EVALUATION OF BOND STRENGTH BETWEEN HOT MIX ASPHALT
SURFACING LAYERS
LIEW YEE SHIAN
A project report submitted in partial fulfillment of the
requirement for the award of the degree of
Master of Engineering (Civil-Highway and Transportation)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
AUGUST 2013
iii
To my beloved father and mother
iv
ACKNOWLEDGEMENT
I would like to express my gratefulness to my supervisor, Dr. Haryati for
giving me encouragement, and guidance to complete this study. She had guided me
throughout every step of my study and spending time on me for discussions.
Special thanks to Chang Fung Lung who contribute a lot to this project. I
hope this project could contribute to the research development. Without him, this
study would not complete on time.
Last but not least, I am grateful to my family members for their love, care,
support and daily encouragement during carrying the study.
v
ABSTRACT
This paper investigates the effect of tack coat types, application rates, and
layer thickness on HMA interface shear strength. The performance of tack coat
materials on AC 10 was evaluated. Three emulsions were selected as tack coat
material which are RS-1K, RS-2K, and RS-2KL.These tack coat materials were
applied at three application rates, namely 0.25 l/m², 0.40 l/m², and 0.55 l/m². The
selected application rates are in accordance with the JKR specification and represents
low, medium and high rates respectively Three different surface thickness were
considered namely 35 mm, 50 mm and 65 mm. Only laboratory scale specimens at
three replicates for each test configuration were used throughout the study. Direct
shear test were carried out shearing rate of 1 mm/min. Results show modified
emulsion can provide better shear strength than conventional emulsion where RS-
2KL performs better than RS-1K and RS-2K due to the present of latex in RS-2KL
which relate to the viscosity that can improve shear strength. On the other hand,
higher thickness of wearing course and application rate can provide higher interfaces
shear strength. However, their relationships were not strong due to inconsistency of
R2 values.
.
vi
ABSTRAK
Kajian ini dijalankan untuk menilai pengaruh salut jelujur, kadar aplikasi, dan
ketebalan lapisan terhadap kekuatan ikatan antara permukaan. Sebanyak tiga jenis
bahan salut jelujur telah digunakan, iaitu RS-1K, RS-2K dan RS-2KL. Ketiga-tiga
bahan ini digunakan pada tiga kadar aplikasi yang berbeza, 0.25 l/m², 0.40 l/m² and
0.55 l/m dan tiga kadar aplikasi tersebut mewakili kadar aplikasi rendah, sederhana
dan tinggi mengikut spesifikasi JKR. Ujian ricih dijalankan pada ricih 1 mm/min.
Analisis yang diperolehi menunjukkan kekuatan ricih antara permukaan lapisan
meningkat apabila ketebalan lapisan and kadar aplikasi meningkat. Selain itu,
keputusan menunjukkan emulsi diubahsuai boleh memberikan kekuatan ricih yang
lebih baik daripada emulsi konvensional di mana RS-2KL melakukan lebih baik
daripada RS-1K dan RS-2K kerana kewujudan lateks pada RS-2KL yang berkaitan
dengan kelikatan yang boleh meningkatkan kekuatan ricih. Walau bagaimanapun,
hubungan mereka tidak kuat kerana nilai R2 diperolehi tidak konsisten.
vii
TABLE OF CONTENT
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENT vii
LIST OF TABLES x
LIST OF FIGURES xi
CHAPTER 1 INTRODUCTION
1.1 Overview 1
1.2 Problem Statement 2
1.3 Aim 3
1.4 Objective 3
1.5 Scope 3
1.6 Thesis Structure 4
CHAPTER 2 LITERATURE REVIEW
2.1 Effects of Interface Poor Bonding 5
2.2 Tack Coat Definition 7
2.3 Factors Influence Interlayers Bond Strength 7
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2.3.1 Tack Coat Types
2.3.1.1 Cutback Asphalt
2.3.1.2 Asphalt Cement
2.3.1.3 Emulsified Asphalt
2.3.2 Tack Coat Application Rate
2.3.3 Tack Coat Curing Time
2.3.4 Temperature
2.3.5 Surface Types
2.3.6 Surface Conditions
2.3.7 Technology, Workmanship and
Construction Quality
7
8
8
9
10
11
14
15
17
18
20
2.4 Shear Testing
2.4.1 Direct Shear Test
2.4.1.1 Leutner Device
2.4.1.2 Modified Device, EMPA
2.4.1.3 Iowa Device
2.4.1.4 NCAT Device
2.4.1.5 Romanoschi Device
2.4.1.6 Debondt Device
2.4.1.7 Ascher Device
2.4.1.8 Romanoschi Dynamic
Device
2.4.2 Simple Shear Test
2.4.2.1 Shear Box
2.4.2.2 ASTRA Device
2.4.2.3 SHRP Shear Test Device
2.4.2.4 MCS Device
23
23
24
24
25
26
27
27
28
28
29
29
30
31
32
CHAPTER 3 METHODOLOGY
3.1 Introduction 33
3.2 Material 33
ix
3.3 Mixture Design 36
3.4 Specimen Preparation
3.4.1 Preparation of Binder Course
3.4.2 Application of Tack Coat
3.4.3 Preparation of Wearing Course
3.4.4 Compact Specimen
37
39
39
41
42
3.5 Shear Test 44
CHAPTER 4 ANALYSIS AND DISCUSSION
4.1 Introduction 46
4.2 Results 46
4.3 Effects of Wearing Course Layer Thickness
and Tack Coat Types on Shear Strength
47
4.4 Effects of Application Rates on Interfaces
Shear Strength
50
CHAPTER 5 CONCLUSION
5.1 Introduction 53
5.2 Conclusions 54
5.3 Recommendations 54
REFERENCE 56-62
x
LIST OF TABLES
TABLE NO TITLE PAGE
3.1 Aggregate gradation of AC 28 34
3.2 Aggregate gradation of AC 10 35
3.3 Designed OBC for different mix types 36
3.4 Marshall Test results and the specifications for Hot Mix
Asphalt AC 10.
36
3.5 Number of specimen 37
3.6 Minimum curing time 40
3.7 Number of compaction blows on the effect of thickness
and degree of compaction for AC 10
42
4.1 Result summary 47
xi
LIST OF FIGURES
FIGURE NO TITLE PAGE
2.1 Slippage cracking caused by poor interface
bonding
6
2.2 Combination of different mix types, (a) DGAC-
DGAC, (b) PAC-DGAC and (c) PAC-SMA.
17
2.3 A view of asphalt distributor truck performing the
tack coat application on a road section to be paved
22
2.4 Asphalt emulsion tack coat application using hand
wand sprayer in Malaysian road construction
22
2.5 Ponding of asphalt emulsion tack coat at certain
location on a pavement.
22
2.6 a) Shear stress distribution at the specimen head in
the direct shear test b) Shear stress distribution in
the simple shear test.
23
2.7 Leutner test device 24
2.8 Modified device, EMPA 25
2.9 Iowa device 25
2.10 NCAT device 26
2.11 Romanoschi device 27
2.12 De Bondt device 27
2.13 Ascher device 28
2.14 Romanoschi dynamic device 29
2.15 Shear box 30
2.16 ASTRA device 31
2.17 SHRP shear test device 31
xii
2.18 MCS device 32
3.1 Aggregate gradation of AC 28 34
3.2 Aggregate gradation of AC 10 35
3.3 Steps of samples preparation 38
3.4 Prepared binder course layer 39
3.5 Curing of tack coat 40
3.6 Application of tack coat 41
3.7 Preparation of wearing course 42
3.8 Effect of compaction blows to achieve the target
density
43
3.9 Prepared specimen 43
3.10 Fabricated mold 44
3.11 Shear box 45
3.12 Destructed specimen after shear test 45
4.1 Effects of surface layer thickness and tack coat
types on interfaces shear strength for (a) 0.25l/m2
(b) 0.40l/m2
(c) 0.55l/m2 application rate
49
4.2 Effects of application rates on interfaces shear
strength for surface layer thickness of (a) 35mm (b)
50mm (c) 65mm
52
1
CHAPTER 1
INTRODUCTION
1.1 Overview
Modern asphalt pavements are characterized by a composition of several
layers. This is true for new pavements as well as for existing pavements following
overlay procedures (Tschegg et al., 1995). Adequate bond between layers ensures
multiple layers perform as a composite structure. As a result, stresses from applied
loads are distributed throughout, subsequently reducing overall pavement damage
(Buchanan and Woods, 2004). Poor interlayer bond of hot mix asphalt (HMA) is the
factor of many pavement problems. Slippage failure often occur at locations where
traffic accelerates, decelerates, or turns, is the most commonly observed problem
related to poor bond between layers (West et al., 2005).
Tack coat is an application of asphalt binder used to improve bonding
between pavement layers and it is most commonly used between an existing surface
and a newly constructed overlay.It is used to ensure adequate bond between the
pavement being placed and the existing surface. A tack coat provides necessary
bonding between pavement layers to ensure that they behave as a single system to
withstand traffic and environmental stresses. Tack coat is normally applied to an
existing pavement surface before a new layer of asphalt concrete is placed. It may
also be applied to the surface of a new hot mix asphalt (HMA) pavement layer before
2
the next layer is placed, such as between an HMA levelling course and an HMA
surface course (Louay et al., 2012).
The most commonly used tack coat material is asphalt emulsion followed by
paving grade asphalt and cutback asphalt. Asphalt emulsion is favoured due to the
simplicity of being capable to be applied at lower temperature and relatively
pollution free. In some places, paving grade asphalt and cutback asphalt is still in
used, but the usage of cutback asphalt as tack coat has been restricted due to issues
related with environmental concern.
1.2 Problem Statement
Interface bonding has always been a major concern in pavement structures.
Loss of bonding or poor bonding between pavement layers can cause early pavement
distresses. Slippage failure occurs when there is insufficient bond between the
interfaces of the two layers in contact. At location where vehicle is likely to exert
high horizontal force, sharp curves and busy junction of continuous acceleration and
deceleration, slippage failures may be frequently encountered as well (Romanoschi et
al. 2001). On the other hand, delamination and potholes can be considered as one of
the most common types of pavement distress related to poor bonding in Malaysia,
though slippage failure can be occasionally found.
Tack coat is intended to bond pavement layers together and ensure that the
layers act monolithically when subjected to traffic loads. Insufficient or improper
application of tack coat can result in a weak bond between HMA pavement layers,
causing the layers to act independently. Hence, an optimum tack coat application rate
needs to be determined. That is the interest of this research to be carried out in order
to solve and improve on the problems related to bond between hot mix asphalt layer
interfaces.
3
1.3 Aim
The aim for this study is to evaluate the performance of bond strength on
HMA surfacing layer.
1.4 Objectives
To determine the effect of tack coat types, application rates, and layer
thickness on HMA interface bond strength.
1.5 Scope
The performance of tack coat materials on AC10 was evaluated. A total of
three tack coat materials, which include three emulsions, RS-1K, RS-2K, and RS-
2KL were selected. These tack coat materials was applied at three application rates,
which is 0.25 l/m², 0.40 l/m², and 0.55 l/m². The selected application rates are in
accordance with the JKR specification and represents low, medium and high rates
respectively. Three different wearing course layer thickness were considered namely
35mm, 50mm and 65mm. Only laboratory scale specimens at three replicates for
each test configuration are used throughout the study. Direct shear test was carried
out at shearing rate of 1mm/min.
4
1.6 Thesis Structure
The thesis has been categorized into specific chapters for better
understanding of the research. The lists of chapters are as follow:
Chapter 1: Introduction – This chapter gives an overview of the thesis including five
important things such as overview of the study, problem definition, objective of the
study, and scope of study of the research.
Chapter 2: Literature review – This chapter provides important theoretical and
conceptual understanding of related topics based on various researches.
Chapter 3: Methodology – The experimental setup of the study will be described.
The experimental procedure including design method, and standard referred will be
presented in this chapter.
Chapter 4: Result and analysis – Results, analysis, and discussion of experiment are
described in this chapter..
Chapter 5: Conclusion – The final chapter will summarize all the results and findings
related to this study which achieved the objective, and all the recommendations for
further works are presented here.
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