THE EFFECT OF AGGREGATE’S ANGULARITY ON
ENGINEERING PROPERTIES AND PERFORMANCE OF POROUS ASPHALT
NADHIR BIN AHMAD TARMUZI
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Engineering (Civil - Transportation and Highway)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
JUNE 2013
iii
DEDICATION…
A special dedication to my beloved mother, Puan Hajah Hadiah binti
Salleh and also to my father, Tuan Haji Ahmad Tarmuzi bin Haji Alem, who
often give encouragement, support and pray for my success during my Degree
Master’s study life.
Not to forget, my siblings, Nazari, Noremilin, Norasmah and Norbaiti
for always giving me support and attention in any situation i had faced.
Not least, my beloved lecturers especially from the Transportation &
Highway Engineering Program (MAP), classmates, and close friends who always
being there during the time I need and their willingness to share knowledge, ideas,
and opinion during study.
The sacrifice and loyalty that have been shown will not be forgotten until
whenever. May all the said prayers will be getting blessings from Allah s.w.t.
InsyaAllah...
Sincerely,
NADHIR BIN AHMAD TARMUZI
iv
ACKNOWLEDGEMENTS
Bismillahirahmanirrahim…
Alhamdulillah, I am grateful to Allah s.w.t for the blessings and grace, I
managed to complete the thesis entitled "The Effect of Aggregate’s Angularity on
Engineering Properties and Performance of Porous Asphalt" properly and
successfully.
The utmost and heartiest gratitude to my supervisor, Dr. Ramadhansyah
Putra Jaya, who always willing to share his invaluable and priceless knowledge and
also giving constructive advice, and enthusiastic support to my research. I am also
grateful to him for spending his precious time to view and evaluate the thesis.
A million thanks to all the technicians in the Transportation & Highway
Laboratory, Faculty of Civil Engineering especially to Mr. Azman, Mr. Azri, Mr.
Sahak, Mr. Muhammad Anwarrasyid, and Mrs. Rosmawati for their guidance and
helps shown during the laboratory works.
A special thanks to my thesis teammates, Thanwa Filza and Nurul Ain, and
also my laboratory mates, Muhammad Zul Hanif, Fung Lung Chang, Muhammad
Naqiuddin, Mohd. Khairul Idham, Nur Hidayah, and Yuniza for their willingness to
share precious knowledge, information, and support for accomplish this research.
Finally, I wish to express my acknowledgement to University Teknologi
Malaysia for providing sufficient and adequate materials, equipments and conditions
in completing this research.
v
ABSTRACT
Porous asphalt is a flexible pavement layer with high percent of
interconnected air void and constructed using open-graded type of aggregate.
Aggregate shape and surface texture plays a vital role in determining the engineering
properties and performance of porous asphalt. Angular-shaped aggregate which has
a clear defined fracture faces and sharp edges are preferable to be used in asphalt
mixture since it encourages better interlocking structures within the aggregate’s
skeleton. This study was carried out to evaluate the effect of aggregate’s angularity
on engineering properties and performance of porous asphalt using a combination of
conventional method and empirical Particle Index Test method. The term of
engineering properties includes experimental works to determine the resilient
modulus and stability while performance deals with the porosity and durability
characteristics of porous asphalt due to variations in the Particle Index Number (Ia).
From laboratory data analysis, it was found that angular particles delivers larger Ia
number compared to those less-angular or non-angular particles. Significant
improvement in the resilient modulus and stability properties has been obtained with
application of angular-shaped aggregate. Angular particles also results in higher
porosity of mixture but causes undesirable durability performance on porous asphalt
against abrasion loss. Some improvements have been recommended to enhance the
strength properties and performance of porous asphalt based on engineering
explanation.
vi
ABSTRAK
Asfalt poros merupakan sejenis lapisan turapan anjal dan mempunyai
peratus liang udara yang tinggi dan berhubung antara satu sama lain serta dihasilkan
menerusi penggunaan agregat jenis gred terbuka. Bentuk agregat serta tekstur
permukaannya memainkan peranan yang penting dalam menentukan ciri-ciri
kejuruteraan dan prestasi asfalt poros. Agregat bersegi serta mempunyai permukaan
pecah yang jelas dan tajam bersifat lebih baik untuk digunakan di dalam campuran
asfalt kerana ia menghasilkan struktur saling-hubung yang lebih baik dalam rangka
agregat tersebut. Kajian ini telah dijalankan untuk menilai kesan kesegian agregat
terhadap ciri kejuruteraan dan prestasi asfalt poros dengan menggunakan gabungan
kaedah konvensional dan kaedah Ujian Indeks Partikel yang bersifat empirikal. Ciri
kejuruteraan yang dinilai dalam kajian ini termasuklah eksperimen bagi menentukan
modulus daya tahan dan kestabilan manakala ciri prestasi melibatkan penentuan
tahap keliangan dan ketahanan asfalt poros disebabkan variasi dalam Nombor Indeks
Partikel (Ia). Daripada analisis data makmal, didapati bahawa agregat bersegi
menghasilkan nombor la yang lebih besar berbanding agregat tidak bersegi
(berbentuk bulat dan sfera). Peningkatan yang ketara dalam nilai modulus daya
tahan dan ciri kestabilan telah diperolehi menerusi aplikasi agregat berbentuk segi.
Partikel bersegi juga menghasilkan ciri keliangan yang lebih tinggi pada asfalt poros
tetapi mengakibatkan prestasi ketahanan yang kurang baik dalam rintangan terhadap
daya lelasan. Justeru, beberapa penambahbaikan telah disyorkan bagi meningkatkan
ciri-ciri kekuatan dan prestasi asfalt poros melalui penjelasan kejuruteraan.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xiii
LIST OF FIGURES xvii
LIST OF ABBREVIATIONS xxi
LIST OF SYMBOLS xxii
LIST OF APPENDICES xxiv
1 INTRODUCTION 1
1.1 Preface 1
1.2 Background of Study 3
1.3 Problem Statement 3
1.4 Aim and Objectives 4
1.5 Scope and Limitations of Study 5
1.6 Significance of Study 6
viii
CHAPTER TITLE PAGE
2 LITERATURE REVIEW 7
2.1 Preface 7
2.2 Properties of Porous Asphalt 8
2.2.1 Advantages of Porous Asphalt 10
2.2.2 Disadvantages of Porous Asphalt 11
2.3 Air Voids in Porous Asphalt 12
2.3.1 Type of Air Voids 13
2.3.2 Air Voids Influence on Porous Asphalt 14
Behavior
2.4 Effect of Binder in Porous Asphalt 15
2.5 Aggregate Shape Properties 16
2.5.1 Angularity of Aggregate 17
2.5.2 Particle Index Number (Ia) and Angularity of 18
Aggregate
2.6 Effect of Angular-Shaped Aggregate on 19
Engineering Properties and Performance of Porous
Asphalt Mix
2.6.1 Resilient Modulus of Porous Asphalt 21
2.6.2 Stability of Porous Asphalt 22
2.6.3 Porosity of Porous Asphalt 23
2.6.4 Durability of Porous Asphalt 24
3 RESEARCH METHODOLOGY 26
3.1 Preface 26
3.2 Specimens and Standards 28
3.3 Laboratory Works 30
3.3.1 Source and Type of Aggregate 30
3.3.2 Test on Aggregate Properties 33
3.3.2.1 Aggregate Impact Value (AIV) Test 33
ix
CHAPTER TITLE PAGE
3.3.2.2 Specific Gravity and Water 34
Absorption Test
3.3.3 Sieving and Blending of Aggregate 36
3.3.4 Design Binder Content 38
3.3.4.1 Specimen Preparation 38
3.3.4.2 Type of Binder 39
3.3.4.3 Mixed Binder Content 39
3.3.4.4 Cantabro Test 40
3.3.4.5 Binder Drain-Down Test 43
3.3.4.6 Determination of Design Binder 45
Content
3.3.5 Classification of Aggregate Shape and 46
Particle Index Test
3.3.5.1 Selection of Rounded / Spherical 46
Shape Aggregate
3.3.5.2 Apparatus for Particle Index Test 47
3.3.5.3 Determination of Mould’s Volume 48
3.3.5.4 Determination of Particle Index 50
Number (Ia)
3.3.5.5 Substitution of Angular Aggregate 53
Samples with Rounded / Spherical
Shaped Particles
3.3.5.6 Determination of Weighted Particle 56
Index Number (Ia)
3.3.6 Specimen Preparation of Porous Asphalt 56
3.3.6.1 Preparation of Aggregate 57
3.3.6.2 Preparation of Binder 57
3.3.6.3 Preparation of Moulds 58
3.3.6.4 Mixing of Materials 58
3.3.6.5 Compaction of Mixture 59
3.3.7 Engineering Properties of Porous Asphalt 60
3.3.7.1 Resilient Modulus Test 60
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CHAPTER TITLE PAGE
3.3.7.2 Stability Test 62
3.3.8 Performance of Porous Asphalt 64
3.3.8.1 Porosity Test 64
3.3.8.1.1 Bulk Specific Gravity 64
of Specimen
3.3.8.1.2 Theoretical Maximum 66
Density of Specimen
3.3.8.1.3 Determination of 68
Specimen’s Voids
Content
3.3.8.2 Durability Test 69
3.3.8.2.1 Determination of 69
Abrasion Loss
4 ANALYSIS AND DISCUSSIONS 71
4.1 Preface 71
4.2 Mechanical and Physical Properties of Aggregate 72
4.2.1 Aggregate Impact Value (AIV) 73
4.2.2 Specific Gravity 74
4.2.3 Water Absorption 75
4.3 Design Binder Content 76
4.3.1 Lower Limit of Binder Content 76
(Cantabro Test)
4.3.2 Upper Limit of Binder Content 79
(Binder Drain-Down Test)
4.3.3 Design Mixed Binder Content 82
4.4 Particle Index Number (Ia) of Aggregate Sample 82
4.4.1 Particle Index Number (Ia) of Angular Shape 83
Aggregate by Size Fractions
4.4.2 Particle Index Number (Ia) of Rounded / 86
Spherical Shape Aggregate
xi
CHAPTER TITLE PAGE
4.4.3 Arrangement of Aggregate Samples for 88
Specimens Making
4.4.4 Substitution of Rounded / Spherical 91
Aggregate Samples into Angular Aggregate
Samples
4.4.5 Weighted Particle Index Number (Ia) of 97
Porous Asphalt Specimen
4.5 Relationship between Aggregate’s Angularity and 98
Engineering Properties of Porous Asphalt
4.5.1 Resilient Modulus (Mr) and Total 99
Recoverable Horizontal Deformation (δ)
4.5.2 Stability and Flow 101
4.6 Relationship between of Aggregate’s Angularity 104
and Performance of Porous Asphalt
4.6.1 Porosity 104
4.6.2 Durability 106
5 CONCLUSION AND RECOMMENDATIONS 109
5.1 Conclusion 109
5.1.1 Correlation between Aggregate’s 110
Angularity and Particle Index Number (Ia)
5.1.2 Effect of Aggregate’s Angularity on 110
Engineering Properties of Porous Asphalt
5.1.3 Effect of Aggregate’s Angularity on 111
Performance of Porous Asphalt
5.2 Recommendations 112
5.2.1 Improvement on Porosity of Laboratory 112
Compacted Specimen
5.2.2 Improvement through Utilization of 114
Aggregate with Better Mechanical Properties
xii
CHAPTER TITLE PAGE
REFERENCES 115
APPENDICES A – G 119 – 152
xiii
LIST OF TABLES
TABLE NO. TITLE PAGE
3.1 Open-graded envelope for Grading B as being suggested by 37
JKR Standard and Specification for Road Works: Section 4
– Flexible Pavement, 2008
3.2 Percent of aggregate retained on each sieve for Grading B 37
(value in bracket represents the median percent for each size
fraction)
3.3 Total number of specimens for determining the design 39
binder content
3.4 Specification of Moulds, Tamping Rods, and Sample Size 48
for Performing Particle Index Test (ASTM D3398-00, 2006)
3.5 Specific volume of water at different temperatures 50
(ASTM D3398-00, 2006)
3.6 Percent of substitution by rounded / spherical shape 54
aggregate into an angular aggregate samples
3.7 Suggested mixing and compaction temperature of PG 76 58
bitumen for laboratory works
xiv
TABLE NO. TITLE PAGE
4.1 AIV for three aggregate samples and the calculated 73
average value
4.2 Specific Gravity values of crushed granite aggregate for 74
different particle size fractions and combined gradation
4.3 Percent of water absorption for different particle size 75
fractions
4.4 Percent of abrasion loss at different mixed binder content 77
from the Cantabro Test
4.5 Average percent of binder retained at different mixed binder 79
content from the Binder Drain-Down Test
4.6 Calculation of design mixed binder content based on the 82
lower limit and upper limit value
4.7 Ia number of aggregate samples at different particle sizes 84
(for engineering properties specimens of porous asphalt)
4.8 Ia number of aggregate samples at different particle sizes 85
(for performance specimens of porous asphalt)
4.9 Ia number of 10.0 mm rounded / spherical shape aggregate 87
samples (for engineering properties specimens of porous
asphalt
4.10 Ia number of 10.0 mm rounded / spherical shape aggregate 87
samples (for performance specimens of porous asphalt)
xv
TABLE NO. TITLE PAGE
4.11 Arrangement of angular aggregate samples based on 88
descending order of Ia number (for engineering properties
specimens of porous asphalt)
4.12 Arrangement of angular aggregate samples based on 89
descending order of Ia number (for performance specimens
of porous asphalt)
4.13 Arrangement of rounded / spherical aggregate samples 90
based on descending order of Ia number (for engineering
properties specimens of porous asphalt)
4.14 Arrangement of rounded / spherical aggregate samples 91
based on descending order of Ia number (for performance
specimens of porous asphalt)
4.15 Recalculated Ia number after substitution of 10.0 mm 92
rounded /spherical aggregates into angular samples (for
engineering properties specimens of porous asphalt)
4.16 Recalculated Ia number after substitution of 10.0 mm 94
rounded /spherical aggregates into angular samples (for
performance specimens of porous asphalt)
4.17 Weighted Ia number for engineering properties specimens 97
of porous asphalt
4.18 Weighted Ia number for performance specimens of porous 98
asphalt
xvi
TABLE NO. TITLE PAGE
4.19 Values of resilient modulus (Mr) and total recoverable 99
horizontal deformation (δ) at different Ia number of porous
asphalt specimens
4.20 Value of stability, flow, and the calculated stiffness of 102
porous asphalt specimens with different Ia number
4.21 Average percent of air voids, Va of porous asphalt 105
specimens with different Ia number
4.22 Average percent of abrasion loss of porous asphalt 107
specimens with different Ia number
xvii
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Comparison of particle size distribution in (a) Dense- 8
graded asphalt mix; and (b) Open-graded asphalt mix
(porous), (Pavia Systems Inc., 2012)
2.2 Comparison of aggregate gradation curve between dense 9
gradation an open gradation (Pavia Systems Inc., 2012)
2.3 Schematic sketch on aggregate and air voids structuring in 13
asphalt mixture (Indiana Department of Transportation,
2012)
2.4 Classification of aggregate particles based on angularity 17
and spherical shape (Samat, 2006)
2.5 Definition of aggregate particle with single fractured face 19
(ASTM D5821-01, 2006)
3.1 Basic steps and phases involved in the research 27
methodology study
3.2 Flowchart of the designed laboratory works 31
xviii
FIGURE NO. TITLE PAGE
3.3 Relationship between abrasion loss limiting value against 41
test temperature (Samat, 2006)
3.4 Determination of designed binder content based on 42
abrasion loss value at the test temperature (Samat, 2006)
3.5 Porous asphalt specimen for Cantabro Test (a). before 42
revolutions in the LAAV machine, and (b). after revolutions
in the LAAV machine
3.6 Relationship between retained binder and mixed binder for 44
identifying the upper limit of binder content for porous
asphalt mix (Samat, 2006)
3.7 Loose porous asphalt specimen for Binder Drain-Down 45
Test (a). placing in oven for 3 hours at mixing temperature,
and (b). binder drained on an aluminum tray
3.8 Comparison of particle shape (a). 10.0 mm angular 47
aggregate, and (b). 10.0 mm rounded / spherical aggregate
3.9 Measurement of mould’s volume using water in the 49
Laboratory
3.10 Procedures involved in Particle Index Test (a). tamping of 52
aggregate sample at 10 blows/layer and 50 blows/layer,
(b). flatten the aggregate surface with glass plate, and
(c). weighing of aggregate sample after tamped
3.11 Load pulse graph indicating load level and timing diagram 61
(Samat, 2006)
xix
FIGURE NO. TITLE PAGE
3.12 Procedures in resilient modulus test (a). arrangement of 62
specimen in UTM machine, and (b). running of resilient
modulus test via software
3.13 Procedures in Marshall Stability test (a). Specimen, 63
loading plats, and flow dial gauge, and (b). arrangement of
specimen and apparatus during test
3.14 Measurement of specimen mass in three distinct condition 65
(a). in air (dry), (b). in water, and (c). in SSD condition
3.15 Measurement of theoretical maximum density TMD of 67
porous asphalt specimen (a). specimen in vacuum
container, and (b). application of vacuum pressure using
Rice apparatus
3.16 Comparison of specimen mass (a). initial mass before the 70
abrasion loss, and (b). final mass after the abrasion loss
4.1 Determination of abrasion loss value based on test 77
temperature at 28.5oC
4.2 Determination of lower limit binder content based on 78
average abrasion loss value at 17 %
4.3 Determination of upper limit binder content based on 80
percent binder retained against mixed binder content
4.4 Relationship between mass of binder drained against mixed 81
binder content
xx
FIGURE NO. TITLE PAGE
4.5 Linear relationship of recalculated Ia number against ratio 96
of angular aggregate (10.0 mm particle size) for engineering
properties specimens of porous asphalt
4.6 Linear relationship of recalculated Ia number against ratio 96
of angular aggregate (10.0 mm particle size) for performance
specimens of porous asphalt
4.7 Relationship between resilient modulus (Mr) and Ia number 100
of porous asphalt specimens
4.8 Relationship between total recoverable horizontal 100
deformation (δ) and Ia number of porous asphalt specimens
4.9 Relationship between stability and Ia number of porous 103
asphalt specimens
4.10 Relationship between flow and Ia number of porous asphalt 103
Specimens
4.11 Relationship between air voids (Va) and Ia number of 105
porous asphalt specimens
4.12 Relationship between abrasion loss and Ia number of 107
porous asphalt specimens
xxi
LIST OF ABBREVIATIONS
ASTM - American Standard on Testing Materials
AIV - Aggregate Impact Value
BS-EN - British Standard European Norm
HMA - Hot Mix Asphalt
JKR - Jabatan Kerja Raya (Public Works Department)
LAAV - Los Angeles Abrasion Value
OGFC - Open-graded Friction Course
PG - Performance Grade
SBS - Styrene-butadiene-styrene
SG - Specific Gravity
SSD - Saturated-surface-dry
TMD - Theoretical Maximum Density
UTM - Universal Testing Machine
WA - Water Absorption
xxii
LIST OF SYMBOLS
A - Average water absorption
B - Initial mass of binder in mix
D - Mass of binder drained
G - Average specific gravity (for either SSD, bulk, or oven-dry)
M - Total mass of mould, glass plate, and water
P - Maximum stability load
R - Mass of binder retained
W - Mass of an aggregate size fraction in one specimen
e - Correction factors for stability value
g - Gravity (9.81 m/s-2
)
h - Amount of substitution by mass of aggregate size fraction
m - Percent of rounded / spherical aggregate used for substitution
n - Percent of remaining angular aggregate in sample
p - Probability
s - Oven-dry specific gravity of an aggregate size fraction
v - Volume of mould
δ - Total recoverable horizontal deformations
An - Water absorption of aggregate by size fraction
Gmb - Bulk specific gravity of specimen
Gmm - Theoretical maximum density of specimen
Gn - Average specific gravity of an aggregate size fraction
Ia - Particle IndexNumber
MSSD - Mass of specimen in saturated-surface-dry condition
Ma - Mass of specimen in air (dry condition)
Mb - Mass of specimen and vacuum container in water (submerged)
xxiii
Ma - Mass of specimen in air (dry condition)
Mb - Mass of specimen and vacuum container in water (submerged)
Mc - Mass of vacuum container in water
Mg - Mass of glass plate
Mm - Mass of mould
Mr - Resilient modulus
Mw - Mass of specimen in water (submerged)
Mwm - Mass of water filling mould
M0 - Initial mass of specimen
M1 - Final mass of specimen
M10 - Average mass of aggregate in mould tamped at 10 blows/layer
M50 - Average mass of aggregate in mould tamped at 50 blows/layer
Pn - Mass percentage of an aggregate by size fraction
Va - Air voids
Vw - Specific volume of water
V10 - Air voids in aggregate sample tamped at 10 blows/layer
V50 - Air voids in aggregate sample tamped at 50 blows/layer
WA - Mass of remaining angular aggregate in sample
WR - Mass of rounded / spherical aggregate required for substitution
xxiv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Mechanical and Physical Properties of Aggregate 119
Laboratory Data
B Design Binder Content Laboratory Data 126
C Particle Index Test Laboratory Data 131
D Resilient Modulus Test Laboratory Data 140
E Marshall Stability Test Laboratory Data 144
F Porosity Test Laboratory Data 147
G Durability Test Laboratory Data 150
CHAPTER 1
INTRODUCTION
1.1 Preface
Porous asphalt has been well-known for its advantages in improving skid
resistance of pavement during rains, reducing splashing effects, preventing
hydroplaning action on moving traffic, and producing lower riding noise (Liu and
Cao, 2009). These criteria made exist due to high porosity possessed by porous
asphalt which then allows for high drainage capability of surface run-off as well as
better riding noise absorption.
The structure of porous asphalt can be distinguished from the conventional
hot mix asphalt through large constituent of coarse aggregate and small amounts of
fine aggregate together with mineral filler. According to Public Works Department
of Malaysia (JKR, 2008), a compacted porous asphalt generally has a total percent of
air voids between the range of 18 % to 25 % in which defined as relatively high if
compared to the conventional dense-mixed asphalt (4 % to 5 % air voids).
2
The high voids content in porous asphalt have been enabled through the use
of open-graded type of aggregate. Open gradation mainly consists of coarse
aggregate with size dimension larger than 2.36 mm (No. 10 sieve) together with
small percentage of fine aggregate (not more than 15 %) and also mineral filler not
exceeding 5 % of the total aggregate weight (JKR, 2008). Hence, this subsequently
produces a permeable layer of bituminous course with high percentage of
interconnected air voids after compaction.
Porous asphalt is considered as a non-structural layer of flexible pavement.
In the early years, porous asphalt was constructed with main purpose to overcome
problems related to rainwater accumulation on pavement surface (Mallick et al.,
2004). However, limitations had occurred in terms of porous asphalt service-life due
to unacceptable performance, lack in durability, and densification of layer under
repetitive load actions (Mallick et al., 2004; Chang and Pei, 2011). Therefore,
porous asphalt should possess a sufficient strength and durability in bearing the
external loads imposed by traffic. Several engineering properties owned by
conventional asphalt such as resilient modulus and stability should also be evaluated
for case of porous asphalt. This is important since porous asphalt forms the
uppermost layer of flexible pavement, thus receiving loads from moving traffic in a
direct way.
The engineering properties and performance of porous asphalt are greatly
depends on several factors and one of them is related to the angularity in the shape of
aggregate used. Angularity of an aggregate is described in terms of how many
fracture face(s) it has to produce better interlocking in which increases the resistance
against rutting and cracks formations (Huang et al., 2009). Thus, angular shape
aggregate is expected to play a critical role not only regarding to the engineering
properties, but also in terms of its capability to maintain the performance criteria of
porous asphalt.
3
1.2 Background of Study
Apart of the bitumen and additives, aggregate is the major constituent of
materials which form most of the total volume and weight of any asphalt mixture.
Due to this, the performance and behavior of asphalt mix in terms of its strength,
durability, and workability are influenced by the properties of aggregate to be used.
Therefore, determination on the basic properties of aggregate is essential to have an
initial prediction on the characteristics of a compacted asphalt mixture.
Similarly in porous asphalt, attentions are given on mix design that capable of
producing surface layer which has sufficient resistance against permanent
deformation due to traffic loading. The resistance of porous asphalt is closely related
to its engineering properties and performance criteria with aggregate shape and
surface texture act as a major determinant to the mix behavior. In this study, an early
assumption may state that porous asphalt with high constituent of angular-shaped
aggregate should deliver better improvements on the engineering properties.
Besides, variation in the particle’s shape is estimated to affect the voids content of
porous asphalt, thus influencing its porosity and durability performance.
1.3 Problem Statement
Considerably as a non-structural layer in flexible pavement, porous asphalt is
greatly exposed for defects due to the imposed traffic loadings. Perhaps, high
porosity owned by porous asphalt has also contributed to the severity of damage
created. Pavement engineering properties such as resilient modulus and stability
plays a vital role in ensuring the resistance of porous asphalt against permanent
deformations and functional failure. This resistance performance is closely related to
4
the physical shape of aggregate which has been the main constituent of materials
used in forming asphalt layers.
Utilization of aggregate particles with undesirable shape might have a significant
impact on the strength of porous asphalt against physical and functional defects.
Therefore, porous asphalt has to have an adequate particle interlocking properties
and at the same time capable of maintaining its porosity and durability characteristic.
It has been a challenge in balancing these two criteria since aggregate’s shape is
quite a subjective parameter used in determining its influence on the engineering
properties and performance of porous asphalt.
1.4 Aim and Objectives
The aim of this study is to investigate the effect of angular-shaped aggregate
on engineering properties and performance of porous asphalt. The term of
engineering properties is referred to the evaluation of resilient modulus and stability
of porous asphalt while performance includes measurement on its porosity and
durability against external forces. Among the objectives to achieve in this study are:
i. To study the correlation between angularity of aggregate with Particle Index
Number (Ia).
ii. To determine the influence of Particle Index Number (Ia) on engineering
properties and performance of porous asphalt.
5
1.5 Scope and Limitations of Study
This study focuses on the effect of aggregate shape on engineering properties
and performance of porous asphalt. Therefore, several scope and limitations were
needed to define clearly before commencing the experimental works. These include
the following:
1. The asphalt mix tested was porous asphalt which uses open-graded type of
aggregate gradation as provided in the Public Works Department (JKR)
specification. In this study, Grading B type of porous asphalt mix has been
selected.
2. The type of aggregate used was quarry crushed granite. However, special
attention has been given on 14.0 mm and 10.0 mm particles with rounded or
spherical shape and having less than two fracture faces. These particles were
used for substitution in amount of 0 % to 100 % by fraction weight in the
aggregate samples. Testing to determine the aggregate mechanical properties
and shape index were following the British Standard European Norm (BS-
EN) and American Standard on Testing Materials (ASTM).
3. The type of binder used is polymer-modified bitumen of PG 76. Testing to
determine the design bitumen content was based on Cantabro Test and Binder
Drain-Down Test as according to the JKR and ASTM standard.
4. Engineering properties measured in this study includes the resilient modulus
and stability while performance relates to the porosity and durability
resistance of porous asphalt. Testing procedure for the mentioned parameters
was based on ASTM standard.
6
1.6 Significance of Study
Porous asphalt has been widely utilized especially in the European and North
American countries, and also Japan. Constructions of porous asphalt are done in
order to achieve specific goals or improvements on the physical performance of
roads and highways. In Malaysia, the application of porous asphalt as permeable
surface course of flexible pavement is still at unsatisfied level. Although so, it can be
seen that the opportunity of using porous asphalt is quite spacious and even a
necessity since our country receives a relatively high quantity of rainfall in a year
(Abustan et al., 2012). Perhaps, this condition exists due to limited research and
study being conducted on the performance of porous asphalt under the influence of
various factors.
Therefore, this study is intended to deliver better understanding on the
improvements that are able to obtain through modification in terms of aggregate
shape. This is essential in giving new ideas to the road engineers on how to
manipulate particular properties of constituent materials in order to increase the
usage value of porous asphalt and make suits of its application in local road
construction. Further research could be performed to investigate the effect of other
factors on the engineering properties and performance of porous asphalt. These
factors may include method of construction applies, aggregate gradation and types,
and even modification on the binder itself using polymers, fibers, and other possible
materials.
REFERENCES
Abustan I., Hamzah M. O., and Rashid M. A., (2012). Review of Permeable
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