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.

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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.

.

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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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