accommodate
the basic necessities of the people in Malaysia, and road construction is one of them.
One of the basic requirements for a pavement to perform to its design life is
the ability to withstand intense loading from repetitive traffic. The pavement should
have sufficient thickness to deal with the stresses at the surface and at the same time,
to protect the subgrade from damage. Therefore, a vital component in the process of
constructing an asphalt pavement is the design of the asphalt mixture that will be
used for the pavement. Beside ESALs loading, these mix designs take into account
many other factors such as environmental conditions, desired surface texture, and the
mix materials.
In 1987, the Strategic Highway Research Program (SHRP) was approved and
established by the United States Congress as a five-year $150 million research
program to improve the performance and durability of roads and to make those roads
safer for both motorists and highway workers (Huang, 2004). Research on asphalt
binder mixture specifications led to a new system for design of hot mix asphalt based
upon mechanistic concepts. $50 million of the SHRP research funds were used for
2
this purpose and it developed the laboratory mixture design method known as
Superpave, an acronym for Superior Performing Asphalt Pavements (Lavin, 2003;
Huang, 2004). Superpave directly correlates laboratory methods with pavement
performance instead of relating basic physical properties and observed performance
as it is with Marshall mix design method.
Superpave mix design involves three major components: the asphalt binder
specification, the mixture design and analysis system. There are three levels of
testing and analysis but only level one, which incorporate material selection and
volumetric proportioning, are currently being practiced routinely by designers. Level
two and three have additional testing machine to check the following pavement
distress, namely low temperature cracking, fatigue cracking, and permanent
deformation.
The key component of Superpave mix design is the Superpave Gyratory
Compactor (SGC). SGC emulates the compaction done at site with its kneading
action of compaction in the laboratory provided by the gyration angle. Specifications
instructed that SGC are to be used with 150mm diameter mould. However, SGC is
also capable of compacting smaller specimens using 100mm diameter mould but
with certain limitations.
With the introduction of Superpave mix design in the United States back in
1993, it was recommended that the nominal maximum aggregate size (NMAS) to be
used in categorizing the mixes. The definition of NMAS is the largest sieve size that
retains not more than 10 percent of the aggregate particle in any mix designs. The
other designation for classifying mix is by the maximum size which is defined as the
smallest sieve size through which 100 percent of the aggregate sample particles pass.
Superpave specifications give advantages and disadvantages. Superpave is
performance-based and it uses Performance Grading System (PG) for its asphalt
binder grading system. Through this way, it adopts both the project temperature and
traffic criteria.
Even though Superpave mixtures have a high coarse aggregate
content and are more difficult to work with, experience has shown that good
smoothness can be obtained. Superpave mixtures tend to provide good surface
3
drainage and result in less spray (NCAT, 1997). This results in good surface friction
properties. The process of compaction by SGC is quieter as compared to Marshall
hammer. This is due to the kneading action of SGC. The Superpave system can be
adapted to suit the requirements of any country or region. The specification needs to
include only those performance grades and requirements that are relevant to the
climate and traffic prevailing in a specific region or country. Furthermore, this
design method is not just restricted to high traffic freeways, but it is also applicable
for low volume roads and low volume parking facilities (Cross and Lee, 2000).
The disadvantages encountered among others are the testing equipment is
more complex and costly.
It requires substantial capital investment and firm
commitment to maintain the equipment in proper working conditions. In the USA, a
complete set of Superpave bituminous binder testing equipment – including bending
beam and direct tension apparatus – costs about US $100,000; the two servohydraulic Superpave mixture testing systems costs approximately US $400,000
(Tappeiner, 1996).
Superpave made its debut in Malaysia through the Kuala Lumpur
International Airport (KLIA) project (Tappeiner, 1996; Harun, 1996).
Juggling
between the short period of time to complete the project and the complexity of
adopting the Superpave’s advanced mix design and quality control system, only the
Superpave bituminous binder specifications have been included with the design and
evaluation procedures similar to those described in NCHRP Report 338: AsphaltAggregate Mixture Analysis System (AAMAS) (after Tappeiner, 1996).
1.2
Problem Statement
Typically, most specifications use NMAS in its mix design. Superpave and
Public Works Department (JKR) gradation limits use NMAS, even though both mix
designs specified a slightly different NMAS. The design of each mix with variation
in the gradation has an effect on the properties of the mix.
4
In a few studies conducted, NMAS is found to be linked to permeability and
rutting in a pavement (Mallick et al., 2003; Kandhal, 1990; Cooley Jr., Prowell, and
Brown, 2002). Permeability is related to the interconnected voids that allow the
water to infiltrate into the pavement. Through the research of Mallick et al. (2003), it
was shown that voids in mineral aggregate (VMA) has a significant effect on inplace permeability of pavements and coarse-graded Superpave mixes in which with
the increment of NMAS, the permeability also increases.
Rutting is normally associated with the extra compaction due to traffic
loading. Lavin (2003) attributed rutting to the fact of low design air voids, excessive
asphalt binder, excessive sand or mineral filler, rounded aggregate particles, and low
VMA.
Each mix design has its own optimum bitumen content. The bitumen content
at a fixed percent of air voids varies according to the NMAS and gradation. The
bitumen content plays a significant role in calculating VMA and voids filled with
bitumen (VFB). However, Kandhal, Foo, and Mallick (1998) argued that VMA
should be calculated based on surface area and to have an average asphalt thickness
coated on the aggregates.
Other problems related to the NMAS are workability and segregation.
Smaller NMAS tends to have good workability but is more unstable while larger
NMAS will cause segregation to happen.
It is also interesting to note that larger
aggregates are being use to minimise rutting (Kandhal, 1990).
The few phenomena described in the paragraphs above can all lead to further
deterioration of a pavement. It is important to get to the root cause of it to overcome
these defects.
Therefore, this study that looked into the fundamental properties of
Malaysian hot mix asphalt (HMA) mixes is essential to provide the knowledge and
understanding of the consequences.
5
1.3
Aim
This study was aimed to probe the effects of nominal maximum aggregate
size on the properties of hot mix asphalt compacted with Superpave Gyratory
Compactor by using the Malaysian mix design.
1.4
Objectives
The primary goal of this study was to evaluate the properties of Malaysian
HMA mixes prepared with different NMAS. The properties evaluated include:
(i)
optimum bitumen content at four percent air voids (OBC);
(ii)
bulk specific gravity of lab compacted mix, (Gmb);
(iii)
theoretical maximum density (TMD) using Rice method;
(iv)
water absorption (WA);
(v)
voids in mineral aggregates (VMA);
(vi)
voids filled with bitumen (VFB); and
(vii)
dust to binder ratio (D:B).
This study also looked into the properties of the mixes when compacted with
different compactive effort.
All mix designs were compacted to 75 and 100
gyrations.
1.5
Scope of the Study
In order to investigate the effects of NMAS on the properties of HMA, four
types of mix designs of asphaltic concrete (AC) were prepared in accordance to the
JKR Specification (SPJ rev2005). They were AC 10, AC 14, AC 20, and AC 28.
All these mix designs were compacted at two different levels of compaction, i.e. 75
and 100 gyrations, simulating the Malaysian traffic loading condition.
6
Based on the National Asphalt Paving Association (NAPA) method, the
optimum bitumen content were determined to obtain a 4% air voids for all the mixes,
regardless of the layer it serves. A minimum of three bitumen content were used for
each mix design, starting with median, and 0.5% before and after the median.
Verification samples were done for all the OBC.
Loose samples of two for each mix design were prepared to get the TMD
values.
Samples were analysed based on the properties and were subsequently
correlated.
1.6
Importance of the Study
The relationship between basic fundamental properties as mentioned in
Section 1.4 is very much related to the behaviour of a pavement. It is from these
properties that one may know the later consequences of the pavement whether it is
under-designed or over-designed. A lot of researchers have used these properties to
look into the deformation or on-site behaviour of a pavement (Brown, 1990;
Kandhal, Foo, and Mallick, 1998; Peterson, Mahboub, and Anderson, 2004).
The JKR Specification (SPJ rev2005) differs a little bit from the Superpave
gradation in terms of the NMAS used. The SPJ rev2005 uses NMAS of 10, 14, 20,
and 28mm while Superpave specifies NMAS of 9.5, 12.5, 19, and 25mm. This study
will be able to help the researchers and engineers understand the properties of the
Malaysian mix when they are using different NMAS in their projects. As Malaysian
Government has allocated the budget to have a good infrastructure, it is only proper
that a study is conducted to look into the basic properties that are related to the
pavement durability.
7
1.7
Summary
This chapter gave an overview of the study that was done. It introduced the
Superpave mix design, which was the outcome of the Strategic Highway Research
Program, the advantages and disadvantages of Superpave, and Superpave’s debut in
Malaysia. The problem that led to this study was also discussed, in which the causes
of pavement deteriorations such as permeability, rutting and segregation were
highlighted. Relating these deteriorations to basic properties, it will be good to know
and understand the mixes used in Malaysia with different NMAS. Therefore, this
study was aimed to observe the effects of NMAS on the HMA properties that were
compacted with the SGC.
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
Hot mix asphalt (HMA) is the most popular mix around the world.
It
combined aggregates and asphalt binder under a dry and heated condition to get a
uniform mix. Generally, HMA is being used to categorize any asphalt mixture that is
mixed while hot. Both the asphalt binder and aggregate are heated to get a fluidity to
coat the aggregate and to dry the aggregate, respectively. Different construction
project will have different kind of mixture to suit to the site conditions. There are
many methods of designing a HMA mix, which among them are the conventional
method of Hveem and Marshall, and the newest method called Superpave.
In this chapter, the discussion is based on Superpave mix design pertaining to
the background, mix design, gyratory compactor, Superpave in Malaysia,
comparison of Superpave and Malaysian mixes, the measurements of compaction,
voids in mineral aggregate, relation of NMAS to pavement deformations, and field
performance.
9
2.2
Superior Performing Asphalt Pavement
Superior Performing Asphalt Pavement, better known as Superpave is a
principal product of Strategic Highway Research Program (SHRP). SHRP desired a
long lasting pavement that requires less maintenance, provide a smooth ride, and is a
good value for taxpayers money. The research ended in 1993, giving several new
elements in the system: asphalt binder being graded by performance grade (PG),
consensus properties of aggregate, new mix design procedure, and mixture analysis
procedure (Roberts et al., 1996). Currently, the Superpave mix design system has
become the choice for the majority of transportation agencies in the United States for
HMA mix design.
The key equipment in Superpave method is the Superpave Gyratory
Compactor (SGC). Barely 10 years of establishment, there are over 2000 SGCs are
in use in the United States for the design and field management of asphalt mixtures
(Harman et al., 2002). This shows that the SGC is a popular choice in the United
States.
2.2.1
Background of Superpave
Throughout the evolution of asphalt mix design; several different types of
laboratory compaction devices have been developed to produce specimens for
volumetric and/or physical characterization (Harman et al., 2002). World War II
triggered the rapid advancement of asphalt mix design and materials evaluation.
Bruce Marshall and Francis Hveem developed mix design methods and by late
1950s, these methods were largely used. Marshall mix design method adopted the
impact type of compaction while Hveem mix design method uses tampering blow
and kneading compactor (Roberts et al., 1996).
The gyratory concept is attributed to Phillipi, Raines, and Love of the Texas
Highway Department (after Harman et al., 2002), which was a manual unit of
gyratory pressing. In the 1950’s, the concept was followed by John L. Macrae, with
10
the U.S. Corps of Engineers, developing a device called “gyratory kneading
compactor”, which was later known as the Gyratory Testing Machine (GTM) in
1993. Another important contribution to the improvement of gyratory concept is
through the Laboratoroire Central des Ponts et Chausées (LCPC) in France, which
has a fixed external, external mould wall angle of one degree with a compaction
pressure to 600kPa.
In 1984, the Transportation Research Board’s (TRB) publication of Special
Report 202, America’s Highways: Accelerating the Search for Innovation mentioned
that despite being the dominant position among highway materials, research into
asphalt cement or binder had been long neglected and recommended a research
program to “develop and improve asphalt binders” (after TRB Superpave
Committee, 2005). In 1987, the United States Congress funded the SHRP and the
effort was conducted from 1987 to 1993. Initially, SHRP focused on asphalt binder
research. In 1990, SHRP expanded efforts to include research in the area of asphalt
mixtures – building on the work of National Cooperative Highway Research
Program (NCHRP) Report 338: Asphalt-Aggregate Mixture Analysis System
(AAMAS) and the work of LCPC in France (after Harman et al., 2002).
Research for SHRP was performed by independent contractors, largely
universities, and paid for by a set-aside of funds appropriated annually from the US
Federal Government budget for distribution to the states in support of the nation’s
primary surface transportation system. Although the competition for funding is
strong at all levels of government, the State Departments of Transportation agreed to
this set-aside for research because it promised better performing roads, lower life
cycle costs, and thus, in the long run a more effective use of funds (after Tappeiner,
1996).
2.2.2
Superpave Mix Design
For all HMA mixes, the mix design procedure involves a process of selecting
and proportioning ingredients to obtain specific pavement performance properties in
11
which it is also economical. The gradation mixture must have the following criteria
(The Asphalt Institute, 1990):
•
Enough asphalt binder to ensure a durable compacted pavement by
thoroughly coating and bonding the aggregate.
•
Enough workability to permit mixture placement and compaction
without aggregate segregation.
•
Enough mixture stability to withstand the repeated loading of traffic
without distortion or displacement.
•
Sufficient voids or air spaces in the compacted mixture to allow a
slight additional amount of added compaction by the repeated loading
of traffic. These air voids will prevent asphalt binder bleeding or a
loss of mixture stability. The volume of air voids should not be so
large to allow excessive oxidation or moisture damage of the mixture.
•
The proper selection of aggregates to provide skid resistance in high
speed traffic applications.
A Superpave mix design incorporates several major steps.
These are
selection of materials, selection of aggregate gradation, selection of asphalt binder,
and evaluation of mix design.
As it is with all hot mix asphalt, the design
compaction levels must be established.
Superpave mix design consists of three levels. These levels relates to the
expected traffic and other considerations for different degree of reliability. Expected
traffic levels for the design life of the pavement characterized by the equivalent
standard axle loads (ESALs) are quantified as low (≤1 million ESALs), medium (1 –
10 million ESALs) , and high (≥10 million ESALs) (after Tappeiner, 1996). The
three levels are described as follow:
•
Level one mixture design incorporates careful material selection and
volumetric proportioning to produce a mixture that will perform
satisfactorily. It is for asphalt pavements exposed to low traffic. The
laboratory compacted effort is adjusted to suit the traffic loading
expected, and compaction temperature.
12
•
Level two and three applies all the level one procedure and at the
same time, included two additional pieces of laboratory equipment to
test a range of mixture performance tests such as permanent
deformation and fatigue cracking to evaluate the asphalt’s response to
various loading and temperature conditions.
The additional
equipment is known as the Superpave Shear Tester (SST) and the
Indirect Tensile Tester (IDT).
The SST can perform six tests on the mixture i.e. volumetric test; uniaxial
test; repeated shear test at constant stress ratio; repeated shear test at a constant
height; simple shear test at a constant height; and frequency sweep test at a constant
height. The IDT can perform test for creep compliance and the strength of the
mixture using an indirect tensile loading at intermediate to low temperatures.
2.2.3
Superpave Gyratory Compactor
The SGC is an electrohydraulic machine consisting of the following
components:
•
Reaction frame, rotating base, and motor;
•
Loading ram and pressure gauge;
•
Specimen height measuring and recording system; and
•
Mould base and plate.
The SGC is based on the Texas gyratory compactor discussed in section 2.2.1
combining the characteristics of the French gyratory compactor. In May 1991, the
Rainhart Company of the United States was awarded a contract for the manufacture
of one modified gyratory shear-testing machine (Harman et al., 2002). The Asphalt
Institute attempted to fabricate a French style gyratory fixed with 1° angle from a
Texas Highway Department manufactured Texas 6 inch gyratory in 1991 and many
of the mixture testing of SHRP was done with this equipment. Investigation by
FHWA on this device showed the mould wall angle was 1.23°, not 1° as originally
13
desired. After discussion and reviews, SHRP researchers came up with the final
specification for the SHRP gyratory compactor with vertical consolidation pressure
of 600 kPa, fixed angle of gyration of 1.25°, and speed of gyration of 30 rpm
(Harman et al., 2002).
The issue of tolerance for manufacturers of the gyratory compactor surfaced
when they were allowed an error of ±0.02° for the angle of gyration, ±10 kPa for the
pressure loading and ±0.5 rpm for the speed of gyration.
However, the
manufacturers indicated that these tolerances were too tight and would raise the cost
of the device by more than half (Harman et al., 2002).
Two company awarded the manufacturing of gyratory compactors are Pine
Instruments Company and Troxler Electronics.
When compared to the Texas
gyratory, the Pine gyratory yielded a result that is within the limit for bulk specific
gravity, Gmb, (AASHTO precision is 0.02). On the other hand, Troxler gyratory
showed lower densities and outside of the allowable tolerance.
After much
discussion with SHRP researchers, the caused was established and the results were
due to the wall thickness. The Pine and the Texas compactors’ mould walls were
very similar in thickness while the mould walls of the Troxler compactor were much
thinner. Thin walls will allow the specimens to cool faster, this increasing the mix
stiffness and decreasing the compacted specimen’s density. Troxler later redesign
the mould in an effort to make the two compactors more comparable.
Currently, there are five companies that are manufacturing SGC for the use in
United States offering a total of eight different models (Harman et al., 2002). All
Superpave gyratory compactors are designed to meet the specification criteria found
in AASHTO T312. For external gyration angle, all SGCs are required to follow the
specification of 1.25°±0.02°, vertical pressure of 600±18 kPa, rotational rate of
30±0.5 rpm, and height recording of 0.1mm per gyration (Buchanan, Brunfield, and
Sheffield, 2004).
With so many manufacturers and models available, different agencies that
used different SGC have reported significant differences in term of bulk specific
14
gravity, which can exceed 0.025 (approximately 1% air voids) (NCHRP, 2000;
Buchanan and Brown, 2001).
In Alabama, the differences in air voids for the
average of three compacted samples of up to 0.8 percent may be expected between
samples compacted in different brands of SGCs. The difference could be as high as
2.3 percent air voids between any two compactors (Prowell, Brown, and Hunner,
2003).
Buchanan, Brunfield, and Sheffield (2004) addressed this issue by
investigating the gyration angle of SGCs.
Internal angle verifications were
conducted with Dynamic Verification Angle (DAV) while the external angle
verifications were conducted in accordance with the SGC manufacturer’s
recommended protocols. Specimens were compacted with a properly verified and
calibrated SGC that is in accordance to the manufacturer’s protocol. Gyration angles
will decrease during compaction depending upon the HMA mix characteristics.
Figure 2.1 shows the change in bulk specific gravity against external and internal
angles for the SGCs used. Buchanan and Brown (2001) also concluded that the
precision of the Superpave gyratory compactor is better than the mechanical
Marshall hammer.
Figure 2.1: External and internal gyration angles versus Gmb (Buchanan et al., 2004)
The observed difference in bulk specific gravity corresponds to an air void
difference of 0.97% and a VMA difference of 0.9%. Buchanan, Brunfield, and
Sheffield (2004) further suggested the possible reason for observed differences may
15
be due to the ram foot deflection or framework movement is likely to have an
internal angle that is different than the unloaded or loaded external measured angle.
The effect of angle of gyration on density was also investigated by Swami,
Menta, and Bose (2004). Figure 2.2 shows the mixture compaction characteristics
with variation in angle of gyration.
The trend shows that percent maximum
theoretical density, TMD, increases with the increase in angle of gyration.
Figure 2.2: Mixture compaction characteristics with variation in angle (Swami et al.,
2004)
In the quest to improve on the provisional standard of AASHTO TP4:
Standard Method for Preparing and Determining the Density of Hot Mix Asphalt
(HMA) Specimens by Means of the SHRP Gyratory Compactor, McGennis et al.
(1997) conducted a ruggedness evaluation of the standard. Seven main factors as
listed in Table 2.1 with the high and low values used in the experiment were
evaluated in the ruggedness experiment.
Table 2.1: Main factors evaluated in ruggedness experiment (McGennis et al., 1997)
Main Factor
Angle of Gyration, degrees
Mould Loading Procedure
Compaction Pressure, kPa
Precompaction
Compaction Temperature, °C
Specimen Height,mm
Aging Period @135°C, hours
Levels
Low (1.22 to 1.24) and High (1.26 to 1.28)
Transfer Bowl Method and Direct Loading Method
582 and 618
None and 10 thrusts with Standard Rod
@ 0.250Pa-s viscosity and @ 0.310Pa-s viscosity
Low (around 110mm) and High (around 120mm)
3.5 and 4
16
The ruggedness evaluation revealed that the tolerance on compaction angle of
1.25° (±0.02°) and the tolerance for compaction temperature in the range of 141 to
146°C with the viscosity between 0.250Pa-s and 0.310Pa-s is reasonable. Method of
loading procedure and precompaction does not give any significant changes to the
results.
The tolerance on compaction pressure (±18kPa) is too high while the
tolerance on specimen height (±1mm) is too narrow. The aging period is inclusive of
the 30min compaction temperature equilibrium period. This specification (AASHTO
TP4), however, has been superseded by the current specification of AASHTO T312.
The SGC is also capable of predicting HMA stability during compaction
(Dessouky, Masad, and Bayoumy, 2004). This method is functional with the help of
mathematical derivation and a new stability index. This will indeed save the cost of
buying other equipments.
2.2.4
Superpave in Malaysian Scenario
The Malaysian government has encourage all its citizens to learn and bring
about new technology to lead the country into becoming a develop country. In doing
so, many organizations have rise to the challenge and among them is Malaysia’s
Public Works Research Institute (IKRAM).
IKRAM has responded to the
government’s call by participating in a SHRP Superpave training program to learn
firsthand about what Superpave has to offer. This was later applied in the technical
specifications for runway and taxiway pavement for the then on-going prestigious
Kuala Lumpur International Airport (KLIA) project (Tappeiner, 1996; Harun, 1996).
Malaysia became the first country in Asia to use Superpave-based
specifications in a large commercial project.
Other countries like the People’s
Republic of China, Japan, South Korea and other Asean nations followed
subsequently in adopting this new technology, with some of these nations have
procured the new testing equipment and are in the process of arranging training
17
programs (Tappeiner, 1996).
The KLIA project was implemented with some
changes to suit the local condition.
In order to look into the modification, a basic understanding of the
bituminous pavement behaviour under the tropical conditions, especially in Malaysia
is needed. Generally, pavements in Malaysia require major maintenance activities in
about four to six years from its construction date as compared to the United States,
between eight to ten years (Badaruddin, 1994). Among the factors that contributed
to the pavement deterioration are traffic loads, pavement age, and environmental
condition. Hameed (1994) stated that the common causes of pavement distress in
this country can be attributed to reflective cracking, age hardening of the bituminous
surfacing, and rutting. Reflective cracking occur as a result of crack or joint pattern
in the underlying layer, and may be either environment or traffic induced (after
Hameed, 1994). Age hardening of bitumen causes the pavement to become brittle
and this type of cracking, most common in tropical countries, starts at the top surface
and propagates downwards. This can be explained as the bitumen in the top few
millimeters of the mix hardens at a higher rate than in the main body of the mix
(Hameed, 1994). Malaysia’s hot (high temperatures with ultra violet light radiation)
and humid condition tends to accelerate the ageing process. The main causes for
rutting in the wheelpaths are secondary compaction, instability of the mix,
insufficient load distribution, inadequate base or subbase and sugrade movement. If
not treated, rutting may lead to cracking and this condition is worsen by the high
rainfall intensity experienced in Malaysia.
Looking at these deteriorations,
Badaruddin (1994) recommended to modify the mix design procedure by modifying
the gradation of the aggregates and characteristics of the bituminous mixtures in
order to produce quality pavements.
On wider basis, Cham (1994) studied on the asphalt mix production
technology in four Asean countries, namely Brunei, Indonesia, Malaysia, and
Singapore.
The HMA is of Marshall design method and the author noted the
differences of the design requirements for asphalt wearing course as can be seen in
Table 2.2 with the exception of Brunei. The differences of the aggregate gradation
of HMA mixtures used in the region for different projects were also given (Figure
2.3). The author also acknowledges the different grade of asphalt binder, which is
18
crucial in a Superpave mix design. Hot mix asphalt for Singapore are produced with
penetration of 60/70 PEN while the other three countries are using penetration grade
of 80/100 PEN.
Table 2.2: Examples of design requirements for asphalt wearing courses (Cham,
1994)
Mix Property
Stability
Flow
Stiffness
Air Voids
Voids in aggregate filled
with bitumen
Retained stability after
24h soaking
Bitumen content
Malaysia
> 500 kg
> 2mm
250 kg/mm
3 – 5%
Singapore
> 9 kN
2 – 4mm
3 – 5%
Indonesia
700 – 1500 kg
2.1 – 50 kN/mm
4 – 6%
75 – 85%
75 – 82%
-
-
-
≥ 75%
5 – 7%
5.5 – 6.5%
≥ 6.7%
Figure 2.3: Aggregate gradation for projects in Brunei, Indonesia, Malaysia, and
Singapore (Cham, 1994)
For the KLIA project, the bituminous binder specification was chosen with
due considerations given to the tropical climate and loading with both the binder and
wearing course used PG76-10 (Tappeiner, 1996). Available sources of unmodified
bitumen did not meet at 76°C the shear stiffness requirement as stipulated in the
19
Superpave specification.
Therefore, polymer-modified asphalt was selected and
specified (Harun, 1996).
Because of the complexity of adopting Superpave’s
advanced mix design and quality control system within the short period of time
allowed by the KLIA project schedule, only the Superpave bituminous binder
specifications have been included in the KLIA project. These performance based
binder specifications were combined with design and evaluation procedures similar
to those described in NCHRP Report 338: Asphalt-Aggregate Mixture Analysis
System (AAMAS) (after Tappeiner, 1996). Two stages were used to evaluate the mix
design; Stage 1 – volumetric properties tested with traditional Marshall mix design
procedure, and Stage 2 – mechanistic mixture tests for several binder contents
determined from Stage 1. Harun (1996) discussed some of the binder specification
tests, which have been incorporated in the quality assurance program of the KLIA
project. It is briefly summarized below:
•
Dynamic Shear Rheometer – to characterize the viscous and elastic
behaviour of binder.
•
Rotational Viscometer – to ensure that the binder is sufficiently fluid
when pumping and mixing.
•
Pressure Aging Vessel – to compress time so that long term aging can
be simulated in only 20 hours.
The application of Superpave binder specification in the KLIA project has set
a path for a new era of mix design in Malaysia, which in return will allow Malaysia’s
researcher, consultants and contractors to become highly competitive in the Asean
and world society.
2.3
Comparison of Superpave and Malaysian Mixes
Despite the effort to introduce the Superpave mix design in Malaysia,
contractors are still more comfortable in using the conventional Marshall mix design.
Furthermore, the initial cost to setup the SGC is very costly. However, this section
will look into the specification.
20
Most Malaysian mixes are designed based on Marshall method as parameters
and limitations specified in JKR/SPJ/rev2005 are from Marshall method.
In
comparison for Superpave and the Malaysian mixes, few major differences are noted.
The differences lay in the aggregate gradation, binder grading system, and air voids
specification. The Superpave gradation exercised a different sieve size from the
Malaysian gradation limits. The difference in sieve sizes is given in Table 2.3.
Table 2.3: Difference in Superpave and Malaysian sieve sizes
NMAS for Superpave
mixes, mm
50.0
37.5
25.0
19.0
12.5
9.5
12.5
9.5
4.75
2.36
1.18
0.6
0.3
0.15
0.075
NMAS for Malaysian
mixes, mm
37.5
28.0
20.0
14.0
10.0
5.0
3.35
1.18
0.425
0.15
0.075
As for binder grading system, Superpave grades the binder with Performance
Grading system while Malaysia draws on the Penetration system. Superpave mix
design specified 4% air voids to be achieved for all the mixes but Malaysia’s design
stipulated an a 3-5% air voids for wearing course and 4-6% air voids for binder
course. Other requirement that differs includes the materials requirements.
The significant difference between Marshall and Superpave is the compaction
effort. Marshall adopts an impact type of compaction with the Marshall hammer
dropping on the samples at fixed height and weight. Superpave uses the kneading
action by a static constant loading and at the same time gyrating the mould with
samples to a given density or number of gyrations. Superpave method also does not
require any stability or flow testing on the samples.
21
2.4
Measurements of Compaction
In a hot mix asphalt mix design, the most important property to evaluate the
mix is the volumetric properties. Marshall and Superpave mix design adopted the
volumetric properties either for laboratory compacted samples or on-site cored
samples. The fundamental volumetric properties of a compacted asphalt mixture are
air voids, voids in mineral aggregate, voids filled with bitumen, and effective
bitumen content (Lavin, 2003).
Other volumetric properties can be further
elaborated in Figure 2.4.
Vtm
Air
Asphalt
Absorbed asphalt
Vfb
Vma
Vb
Vba
Vmm
Vsb
Vmb
Vse
Aggregate
Figure 2.4: Volumetric diagram
As such, volumetric properties are based on weight-volume relationships.
This can be traced to the contribution of Mc Leod (1956) where he pointed out that
the design and analysis of asphalt paving mixtures should be based on volumetric
properties instead of using the basis of weight as have been practiced widely at that
time. Most specifications in those days tended to specify a range of asphalt content
by weight along with grading bands or limits for the aggregate, which in effect
required a design on the basis of weight. The most serious problem concerning the
design of bituminous paving mixtures in Canada is found to be the coarse and fine
aggregate combinations, which resulted in a too densely graded mix. He developed
the volumetric criteria such as VMA, VFA, and volume of air voids and reported that
it contain errors when calculated by weight. Kandhal, Foo, and Mallick, (1998)
reported that McLeod worked with Marshall hammer of 75 blows, and recommended
22
that the VMA should be restricted to a minimum value of 15%, the volume of air
voids (within the VMA) should lie between 3 to 5%, which in turn restricted the
volume of asphalt binder in the compacted mixture to a permissible minimum of
10% by volume. This automatically established minimum asphalt content of about
4.5% by weight (10% by volume). High air voids lead to permeability of water and
air resulting in water damage, oxidation, and cracking. Low air voids lead to rutting
and shoving of the asphalt mixture (Brown, 1990).
The voids in an asphalt mixture and density are directly related. Thus, the
density must be controlled to ensure that the voids are within a specified range. The
basic physical property of any material in weight-volume relationships is the specific
gravity (Lavin, 2003).
Density of the compacted samples can be obtained by
multiplying the bulk specific gravity of the mix by the density of water (1000 kg/m3)
(The Asphalt Institute, 1983).
Specific gravity is a ratio of the mass of a material of a given volume to the
weight of an equal volume of water, both at same temperature. The specific gravity
of a material is used to bridge the gap between weight and volume relationships in
asphalt mixture design. Lavin (2003) stated five different types of specific gravity
measurements used in the volumetric analysis of asphalt mixtures:
•
Apparent specific gravity, Gsa: the ratio of the mass in air of a unit
volume of an impermeable aggregate or stone at a stated temperature.
•
Bulk specific gravity, Gsb: the ratio of the mass in air of a unit volume
of a permeable (including both permeable and impermeable voids)
aggregate at a stated temperature.
•
Effective specific gravity, Gse: the ratio of the mass in air of a unit
volume of permeable (excluding voids permeable to the asphalt
binder) aggregate at a stated temperature.
•
Bulk specific gravity of the compacted asphalt mixture, Gmb: the ratio
of the mass in air of a unit volume of a compacted specimen of an
asphalt mixture at a stated temperature.
•
Theoretical maximum specific gravity of an asphalt mixture, TMD:
the ratio of the mass in air of a unit volume of an uncompacted or
23
loose asphalt mixture at a stated temperature. It is also known as the
Rice specific gravity, named after James Rice, the developer of the
test procedure to measure the maximum specific gravity.
In another paper presented by McLeod (after Kandhal, Foo, and Mallick,
1998), he pleaded for the use of bulk specific gravity of the aggregate for calculating
both the VMA and the air voids. In the previous research, McLeod did not consider
asphalt absorption but this subsequent work took into account the absorption of the
asphalt binder into the aggregate. Again, McLeod recommended that the lowest
permissible asphalt content in a hot mix asphalt mix should be 4.5% by weight, to
ensure the mix durability. He also proposed a relationship between the minimum
VMA and the nominal maximum particle size of the aggregate, which is based on the
relationship of the bulk specific gravity of the aggregate and an air voids content of
5%. This was later revised by the Asphalt Institute to 4% and is now incorporated in
the Superpave mix design (Asphalt Institute, 1993).
In an evaluation of selected methods for measuring the bulk specific gravity
of compacted HMA mixes, Buchanan (after NCAT, 2000) studied on four methods
available, namely water displacement method, dimensional analysis, parafilm, and
the vacuum sealing method. The selected conclusions drawn from the study are:
•
The vacuum sealing and the water displacement methods provided
similar results for the fine and coarse graded Superpave mixes.
•
A good relationship between the percent absorbed water and the
differences between the vacuum sealing and the water displacement
methods was observed. Significant errors in the calculated air voids
can result by using the water displacement method even though the
percent absorbed water is less than the currently specified maximum
limit of 2%. These errors were shown to be as much as approximately
1% for 0.5% absorbed water and as high as 6% for 2% absorbed
water.
•
Significant errors in the calculated air voids contents can result from
only small errors in the volume calculation using dimensional
analysis. A 1% error was shown to yield a 1% error in air voids.
24
•
The vacuum sealing method appears to most accurately measure the
bulk specific gravity of all the samples evaluated; regardless of mix
type, aggregate type, compaction level, or sample state (cut or uncut).
This was also reported by Bhattacharjee and Mallick (2002).
However, the water displacement method generally provides
acceptable results for the majority of dense graded mixes.
Maximum theoretical specific gravity of HMA can be obtained by two
methods, namely the Rice method, and the Texas C-14 method. Rice approved of
using backcalculation from a single Rice test to get the maximum theoretical specific
gravities. However, he rejected the idea of theoretical approach based on bulk
specific gravity of aggregate due to low maximum theoretical specific gravities and
high relative densities (Solaimanian and Kennedy, 1989). As for the Texas C-14
method, it has lower design asphalt content than the uncorrected Rice method for
water absorption. To have a same result, it is recommended that asphalt content for
Rice method adopts 96% relative density while Texas C-14 method adopts 97%
relative density.
Brown (1990) stated three methods to specify density at site: percent of
laboratory density, percent of theoretical density, and percent of control strip.
Percent of laboratory density requires that the in-place material be compacted to
some percentage of the laboratory density, typically at least 95%.
The second
method requires that mix to be compacted to some minimum percentage of the
theoretical maximum density. This method is direct in specifying the maximum inplace air voids and an indirect method for controlling compaction. The third method
to specify density as percent of control strip is to compare the bulk density of the inplace asphalt mix to the bulk density of a control strip that had been constructed
using standard compaction techniques. However, this method is the least desirable
of the three methods as it does not allow the compactibility of a mix to be evaluated.
In the Superpave mix design method, the compaction of mixtures is a
function of the number of gyrations completed by the SGC. The traffic loading
specific number of gyrations is known as the design number of gyrations, or Ndes. It
is based on estimated ESALs for 20 years design life.
Two other parameters
25
introduced are Ninitial and Nmaximum or Nmax. Both Ninitial and Nmax are mathematically
related to Ndes as follow:
Log Ninitial = 0.45 Log Ndes
(1)
Log Nmax = 1.1 Log Ndes
(2)
Initially, the specimens were compacted to Nmax.
The densities and
volumetric properties were then backcalculated from Nmax. Vavrik and Carpenter
(1998) pointed out that there were errors when performing backcalculation. They
stated that samples that were compacted to Nmax yielded about 2% air voids but when
backcalculated to Ndes, the 4% desired air voids cannot be achieved. This is true for
both mix design and field quality control testing. As a result of this, specimens are
compacted to Ndes (96% relative density) instead of Nmax (Jackson and Czor, 2003).
The Ninitial is used to give an estimate of the asphalt mixture’s ability to be
compacted by rollers during placement of the mixture in the field. The mixture is
compacted by the SGC to Ninitial, and an estimated bulk specific gravity is determined
by the SGC. The design ESALs determines the maximum density amount at Ninitial.
The mixture is then further compacted to Ndes, where another estimated bulk specific
gravity is determined by the SGC. The specimen is then extruded and its actual or
measured specific gravity is determined. The specific gravity of the specimen at the
maximum number of gyrations, Nmax is extrapolated from the information provided
at Ninitial and Ndes. The density at Nmax is relevant in that the specific gravity or
density of the specimen at Nmax should not be greater than 98% of the theoretical
maximum specific gravity.
A high density at Nmax is undesirable, since Nmax
represents a traffic level much higher than that for which the project is designed. By
limiting the density at Nmax, it is expected that the mixture will not densify to
extremely low air voids with unexpectedly high traffic or ESALs (after Lavin, 2003).
Table 2.4 shows the various density requirements at different ESALs loading.
Table 2.4: Density requirements (Lavin, 2003)
Design ESALs 20 years
< 300,000
300,000 to < 3,000,000
3,000,000 to < 30,000,000
≥ 30,000,000
Required relative Density (% of Gmm)
Ninitial
Ndes
Nmax
≤98.0
96.0
≤91.5
≤98.0
96.0
≤90.5
≤98.0
96.0
≤89.0
≤98.0
96.0
≤89.0
26
2.4.1
Voids in Mineral Aggregates
Research has shown that many organizations found difficulty in
implementing the minimum requirement of VMA for Superpave mixes (Kandhal,
Foo, and Mallick, 1998). This can generally be attributed to the increase compaction
effort by SGC.
The rationale behind the minimum VMA requirement was to
incorporate at least a minimum permissible asphalt content into the mix in order to
ensure the pavement durability. This is especially true for coarse graded mixes
where the surface area is low and thus, having difficulty in meeting the minimum
VMA requirement. Kandhal, Foo, and Mallick, (1998) also suggested the usage of
minimum average asphalt film thickness to ensure mix durability instead of
minimum VMA. A minimum average thickness of 8 microns was recommended,
which can actually be calculated from the asphalt content and surface area of the
aggregate.
In reviewing the validity of the minimum VMA requirement vs. NMAS
required in Superpave volumetric mix design, Hislop and Coree (2000) found that
the measured minimum VMA requirements fit the data trend reasonably well.
However, the values are typically less than the Superpave criteria. This measured
minimum VMA refers to VMA values when the mixes became unsound or unstable.
Table 2.5 shows the values for observed VMA and the minimum required VMA. An
ANOVA analysis revealed that NMAS becomes insignificant when other aggregate
properties such as gradation and surface texture were introduced. This also confirms
the work by Abdullah, Obaidat, and Abu-Sa’da (1998), who concluded that the
coarser the mix, the higher the VMA and VTM would be, thus making the mix
porous and water permeable. This contributed to the rate of increase in the water
permeability for the same type of aggregate.
Table 2.5: Comparison of observed critical VMA values with Superpave
requirements (Hislop and Coree, 2000)
Nominal Maximum
Aggregate Size
9.5 mm
12.5 mm
19 mm
Observed VMA,
Average Value
13.5
12.3
11.2
Observed VMA,
Standard Deviation
1.5
1.1
1.7
Minimum Required
VMA
15
14
13
27
In a report on the guidelines to increase VMA of Superpave mixes prepared
by the Ad-Hoc Mix Design Task Group, they stated three factors that contributed to
the VMA values, namely gradation, surface texture, and aggregate shape. Among
some recommendations that were given to increase the VMA value include lowering
the dust content, blending the aggregates to give a gap graded mix, and having a
rougher surface texture.
2.5
Relation of NMAS to Pavement Deformations
NMAS is defined as the largest sieve size that retains some of the aggregate
particles, but generally not more than 10 percent (Roberts et al., 1996). Design of a
pavement must be able to give strength and durability, while effects such as rutting,
bleeding, tenderness, permeable pavement, cracking, and other deformations must be
avoided.
Studies by Mallick et al. and Cooley et al, (after Hainin, Cooley, and Prowell,
2003) indicated that NMAS has a great influence on the permeability characteristics
of a pavement. The increment of NMAS has resulted on the higher potential for
interconnected voids, thus increasing the permeability. However, Hainin, Cooley,
and Prowell (2003) found an interestingly different position when their study showed
that NMAS was not among the factors identified as affecting permeability. The
explanation offered was that 39 out of the 42 projects included for their study have
either a 9.5 or 12.5mm NMAS.
Back in the early 90s, rutting is a major problem experience on most
pavements in United States. This is primarily attributed to the high tyre pressures
and increased wheel loads (Kandhal, 1990). Therefore, in order to minimize rutting,
the use of large size stone, categorized as larger than one inch, was proposed to be
incorporated into the binder and base courses.
28
2.6
Field Performance
One of the goals of laboratory testing is to determine the performance of the
pavement and ascertain the field samples properties. In 1991, Brown and Cross
investigated relationships between the measured density of the mixture obtained in
the mix design, during quality control of the mixture (laboratory compaction of field
produced mix), after initial compaction (cores obtained after construction and before
traffic), the final density obtained from pavement cores after densification by traffic
and the density of recompacted samples. These samples were compacted with 75
Marshall blows and 300 revolutions on the GTM set at 120 psi and 1°. They
concluded that in-place unit weight of the pavement after traffic usually exceeded the
mix design unit weight resulting in low air voids and hence premature rutting. Mix
containing air voids below 3% greatly increase the probability of premature rutting
and the in-place unit weights of the pavement after traffic usually exceed the mix
design unit weight resulting in low air voids and hence premature rutting. They
further mentioned that the GTM gives reasonable design density and void content for
up to 9 million ESALs while the Marshall compaction only gives reasonable design
density and void content for up to 6 million ESALs. Even though Ford (after Brown,
1990) used Marshall compaction method, he agreed that low air voids lead to
premature rutting and suggested that air voids should at least be of 2.5%. Figure 2.6
shows relationship of air voids and rut depth in Arkansas.
Figure 2.6: Relationship of air voids and rut depth in Arkansas (after Brown, 1990)
29
Supporting the work of Brown and Cross, Peterson, Mahboub, and Anderson,
(2004) showed that there was significant difference in terms of mechanical properties
in the final HMA pavement constructed and the laboratory data. The laboratory
specimens and field cores were made of the same material and compacted to the
same air voids. The air voids in HMA were used as a key parameter linking
laboratory to field compaction. The laboratory compacted specimens showed higher
stiffness. They also found that the best result may be achieved by using the current
1.25° gyratory angle and 400 kPa pressure.
A phenomenon referred to as “VMA collapse” is suspected to have
contributed to many pavement failures despite the fact that the mix produced and
compacted at laboratory has sufficient VMA, yet after construction, the measured
VMA is significantly lower (Chadbourn et al., 1999). In general, VMA collapse is
caused by a combination of two elements, i.e. generation of fines during construction
due to aggregate degradation, and higher asphalt absorption due to high plant mix
temperatures, long hauling distances, and aggregate porosity. They also reported that
is a HMA has about the same asphalt film thickness from mix design to production,
there will be little or no change in VMA.
2.7
Summary
Researches and studies done by others were reviewed in this chapter. It
began with the discussion of Superpave. Superpave originated from the SHRP, a
collaborative research program that has initially focused on the asphalt binder.
Superpave mix design consisted of three levels, but only level one is widely in use.
The centrepiece of Superpave revolves around the Superpave Gyratory Compactor.
The gyratory concept is not entirely new but was modified from the Texas gyratory
compactor and French gyratory compactor. Many models of SGC are available in
the market but this has led to inconsistency of data obtained. A lot of researches
were conducted to evaluate the influence of different parameters of SGC on the
properties of mix. In Malaysia, the Superpave was adopted for the KLIA project.
30
The difference between Superpave and Malaysian mixes are noted in terms of the
aggregate gradation, binder grading system, and air voids specification.
Volumetric properties are the basic for evaluation of a mix. It is based on
weight-volume relationships, which uses the specific gravity to convert one
parameter to the other. Initially, design and analysis were based on weight, but
yielded some errors when calculating for volumetric criteria such as VMA, VFA, and
volume of air voids. Air voids and density are directly related. There are four
methods of measuring bulk specific gravity of compacted mixes, i.e. water
displacement method, dimensional analysis, paraffin, and the vacuum sealing
method. Compaction with SGC has three specific numbers of gyrations for certain
purposes: Ndes is related to the desired percent of air voids, Ninitial is related to
compaction by rollers at site, and Nmax relates to rutting behaviour.
Research has shown that many organizations found difficulty in
implementing the minimum requirement of VMA for Superpave mixes. He steps
recommended to achieve the required VMA, among others, include using a minimum
average asphalt thickness of 8 microns, and using VMA values when the mix became
unsound or unstable.
Researchers have found that NMAS was linked to pavement deformation
such as permeability and rutting. Comparison between field cores and laboratory
compacted specimens showed some differences such as lower air voids and stiffness
for field cores. Also, a phenomenon called “VMA collapse” is seen to be one of the
contributing factors to pavement failures.
CHAPTER 3
METHODOLOGY
3.1
Introduction
The purpose of this study was to look into the effects of nominal maximum
aggregate size on the properties of hot mix asphalt. This study used the Superpave
method as published by National Asphalt Paving Association along with the Public
Works Department of Malaysia’s specifications for the different type of mixes. The
types of mixes that were designed are AC10, AC14, AC20, and AC28.
The
specimens were subjected to compaction by the Superpave Gyratory Compactor.
Two levels of compaction that have been specified were 75 and 100 gyrations,
specifying the Malaysian traffic loading conditions. Specimens for each of the mix
types were prepared using minimum of three binder contents to obtain the optimum
bitumen content.
All tests were conducted at Universiti Teknologi Malaysia’s Transportation
Laboratory. Tests were conducted on the aggregates, loose mix, and compacted mix
in order to obtain the properties of all the mixes.
32
3.2
Operational Framework
The laboratory work consisted of two series of tests with the first being tests
done prior to mixing and second series being the tests done on prepared specimens.
The tests to be conducted for the first series are sieve analysis, and determination of
specific gravity for aggregate (coarse and fine). The aggregates obtained from the
Malaysian Rock Product Quarry (MRP) were dried sieve to separate the aggregates
into different sizes for later use. Washed sieve analysis was done to determine the
percentage of dust and silt-clay material in order to check the need for filler material.
Aggregate blending satisfying the JKR gradation limits were used. Subsequently, the
process of specific gravity determination for coarse and fine aggregate took place.
Bitumen of 80-100 PEN was used in this study.
The second series involved the mix design. A total of 90 specimens were
prepared.
The sample preparation incorporates specifying the mixing and
compaction temperatures, sample shot-term aging, and determining the optimum
bitumen content. The Rice method will be used in determining the TMD, and water
displacement method was used in determining the bulk specific gravity of the mix.
The general procedures for laboratory work are illustrated in Figure 3.1.
33
Aggregates from the MRP Quarry
Wash sieve analysis to determine the
percentage of dust and silt-clay
Dry sieve analysis to distribute the
aggregates into different sizes
Determination of specific gravity for
coarse and fine aggregate
Aggregate blending to obtain the
desired gradation that is well within
the gradation limits
Mixing
Short Term Aging
Compaction (75 or 100
Determination of Theoretical
Maximum Density, TMD
Determination of Bulk Specific
Gravity, Gmb
Determination of OBC at 4±1% air
Determination of VMA, VFB, WA, and
D:B
Verification Samples
Analyses and Discussion
Figure 3.1: Flow diagram for laboratory analysis process
34
3.3
Preparation of Materials for Mix
Materials that are going to be use for this study are aggregate, bituminous
binder, filler, and anti-stripping agent. All materials are to be prepared in accordance
with
the
Standard
Specification
for
Roadworks
published
by
JKR
(JKR/SPJ/rev2005).
3.3.1 Aggregates
According to JKR/SPJ/rev2005, aggregate for asphaltic concrete shall be a
mixture of coarse and fine aggregates, and mineral filler.
The coarse aggregate conformed to the requirements – the Los Angeles
Abrasion Value shall not be more than 25% (ASTM C 131), the weighted average
loss of weight in the magnesium sulphate soundness test of 5 cycles shall not be
more than 18% (AASHTO T 104), flakiness index shall not be more than 25%
(MS30), water absorption shall not be more than 2% (MS30), and polished stone
value shall not be less than 40 (MS30).
Fine aggregate normally consists of quarry dusts. Fine aggregate conformed
to the requirements – sand equivalent of aggregate fraction passing the 4.75mm sieve
shall be not less than 45% (ASTM D 2419), fine aggregate angularity shall not be
less than 45% (ASTM C 1252), the Methylene Blue value shall be not more than
10mg/g (Ohio Department of Transportation Standard Test Method), the weighted
average loss of weight in the magnesium sulphate soundness test of 5 cycles shall not
be more than 18% (AASHTO T 104), and the water absorption shall not be more
than 2% (MS 30).
35
3.3.2
Bituminous Binder
Bituminous binder for asphaltic concrete was bitumen of penetration grade
80-100, which conformed to MS 124. The specific gravity was 1.03.
3.3.3
Mineral Filler
Mineral filler for this study was ordinary Portland cement, which was
sufficiently dry and essentially free from agglomerations. The mineral filler also
served the purpose as an anti-stripping agent.
3.4
Sieve Analysis
There are two methods for determining aggregate gradation, i.e. dry sieve
analysis and washed-sieve analysis.
3.4.1
Dry Sieve Analysis
Dry sieve analysis were performed on aggregates obtain from quarry,
Malaysian Rock Product Sdn. Bhd. (MRP), Ulu Choh, Kulai, Johor. This test was
done to separate the aggregate into different sizes. Dry sieve analysis were in
accordance with ASTM C 136 and AASHTO T 27.
The apparatus that were used for dry sieve analysis included:
(i)
Sieves with various sizes starting from 37.5mm to pan;
(ii)
Mechanical Sieve Shaker; and
(iii)
Balance with the accuracy of 0.5 g.
36
The procedures for dry sieve analysis are as follow:
(i)
The sieves were arrange in order of decreasing size of opening from
top to bottom on the sieve shaker.
(ii)
The aggregate were placed on the top sieve and started sieving.
(iii)
Aggregate that have been sieved were separated according to the size.
(iv)
For mixing, total aggregate of different sizes as designed were
weighed.
3.4.2 Wash Sieve Analysis
Wash sieve analysis was done to determine the amount of weight of dust and
silt-clay material in the original sample. It is also used to determine the total filler
needed for the particular mix. Wash sieve analysis was in accordance with ASTM C
117 and AASHTO T 27.
The apparatus used for washed sieve analysis were:
(i)
Sieve size of 600 and 75μm;
(ii)
Container;
(iii)
An oven capable of maintaining a temperature of 110±5°C; and
(iv)
Balance with the accuracy of 0.1g.
The procedures for washed sieve analysis are as follow:
(i)
The aggregate samples were weighed before being placed on the
600μm sieve, with the 75μm sieve at the bottom..
(ii)
The aggregate were thoroughly washed until no particles pass the
75μm sieve.
(iii)
Carefully, the sample was poured into the container and was left to
allow all the aggregate to sink before draining the water out of the
container.
(iv)
The washed sample was dried in an oven at a temperature of 110±5°C
for 24 hours.
37
(v)
The sample was weighed after 24 hours and the percentage of material
finer than 75μm was calculated as follow:
Percentage of Material Finer than 75μm =
A− B
× 100
A
Where,
A = Original dry mass of sample, g
B = Dry mass of sample after washing, g
3.5
Aggregate Blending
Aggregate blending involved the process of proportioning the aggregates to
obtain the desired gradation that were well within the gradation limits. The gradation
limits for the mixes that were prepared as specified by JKR/SPJ/rev2005 are shown
in Table 3.1. For this study, the mixes that will be prepared are AC10, AC14, AC20,
and AC28. The mixes combined coarse aggregates, fine aggregates, and mineral
filler. A smooth curve within the appropriate gradation envelope is desired.
Table 3.1: Gradation limits for asphaltic concrete (JKR, 2005)
Mix Design
BS Sieve Size, mm
37.5
28.0
20.0
14.0
10.0
5.0
3.35
1.18
0.425
0.150
0.075
AC10
100
90 – 100
58 – 72
48 – 64
22 – 40
12 – 26
6 – 14
4–8
AC14
AC20
Percentage Passing (by weight)
100
100
76 – 100
90 – 100
64 – 89
76 – 86
56 – 81
50 – 62
46 – 71
40 – 54
32 – 58
18 – 34
20 – 42
12 – 24
12 – 28
6 – 14
6 – 16
4 – 18
4–8
ACB28
100
90 - 100
72 – 90
58 – 76
48 – 64
30 – 46
24 – 40
14 – 28
8 – 20
4 – 10
3–7
38
3.6
Determination of Specific Gravity for Aggregate
The specific gravity of an aggregate provides a mean of expressing the
weight-volume characteristics of material.
Specific gravity for coarse and fine
aggregate was determined separately. By coarse aggregate, it is the aggregates that
are retained on the 4.75mm sieve while fine aggregates are those that passing
4.75mm sieve.
3.6.1
Coarse Aggregate
The procedure for determining specific gravity for coarse aggregate was in
accordance with AASHTO T 85 and ASTM C 127.
The apparatus needed were:
(i)
Balance that is accurate to 0.5g of the sample weight;
(ii)
Sample container;
(iii)
Water tank; and
(iv)
Sieves of 4.75mm sieve.
The procedure for determining specific gravity for coarse aggregate was as
follow:
(i)
The aggregate was weighed and washed so as to clean it from dust.
(ii)
The aggregate was soaked in water for 24 hours.
(iii)
After 24 hours, the aggregate was weighed together with the water
and the mass is recorded as ‘A’.
(iv)
The aggregate was dried with a damp towel until it was saturated
surface dry and was weighed again. The mass of aggregate was
recorded as ‘B’.
(v)
Subsequently, the aggregate was dried in an oven for 24 hours at
110±5°C and cooled before weighing for the third time and the mass
of aggregate was recorded as ‘C’.
39
(vi)
Specific gravity for coarse aggregate was determined with the
following formula:
Specific Gravity (Coarse Aggregate) =
C
B− A
Where,
A = Weight of aggregate in water, g
B = Weight of saturated surface dry aggregate in air, g
C = Weight of oven dry aggregate, g
3.6.2
Fine Aggregate
The procedure for determining specific gravity for fine aggregate was in
accordance with AASHTO T 84 and ASTM C 128.
The apparatus needed were:
(i)
Balance having the capacity of 1kg with the accuracy of 0.1g;
(ii)
Pycnometer;
(iii)
Mould in the form of a frustrum of a cone with dimensions as follow:
40±3mm inside diameter at the top, 90±3mm inside diameter at the
bottm, and 75±3mm in height; and
(iv)
Tamper weighing 340±15g and having a flat circular face 25±3mm in
diameter.
The procedure for determining the specific gravity of fine aggregate were as
follow:
(i)
A ¾ filled pycnometer was weighed and recorded as ‘A’.
(ii)
The water was poured away until the pycnometer is left to about ¼
filled. About 500g fine aggregate was added in and shake well to get
rid of the air.
(iii)
Again, the pycnometer is filled with water until the original level of ¾
of its volume. The pycnometer was weighed and record as ‘B’.
40
(iv)
The aggregate was dried in an oven until the aggregate achieve a
constant weight. The oven dry aggregate was weighed and recorded
as ‘C’.
(v)
The aggregate was mixed with water until the aggregate sticks
together. Then, the cone test was performed. If about 1/3 of the
aggregate slumps after 25 light drops of tamper about 5mm above the
top surface of the fine aggregate in a cone, the aggregate is saturated
surface dry.
The weight of saturated surface dry aggregate was
weighed record as ‘D’.
(vi)
Specific gravity for fine aggregate were determined with the
following formula:
Specific Gravity (Fine Aggregate) =
C
D − ( B − A)
Where,
A = Weight of pycnometer filled with water,g
B = Weight of pycnometer with water and aggregate, g
C = Weight of oven dry aggregate in air, g
D = Weight of saturated surface aggregate, g
3.7
Superpave Mix Design
The Superpave mix design procedure has been published by several
organizations. The publications are the Asphalt Institute’s Superpave Mix Design,
SP-2, third edition, the AASHTO test procedure, T 312, Preparing and Determining
the Density of Hot Mix Asphalt Specimens by Means of the Superpave Gyratory
Compactor, and the AASHTO practice, PP-28-2000, Standard Practice for
Superpave Volumetric Design for Hot Mix Asphalt. For the purpose of this study,
the AASHTO T 312 procedure was adopted.
A total of 100 specimens were prepared for two compaction levels (75 and
100 gyrations), four types of mix (AC10, AC14, AC20, and AC28), three binder
41
contents for each type of mix with two specimens for each binder content, and two
loose specimens for each to determine the theoretical maximum density.
3.7.1 Procedures
Generally, the AASHTO T 312 procedure will be divided into two parts, i.e.
sample preparation and sample compaction.
The sample preparation involves
determining the number of gyration from estimated traffic level, specifying mixing
and compaction temperatures, and sample short-term aging..
The sample compaction involves heating the specimen moulds and base
plates, compaction until Ndes, and determining the asphalt binder content.
3.7.2 Apparatus
The apparatus needed for producing the specimens were:
(i)
An oven to heat up the aggregate, bitumen, and compaction mould;
(ii)
A pan for aging process;
(iii)
Scoop for mixing process and to transfer the aggregate into the mould;
(iv)
Gloves for blending and compaction process;
(v)
Container for heating bitumen;
(vi)
Thermometer readable to 200°C for checking and maintaining the
temperature of aggregate, bitumen, and the mix;
(vii)
Balance;
(viii) Marker to mark the specimens;
(ix)
Mixing wok;
(x)
Paper disc for compaction;
(xi)
Superpave Gyratory Compactor
42
3.7.3
Specimen Preparation
The procedure for specimen preparation listed below is a summary of the
AASHTO T 312.
(i)
The levels of gyrations specified are 75 and 100 gyrations. The
gyration number that relates to the ESALs is given in Table 3.2.
(ii)
For each mix type, a minimum of three percentage of bitumen content
were used, starting with the median, and ±0.5% of the median. Each
of the bitumen content has two replicate samples requiring 4600g of
aggregate each.
(iii)
Prior to mixing, the aggregate and bitumen were heated in an oven at
mixing temperature (160°C) for 24 hours and 1 hour respectively.
(iv)
During mixing, temperature was controlled at 160°C to allow the
aggregate to be thoroughly coated with bitumen.
(v)
Immediately after mixing, each individual mix was placed in a flat
pan in an oven for two hours of short-term aging at compaction
temperature of 140°C.
Table 3.2: Superpave gyratory compactive effort
Design ESALs 20 years
<300,000
300,000 to <3,000,000
3,000,000 to <30,000,000
≥30,000,000
SGC compactive effort (number of gyrations)
Ndesign
Nmax
Ninitial
6
50
75
7
75
115
8
100
160
9
125
205
The procedure for specimen compaction is listed below:
(i)
The specimen mould and the base plate were preheated at the
compaction temperature.
(ii)
Once the short-term aged mixture reaches compaction temperature, it
was placed in the preheated mould, levelled, and a paper disk was
placed on top of the mix. The loaded mould was then placed into the
SGC, making sure that the mould is centre under the loading ram.
The pressure applied was 600kPa and the angle of gyration was 1.25°.
43
(iii)
Compaction will proceed until Ndes has been completed, either 75 or
100 gyrations. During compaction, height is measured after each
revolution and recorded on the SGC printer.
(iv)
Compaction process was completed with the extrusion of the
compacted specimen and cooling it to room temperature.
(v)
Identification of the compacted specimen was achieved by marking it
with the specimen code.
3.8
Measurement of Density
To measure the relative compaction for a HMA mix, the specific gravity is
used. This section discusses the method of analysis that will be carried out on the
specimens to obtain OBC. To calculate the air voids content for a specimen, the bulk
specific gravity of the specimens along with the theoretical maximum density is
needed.
3.8.1
Bulk Specific Gravity
This test is useful in determining the unit weight of compacted dense mixes.
The specimens that have been compacted were taken out from the mould and let to
cool at room temperature. Bulk specific gravity was determined using the water
displacement method. The specimens were weighed in three conditions, i.e. in air, in
water, and saturated surface dry. The method was in accordance with ASTM D
2726.
Apparatus:
(i)
Balance; and
(ii)
Water bath.
The procedure for determining bulk specific gravity is:
44
(i)
Mass of specimen in water – immerse the specimen in a water bath at
25°C for 3 to 5 min then weigh in water. Designated the mass as ‘C’.
(ii)
Mass of saturated surface dry specimen in air – surface dry the
specimen by blotting quickly with a damp towel and then weigh in air.
Designated the mass as ‘B’.
(iii)
Mass of oven-dry specimen – compacted specimens that were
extracted from the mould and cooled to room temperature.
Designated the mass as ‘A’.
(iv)
The bulk specific gravity for the specimens was calculated using the
following equation:
Bulk Specific Gravity =
A
B −C
Where,
A = Weight of dry specimen in air
B = Weight of saturated surface dry specimen in air
C = Weight of saturated specimen in water
Density = Bulk SG X 997.0
Note: 997.0 = density of water in kg/m3 at 25°C
3.8.2
Theoretical Maximum Density
The purpose of conducting this test is to determine the density and theoretical
maximum density of loose HMA specimens. The theoretical maximum density was
determined using the Rice method (also in accordance with ASTM D 2041).
The apparatus needed were:
(i)
Vacuum container;
(ii)
Balance;
(iii)
Vacuum pump or water aspirator;
(iv)
Residual pressure manometer;
(v)
Manometer or vacuum gauge;
45
(vi)
Thermometer; and
(vii)
Water bath.
The procedure involved will be as follow:
(i)
The size of the sample conformed to the requirements as shown in
Table 3.3.
(ii)
The particles of the sample of mixture were separated by hand, taking
care to avoid fracturing the aggregate, so that the particles of the fine
aggregate portion are not larger than 6.3mm.
(iii)
After mixing, the sample was cooled to room temperature and
weighed (designated as ‘A’).
Sufficient water was added at a
temperature of approximately 25°C to cover the sample completely.
(iv)
The air trapped in the sample was removed by applying gradually
increased vacuum until the residual pressure manometer reads 30mm
of Hg or less. This residual pressure was maintained for 5 to 15 min.
As the vacuum is working, a mechanical device agitated the container.
(v)
At the end of the vacuum period, the vacuum was gently released.
(vi)
The container and contents were suspended in the water bath and for
about 10min in which the mass is designated as ‘B’.
(vii)
The theoretical maximum density were calculated as follow:
Theoretical Maximum Density =
A
A− B
Where,
A = Mass of oven dry sample in air, g
B = Mass of water displaced by sample, g
Table 3.3: Minimum sample size requirement for theoretical maximum density
(ASTM D 2041)
Size of Largest Particle of
Aggregate in Mixture, mm
50.0
37.5
25.0
19.0
12.5
9.5
4.75
Minimum Sample Size, g
6000
4000
2500
2000
1500
1000
500
46
3.9
Determination of Optimum Bitumen Content
The optimum bitumen content is the amount that provides the desired air
voids of 4%, according to National Asphalt Paving Association. Table 3.4 shows the
specification of bitumen content as stated in JKR/SPJ/rev2005.
Table 3.4: Design bitumen contents (JKR/SPJ/rev2005)
Mix
AC10 – Wearing Course
AC14 – Wearing Course
*AC20 – Wearing Course
AC28 – Binder Course
Bitumen Content
5.0 – 7.0%
4.0 – 6.0%
4.5 – 6.5%
3.5 – 5.5%
*AC20 specification is taken from JKR/SPJ/1988
From the Gmb and TMD values, the air voids content for each sample were
determined using the following formula:
G ⎞
⎛
Voids in Total Mix, VTM = 100 × ⎜1 − mb ⎟
⎝ TMD ⎠
Where,
Gmb = Bulk specific gravity of mix
TMD = Theoretical maximum density
The OBC were determined from the graph voids in total mix versus bitumen
content where the targeted VTM is 4%.
With these OBC values, another two
specimens were fabricated to verify that the OBC obtained earlier will give a 4% air
voids.
3.10
Determination of Other Properties
Once the OBC has been determined, other properties as mentioned in Section
1.4 were also determined from the verified samples. The formulas to determine the
properties are include:
47
⎛ B − A⎞
Water Absorption, WA = ⎜
⎟ × 100
⎝ A ⎠
Where,
A = Mass of oven-dry specimen, g
B = Mass of saturated surface dry specimen, g
Voids in Mineral Aggregate, VMA = 100 −
Gmb ( Ps )
SGaggblend
Where,
Gmb = Bulk specific gravity of mix
Ps = percent by weight of the total amount of aggregate in the mix
SGagg blend = bulk specific gravity of the combined aggregate
Voids Filled with Bitumen, VFB =
VMA − VTM
× 100
VMA
Where,
VMA = Voids in Mineral Aggregate
VTM = Voids in Total Mix
3.11
Summary
Chapter 3 describes the methodology that will be used for the study. All the
data were obtained through laboratory testing. The operational framework was given
to illustrate the whole testing program. Mixes that were prepared are AC10, AC14,
AC20, and AC28. Specimens were subjected to compaction using the SGC with 75
and 100 numbers of gyrations. Tests that were conducted are dry and washed sieve
analysis, aggregate blending, determination of specific gravity for coarse and fine
aggregate, determination of bulk specific gravity, determination of theoretical
maximum density, and finally, determining the properties. The properties include
optimum bitumen content, bulk specific gravity, theoretical maximum density, water
absorption, voids in mineral aggregate, voids filled with bitumen, and dust to binder
ratio.
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1
Introduction
The aim of this study was to look into the effects of nominal maximum
aggregate size on the properties of hot mix asphalt when designed with the
Malaysian gradation limits but at the same time adopting the Superpave method as
published by the National Asphalt Paving Association. The methodology used for
this study has been discussed in Chapter 3. Results of each procedure in determining
the properties are presented in this chapter and will be further analysed and discussed
in depth.
4.2
Results of Tests Conducted on the Materials
The constituents of a hot mix asphalt are aggregate (both coarse and fine),
mineral filler, and bitumen. All these materials were tested for their specific gravity.
Besides that, the aggregates obtained from the MRP Quarry were also tested for the
total amount of coated dust.
49
4.2.1
Sieve Analyses
Two types of sieve analysis were performed on the aggregates, one being the
dry sieve and the other being the wash sieve analysis. The dry sieve analysis was
performed to separate the aggregates according to the sieve sizes used in the
gradation so as to make it easier to batch the mixes. The gradation of each mix will
be further discussed in Section 4.3
Wash sieve analysis were conducted to determine the total amount of dust
coated on the aggregates. This is so to calculate the amount of filler and/or dust that
might need to be added to the mix.
Therefore, the wash sieve analysis was
conducted for every mix and the result can be viewed in Appendix A.
4.2.2
Determination of Bulk Specific Gravity of Aggregate
The specific gravity test has been carried out for all the materials used in the
study, including aggregates, mineral filler, and bitumen.
The aggregates were
divided into coarse and fine with the earlier defined as aggregates larger than
4.75mm and the latter being defined as aggregates smaller than 4.75mm until
0.075mm. This categorization is in accordance with ASTM standard. In this study,
the specific gravity for the aggregates has been determined based on the gradation of
AC10.
4.2.2.1 Specific Gravity of Coarse Aggregate
As the sample for testing specific gravity of aggregate is based on AC10, the
coarse sizes are in the range of 5-10mm. The full results of the test conducted are
shown in Appendix B and the specific gravity for coarse aggregate is 2.586. This
value was used in determining the bulk specific gravity of aggregate.
50
4.2.2.2 Specific Gravity of Fine Aggregate
The specific gravity testing for fine aggregate also utilizes the gradation of
AC10. The sizes of aggregates tested range from 0.075mm to 3.35mm. The full
results of the test conducted are shown in Appendix C and the specific gravity for
fine aggregate is 2.522. This value was used in determining the bulk specific gravity
of aggregate.
4.2.2.3 Specific Gravity of Mineral Filler
Functioning as an anti stripping agent, the mineral filler chosen for this study
was Ordinary Portland Cement (OPC). Studies conducted at the Transportation and
Highway Laboratory of Universiti Teknologi Malaysia has found that the specific
gravity for OPC is 2.980. This value was used in determining the bulk specific
gravity of aggregate.
4.2.2.4 Bulk Specific Gravity of Aggregate
The bulk specific gravity of aggregate, also known as specific gravity of
aggregate blend, has been calculated using the following equation:
SGblend =
100
⎛
⎞ ⎛
⎞ ⎛
⎞
⎜ % Coarse Aggregate ⎟ ⎜ % Fine Aggregate ⎟ ⎜ % Mineral Filler ⎟
+
+
⎜
⎟ ⎜
⎟ ⎜
⎟
SGcoarse
SG fine
SG filler
⎜
⎟ ⎜
⎟ ⎜
⎟
⎝
⎠ ⎝
⎠ ⎝
⎠
Based on the mix, the percentage of coarse aggregate, fine aggregate and
mineral filler varies accordingly. The determination of SGblend was done for each
mix. The percentage of coarse aggregate was taken as the percentage of aggregate
retained on sieve size larger than 4.75mm, which was 5.0mm and above while fine
51
aggregate was taken from sieve size smaller than 4.75mm, which was 3.35mm.
Mineral filler was fixed at 2% of the total weight of the aggregate. Table 4.1 shows
the values of bulk specific gravity of aggregate.
Table 4.1: Values of bulk specific gravity of aggregate
Mix Type
% Coarse Aggregate
% Fine Aggregate
% Mineral Filler
SGblend
AC10
35
63
2
2.552
AC14
44
54
2
2.558
AC20
42
56
2
2.556
AC28
64
34
2
2.571
4.2.2.5 Specific Gravity of Bitumen
The bitumen provides the cohesive forces that hold the aggregate particles
together. The cohesive forces grow with increasing bitumen viscosity. In this study,
bitumen of 80/100 PEN has been used. Based on previous studies conducted at
Transportation and Highway Laboratory of Universiti Teknologi Malaysia, the
specific gravity of bitumen is taken as 1.03.
This value was used in the
determination of effective specific gravity of aggregate.
4.3
Aggregate Gradation
Aggregate gradation allows the distribution of aggregate into sizes expressed
as a percent of total weight. A good gradation will lead to the durability and strength
of a pavement. For all the four mixes, the gradation limits was in accordance with
JKR Standard Specification as described in Section 3.5. The best design curves that
fit the gradation envelopes were chosen based on the 0.45 power chart method. The
curves were designed to be far away from the maximum density line (MDL) to
provide more room for the bitumen and air voids. Based on this method, the curves
were plotted on a normal graph as shown in Figures 4.1 to 4.4. The gradation is
attached in Appendix D.
52
AC10 Gradation
120
100
Percentage Passing
80
60
40
20
0
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
Sieve Size to the Power of 0.45
Lower Limit
Upper Limit
MDL
AC10 Gradation
Figure 4.1: Gradation limits and design curve for AC10
AC14 Gradation
120
100
Percentage Passing
80
60
40
20
0
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
Sieve Size to the Power of 0.45
Lower Limit
Upper Limit
MDL
AC14
Figure 4.2: Gradation limits and design curve for AC14
4.500
53
AC20 Gradation
120
100
Percentage Passing
80
60
40
20
0
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
4.500
5.000
Sieve Size to the Power of 0.45
Lower Limit
Upper Limit
MDL
AC20
Figure 4.3: Gradation limits and design curve for AC20
AC28 Gradation
120
100
Percentage Passing
80
60
40
20
0
0.000
1.000
2.000
3.000
4.000
5.000
6.000
Sieve Size to the Power of 0.45
Lower Limit
Upper Limit
MDL
AC28
Figure 4.4: Gradation limits and design curve for AC28
4.4
Results and Discussions of the Properties
The results of the properties obtained from the study are presented in this
section. For each gyration level, there are four mixes, i.e. AC10, AC14, AC20, and
AC28. A minimum of three bitumen contents were used in preparing two replicate
54
samples for each bitumen content that are compacted to 4±1% air voids. Table 4.2
show the summary of results of the study for 75 and 100 gyrations respectively. The
full results are tabulated in Appendices E1 and E2. Results of water absorption and
bulk specific gravity was very much dependant on the weight of samples in air,
water, and saturated surface dry. The TMD values were obtained from an average of
two loose samples with the precision of not more than 0.011 as recommended by
ASTM. This precision was also adopted in the bulk specific gravity determination of
the verification samples. Other properties were calculated based on the bulk specific
gravity.
Table 4.2: Summary of results from samples compacted to 4±1% air voids
No. of
Gyrations
75
100
4.4.1
Mix
Type
AC10
AC14
AC20
AC28
AC10
AC14
AC20
AC28
OBC
(%)
7.3
6.1
4.3
6.0
6.3
5.8
4.2
5.3
Gmb
TMD
2.284
2.278
2.344
2.308
2.278
2.297
2.352
2.322
2.367
2.391
2.438
2.394
2.391
2.400
2.443
2.418
WA
(%)
0.13
0.24
0.54
0.38
0.14
0.22
0.44
0.34
VMA
(%)
16.8
16.4
12.3
15.6
16.0
14.7
11.9
13.6
VFB
(%)
79.0
71.2
68.4
76.9
70.4
70.9
68.6
70.9
D:B
0.82
0.96
1.37
0.64
0.96
1.01
1.41
0.81
Optimum Bitumen Content
The OBC was obtained from Figures 4.5 and 4.6 for 75 and 100 gyrations
respectively.
These figures were plotted from the results shown in Table 4.2.
According to NAPA method, bitumen content that corresponds to a 4% air voids was
chosen as the OBC. Another two samples were prepared using the OBC value for
verification purpose. Some of the OBC obtained did not give a 4±1% air voids
content when verified. These values were added to the original data and used to get a
new OBC for verification.
55
10.00
9.00
8.00
7.00
VTM (%)
6.00
5.00
4.00
3.00
2.00
1.00
0.00
3.0
4.0
5.0
6.0
7.0
8.0
Bitumen Content (%)
AC 10
AC14
AC 20
AC 28
Figure 4.5: Determination of optimum bitumen content for 75 gyrations
8.00
7.00
6.00
VTM (%)
5.00
4.00
3.00
2.00
1.00
0.00
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
-1.00
Bitumen Content (%)
AC 10
AC14
AC 20
AC 28
Figure 4.6: Determination of optimum bitumen content for 100 gyrations
From Table 4.2, it was observed that when the mixes were compacted to
4±1% air voids, the optimum bitumen content showed a variation for each mix. The
OBC is also affected by the level of compaction as can be seen in Figure 4.7. For 75
gyrations, the OBC was reported to be 7.3% for AC10, 6.1% for AC14, 4.3% for
AC20, and 6% for AC28. The OBC needed for 100 gyrations were 6.3% for AC10,
5.8% for AC14, 4.2% for AC20, and 5.3% for AC28.
It can be seen that the
bitumen needed is getting lesser as the NMAS increases. However, the OBC
56
increases at NMAS of 28mm. This could be due to more bitumen is needed to coat
the aggregate surface area for the smaller NMAS. However, even though the surface
area at NMAS of 28mm is lesser, more bitumen is needed to fill the voids in order to
get a 4±1% air voids.
8.0
7.0
6.0
5.0
4.0
3.0
2.0
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.7: Optimum bitumen content versus nominal maximum aggregate size
According to Asphalt Institute Manual Series No. 22 (1983), excess asphalt
may lead to rutting and bleeding, which affect the pavement stability, and poor skid
resistance. On the other hand, low asphalt content causes the asphalt film to be
thinner, causing early aging. Low asphalt content may also contribute to dryness and
raveling. In return, both effects could cause the pavement to be lack of durability and
permeable.
Except for AC20, all the mixes were in the range of the bitumen content as
recommended by JKR when it was compacted to 100 gyrations. For 75 gyrations, all
the mixes have an OBC more than specified with the exception of AC20. This
obviously shows that lesser compactive effort will need more bitumen in order to
have the same air voids content.
This pattern is very true for both level of
compaction as the gap between the lines is of similar distance. Economical wise,
AC20 shows the lowest OBC and this indeed is economical to be use in construction
and at the same time providing the mix with sufficient binder to hold the aggregates.
57
4.4.2
Bulk Specific Gravity
Gmb was determined for each of the mixes at 75 and 100 gyrations using the
water displacement method. Figure 4.8 illustrates the pattern of Gmb for all the
mixes. AC20 shows the highest value of Gmb which means that the mix is denser.
The total surface area for AC20 is 6.08m2/kg, which is higher than the rest of the
mixes (AC10 – 5.49m2/kg, AC14 – 5.27m2/kg, and AC28 - 3.47m2/kg). This makes
sense as higher surface area consists of finer aggregates and thus the fine aggregates
will work its way in between the coarser aggregates. This has contributed to a denser
mix. The sample calculation for the surface area is attached in Appendix F. High
Gmb implies that the VMA in HMA will be low. This is addressed later in the report
when VMA test results are presented. It is also interesting to note that the Gmb for
AC10 is higher than Gmb for AC14, which may be caused by the large difference in
the air voids content even though both are within the 4±1% air voids.
2.360
2.350
2.340
2.330
2.320
2.310
2.300
2.290
2.280
2.270
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.8: Bulk specific gravity versus nominal maximum aggregate size
For AC14, AC20, and AC28, the Gmb is on a constant pattern for both level of
compaction, with 100 gyrations giving a higher Gmb. As for AC10, 75 gyrations
gave a higher Gmb. This is due to the difference in percent of air voids as the samples
compacted to 75 gyrations are on the lower side of 4±1% air voids (3.52%) while the
samples compacted to 100 gyrations are on the higher side of 4±1% air voids
(4.73%). It is suggested that if the range of the two compaction efforts are within 1%,
the Gmb for 75 gyrations might be lower than 100 gyrations.
58
4.4.3
Theoretical Maximum Density
TMD values obtained were based on the OBC used as the Rice method uses
the calculation of effective bulk specific gravity to back calculate the bulk specific
gravity. The full results for TMD are shown in Appendix G. Figure 4.9 presents the
similar pattern to the specific bulk gravity, where the TMD values rises over the
NMAS of 10, 14, and 20mm, before descending to the size of 28mm.
It was noticed that for AC10, the TMD values does not cross each other as it
did with the bulk specific gravity. As TMD is not dependant on the air voids
content, therefore, the values are only influenced by the OBC and NMAS. From the
discussion on OBC, it was concluded that the OBC increases with the size of NMAS
until 20mm and then decreases.
Therefore, when this OBC were used in
calculations, the TMD values were in line with the earlier results in which when the
OBC decreases, the TMD increases.
2.450
2.440
2.430
2.420
2.410
2.400
2.390
2.380
2.370
2.360
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.9: Theoretical maximum density versus nominal maximum aggregate size
TMD values that were plotted on Figure 4.9 were obtained from the OBC
used to prepare the mixes for other properties. The OBC values were used for both
75 and 100 gyrations. Therefore, the TMD values that correspond to OBC gave
Figure 4.9 two lines, plotted as 75 and 100 gyrations.
59
4.4.4
Water Absorption
As observed from Figure 4.10, the water absorption for AC10, AC14, and
AC28 is quite similar for both level of compaction with 75 gyrations generally had
higher water absorption.
It is significantly different for AC20 where samples
compacted to 75 gyrations has a higher percentage of water absorption. This may be
attributed to the fact that with almost similar bitumen content (4.3% and 4.2% for 75
and 100 gyrations respectively) yet different compaction effort, the samples with
lesser compaction had more interconnected voids, making it easier for water to be
absorbed.
0.60
0.50
0.40
0.30
0.20
0.10
0.00
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.10: Water absorption versus nominal maximum aggregate size
In terms of size, NMAS of 10mm have lower water absorption percentage
and it steadily increase until NMAS of 20mm where it started to decrease. Smaller
NMAS may not have as much interconnected voids that allow the water to be
absorbed while NMAS of 20mm (with lesser bitumen content) will have more
interconnected voids to allow more water to be absorbed easily. Pavement easily
infiltrated with water will have a tendency to be low in strength.
60
4.4.5
Voids in Mineral Aggregate
According to the study of Kandhal, Foo and Mallick (1998), the rationale
behind the minimum VMA requirement was to incorporate minimum desirable
asphalt content into the mix to ensure its durability by allowing sufficient space for
the amount of asphalt binder and the correct percentage of air voids.
In this study, the VMA for AC10, AC14, and AC28 met the minimum
requirement of the Superpave mix design. AC20 has VMA values of 12.28% and
11.85% for 75 and 100 gyrations respectively, which is lower than the minimum
requirement of 13% (Figure 4.11). However, when the VMA is calculated based on
an average asphalt film thickness of 8 microns that was used by Kandhal, Foo, and
Mallick (1998), the VMA value is 14.6%. This also supports their result that the
minimum VMA incorporation based on asphalt film thickness can meet the
minimum requirement of VMA. Therefore, AC20 is also acceptable from the point
of VMA requirement.
18.00
17.00
16.00
15.00
14.00
13.00
12.00
11.00
10.00
5
10
15
20
25
30
N o m ina l M A xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Control
Figure 4.11: Voids in mineral aggregate versus nominal maximum aggregate size
As discussed in Section 4.4.2, higher Gmb implies a lower VMA in the mix.
The trend of the VMA is totally opposite with the trend of the Gmb as discussed.
Samples with 75 gyrations have higher VMA and this trend is seen to be constant for
all the NMAS. This can be explained that with lesser compaction effort, more
bitumen is needed to fill the voids in order to get 4±1% air voids. Therefore, the
61
OBC increases with the decrease in compactive effort and this is in line with the
findings on OBC.
4.4.6 Voids Filled with Bitumen
Looking at Figure 4.12, the NMAS has no significant impact on VFB of
samples compacted to 100 gyrations as the line is almost parallel with x-axis and is
well within the given range of 65-75%. However, not much can be said the same for
samples compacted to 75 gyrations as VFB for AC10 and AC28 are relatively high.
The computation of VFB is dependant on VMA and bitumen content.
As put forth by Abdullah, Obaidat, and Abu-Sa’da (1998) the conclusion of
Lees in 1987, air voids in mineral aggregates and voids filled with bitumen are
merely physical parameters with no direct engineering significance. In the example
given, it was mentioned that strength, flow, permeability to air, and permeability to
water of two mixes of identical air voids may not necessarily identical.
80.00
75.00
70.00
65.00
60.00
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.12: Voids filled with bitumen versus nominal maximum aggregate size
62
4.4.7
Dust to Binder Ratio
The dust to binder ratio recommended range is 0.6-1.2 (AASHTO, 2001). In
this study, AC20 has difficulty falling in the given range. As discussed earlier, AC20
has more fine materials and dust, therefore, the ratio to binder will also be higher.
From the point of compactive level, samples with 75 gyrations utilized more
bitumen where as the dust content for the mix are the same. This increased the dust
to binder ratio.
When the ratio is relatively lower, a coarser mix will be obtained, thus
increasing the VMA. The Asphalt Institute Manual Series No. 22 (1983) associated
the workability problems with mineral filler. If the mix has a low mineral filler
content, the pavement may experience tender mix or highly permeable.
High
mineral filler content may cause the mix to be dry or gummy, hard to handle, and not
durable.
1.50
1.40
1.30
1.20
1.10
1.00
0.90
0.80
0.70
0.60
0.50
5
10
15
20
25
30
N o m ina l M a xim um A ggre ga t e S ize ( m m )
75 Gyrations
100 Gyrations
Figure 4.13: Dust to binder ratio versus nominal maximum aggregate size
4.5
Statistical Analysis
Statistical analysis of the test results were performed using the Microsoft
Excel Data Analysis.
Paired t-tests were performed on all the data to see the
63
significance of the NMAS and the levels of compaction on the properties. The Pvalue approach is an aid in decision making. The P-values from the t-tests are
summarized in Table 4.3. With a confidence level of 95%, the variables that have pvalues of less than 0.05 is said to be significantly related to each other.
Table 4.3: Summary of statistical analysis, t-tests
75 & 100
Gyrations
NMAS & Properties
OBC
Gmb
TMD
WA
VMA
VFB
D:B
Mean Value
75
100
Gyrations
Gyrations
5.9
5.4
2.303
2.309
2.398
2.413
0.32
0.30
15.3
14.2
73.9
69.9
0.95
1.05
P-Value
75
Gyrations
0.033
0.014
0.014
0.010
0.289
0.001
0.011
100
Gyrations
0.029
0.014
0.014
0.010
0.232
0.000
0.012
P-Value
0.036
0.144
0.028
0.190
0.025
0.056
0.024
From the analyses, NMAS was found to have a significant relationship with
all the properties except VMA for both level of compaction. Meanwhile, compaction
effort has the effect on OBC, TMD, VMA, and D:B.
As mentioned in the paragraph before, the VMA was found to be not
significant with the variation of NMAS.
established.
The cause of it was not immediately
The consideration of SGaggblend together with the percentage of
aggregate by weight of total mix may have been the contributing factor towards the
insignificancy. SGaggblend have taken into account the percentages of coarse and fine
aggregates, and mineral filler at the earlier stage.
Therefore, the sizes of the
aggregates have been considered initially and the end results for VMA were not
significantly impacted by the NMAS. Furthermore, there are different methods that
could be used to determine the VMA.
64
4.6
Summary
This chapter presented the results of the study and discussed the results in
depth to give a better understanding of the properties of different NMAS. The
properties included optimum bitumen content, bulk specific gravity, theoretical
maximum density, water absorption, voids in mineral aggregate, voids filled with
bitumen, and dust to binder ratio. All data were statistically analysed to see the
significance of NMAS and levels of compaction on the properties.
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1
Conclusions
The analyses presented in the Chapter 4 presents the pattern of the HMA
mixes properties, which include optimum bitumen content, bulk specific gravity,
theoretical maximum density, water absorption, voids in mineral aggregate, voids
filled with bitumen, and dust to binder ratio. The following conclusions can be
drawn from the study.
1.
As the NMAS increases, the bitumen content and voids in mineral aggregate
decrease. This is only true until the NMAS of 20mm where both properties
showed an increase after the NMAS of 20mm.
2.
The bulk specific gravity, theoretical maximum gravity, water absorption,
and dust to binder ratio increases with the increment of NMAS and peaked at
20mm.
3.
Voids filled with bitumen showed a different pattern where at 100 gyrations,
the VFB is constant, and at 75 gyrations, the VFB is relatively higher at
NMAS of 10mm and 28mm.
4.
Statistical analysis indicated that NMAS had a very significant impact on the
properties with the exception of VMA.
5.
Different level of compaction (75 and 100 gyrations) gave the same trend.
Analyses showed that OBC, TMD, VMA, and D:B are influenced by the
level of compaction.
66
6.
The recommended mix based on the properties behaviour is AC20 due to
economical reason and the mix has achieved all the necessary requirements.
5.2
Recommendations
From all the properties discussed, it was observed that all the properties are
connected with each other. The foremost effect of NMAS is on the bitumen content.
It was obvious that from this study, the bitumen content varies with the NMAS and is
further influenced by the total surface area, which can be calculated from the
aggregate gradation. It is suggested to further this study with variation in gradation
and to look into the surface area.
Apart from gradation, it will be good to research further on the effect of
surface texture and the NMAS as surface area also contributes to the differences in
results obtained. Surface texture may include the crushed and uncrushed aggregate.
It is also recommended to continue this work with more sizes as the NMAS
to really establish the effect of NMAS as this study only include four sizes with one
gradation each. This may also be in collaboration with the work by Cooley, James,
and Buchanan (2002) who developed the mix design criteria for 4.75mm mixes.
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Washington, D. C.
Buchanan, M. S. and Brown, E. R. (2001).
Compactor
Type
on
Compacted
Hot
Effects of Superpave Gyratory
Mix
Asphalt
(HMA)
Density.
Transportation Research Record 1761. Transportation Research Board, National
Research Council, Washington, D. C., 50-60
Buchanan, M. S., Brumfield, J. and Sheffield, R. (2004).
Investigation of the
Gyration Angle of Superpave Gyratory Compactors. Journals of Materials in
Civil Engineering. Volume16, No. 5: 444-451.
Chadbourn, B. A., Skok, E. L. Jr., Newcomb, D. E., Crow, B. L., and Spindler, S.
(1999). The Effects of Voids in Mineral Aggregate (VMA) on Hot-Mix Asphalt
Pavements.
Final Report MN/RC-2000-13.
Minnesota Department of
Transportation, Minnesota.
Cham, T. S. (1994). A Study of Asphalt Mix Production Technology in Four Asean
Countries. Proceedings of the First Malaysian Road Conference. June 20-23.
Kuala Lumpur: MRC, Paper No. 7.
Cooley, Jr., L. A., Prowell, B. D., and Brown, E. R. (2002). Issues Pertaining to the
Permeability Characteristics of Coarse-Graded Superpave Mixes. NCAT Report
02-06, National Center for Asphalt Technology, Auburn, Alabama.
Cooley, Jr., L. A., James, R. S., and Buchanan, M. S. (2004). Development of Mix
Design Criteria for 4.75mm Mixes – Final Report.
NCAT Report 02-04.
National Center for Asphalt Technology, Auburn, Alabama
Cross, S. A. and Lee, J. C. (2000). Evaluation of the Superpave Gyratory Compactor
for Low Volume Roads.
Report No. KS-00-2.
Kansas Department of
Transportation, Topeka, Kansas.
Dessouky, S., Masad. E. and Bayoumy, F. (2004).
Prediction of the Hot Mix
Asphalt Stability Using Superpave Gyratory Compactor. Journal of Materials in
Civil Engineering. Volume 16, No.6: 578-587.
69
Hainin, M.R., Cooley, Jr., L. A. J., and Prowell, B. D. (2003), An Investigation of
Factors Influencing Permeability of Superpave Mixes. 82nd Annual Meeting of
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Hameed, A. M. A. (1994).
Bituminous Pavement Behaviour Under Tropical
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Harman, T., Bukowski, J., Moutier, F., Huber, G., and McGennis, R. (2002). The
History and Future Challenges of Gyratory Compaction 1939 to 2001. Journal of
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Harun, M. H. (1996). The Performance of Bituminous Binders in Malaysia. 2nd
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Aspahlt. Mid-Continent Transportation Symposium Proceedings.
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Jersey: Prentice Hall.
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Lumpur, Malaysia, JKR/SPJ/rev2005.
Jackson, N. M. and Czor, L. J. (2003).
100-mm-Diameter Mold Used with
Superpave Gyratory Compactor. Journals of Materials in Civil Engineering.
Volume 15, No. 1: 60-66.
Kandhal, P. S. (1990). Design of Large Stone Asphalt Mixes to Minimize Rutting.
NCAT Report No. 90-1.
National Center for Asphalt Technology, Auburn,
Alabama.
Kandhal, P. S., Foo, K. Y., and Mallick, R. B. (1998). A Critical Review of VMA
Requirements in Superpave. NCAT Report No. 98-1, National Center for Asphalt
Technology, Auburn, Alabama.
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Maintenance for Engineers and Architects. London: Spon Pess.
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(2003). An Evaluation of Factors Affecting Permeability of Superpave Designed
Pavements.
NCAT Report 03-02, National Center for Asphalt Technology,
Auburn, Alabama.
70
McGennis, R. B., Perdomo, D., Kennedy, T. W., and Anderson, V. L. (1997).
Ruggedness Evaluation of AASHTO TP4 The Superpave Gyratory Compactor.
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Relationships between Density, Bitumen Content, and
Voids Properties of Compacted Bituminous Paving Mixtures. Proceedings of
Highway Research Board, Volume 35.
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Asphalt Technology News.
Auburn, Alabama: Fall’s Issue.
National Center for Asphalt Technology (2000).
Asphalt Technology News.
Auburn, Alabama: Fall’s Issue.
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of the Gyration Levels in the Ndesign table. Interim Report. National Academy of
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Peterson, R. L., Mahboub, K. C., and Anderson. R. M. (2004).
Comparing
Superpave Gyratory Compactor Data to Field Cores. Journals of Materials in
Civil Engineering. Volume 16, No. 1: 78-83.
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Angle of Superpave Gyratory Compactors in Alabama. NCAT Report 0.-04.
National Center for Asphalt Technology, Auburn, Alabama.
Roberts, F. L., Kandhal, P. S., Brown, E. R., Lee, D. Y., Kennedy, T. W. (1996).
Hot Mix Asphalt Material, Mixture Design, and Construction.
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the Theoretical Maximum Specific Gravity of Asphalt Concrete Paving Mixtures
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SHRP Superpave: Background and Significance for
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Principles of Construction of Hot-Mix Asphalt
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71
The Asphalt Institute (1990). Design of Hot Asphalt Mixtures, ES-3. Lexington,
Kentucky: The Asphalt Institute.
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Number of Gyrations in the Superpave Gyratory Compactor. Transportation
Research Record 1630, Transportation Research Board, Washington, D.C.:117125.
AC10
Sample
AC14
AC20
AC28
I
II
I
II
I
II
I
II
Mass Before Washing,
g
1128.0
1128.0
1128.0
1128.0
1128.0
1128.0
1152.0
1152.0
Mass After Washing,
g
1079.3
1076.0
1084.3
1086.1
1087.5
1090.0
1128.0
1131.1
Mass of Dust,
g
48.7
52.0
43.7
41.9
40.5
38.0
24.0
20.9
Average,
g
50.4
42.8
39.3
22.5
Percentage,
%
4.5
3.8
3.5
1.9
Weight of Dust for 4600g,
g
205.3
174.5
160.1
89.6
APPENDIX A: WASH SIEVE ANALYSIS
Mix
72
73
APPENDIX B: SPECIFIC GRAVITY OF COARSE AGGREGATE
Sample No.
1
2
3
Avg.
Weight of oven dry specimen in air, A (g)
1045.3
1045.6
1044.5
1045.1
Weight of saturated surface dry specimen, B (g)
1056.9
1054.2
1053.7
1054.9
Weight of saturated specimen in water, C (g)
650.7
651.7
650.00
650.8
2.573
2.598
2.587
2.586
2.602
2.619
2.610
2.610
2.649
2.654
2.648
2.650
1.110
0.822
0.881
0.938
1. Bulk Specific Gravity, Gsb
=A/(B-C)
2. Bulk SSD Specific Gravity, Gssd
=B/(B-C)
3. Apparent Specific Gravity, Gsa
=A/(A-C)
4. Water absorption (%)
=100(B-A)/A
74
APPENDIX C: SPECIFIC GRAVITY OF FINE AGGREGATE
Test No
1
2
3
Avg.
Pycnometer Weight
280.7
281.4
294.1
285.4
Weight of oven dry material, A (g)
493.3
491.2
493.6
492.7
Weight of saturated surface dry aggregate , S (g)
500.2
500.4
501.1
500.6
Weight of Pycnometer filled with water, B (g)
875.5
877.1
878.4
877.0
1172.3
1184.7
1189.1
1182.0
2.425
2.548
2.592
2.522
2.459
2.595
2.632
2.562
2.510
2.675
2.699
2.628
1.399
1.873
1.519
1.597
Weight of Pycnometer with specimen and water
to the calibration mark, C (g)
1. Bulk Specific Gravity, Gsb
=A/(B+S-C)
2. Bulk SSD Specific Gravity, Gssd
=S/(B+S-C)
3. Apparent Specific Gravity, Gsa
=A/(A+B-C)
4. Water absorption (%)
=100(S-A)/A
AC10
BS Sieve
Size, mm
^0.45
AC14
AC20
ACB28
LL
Grad
UP
LL
Grad
UP
LL
Grad
UP
LL
Grad
UP
37.5
5.109
-
-
-
-
-
-
-
-
-
100
100
100
28.0
4.479
-
-
-
-
-
-
100
100
100
90
95
100
20.0
3.850
-
-
-
100
100
100
76
94
100
72
85
90
14.0
3.279
100
100
100
90
93
100
64
80
89
58
70
76
10.0
2.818
90
95
100
76
79
86
56
72
81
48
56
64
5.0
2.063
58
65
72
50
56
62
46
58
71
30
36
46
3.35
1.723
48
56
64
40
47
54
32
49
58
24
28
40
1.18
1.077
22
27
40
18
23
34
20
33
42
14
17
28
0.425
0.680
12
15
26
12
14
24
12
22
28
8
10
20
0.150
0.426
6
10
14
6
10
14
6
12
16
4
5
10
0.075
0.312
4
6
8
4
6
8
4
6
8
3
4
7
APPENDIX D: AGGREGATE GRADATION
Percentage Passing (by weight)
Mix Design
LL – Lower Limit
Grad – Gradation
75
UP – Upper Limit
TMD Values at Specificied % Bitumen
Content =100 / [(%BC/Gb) + ((100BC)/Gse)]
1
2210.5
1393.7
3426.0
1215.5
2103.7
AC10
2
2210.8
1393.7
3425.8
1215.0
2101.8
Avg.
2210.7
1393.7
3425.9
1215.3
2102.8
2.405
2.397
2.401
1
2210.5
1393.7
3426.0
1215.5
2103.7
AC14
2
2210.8
1393.7
3425.8
1215.0
2101.8
Avg.
2210.7
1393.7
3425.9
1215.3
2102.8
2.405
2.397
2.401
6.0
1.03
2.628
2.619
1
2210.2
1392.5
4258.3
2048.1
2587.0
Avg.
2210.4
1392.5
4198.5
1988.1
2551.5
1
2394.7
1393.4
4797.1
2402.4
2812.1
2
2210.0
1393.0
4729.1
2519.1
2883.6
Avg.
2302.4
1393.2
4763.1
2460.8
2847.9
2.399
2.397
2.398
2.442
2.449
2.446
6.0
1.03
2.624
2.628
2.619
AC28
AC20
2
2210.6
1392.4
4138.7
1928.1
2516.0
5.5
1.03
2.624
Bit. Content
TMD Values
Bit. Content
TMD Values
5.5
5.9
6.0
6.3
6.5
7.0
7.3
2.418
2.404
2.401
2.391
2.384
2.367
2.357
4.5
5.0
5.3
5.5
5.8
6.0
6.1
6.8
2.450
2.432
2.425
2.415
2.400
2.393
2.391
2.367
2.601
2.597
4.5
1.03
2.599
Bit. Content
TMD Values
4.0
4.2
4.3
4.5
5.0
5.5
2.450
2.443
2.439
2.432
2.415
2.398
2.611
2.619
2.615
Bit. Content
TMD Values
3.3
3.8
4.0
4.3
4.5
5.0
5.3
6.0
2.489
2.471
2.464
2.453
2.446
2.428
2.418
2.394
APPENDIX E: RESULTS OF THEORETICAL MAXIMUM DENSITY
Mix Type
Sample Number
Weight of Bowl in Air, g (A)
Weight of Bowl in Water, g (B)
Weight of Bowl & Sample om Air, g (C)
Weight of Sample, g (D) = C - A
Weight of Bowl & Sample in Water, g (E)
Maximum Specific Gravity of Mix, TMD
(F) = D / (D+B-E)
Bitumen Content of Mix, % (G)
Specific Gravity of Bitumen, Gb (H)
Effective Specific Gravity of Aggregate,
Gse = (100-G) / [(100/F)-(G/H)]
76
Bitumen
Content (%)
5.5
6.0
AC10
6.5
7.0
Verification
7.3
4.5
5.0
5.5
AC14
6.0
6.8
Verification
6.1
4.0
4.5
AC20
5.0
Verification
4.3
3.3
3.8
AC28
4.3
5.0
Final
Height
Wt Air
Wt
Water
Wt
SSD
Water
Absorption
SG
Bulk
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
120.7
120.6
120.4
120.1
119.5
119.4
121.4
120.9
119.0
118.0
119.6
119.2
119.4
120.1
118.7
119.1
119.6
119.6
117.0
119.6
120.7
118.7
117.1
115.0
113.9
114.2
113.7
113.5
114.7
113.7
121.7
120.5
121.0
121.4
119.3
122.1
113.6
113.6
120.0
119.2
4676.8
4660.0
4635.5
4681.8
4729.3
4702.8
4736.5
4709.3
4727.5
4701.4
4645.9
4652.1
4636.9
4663.8
4665.6
4663.8
4671.4
4665.4
4748.0
4689.3
4760.2
4675.7
4617.1
4611.6
4656.4
4649.3
4651.3
4671.1
4651.6
4623.8
4621.5
4650.4
4656.5
4661.3
4655.8
4673.0
4439.3
4454.8
4718.2
4709.2
2598.3
2591.0
2577.6
2612.2
2661.5
2641.3
2639.7
2617.8
2659.2
2653.9
2636.1
2641.8
2613.3
2638.4
2642.8
2638.4
2630.5
2625.1
2725.8
2641.6
2678.6
2638.6
2638.4
2636.4
2691.9
2681.3
2698.6
2719.2
2691.3
2676.8
2682.7
2701.4
2685.3
2681.1
2678.3
2672.0
2525.0
2528.5
2689.5
2688.0
4701.8
4689.8
4672.2
4697.8
4735.6
4711.5
4747.1
4719.5
4731.9
4709.5
4692.7
4696.1
4665.3
4687.5
4686.0
4687.5
4686.3
4680.5
4753.1
4701.1
4770.4
4688.3
4643.0
4640.5
4675.7
4665.6
4662.2
4681.4
4678.5
4647.4
4695.2
4722.9
4720.5
4723.6
4694.8
4723.8
4459.4
4483.1
4738.3
4724.5
0.53
0.64
0.79
0.34
0.13
0.18
0.22
0.22
0.09
0.17
1.01
0.95
0.61
0.51
0.44
0.51
0.32
0.32
0.11
0.25
0.21
0.27
0.56
0.63
0.41
0.35
0.23
0.22
0.58
0.51
1.59
1.56
1.37
1.34
0.84
1.09
0.45
0.64
0.43
0.32
2.223
2.220
2.213
2.245
2.280
2.272
2.248
2.241
2.281
2.287
2.259
2.265
2.260
2.276
2.283
2.276
2.272
2.270
2.342
2.277
2.276
2.281
2.303
2.301
2.347
2.343
2.369
2.381
2.341
2.346
2.296
2.300
2.288
2.282
2.309
2.278
2.295
2.279
2.303
2.312
Diff
Average
TMD
VTM
0.003
2.222
2.418
8.11
0.032
2.229
2.401
7.17
OBC
VMA
VFB
17.73
54.23
17.90
59.97
7.3
0.009
2.276
2.384
4.53
16.62
72.71
0.007
2.244
2.367
5.20
18.22
71.46
-0.006
2.284
2.357
3.52
17.04
79.36
0.006
2.262
2.450
7.68
15.56
50.63
0.016
2.268
2.432
6.75
15.78
57.22
0.007
2.280
2.415
5.60
15.78
64.51
0.002
2.271
2.393
5.10
16.54
69.20
0.065
2.309
2.367
2.41
15.86
84.80
0.006
2.278
2.391
4.72
16.36
71.18
0.002
2.302
2.450
6.02
13.53
55.51
0.004
2.345
2.432
3.58
12.38
71.08
0.012
2.375
2.415
1.67
11.74
85.78
0.006
2.344
2.439
3.88
12.25
68.32
0.004
2.298
2.489
7.65
13.58
43.69
0.006
2.285
2.471
7.51
14.50
48.19
6.1
4.3
6.0
0.031
2.293
2.453
6.51
14.62
55.50
0.016
2.287
2.428
5.82
15.49
62.46
0.009
2.308
2.394
3.61
15.63
76.90
77
Verification
6.0
Sample
APPENDIX F1: RESULTS OF PROPERTIES – 75 GYRATIONS
Mix Type
Bitumen
Content (%)
5.5
5.9
AC10
6.0
6.5
Verification
6.3
4.5
5.0
5.0
AC14
5.3
5.5
Verification
5.8
4.0
4.5
AC20
5.0
5.5
Verification
4.2
3.3
4.0
4.3
AC28
4.5
Verification
5.3
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
I
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
I
II
Final
Height
118.4
116.7
121.2
119.7
113.8
111.8
118.3
115.8
117.8
118.8
117.5
116.2
114.7
116.5
118.0
119.0
119.7
119.7
114.2
115.1
118.1
117.1
113.6
115.3
114.1
114.3
111.0
113.2
112.3
112.5
114.2
113.8
121.5
121.1
117.6
117.3
119.4
121.0
118.2
118.7
117.7
117.9
118.9
117.6
Wt Air
4632.7
4612.9
4687.7
4658.1
4520.6
4517.9
4876.2
4730.8
4678.6
4696.2
4633.4
4619.6
4678.9
4650.6
4660.4
4653.2
4704.3
4704.3
4628.8
4670.0
4669.5
4650.3
4606.6
4624.7
4664.7
4647.7
4634.1
4712.4
4641.4
4689.8
4665.9
4634.0
4635.1
4670.1
4694.8
4650.7
4664.2
4699.2
4685.5
4719.9
4663.9
4731.2
4722.1
4656.7
Wt
Water
2587.0
2596.9
2605.3
2601.8
2554.0
2581.4
2810.9
2717.2
2633.6
2638.2
2640.5
2636.0
2699.4
2657.0
2638.6
2616.3
2642.2
2642.2
2661.2
2682.9
2636.0
2628.7
2660.7
2671.8
2710.5
2696.3
2714.7
2756.0
2709.0
2738.6
2707.4
2679.2
2681.9
2696.8
2727.0
2697.7
2668.7
2693.0
2702.4
2732.7
2694.0
2737.2
2706.6
2665.4
Wt SSD
4651.7
4624.8
4713.1
4675.2
4530.8
4524.1
4878.4
4733.7
4684.8
4703.2
4661.3
4640.9
4685.0
4669.3
4678.3
4678.5
4727.6
4727.6
4634.1
4675.1
4683.9
4659.9
4629.0
4653.6
4683.8
4658.0
4640.7
4719.7
4647.4
4696.7
4685.1
4655.8
4702.0
4736.4
4723.2
4676.2
4703.8
4737.1
4710.0
4740.6
4680.4
4745.2
4739.3
4671.7
Water
Absorption
0.41
0.26
0.54
0.37
0.23
0.14
0.05
0.06
0.13
0.15
0.60
0.46
0.13
0.40
0.38
0.54
0.50
0.50
0.11
0.11
0.31
0.21
0.49
0.62
0.41
0.22
0.14
0.15
0.13
0.15
0.41
0.47
1.44
1.42
0.60
0.55
0.85
0.81
0.52
0.44
0.35
0.30
0.36
0.32
SG Bulk
2.244
2.275
2.224
2.247
2.287
2.326
2.359
2.346
2.281
2.274
2.293
2.304
2.356
2.311
2.285
2.256
2.256
2.256
2.346
2.344
2.280
2.289
2.340
2.334
2.364
2.369
2.406
2.400
2.394
2.395
2.359
2.344
2.294
2.290
2.352
2.351
2.292
2.299
2.334
2.351
2.348
2.356
2.323
2.321
Diff
Average
TMD
VTM
0.031
2.259
2.418
6.57
0.023
2.235
2.404
7.06
OBC
VMA
VFB
16.34
59.82
17.58
59.86
6.30
0.039
2.306
2.401
3.95
15.05
73.77
0.012
2.352
2.384
1.33
13.82
90.37
0.007
2.278
2.391
4.73
16.38
71.13
0.011
2.299
2.450
6.18
14.19
56.42
0.045
2.334
2.432
4.04
13.33
69.69
0.028
2.271
2.432
6.40
15.71
59.24
0.000
2.256
2.425
6.67
16.49
59.55
0.002
2.345
2.415
2.89
13.36
78.36
0.009
2.285
2.400
4.80
15.86
69.75
0.007
2.337
2.450
4.60
12.23
62.38
0.005
2.367
2.432
2.70
11.58
76.70
5.8
4.2
0.006
2.403
2.415
0.50
10.69
95.33
-0.001
2.395
2.398
0.14
11.46
98.82
0.015
2.352
2.443
3.72
11.85
68.64
0.005
2.292
2.489
7.90
13.82
42.82
0.001
2.351
2.463
4.56
12.21
62.67
0.007
2.295
2.451
6.36
14.59
56.39
0.017
2.342
2.446
4.23
13.00
0.008
2.352
2.428
3.14
13.09
76.02
0.002
2.322
2.418
3.96
14.47
72.60
5.3
67.44
78
5.0
Sample
APPENDIX F2: RESULTS OF PROPERTIES – 100 GYRATIONS
Mix Type
79
APPENDIX F: SAMPLE CALCULATION OF SURFACE AREA
Sample Calculation for AC20
Percent Passing
Surface Area
Sureface Area,
(%)
Factor, m2/kg
m2/kg
28
100
0.41
0.41
20
94
14
80
10
72
5
58
0.41
0.2378
3.35
49
0.82
0.4018
1.18
33
1.64
0.5412
0.425
22
4.78
1.0516
0.15
12
12.29
1.4748
0.075
6
32.77
1.9662
Sieve Size, mm
∑ = 6.0834
80
APPENDIX H: SAMPLE CALCULATION OF VMA USING AVERAGE
ASPHALT FILM THICKNESS OF 8μm
Surface area
= Percent Passing X Surface Area Factor
= 72(0.41) + 58(0.41) + 49(0.82) + 33(1.64) + 22(4.78) + 12(12.29) + 6(32.77)
= 6.08 m2/kg
Specific Gravity of Asphalt = 1.03
Bulk Specific Gravity of Agrgegate = 2.571
Weight of effective asphalt binder
= 6.08 m2/kg of aggregate X 8 X 10-6 m X 1.03 X 1000 kg/m3
= 0.0500992
Asphalt content by weight of total mix
= 0.0500992 / (1+0.0500992) X 100
= 4.77%
Volume of asphalt binder = 4.77 kg / (1.03 X 1000 kg/m3)
= 0.004631 m3
Volume of aggregate = 95.75 kg / (2.556 x1000 kg/m3)
= 0.037257m3
Total volume of mix with 4% air voids = (0.004631 + 0.037257) / 96 X 100
= 0.043633
Since volume of air = total volume of mix – volume of effective asphalt
– volume of aggregate
Volume of air = 0.0043633 – 0.004631 – 0.037257
= 0.001745
VMA = (0.001745 + 0.004631) / 0.043633 X 100
= 14.6%
81
APPENDIX I: PHOTOS OF LABORATORY WORKS
Dry sieve
Aggregates sieved into different sizes
Aggregates being weighed
Mix batched
Aggregates and bitumen being manually
Sample ready for short-term aging
mixed
82
Sample being poured into
The Superpave Gyratory
Sample being put into the
the mould
Compactor
SGC
Compacted sample
Sample being weighed in water during
determination of bulk specific gravity of
mix
Theoretical maximum density apparatus