UTILIZATION OF WASTE HIGH DENSITY POLYETHYLENE (HDPE) AS COARSE
AGGREGATE REPLACEMENT AND GLASSES AS FILLER IN HOT MIX ASPHALT
NURMAZIDAH BINTI ABDULLAH ZA WA WI
Thesis submitted in fulfillment of the requirements for the award of the degree of
B.Eng (Hons) Civil Engineering
Faculty of civil Engineering and Earth Resources
UNIVERSITI MALAYSIA PAHANG
JANUARY 2015
IIA
ABSTRACT
Flexible, rigid and composite are the three typical types of pavements. Commonly, flexible pavement is used especially in municipal, state and federal road in Malaysia. It consists five layers such as subgrade, subbase, base, base course and wearing course. In addition, the main structural function of pavement is to support the vehicles wheel load applied to the road 'and distribute to the . subgrade. High Density Polyethylene (HDPE) which is one of the polymers which is very familiar material used to produce many kind of product such as packing films, pipes and large blow and rotating moulding items while crushed glasses in non-metallic and inorganic material with 2.67 of specific gravity. Flexible pavement is commonly facing three major failures such as rutting, fatigue cracking and thermal cracking. The objective of this research is to investigate the optimum and effect usage of recycled HDPE as coarse aggregate replacement with crushed glasses as filler in modified asphalt mixture by determining the stiffness and permanent deformation. The modified asphalt mixture were produced from content concentrate of waste HDPE fillet range 2%, 4%, 6%, 8% and 10% of the weight of asphalt mixture with sieve size from 3.35 mm to 1.18mm and 4% to 6% is the range of the optimum bitumen content of hot mix asphalt wearing course 14 (ACWI4) with 80/100 of penetration grade of bitumen by referring Standard Specification for Road Works in Malaysia. The performance of the aggregate and bitumen is complying with Specification of Public Work Department 2008 in Malaysia. Therefore, these aggregates and bitumen can be used as asphalt for modified and unmodified sample. The Repeated Load Axial Test (RLAT), Indirect Tensile Stiffness Modulus Test (ITMS) were used to determine the permanent deformation and stiffness of asphalt, respectively. The density-void analysis indicates that the optimum bitumen content is 5.37% of weight of bitumen content. The result shows that the HDPE modified asphalt with crushed glass could enhance the stiffness of asphalt at 6% aggregate replacement at temperature 30°C. This modification also improves permanent deformation at 1800 cycles. Therefore the HDPE modified asphalt with crushed glasses is suitable to use for road pavement in term of economic and environmental aspects.
V
ABSTRAK
Lentur, tegar dan komposit adalah tiga jenis turapan jalan. Biasanya, turapan lentur digunakan terutama di kawasan bandar, negeri dan jalan persekutuan di Malaysia. la mengandungi lima lapisan seperti subgred, subtapak, asas, lapisan tapak dan lapisan kursus. Selainv, itu,, fungsi utama struktur turapan adalah untuk menyokong beban kenderaan yang dikenakan kepada jalan dan mengagihkan kepada subgred. Berketumpatan tinggi Polyethylene (HDPE) yang merupakan salah satu polimer yang sangat biasa digunakan untuk menghasilkan pelbagai jenis produk seperti pembungkusan filem, paip dan tamparan besar clan berputar item acuan manakala gelas dihancurkan ada!ah bukan logam dan bahan bukan organik dengan graviti tertentu iaitu 2.67. Turapan lentur biasanya menghadapi tiga kegagalan utama seperti aluran, keretakan kelelehan clan keretakan haba. Objektif kajian mi adalah untuk menyiasat penggunaan yang optimum dan kesan HDPE dikitar semula sebagai pengganti agregat kasar dengan kaca dihancurkan sebagai pengisi dalam campuran asfalt diubahsuai dengan menentukan kekukuhan dan ubah bentuk kekal. Campuran asfalt diubahsuai dihasilkan daripada pekatan kandungan sisa HDPE pelbagai dalam bentuk fillet dalam lingkungan 2%, 4%, 6%, 8% clan 10% daripada berat campuran asfalt dengan saiz ayak clan 3.35mm ke 1.18mm dan 4% hingga 6% adalah lingkungan kandungan optimum bitumen bagi campuran asfalt panas lapisan asphalt konkrit 14 (ACWI4) dengan 80/100 gred penetrasi bitumen dengan merujuk Standard Spesifikasi untuk Jalan Raya di Malaysia. Prestasi agregat dan bitumen telah mematuhi spesifikasi Jabatan Kerja Raya 2008 di Malaysia. Oleh itu, agregat dan bitumen boleh digunakan sebagai asfalt untuk sampel diubahsuai dan tidak diubah suai. Ujian Beban Paksi Berulang (RLAT), Ujian Modulus Tegangan Kekukuhan Secara Tidak Langsung (ITMS) telah digunakan untuk menentukan ubah bentuk kekal dan kekukuhan asfalt. Analisis rongga berkepadatan menunjukkan bahawa kandungan optimum bitumen adalah 5.37% daripada berat kandungan bitumen. Hasil kajian menunjukkan bahawa FIDPE asfalt diubahsuai dengan kaca dihancurkan boleh meningkatkan kekukuhan asfalt pada 6% penggantian agregat pada suhu 30 0 C. Pengubahsuaian mi juga meningkatkan ubah bentuk kekal di 1800 kitaran. Oleh itu HIDPE asfalt diubahsuai dengan kaca dihancurkan sesuai untuk digunakan untuk turapanjalan raya dari segi aspek ekonomi dan alam sekitar.
vi
TABLE OF CONTENTS
PAGE
SUPERVISOR'S DECLARATION
STUDENT'S DECLARATION
ACKNOWLEDGEMENT
ABSTRACT iv
ABSTRAK v
TABLE OF CONTENTS vi
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS xii
LIST OF ABBREVIATIONS xiii
CHAPTER 1 INTRODUCTION
1.1 Introduction
1.2 Problem Statement 4
1.3 Objective 5
1.4 Scope of Study 5
1.5 Significant of Study 7
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction
2.2 Flexible Pavement
2.3 Flexible Pavement Failure
2.4 Asphalt Mixture Properties Evaluation
2.4.1 Indirect Tensile Strength Test 2.4.2 Static Creep Test 2.4.3 Repeated Load Axial Test (RLAT) 2.4.4 Hamburg Wheel Tracking Test
8
9
10
13
14 14 15 16
vii
2.5 Hot Mix Asphalt 17
2.5.1 Asphalt 17 2.5.2 Aggregate 19
2.5.2.1 Aggregate Gradation (ASTM C136) 22 2.5.2.2 Type of Aggregate Gradation 23
253 Mineral Filler 25
2.5.3.1 Types of Mineral Filler 25 2.5.3.2 Filler Gradation 26
2.6 Polymer 27
2.6.1 High Density Polyethylene (HDPE) 28 2.6.2 HDPE Modified Bitumen 29
2.7 Waste Glass 29
CHAPTER 3 METHODOLOGY
3.1 Introduction 31
3.2 Materials 32
3.2.1 Aggregates 33 3.2.2 Bitumen 34 3.2.3 Portland Cement 34 3.2.4 High Density Polyethylene (HDPE) 35 3.2.5 Crushed Glasses 36
3.3 Experimental Design 37
3.4 Asphalt Mix Design 39
3.4.1 Aggregate Gradation 39 3.4.2 Optimum Bitumen Content 39
3.5 Los Angeles Abrasion Test (LA) 40
3.6 Aggregate Crushing Value (ACV) 41
3.7 Aggregate Impact Value (AIV) 42
3.8 Ten Percent Fines (TPF) 44
3.9 Penetration Test 45
3.10 Softening Point Test 47
3.11 Density and Void Analysis 48
3.11.1 Bulk Density 48 3.11.2 Void In Total Mix (VTM) 49 3.11.3 Void In Mineral Aggregate (VMA) 50 3.11.4 Void Filled with Bitumen (VFB) 50
viii
3.12 Indirect Tensile Stiffness Modulus Test (ASTM D4123) 51
3.13 Repeated Load Axial Test 53
CHAPTER 4 RESULTS AND DISCUSSIONS
4.1 Introduction 55
4.2 Performance of Aggregate and Bitumen 56
4.3 Density and Void Analysis 56
4.3.1 Void in Total Mix (VTM) 57 4.3.2 Void In Mineral Aggregate (VMA) 58 4.3.3 Void Filled with Bitumen (VFB) 59 4.3.4 Bulk Density 60
4.4 Indirect Tensile Stiffness Modulus Test (ITSM) 61
4.4.1 Indirect Tensile Stiffness Modulus Test for 61 Unmodified Sample
4.4.2 Indirect Tensile Stiffness Modulus Test for 62 Modified Sample
4.5 Repeated Load Axial Test (RLAT) 63
4.5.1 Repeated Load Axial Test (RLAT) of modified sample 63 (HDPE with Portland cement)
4.5.2 Repeated Load Axial Test (RLAT) of modified sample 65 (I-IDPE with crushed glasses)
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions 66
5.2 Recommendations 68
REFERENCES 69
APPENDICES 71
Al Performance of Aggregate and Bitumen 71
A2 Density and Void Analysis Result (Control or Unmodified Sample) 73
A3 Indirect Tensile Stiffness Modulus Test for Unmodified Sample 76
A4 Indirect Tensile Stiffness Modulus Test for Modified Sample 77
(HDPE with Portland Cement)
A5 Indirect Tensile Stiffness Modulus Test for Modified Sample 78
(HDPE with Crushed Glasses)
A6 Repeated Load Axial Test for Unmodified Sample 79
ix
A7 Repeated Load Axial Test for Modified Sample 84
(HDPE with Portland Cement)
A8 Repeated Load Axial Test for Modified Sample 85
(HDPE with Crushed Glasses)
x
LIST OF TABLES
Table No. Title Page
1.1 Gradation Limit of Asphaltic Concrete 6
1.2 Design Bitumen Content 6
2.1 Bitumen Properties 19
2.2 Typical aggregate requirement and for road awareness 21
2.3 Size of Aggregate 24
2.4 Example of dense graded aggregate 25
2.5 Physical Properties of Mineral Fillers 27
2.6 Mineral Filler for Bituminous Mix 27
3.1 Gradation Limit for ACWI4 for I 136g of asphalt mix design 32
3.2 Indirect Tensile Modulus Stiffness Parameter 51
3.3 Dynamic Creep Test Parameter 53
4.1 Performance Quality of Bitumen and Aggregate 56
4.2 Results of Density and Void Analysis with PWD requirement 57
xl
LIST OF FIGURES
Figure No. Title Page
1.1 Typical cross section of flexible pavement 2
1.2 Rutting along the wheel path 3
2.1 Fatigue cracking formation 12
2.2 Bottom up of fatigue cracking (i), Top down of fatigue cracking (ii) 13
2.3 Repeated Load Axial Test 40°C (mixture A/D) 16
2.4 Main Type of Aggregate in Malaysia 21
2.5 Typical Aggregate Gradation Plot 22
2.6 Stationary Polymer Bending System 29
3.1 Aggregates 33
3.2 Bitumen Penetration Grade 80/100 34
3.3 Ordinary Portland Cement 35
3.4 High Density Polyethylene (HDPE) 36
3.5 Crushed Waste Glass 37
3.6 Experimental Design Flow 38
3.7 Los Angeles Abrasion Machines 41
3.8 Aggregate Crushing Value 42
3.9 Aggregate Impact Value 44
3.10 Penetration Test 46
3.11 Softening Point 48
3.12 Indirect Tensile Modulus Stiffness Test 52
3.13 Repeated Load Axial Test 54
4.1 Relationship between air void and bitumen content 57
(VTM versus bitumen)
4.2 Relationship between void in mineral aggregate and bitumen content 58
(VMA versus bitumen content)
xii
4.3 Relationship between void filled and bitumen content 59
(VFB versus bitumen Content)
4.4 Relationship between bulk density and bitumen content 60
4.5 Relationship between resilient modulus and bitumen content of 61
unmodified sample
4.6 Relationship between resilient modulus and HDPE content of 62
modified samples
4.7 Relationship between Axial Strain and cycle of the samples between 64
unmodified and modified sample (HDPE with Portland Cement)
4.8 Relationship between Axial Strain and cycle of the samples between 65
unmodified and modified sample (T-IIJPE with crushed glasses)
LIST OF SYMBOLS
Micrometre
Pw Density of Water
% Percentage
Total Strain, Bandwidth Parameter
LIST OF ABBREVIATION
mm Millimetre
HDPE High Density Polyethylene
PET Polyethylene Terephthalate
HMA Hot Mix Asphalt
ACW Asphalt Concrete Wearing
JTSM Indirect Tensile Stiffness Modulus
ITS Indirect Tensile Strength
RLAT Repeated Load Axial Test
ACB Asphalt Concrete Binder
DMA Dynamic Mechanical Analysis
Pmax Maximum Applied Load
kPa Kilopascal
UTM Universal Testing Machine
LVDTs Linear Vertical Displacement Transducers
ASTM American Society for Testing and Materials
C Celcius
RPM Revolutions Per Minute
TPF Ten Percent Fines
kg Kilogram
cm Centimetre
BS British Srandard
Max Maximum
Min Minimum
AASHTO American Association of State Highway and Transportation Officials
OPC Ordinary Portland Cement
PE Polyolefins
PP Poly-Propylene
xl"
EVA Ethylene Vinly Acetate
SBS Styrene Butadiene Styrene
LDPE Low Density Polyethylene
TPs Thermoplastics
CaCO3 Calcium Carbonate
LA Los Angeles Abrasion
ACV Aggregate Crushing Value
AIV Aggregate Impact Value
VTM Voids in Total Mix
VMA Voids In Mineral Aggregate
VFA Voids Filled with Biumen
MS Malaysian Standard
PWD Public Work Department
xlv
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Flexible, rigid and composite are the three typical types of pavements.
Commonly, flexible pavement is used especially in municipal, state and federal road in
Malaysia. Flexible pavement typically consists of asphalt mixture placed over granular
base or subbase layers which supported by the compacted soil referred to as the
subgrade (Papagiannakis et al., 2008). Flexible pavement structure consists of subgrade,
subbase, base, base course and wearing course. In addition, the main structural function
of pavement is to support the vehicles wheel load applied to the road and distribute to
the subgrade. The best design of wearing coarse by selection of materials, gradation and
bitumen content able to form good skid resistance, desirable stability, durability and
good workability which allow the rapid drainage of surface water, minimize traffic
noise, resistance cracking, withstand traffic turning and braking force, protect
underlying road structure, require nominal maintenance, be capable of being recycled or
overlaid and be durable and give the value or money (O'Flaherty,2002).
2
The sizes and materials of aggregate are different depend on the classification of
aggregate which is coarse aggregate and fine aggregate. Coarse aggregate should be
retained on 2.4mm sieve opening of crush rock or crushed gravel and free from foreign
materials. Meanwhile, fine, aggregate should be passing on 2.4mm sieve opening and
shall be clean, ';hard, durable and free from clay, mud and other foreign materials. The
typical cross section of a flexible pavement is shown in Figure 1 .1.
So I Cost Prime cost
Surface Coure(-5O in
I BIrgec courae(50—laO mm) t I
Base course (100-300 mm)
I Subbase Course (100-300 fun) I
MM)
?tural Subie
Figure 1.1:Typical cross section of a flexible pavement
Bitumen consists two types of penetration grades, the range is between 60 - 80
and 80 -100. Based on the specification of the JKR/SPJ/2008-S4, the bitumen of
penetration grade 60 -80 is recommended to be used for heavy traffic roads in order to
achieve higher stability of mixture and to lessen the possibility of bitumen bleeding or
flushing at high temperature.
Permanent deformation or rutting is one of the pavement failures due the stress
caused by the traffic load pressure. The results from many agencies in world had
showed that the failure of permanent deformation is related to the materials in asphalt
mixture use for the wearing coarse layer of the pavement (Tayfur et al., 2005).
Therefore, reconstruction the sub base or base to increase the strength or overlay rutted
area with bituminous surfacing is probable treatment for this 'condition of flexible
pavement.
3
Rutting from weak subgrade occur in the wheel paths of the vehicle travelling on
a flexible pavement as shown in Figure 1.2. The thickness of pavement layers does not
provide enough strength to reduce the applied stress to the tolerable level as well as it is
weakened by the intrusion of moisture.
Figure 1.2: Rutting along the wheel path
Nowadays, the pavement layer consists of recycled materials such as plastics
and crushed glass. High Density Polyethylene (HDPE) which is one of the types of
polymer is a very familiar material used to produce many kind of product such as
packing films, pipes and large blow and rotating molding items (Rosato, 2004). The
HDPE products are often flexible, corrosion and chemical resistance, lightweight while
being extremely tough and at the same time, it can be recycled and reused. In addition,
HDPE resins have high strength (Campo, 2008).
Meanwhile the waste glass is non-metallic and inorganic, it can neither be
incinerated nor decomposed, so it may difficult to reclaim. It had been used in highway
construction as an aggregate substitute in hot mix asphalt paving and most of countries
in the world incorporated glass into their road specification which encouraged greater
use of the materials. While the use of waste glass as filler in hot mixed asphalt is still
not widely experimented (Johy H. Et al.,201 1).
4
Recently, several experiments and testing had been done to improve the
properties of asphalt mixture. The properties of waste glass as a filler in hot mix asphalt
(HMA) is used to improve the engineering properties of asphalt mixture.
Meanwhile HDPE had proved by modified the bitumen or asphalt mixture using
polymers, several properties of asphalt mixture such as temperature susceptibility,
fatigue life, and resistance to permanent deformation can be improved (Jain et al., 1992;
Panda and Mazumdar, 2002; Tayfur et al., 2005; Yildirim, 2005; Hassani et al., 2005).
1.2 PROBLEM STATEMENT
Malaysia is the developing country where the roads and highways are an
important role to connect a place to the other destination or place. Flexible pavement is
commonly used in Malaysia and it facing three major failures such as rutting, fatigue
cracking and thermal cracking. In this case, I referred at Gambang road because the road
condition was very bad and unsatisfactory due to the failures of the road. The failure
occurs due to.traffic load and the materials use for the construction (Thom, 2008).
In addition, the condition of roads are affecting the safety of road users,
therefore the bad condition of road may make the hazard of the road and cause accident
frequently during raining day and monsoon season. In the other words, the government
and private agencies will spend a lot of money for maintenance works.
Recently, the amount of solid waste such as waste glasses and waste plastics, the
waste plastics majority comes from PET and HDPE in Malaysia increase due to human
needs. According to the Global Environment Centre, a non-government organization in
Malaysia in year 2008, 23 000 tonnes of waste was produced each day in Malaysia, with
less 5% of the waste being recycled. However, this amount is expected to rise to 30 000
tonnes by the year 2020 (Global Environment Centre, 2009). The amount of waste
generated continues to increase due to the increasing population and development. By
applying unsystematic process of extracting a proportion of recyclable items from the
main waste, it make all waste simply disposed of in landfills.
5
1.3 OBJECTIVE
The permanent deformation on asphalt pavement cause rutting, corrugation,
depression and shoving on the flexible pavement. Therefore, in the effort to produce
durable and long life service asphalt pavement, the study on the modification of asphalt
mixture using waste HDPE and crushed glasses as partial replacement aggregate on
asphalt concrete wearing 14 (ACW 14). This study is experimental work by using
Universal Technical Machine (UTM). The main objectives of the study are:-
1. To determine optimum bitumen content of the asphalt mixture
2. To investigate stiffness modulus by using Indirect Tensile Strength Test
(ITMS)
3. To determine permanent deformation behavior of HDPE as replacement
coarse aggregate in modified asphalt and crushed glasses as a filler
1.4 SCOPE OF STUDY
This study is mainly based on laboratory experiment. '1 he scope ottlie research is
mainly divided into two part; (i) control mixture and (ii) modified mixture of asphalt for
flexible pavement. The both sample, the ACW 14 of aggregate gradation size is used in
the design pavement. The modified asphalt is proposed to use in the wearing course. In
addition, construction of bituminous layer required a higher cost than the other layers.
Aggregate gradation ACW 14 is mixed with bitumen 80/100 grade of penetration
will be used for control asphalt and modified asphalt. The density and air void analysis
is made to determine the optimum bitumen content of the control mixture for modified
mixture of asphalt. In addition, some portion of coarse aggregate are replaced with the
waste HDPE in fillets in range 2% to 10% of modified HDPE with crushed glasses for
asphalt mixture modification purpose and to investigate the stiffness of ACW 14 by
Indirect Tensile Stiffness Modulus test (ITSM). The Repeated Load Axial Test (RLAT)
on the control and modified mixture of asphalt to determine the permanent deformation
behavior.
In order to achieve the objective of this research, there are several testing will be
conduct which are bitumen and aggregate test, void-density analysis, Indirect Tensile
Stiffness Modulus test (ITSM) and Repeated Load Axial test (RLAT). This study will
be conducted as follow which is hot mix asphalt wearing course 14 (ACW 14). The
gradation limits for asphaltic concrete is shown in Table 1.1 and the design bitumen
contents is shown in Table 1.2.
Table 1.1: Gradation Limit of Asphaltic Concrete
B.S Sieve Size ACW 10 ACW 14 ACB 28
(mm) % Passing by weight
37.5 - -
28 - - 100
20 - 100 72-90
14 100 90-100 58-76
10 90-100 76-86 48-64
5 58-73 50-62 30-46
3.35 48-64 40-54 24-40
1.18 22-40 18-34 14-48
0.425 12-26 12-24 8-20
0.15 6-14 6-14 4-10
0.075 4-8 4-8 3-7
Table 1.2: Design Bitumen Contents
ACW 10 (Wearing Coarse) 5.0%— 7.0%
ACW 14 (Wearing Coarse) 4.0%-6.0%
ACB 28 (Binder Coarse) 3.50/o— 5.5%
7
1.5 SIGNIFICANT OF STUDY
The permanent deformation is the structure damage will cause the accidents to
the users. Therefore, a solution for this problem has to be found out. The way to solve
this problem i by reduce the probability of the structure failure and increase the service
life of roads. Many researchers had proved that the modification of asphalt mixture with
the modifier such as polymer can improve the properties of asphalt mixture (Haasani et
al., 2005; Zoorob and Suparma, 2000). By improving the properties of permanent
deformation performance of asphalt concrete pavement, it will be increase the life
service of pavement.
The HDPE product is one of the most popular recyclable plastic solid wastes.
Due to mechanical and chemical characteristics of this plastic, it is suitable to be used as
modifier in asphalt mixture. This advantage of HDPE is used in this study to design the
asphalt mixture that can resist permanent deformation behavior. Besides, from this
research, it will help to investigate stiffness characteristics of the modified asphalt
compare with the control asphalt and able to determine the optimum effects of the
HDPE as an additive in asphalt. By contributing the plastic solid waste into the
pavement construction, it can be solve the landfill capacity problem and may reduce the
negative impact of the waste materials to the environment with reused it in asphalt
pavement.
CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
This chapter is divided by four main parts: flexible pavement, asphalt mixture,
polymer and mineral filler (crushed glasses). First part of this chapter is the review on
flexible pavement. The flexible pavement consists of major component of flexible
pavement structure and types of flexible pavement failure. The levels of flexible
pavement structures are wearing course, base, subbase, and subgrade. Besides, the
flexible pavement failures are including the permanent deformation, fatigue cracking,
stiffness and thermal cracking.
The second part of this chapter is regarding to the asphalt mixture. There are
several experiments to evaluate the properties of asphalt mixture such as Indirect
Tensile Strength, Static Creep Test and Repeated Load Axial Test. In sub topic
aggregate, there are review on aggregate gradation, types of aggregate gradation and
aggregate properties.
The polymer part is described about the high density polyethylene (HDPE) and
the function of HDPE in modified asphalt. The waste glass or crushed glasses as
mineral filler are the last part in this literature review
2.2 FLEXIBLE PAVEMENT
The component of flexible pavement consists of surface course, base, subbase
and subgrade. The function of pavement structure is to distribute imposed wheel load
over a large area of the natural soil. Flexible pavement which include asphalt concrete,
stabilized or granular material, or bound granular material distribute the load over a
cone shape area under the wheel, by reducing the imposed unit stresses as depth
increases. The shear strength of the soil is usually not high enough to support the traffic
load. The shear failures would occur in the wheel path in soils and ruts would form if
the vehicles were travel on it. Therefore, the structure of the flexible pavement helps the
distribution of load to the lower layer and decreases the failure of the flexible pavement.
Surface course consist of asphalt concrete. The layer is directly contact with the
traffic load and provides several characteristics such as friction, smoothness, noise
control, rut resistance and drainage. In addition the safety of road users will be assured
by the availability of these characteristics and able to prevent the surface water from
entering into underlying base, subbase and subgrade. This upper structural layer of
material is sometimes is subdivided into two layers: wearinc' cmimp. nnd
intermediate/binder course. The wearing course is the upper layer of the road surface. It
must be capable of withstanding the wear and abrasive effects and must. possess
sufficient stability to prevent it from shoving and rutting under traffic loads. Otherwise,
it may improve the skid resistance, minimize the hydroplaning effects at high speeds
and improve the wet night visibility. In addition, it serve a useful propose in preventing
the entrance of excessive quantities of surface water into the base and subgrade from
directly above (John Wiley & Sons, 2004)
Base course located beneath the surface course with the high stability and
density. Its principal purpose is to distribute the stresses created by wheel loads acting
on sufficiently great to result in excessive deformation or displacement of that
foundation layer. The base courses are usually constructed out of aggregate or hot mix
asphalt (HMA). Thus layer receive load from upper layer and distribute to the subbase.
The rutting and shear failure does not occur in best design of base course (Lavin, 2003).
10
Subbase is located between the base course and subgrade. The subbase course is
composed of either solely granular materials (aggregate), soils or granular material
stabilized by an additive. The granular may contains aggregate from sand, deposit from
quarry, recycled concrete pavement, slag or other material. The subbase generally
consists of lower quality materials than the base course but better than the subgrade
soils. Subbase , course must have ability to distribute the load and functioning as
structural support and also can minimize the intrusion of fines from the subgrade into
the pavement structure, improve drainage and minimize frost action damage. In certain
case, the subbase course is not always needed or used in flexible pavement structure
(Lavin, 2003).
Subgrade is the native material which the pavement structure is placed. It is
consisted of natural ground, commonly from cut and fill process. In some cases,
subgrade were often been called as the formation level. Two most important
characteristic of subgrade are the loads bearing capacity and volume changes. The
subgrade must be able to support the loads transmitted from the upper pavement
structure. This load bearing capacity is affected by degree of compaction, moisture
content and soil type. For soil volume changes due to the exposed to excessive moisture
content, while soils with excessive fines may be susceptible to frost heave in freezing
areas, (Lavin, 2003)
2.3 FLEXIBLE PAVEMENT FAILURE
Asphalt pavement failure is a complicated phenomenon. It is a result of
cumulative damage in different pavement layer (Qudais, 2005). Nowadays, asphalt
pavement. Nowadays, asphalt pavement has to sustain increasingly large loads. When
these loads are combined with adverse environmental conditions, the distress modes in
pavements lead to the rapid deterioration of road structures (Vlachovocova,2005).
Flexible pavement is facing the risk of failure in form of rutting (permanent
deformation), fatigue cracking and thermal cracking. Indirect Tensile Strength test is to
evaluate the asphalt mixture performance.
I
The permanent deformation or rutting in the asphalt pavement is one of the
main reason cause the pavement damage. The permanent deformation in pavement has
long been recognized to include two different modes which is compactive deformation
(consolidation of layer) and plastic deformation (asphalt shear flow) (Huang, 1996;
Gokhale et al.1, 2005).
Thermal cracking is the cracking in flexible pavement due to cold temperature
cycling is commonly referred to as thermal cracks. Thermal cracks typically appear, as transverse cracks on the pavement surface roughly perpendicular to the pavement
centerline. In addition, these cracks can be caused by shrinkage of the HrvIA surface due
to low temperatures, hardening of the asphalt, and daily temperature cycles. Low
temperature cracking is associated with regions of extreme cold whereas thermal fatigue
cracking is associated with regions that experience large extremes in daily and seasonal
temperatures.
Besides, there are two types of non-load related thermal cracks which are
transverse cracking and block cracking. The transverse cracks usually occur first and are
followed by the occurrence of block cracking is the type that is predicted by models in
this design guide, while the block cracking is handled by material and construction
variables (Ara,2004).
Stiffness is the important mechanical characteristic of unbound materials in
pavements and the relative stiffness of the various layers dictate the distribution of
stresses and strains within the pavement system. Besides, the stiffness of the subgrade
and unbound base layer is influence the horizontal tensile strain at the bottom of the
asphalt and the compressive vertical strain at the top of the subgrade for a simple three-
layer flexible pavement system and those parameters are directly related to the
performance of the asphalt fatigue and subgrade rutting. The preferred method use for
characterizing the stiffness is the resilient modulus MR which is defined as the
unloading modulus in cyclic loading for unbound pavement. In 1986, the AASTHO
Design Guides have recommended the resilient modulus for characterizing subgrade
support for determining structural layer coefficients for flexible pavements.
12
Fatigue cracking of flexible pavement is due to horizontal tensile strain at the
bottom of the asphaltic concrete. It is commonly referred to as "bottom-up" or "classical" fatigue cracking. The cracks most likely initiate from the top in areas of high
localized tensile stresses resulting from tire-pavement interaction and asphalt binder
aging (top-dowri cracking) in thick pavement. Besides, the longitudinal cracks connect
forming many sided sharp-angled pieces that develop into a pattern resembling the back
of an alligator or crocodile after the repeated loading. The early stage of fatigue
cracking on the flexible pavement is shown in Figure 2.1 and types of fatigue in Figure
2.2.
Figure 2.1: Fatigue cracking formation,
Source: Halifax NS, October 29, 2013