evaluation of polymer modified asphalt binder...

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Universidade do Minho

Escola de Engenharia

Huthaifa Issam Ashqar

Evaluation of Polymer Modified Asphalt

Binder Aging

February 2015

Master Thesis

Urban Engineering

This work was carried out under the supervision of

Doctor Hugo Manuel Ribeiro Dias da Silva


Evaluation of Polymer Modified Asphalt

Binder Aging

February 2015

Universidade do Minho

Escola de Engenharia

Acknowledgment

iii


ACKNOWLEDGMENT

I am using this opportunity to express my gratitude to everyone who supported me

throughout this thesis. I express my warm thanks to my supervisor Prof. Hugo Silva for his

fabulous dedication.

I would also like to thank everyone in the Civil Engineering Department and in particular

Prof. José Pinho and Prof. Joel Oliveira for their help and cooperation. I am grateful to

everyone in the Civil Engineering Laboratory, especially Mr. Carlos Palha, Mr. Hélder Torres,

and Ms. Liliana Costa for sharing their illuminating help and views.

I would like to thank Erasmus Mundus Program (Peace) for funding my master course at

University of Minho.

This work is funded by FEDER funds through the Operational Competitiveness Program

COMPETE and by National funds by FCT (Portuguese Foundation for Science and Technology)

in the scope of Project FCOMP 01 0124 FEDER 020335 (PTDC/ECM/119179/2010).

Thanks are also due to the Companies Gintegral (for the supply of polymers) and CEPSA (for

the supply of bitumen).

I dedicate this Master’s thesis to pare ts Prof. Issam and Wafaa, my sister, and my

brothers. Thank you for your support.

Abstract

v


Evaluation of polymer modified asphalt binder aging

ABSTRACT

Asphalt binders used in road pavements basically age in two phases, the short-term aging

and the long-term aging. Short-term aging occurs in binders due to mixing, transporting,

placing, and compaction of asphalt mixtures, while long-term aging occurs in situ during the

lifetime of the pavement. The effect of short-term and long-term aging on the binder reveals

in its chemical structure, mainly by increasing the rate of oxidation, and in its physical or

rheological properties by hardening.

The main aim of this work was the study of the short-term aging, especially addressing the

assessment of polymer modified asphalt binders. In fact, these binders are being increasingly

used, but the evolution of their properties during aging is still not well known.

A 35/50 penetration grade unmodified bitumen (B1), a 70/100 penetration grade Ethylene

Vinyl Acetate (EVA)-modified bitumen (PmB1), and a 70/100 penetration grade High-Density

Polyethylene (HDPE)-modified bitumen (PmB2) were aged applying two different methods.

In one method, the binders were exposed to 75-min in RTFOT testing (binder aging). In the

other method, the binders were used to produce asphalt mixture samples, and the aged

binders were recovered (short-term aging of the mixture and binder recovery) after

mechanical testing of samples.

The rheological properties of all binders were assessed for each one of their states, namely

unaged, after-RTFOT aging, and after-recovery aging. These rheological measurements after

RTFOT aging o iousl i di ated a i rease i the i ders’ stiffness. However, the

rheological results after-recovery appeared to be unreasonable. Hence, the binders PmB1

and PmB2 were also subjected to DSC testing trying to explain these unexpected results. DSC

analysis indicated that the polymers were absent from PmBs after recovery process. Yet, the

FTIR analysis had demonstrated that the recovered bituminous parts of PmBs were indeed

aged chemically when the mixtures were produced and compacted.

Keywords: Short-Term Aging, Polymer Modified Bitumen, Rheological Properties, Recovered

Binder

Resumo

vi


Avaliação do envelhecimento de betumes modificados com polímeros

RESUMO

Os ligantes betuminosos utilizados na pavimentação de estradas envelhecem basicamente

de duas formas, a curto prazo e a longo prazo. O envelhecimento de curto prazo ocorre nos

ligantes devido à produção, transporte, colocação e compactação das misturas betuminosas,

enquanto o envelhecimento a longo prazo ocorre in situ durante o período de vida do

pavimento. O efeito do envelhecimento do ligante a curto e a longo prazo revela-se na sua

estrutura química, principalmente através do aumento da taxa de oxidação, e nas suas

propriedades físicas ou reológicas pelo aumento da rigidez.

O objetivo deste trabalho foi o estudo do envelhecimento a curto prazo, e será

especialmente orientado para a avaliação de ligantes betuminosos modificados com

polímeros. De facto, estes ligantes têm vindo a ser cada vez mais utilizados, mas ainda não

se conhece bem a evolução das suas propriedades durante o envelhecimento.

Um betume não modificado de penetração 35/50 (B1), um betume de penetração 70/100

modificado com EVA (PmB1), e um betume de penetração 70/100 modificado com PEAD

(PmB2) foram envelhecidos aplicando dois procedimentos diferentes. Num dos

procedimentos os ligantes foram expostos a 75-min no ensaio de RTFOT (envelhecimento do

ligante). No outro método, os ligantes foram usados para a produzir amostras de mistura

betuminosa, recuperando-se os ligantes envelhecidos (envelhecimento a curto prazo da

mistura e recuperação do ligante) depois de realizados ensaios mecânicos.

Para todos os ligantes, foram determinadas as propriedades reológicas de cada um dos seus

estados: não envelhecido, envelhecido por RTFOT e recuperado após envelhecimento. Estes

ensaios reológicos indicam obviamente um aumento na rigidez devido ao envelhecimento

por RTFOT. No entanto, os resultados reológicos após recuperação apresentaram-se pouco

coerentes. Daí, os ligantes PmB1 e PmB2 foram também sujeitas a ensaios de DSC de modo

a tentar esclarecer estes resultados inesperados. A análise dos resultados de DSC indicou a

ausência dos polímeros nos ligantes betuminosos modificados com polímero após o

processo de recuperação. No entanto, a análise dos resultados FTIR demonstraram que as

frações betuminosas recuperadas dos ligantes modificados foram efetivamente envelhecidas

quimicamente quando as misturas foram produzidas e compactadas.

Palavras-chave: Envelhecimento a Curto Prazo, Betume Modificado com Polímero,

Propriedades Reológicas, Ligante Recuperado

Table of contents

vii


TABLE OF CONTENTS

1 INTRODUCTION .......................................................................................................... 1

1.1 Background ................................................................................................................... 1

1.2 Objective....................................................................................................................... 2

1.3 Study Outline ................................................................................................................ 3

2 LITERATURE REVIEW ................................................................................................... 5

2.1 Bitumen Aging .............................................................................................................. 5

2.1.1 Bitumen Aging Process ..................................................................................... 5

2.1.2 Aging Factors .................................................................................................... 6

2.1.3 Types of Aging................................................................................................... 7

2.2 Short-Term Aging ......................................................................................................... 8

2.2.1 Simulation Methods of Short-Term Aging ........................................................ 9

2.2.2 Effect of Short-Term Aging ............................................................................... 9

2.3 Bitumen Modification ................................................................................................ 10

2.3.1 Bitumen Modification as Anti-Aging Process ................................................. 11

2.3.2 EVA and HDPE as Asphalt Modifying Polymers .............................................. 12

2.4 Previous Work on Aging of Modified Bitumens ......................................................... 14

2.4.1 Laboratory and In-Situ Aging .......................................................................... 14

2.4.2 Previous Methods to Evaluate Aging of Different Modified Bitumens .......... 15

3 MATERIALS AND METHODS ...................................................................................... 21

3.1 Basic Materials ........................................................................................................... 21

1.3.3 Aggregates ...................................................................................................... 21

3.1.2 Binders ............................................................................................................ 22

3.2 Methodology Overview .............................................................................................. 23

Table of contents

viii


3.3 Testing Programme .................................................................................................... 24

3.3.1 Specimens Preparation .................................................................................. 24

3.3.2 Volumetric Properties .................................................................................... 25

3.3.3 Indirect Tensile Strength (ITS) Test ................................................................ 26

3.3.4 RTFOT Aging Method ..................................................................................... 27

3.3.5 Binder Recovery Method ............................................................................... 28

3.3.6 Dynamic Shear Rheometer (DSR) .................................................................. 29

3.3.7 Fourier Transform Infrared Spectroscopy (FTIR) ........................................... 30

3.3.8 Differential Scanning Calorimetry (DSC) ........................................................ 30

4 TESTS RESULTS AND DISCUSSION .............................................................................. 33

4.1 Mass loss in RTFOT..................................................................................................... 33

4.2 Volumetric Properties of Studied Mixtures ............................................................... 33

4.3 Indirect Tensile Strength (ITS).................................................................................... 34

4.4 Rheological Measurements ....................................................................................... 37

4.5 Viscosity Results ......................................................................................................... 40

4.6 Softening point, Penetration, and Resilience Results................................................ 43

4.7 Differential Scanning Calorimetry (DSC) Results ....................................................... 46

4.8 Fourier Transform Infrared Spectroscopy (FTIR) Results .......................................... 49

5 CONCLUSION ............................................................................................................ 53

5.1 Final conclusions ........................................................................................................ 53

5.2 Future works .............................................................................................................. 54

REFERENCES AND BIBLIOGRAPHY .................................................................................... 57

List of tables

ix


LIST OF TABLES

Table 3-1 Quantities of each material or aggregate fraction used to produce the

asphalt mixtures .................................................................................................... 25

Table 4-1 Volumetric properties of the studied mixtures ........................................................ 33

Table 4-2 Changes of aging index before and after aging ........................................................ 51

List of figures

xi


LIST OF FIGURES

Figure 2-1 Types of aging and factors......................................................................................... 7

Figure 2-2 Comparison between the aging of PPA modified bitumen and pure bitumen

SK70 (F. Zhang & Yu, 2010) .................................................................................... 11

Figure 2-3 Softening point increment of the binders after UV aging (H. Zhang et al.,

2011) ...................................................................................................................... 16

Figure 2-4 Aging indices corresponding to polymer content (B. Sengoz & G. Isikyakar,

2008) ...................................................................................................................... 16

Figure 2- MCR a d Δ“ after in situ thermal aging (Henglong Zhang, Yu, & Kuang, 2012) ..... 17

Figure 2-6 LOI variation for different flame retardants contents (Henglong Zhang, Shi,

et al., 2013) ............................................................................................................ 18

Figure 2-7 Effect of aging on the penetration ratio of bitumens with different amounts

of flame retardant (Cong et al., 2010) ................................................................... 18

Figure 2-8 Viscosity ratio of three modified asphalt binders (Yin et al., 2013) ........................ 19

Figure 3-1 Gradation curve for AC 14 Surf mixture produced in this study ............................. 21

Figure 3-2 Aggregates used to produce the asphalt mixture: (a) fraction 0/4; (b)

fraction 6/14 .......................................................................................................... 21

Figure 3-3 Polymers used to modify a 70/100 bitumen: (a) EVA; (b) HDPE ............................ 22

Figure 3-4 High shear mixer used to produce polymer modified binders ............................... 22

Figure 3-5 Conventional tests specified for bitumen characterization: (a) Viscometer

test; (b) Ring and Ball softening point test; (c) Penetration test; (d)

Resilience test ........................................................................................................ 23

Figure 3-6 Commercial filler used in the mixture ..................................................................... 25

Figure 3-7 Indirect tensile testing frame (ITS) .......................................................................... 26

Figure 3-8 Rolling thin film oven test (RTFOT) ......................................................................... 27

Figure 3-9 Rotary evaporator ................................................................................................... 28

Figure 3-10 Dynamic shear rheometer (DSR) used in this work .............................................. 29

Figure 3-11 Fourier transform infrared spectroscopy (FTIR) equipment ................................. 30

Figure 3-12 Differential scanning calorimetry (DSC) equipment ............................................. 31

List of figures

xii


Figure 4-1 Modes of failure (a) B1, single cleft failure (b) PmB1, ideal failure (c) PmB2,

localized crushing failure ........................................................................................ 35

Figure 4-2 Results of ITS testing of the several mixtures at 20 °C (with or without

extended aging) ...................................................................................................... 36

Figure 4-3 Results of ITS testing of the several mixtures at 40 °C (with or without

extended aging) ...................................................................................................... 36

Figure 4-4 Rheological properties of B1 bitumen (phase angle and G*) .................................. 38

Figure 4-5 Rheological properties of PmB1 binder (phase angle and G*) ................................ 38

Figure 4-6 Rheological properties of PmB2 binder (phase angle and G*) ................................ 39

Figure 4-7 Viscosity of B1 bitumen in the DSR and in the rotational viscometer .................... 40

Figure 4-8 Viscosity of PmB1 binder in the DSR and in the rotational viscometer .................. 40

Figure 4-9 Viscosity of PmB2 binder in the DSR and in the rotational viscometer .................. 41

Figure 4-10 VAI values obtained with the viscosity results from DSR and from rotational

viscometer .............................................................................................................. 42

Figure 4-11 Base properties of B1 bitumen .............................................................................. 43

Figure 4-12 Base properties of PmB1 binder ............................................................................ 44

Figure 4-13 Base properties of PmB2 binder ............................................................................ 44

Figure 4-14 SPI and PI values for B1, PmB1, and PmB2 binders ............................................... 46

Figure 4-15 DSC curves for PmB1 and PmB2 binders ............................................................... 47

Figure 4-16 FTIR spectra analysis of B1 Binder before and after aging .................................... 50

Figure 4-17 FTIR spectra analysis of PmB1 Binder before and after aging ............................... 50

Figure 4-18 FTIR spectra analysis of PmB2 Binder before and after aging ............................... 51

List of symbols and abbreviations

xiii


LIST OF SYMBOLS AND ABBREVIATIONS

B1 - 35/50 penetration grade binder

Def. - Indirect tensile deformation

Def.’ - Indirect tensile deformation of the mixtures with extended aging (2-hour at 163 °C)

DSC - Differential scanning calorimetry

DSR - Dynamic shear Rheometer

EVA - Ethylene vinyl acetate polymer

FTIR - Fourier transform infrared spectroscopy

G* - Complex (shear) modulus

HDPE - High-density polyethylene

ITS - Indirect tensile strength

IT“’ - Indirect tensile strength of the mixtures with extended aging (2-hour at 163 °C)

PI - Penetration index

PmB1 - 70/100 penetration grade EVA-modified binder

PmB2 - 70/100 penetration grade HDPE-modified binder

RTFOT - Rolling thin film oven test

SPI - Softening point index

VAI - Viscosity aging index

Vv - Void ratio

Vv’ - Void ratio of the mixtures with extended aging (2-hour at 163 °C)

ρ - Density

ρth - Maximum theoretical density

Introduction

1


1 INTRODUCTION

1.1 Background

Bitumen has recently become one of the most used materials in the worldwide industry.

More than 95% is used in paving works for roads, highways, and bridges. It is used as a

binder for mineral aggregate to form the asphalt mixtures. Chemically, bitumen is a complex

heterogeneous mixture of hydrocarbons usually collected as a byproduct of the refining

process of crude oil in petroleum refineries (Krishnan & Rajagopal, 2005).

There are various properties of the bitumen, especially rheological ones, which control the

behavior of bitumen throughout mixing, construction, and in-site throughout the service life,

imply the need to study the effect of aging on these properties. Like other organic

substances, asphalt binder is directly affected by the presence of oxygen, ultraviolet

radiation, moisture and temperature that cause aging (Araujo, Lins, Pasa, & Leite, 2013).

Thus, bitumen aging is the hardening of the material, which means changes of its chemical

and/or physical characteristics. Generally, aging causes a deterioration (i.e. hardening) of

asphalt binders, which leads to the decrease of its performance (especially its flexibility) and

service life in road pavements. Important aging related modes of failure are traffic and

thermally induced cracking, as well as raveling (X. Lu & Isacsson, 2002). Aging of the

bituminous binder is manifested as an increase in its stiffness or viscosity (G. D. Airey, 2003),

and this factor could be beneficial to rutting resistance of asphalt mixtures. The aging

resistance of the binders is considered as one of the key factors that influence the service life

of a road pavement (F. Zhang & Yu, 2010).

Thus, the aging effect on different types of asphalt binders, particularly the short-term aging

effect, is an area for consideration in recent road engineering investigation. This area of

research can evaluate and analyze the extent of aging effect, the behavior of different types

of binder after aging, the rate of aging, the properties that could reflect this aging behavior,

and the potentials of some additives to protect the asphalt binders from aging or reducing

its consequences. These studies would eventually lead to a methodology of applying the

Introduction

2


best production, transporting, and placing conditions to the binders, and corresponding

asphalt mixtures, in order to extend their service life in roads.

In asphalt mixes for roads, most of the properties of bitumen that allow the mixtures to

resist to traffic and climate actions are rheological. Bitumen is workable and homogeneous

in a certain conditions. Furthermore, it should be stiff enough at high temperatures to resist

rutting and remains soft enough at low temperatures to resist cracking. However, these

opposite properties lead the experts to apply methods that can increase the temperature

range in which the binders present adequate properties for their use in road pavements,

such as using additives, namely asphalt polymer modification. The aging effect on these

asphalt modified binders is less well known, and the higher complexity of these materials

makes this investigation a challenge even more attractive, which should be pursued.

1.2 Objective

This study aims to investigate the short-term aging of unmodified bitumen and polymer

modified bitumen. This short-term aging was evaluated on these types of binders by using

two different types of aging procedures. The aging of the binders that occurs while they are

exposed to the rolling thin film oven test (RTFOT), and the short-term aging of the bitumen

that occurs directly in the asphalt mixture because of the mixing and compacting of the

mixtures on the laboratory.

A compariso et ee the differe t i ders’ characteristics before and after aging is

discussed. It is also important to determine if polymer modified bitumen has different aging

processes from unmodified bitumen.

In addition, the influence of adding polymers o the i ders’ eha ior efore a d after agi g

is presented, in order to assess if polymers are protecting bitumen from aging causes.

Particularly, the difference between the effect of adding Ethylene Vinyl Acetate (EVA)

polymer to PmB1 and High-Density Polyethylene (HDPE) polymer to PmB2 on the asphalt

binder properties, before and after aging, is illustrated.

Introduction

3


The distinction between the RTFOT aging and the aging caused by the preparation of

specimens from asphalt mixtures produced in laboratory is also a significant area of

investigation in this work. Another objective of this work is to evaluate the adequacy or the

extent of potential of some processes (e.g. recovery process) used during the study of

asphalt aging to be used with different types of binders, while certain tests such as Fourier

transform infrared spectroscopy (FTIR) are also used to complement the aging evaluation

carried out.

1.3 Study Outline

This study consists of five chapters. The first chapter is the introduction, which gives a

general background about the study theme and determines its objectives.

The second chapter attempts to find and present the most relevant previous-work regarding

the theme of the study, namely regarding asphalt binder aging and asphalt polymer

modification.

The materials used and the methods applied in this study to achieve the project's objectives

are presented in the third chapter.

The fourth chapter covers the analysis and the discussion of the results obtained after the

laboratorial study carried out in accordance with the methodology previously presented.

Finally, the fifth chapter reveals some essential conclusions obtained in this study and the

needs of future work in this area of investigation.

Literature review

5


2 LITERATURE REVIEW

2.1 Bitumen Aging

2.1.1 Bitumen Aging Process

Bitumen aging is one of the principal factors causing the deterioration of asphalt pavements.

In bitumen aging, two types of mechanisms are involved. The main aging mechanism is an

irreversible one, characterized by chemical changes of the binder, which in turn has an

impact on the rheological properties. The processes contributing to this type of aging include

oxidation, loss of volatile components, and exudation migration of oily components from the

bitumen into the aggregate. The second mechanism is a reversible process called physical

hardening. Physical hardening may be attributed to molecular structuring, i.e. the

reorganization of bitumen molecules (or bitumen microstructures) to approach an optimum

thermodynamic state under a specific set of conditions (X. Lu & Isacsson, 2002).

Generally, the rheological hardening or stiffness is attributed to the asphalt compositional

changes upon aging. Asphalt aging can significantly affect asphaltene and aromatic

quantities, without altering saturates and resins content. Aging converts aromatic

components into toluene soluble asphaltenes, which will be used as a solvent in this study.

Furthermore, field aging dramatically increases total peri-condensed aromaticity as well as

carbonyl and sulfoxide functional groups (X. Lu & Isacsson, 2002; Qin, Schabron, Boysen, &

Farrar, 2014). This can be defined as the chemical effect of aging.

Although aging is highly studied because of its impact on the mechanical properties of the

binder (hardening), it is important to continue studying this phenomenon. It was observed

that all rheological indicators can be used to quantify the aging importance. In general,

viscosity is mostly used as an indicator for aging, an aging index being usually defined either

directly as the viscosity ratio or as the relative increase in viscosity versus time (X. Lu &

Isacsson, 2002).

Bitumen structure is quite complex with slow temperature-dependent evolutions arising

from molecular organization processes that are far from being fully understood. In addition

Literature review

6


to that, the molecules may irreversibly evolve through chemical aging, which is generally

thought to be a sum of oxidation reactions and polymerization, and to a lesser extent, lighter

components evaporation. As a result, chemical aging leads to a global hardening of the

material, which in turns increases the cracking probability (Lesueur, 2009).

During aging, significant decomposition of saturates and evaporation of small molecular-

weight hydrocarbon were observed. Ketones and sulfoxides account for most of the

oxidative reactions in the simulation of asphalt aging (Pan, Lu, & Lloyd, 2012).

2.1.2 Aging Factors

Aging leads to a hardening of asphalt, mainly due to the oxidation of the asphalt binder

itself. Oxidation rate is influenced by several parameters, namely outside temperature,

ultraviolet (UV) radiation and intrinsic characteristics of the mixture constituents (Lopes et

al., 2014).

One of the important and influential factors, which principally affect the in-situ aging (i.e.

long-term aging), is UV radiations. Although the influence of solar radiation on bituminous

binders has been known for some considerable time, the influence of ultraviolet (UV) light

on bitumen aging is often ignored in laboratory simulations of aging due to the fact that UV

radiation only affects the upper layers of the pavement surfacing (Mouillet, Farcas, &

Besson, 2008; Pang, Liu, Wu, Lei, & Chen; S. Wu, Pang, Liu, & Zhu, 2010; H. Zhang, Yu, Wang,

& Xue, 2011). Other factors may also contribute to aging, such as molecular structuring over

time (steric hardening) and actinic light (primarily ultraviolet radiation, particularly in desert

conditions). Oxidation, volatile loss and thixotropic effects (steric hardening) tend to be

universally accepted as the three dominant factors affecting age hardening (G. D. Airey,

2003; Lesueur, 2009).

Literature review

7


2.1.3 Types of Aging

There are mainly two types of aging types (Figure 2-1). The one that is primarily associated

with the loss of volatile components and oxidation of the bitumen during asphalt mixture

construction is called short-term aging. The other one is the long-term aging that is the

progressive oxidation of the in-place material in the field. Both types cause an increase in

viscosity of the bitumen and consequential stiffening of the mixture.

Figure 2-1 Types of aging and factors

Lopes et al. (2014) proposed that bitumen undergoes different types of aging, distinguished

by their mechanisms, which can be classified as physical and chemical. Thus, to simulate

bitumen aging, a distinction can be made between short-term aging (which occurs during

asphalt mixture production and its laying down) and long-term aging (which relates to

changes during the service life as a result of oxidation and UV radiation). Physical aging is a

reversible phenomenon whereas chemical aging is irreversible. Chemical aging is mainly due

to an oxidation process. It is generally assessed by the measurements of the sulfoxide and

carbonyl chemical groups, which are created by oxidation.

Ag

ing

Short-term

Through mixing

Laboratory

High temperature

Long-term

Through life service

In-situ aging

Weather temperature

Type Characteristics

Literature review

8


Several methods have been proposed to replicate the effect of aging and, therefore, to

foresee bitumen behavior during application and service life. To simulate the age hardening

occurring during plant mixing and laydown the most utilized tests are Thin Film Oven Test -

TFOT (EN 12607-2 or ASTM D-1754) and Rolling Thin Film Oven Test - RTFOT (EN 12607-1 or

ASTM D-2872). In both tests, the age hardening is evaluated by observing how viscosity,

penetration and softening point change with aging. To simulate long-term aging during

service, the Pressure Aging Test – PAV (EN 14769 or ASTM D-6521) was adopted in SHRP

binder specifications, being used later transferred into other specifications. In this test, aging

is evaluated by means of complex modulus (G*) and phase angle changes, determined after

carrying out dynamic rheological analysis (Mastrofini & Scarsella, 2000).

However, a correlation between the short-term and long-term aging showed that the rank

order of the short-term aged mixtures, in terms of their fatigue cracking resistance, did not

change significantly after long-term aging. The ranking of fatigue cracking resistance of

short-term aged specimens using different binders correlated well with the ranking of

fatigue cracking resistance of long-term aged specimens (Arega, Bhasin, & Kesel, 2013).

Nevertheless, some studies showed that reducing mixing and compaction temperatures

could improve the long-term durability of the mix due to reduced short-term aging

(Banerjee, de Fortier Smit, & Prozzi, 2012).

2.2 Short-Term Aging

Short-term aging is a rapid chemical aging upon mixing of the hot bitumen in a thin film

around the hot aggregates. It occurs for a short time at a high temperature, typically around

160 °C, and is well simulated by the Rolling Thin Film Oven Test hi h ooks the itu e

in thin moving films (1.25-mm thick) at 163 °C for 75 min. Under average processing

conditions, this leads typically to a doubling of the viscosity, although the extent of

hardening is bitumen-dependent and ranges typically between 1.5 and 4.0 for the viscosity

at 60 °C, even though higher values are sometimes found. In the meantime, the asphaltenes

content of the aged binder typically increases (Lesueur, 2009).

Literature review

9


2.2.1 Simulation Methods of Short-Term Aging

Tests related to the aging of bituminous materials can be divided into tests performed on

the bitumen and those performed on the asphalt mixture. The most commonly used

short-term binder aging tests are the high temperature TFOT and RTFOT, used to simulate

the hardening that occurs during asphalt mixture production. Considerable evidence exists

to indicate that the RTFOT and similar extended, high temperature, heating test methods are

able to simulate short-term aging for conventional bituminous binders. However, generally,

the most promising method for short-term aging of asphalt mixtures are extended heating of

the loose material and extended mixing. Particularly, the RTFOT is probably the most

significant modification of the TFOT involving the placing of bitumen in a glass jar (bottle)

and rotating it in thinner films of bitumen than the 3.2mm film used in the TFOT. The RTFOT,

therefore, simulates far better the hardening which bitumen undergoes during asphalt

mixing (G. D. Airey, 2003). In addition, short-term oven aging (STOA) in the laboratory are

intended to represent the aging of an asphalt binder during hot-mix asphalt (HMA)

production and construction (Lee, Amirkhanian, Shatanawi, & Kim, 2008).

2.2.2 Effect of Short-Term Aging

To summarize the effect of the short-term aging, aging significantly influences bitumen

chemistry and rheology. Chemical changes include the formation of carbonyl compounds

and sulfoxides, transformation of generic fractions, and increases in amount of large

molecules (or molecular association), molecular weight and polydispersity. As a result of

those chemical changes, the mechanical properties of aged bitumens become more solid

like, as indicated by increased complex modulus and decreased phase angle (Lesueur, 2009).

In addition, Lee, Amirkhanian, and Kim (2009) prepared nine asphalt mixtures (three control,

three SBS-modified, and three rubber-modified) and used five short-term aging treatments

in order to study the effect of short-term aging. In terms of the effects of aging on asphalt

mixtures, as expected, the longer aging period and the higher aging temperature led to an

increase in the large molecular size (LMS) ratios.

Literature review

10


Many studies argued that short-term aging have a large effect on the rheological properties

of the binders. It could lead to an increase of the viscosity, softening point, and complex

modulus (G*), but on the other hand, it could decrease the phase angle and penetration (G.

D. Airey, 2003; Lee et al., 2008; X. Lu & Isacsson, 2002).

2.3 Bitumen Modification

Mixing polymers into bitumen has important consequences on the engineering properties of

bituminous binders. Pilot plant scale and laboratory scale mixers have been used for such

unit operation. Structural and chemical changes have been observed during the processing

of binders and straight bitumen. Chemical compatibility and processing conditions, such as

type of mixing or dispersing device, time and temperature, are crucial to obtain the desired

properties and stable compositions (García-Morales, Partal, Navarro, & Gallegos, 2006;

Pérez-Lepe et al., 2003).

Yet, the mechanical properties of asphalt mixtures depend to a large extent on the type and

quantity of asphalt used and hence it is imperative that a better understanding of asphalt

can be developed. Modifiers in the form of polymer, crumb tire rubber, fillers, among

others, are being added to asphalt in an attempt to improve its mechanical properties. As

each and every modifier can interact with asphalt in a widely different manner, the

complexity in modeling the constitutive behavior of modified asphalt is increased (Krishnan

& Rajagopal, 2005; Lesueur, 2009).

Generally, polymeric additives have been widely used to enhance the in-service properties of

bitumen. Polymers commonly used to modify bitumen include styrene–butadiene–styrene

copolymer (SBS), styrene–butadiene rubber (SBR), ethylene vinyl acetate (EVA),

polyethylene (HDPE, LDPE) and waste polymers (plastics from agriculture, crumb tire rubber,

among other). The characteristics of their mixing with bitumen may significantly affect the

technical properties of the resulting blend, as well as the costs of the whole operation

(Cuadri, Carrera, Izquierdo, García-Morales, & Navarro, 2014).

Literature review

11


2.3.1 Bitumen Modification as Anti-Aging Process

Most of the studies that argued the effect of bitumen modification on the short-term aging

changes seem to be attempts to improve the mixtures performance in order to resist that

short-term aging. They compared the characteristics, namely rheological and mechanical

properties, of the modified bitumen before aging and its characteristics after aging. They

also contrasted these characteristics with those of the pure bitumen. Apparently, these

characteristics, such as viscosity, ductility, and softening point, are supposed to be

connected to the effect of aging on asphalt materials.

Moreover, pure bitumen commonly tends to be more influenced by aging than the modified

bitumen. As a case study, Zhang and Yu (2010) compared the aging of polyphosphoric acid

(PPA) modified bitumen and pure bitumen (Figure 2-2).

Figure 2-2 Comparison between the aging of PPA modified bitumen and pure bitumen SK70 (F. Zhang

& Yu, 2010)

The results showed that the aging reaction rate of PPA-modified asphalt was lower than that

of original asphalt, the activation energy of PPA-modified asphalt was higher than that of

original asphalt, and the anti-aging performance of PPA-modified asphalt was better than

that of original asphalt.

Literature review

12


2.3.2 EVA and HDPE as Asphalt Modifying Polymers

Many studies manifested that due to the excellent engineering property and relatively low

cost, styrene–butadiene–styrene (SBS) has been widely applied in the modification of

bitumen and the aging of SBS modified bitumen has also been commonly examined (Durrieu,

Farcas, & Mouillet, 2007; Liu, Nielsen, Komacka, Greet, & Ven, 2014; S. p. Wu, Pang, Mo,

Chen, & Zhu, 2009; H. Zhang et al., 2011). Yet, ethylene vinyl acetate (EVA) and high-density

polyethylene (HDPE), which are the polymers used in this specific study, have also been used

as bitumen modifiers in some studies.

Burak Sengoz and Giray Isikyakar (2008) analyzed the mechanical properties of the hot-mix

asphalt (HMA) containing SBS and EVA polymer modified bitumens (PMBs) and compared

them with HMA incorporating base bitumen. They found that at low polymer contents, the

samples revealed the existence of dispersed polymer particles in a continuous bitumen

phase, whereas at high polymer contents a continuous polymer phase has been observed.

Polymer modification improved the conventional properties of the base bitumen such as

penetration, softening point, temperature susceptibility, among other.

Specifically, other studies investigated the effects of both addition of commercial EVA and

manufacturing mode on the performances of asphalt mixtures. Different concentrations of

EVA have been incorporated either in the asphalt bitumen 80/100 or during the Hot Mix

Asphalt production process. Three percentages of EVA by weight of optimum bitumen

content (estimated at 6%) were considered: 3%, 5% and 7%. Softening temperature,

penetration and Fraass breaking temperature tests indicate that EVA additions lead to an

increase in the stiffness and thermal resistance of the binders. Moreover, it was observed

that oxidative aging induces an increase in the hardness of the EVA modified bitumen

(Haddadi, Ghorbel, & Laradi, 2008).

The addition of EVA to the bitumen also resulted in an increase in the zero shear viscosity

and in the relaxation time of the PMB binders to be used in asphalt mixtures (Brovelli et al.,

2013).

Similarly, EVA modification increases binder stiffness and elasticity at high service

temperatures and low loading frequencies with the degree of modification being a function

Literature review

13


of bitumen source, bitumen–polymer compatibility and polymer concentration (Gordon D.

Airey, 2002).

Moreover, the viscoelastic properties related to the performance of a bitumen as a binder

for road pavement, are considerably improved when only 1% of recycled EVA or virgin EVA

CP-636 is added to the bitumen (González et al., 2004).

In the same context, Gar ıa-Morales et al. (2004) concluded that the viscoelastic properties

of bitumen at high temperatures are improved by adding recycled EVA copolymer in

amounts that depend on the bitumen penetration grade. Moreover, significant

microstructural changes, related to the development of a polymer-rich phase, tend to occur

in the bitumen as polymer concentration increases. These changes in microstructure have a

significant influence on the flow behavior of the binder and on its in-service performance.

At the same time, Pérez-Lepe, Martínez-Boza, and Gallegos (2005) studied the influence of

high-density polyethylene (HDPE) concentration on the rheological properties and

microstructure of HDPE-modified binders prepared in a rotor-stator mixing device. They

concluded that the addition of HDPE to bitumen enhances the mechanical properties of the

binders, especially in the high-temperature region, which is mainly interesting when some

pavements typically have permanent deformation problems.

Likewise, waste HDPE-modified bituminous binders provide better resistance against

permanent deformations due to their high stability and high Marshall Quotient. This solution

also contributes to the recirculation of plastic wastes as well as to the protection of the

environment (Hı ıslıoğlu & Ağar, 200 ).

Regarding the aging effect on EVA modified bitumens, Lu and Isacsson (2000) summarized

this effect using artificial aging on EVA modified bitumen and assessing the changes of its

characteristics. The effect of aging on the rheology of polymer-modified binders is strongly

dependent on the characteristics of polymers, and it was observed that aging increases the

complex modulus and the elastic response (decreased phase angle). The temperature

susceptibility is reduced by aging (Xiaohu Lu & Isacsson, 2000; Luo & Chen, 2011).

Literature review

14


2.4 Previous Work on Aging of Modified Bitumens

Some significant previous attempts were made to study the aging effect on modified

bitumens in different ways. In fact, various types of aging causes were analyzed, in order to

understand the trends of their effect on the modified binders.

2.4.1 Laboratory and In-Situ Aging

The main concept of the laboratory and in-situ aging is the attempt to represent either the

short-term or the long-term aging occurred in the field through procedures or tests in the

laboratory. Various factors could affect these attempts: the different parameters of the

aging process, the bitumen and aggregate type, the aging period that ought to be simulated,

and the effect of the binder-aggregate interaction on the aging of the mixtures (Bell, 1989;

Bell, Wieder, & Fellin, 1994; Huber & Decker, 1995; Liu et al., 2014).

In general, Bell (1989) claimed that the extended mixture heating was shown to be the most

promising procedure for short-term aging, and pressure oxidation or extended mixture

heating were the most promising procedures for long-term aging. He also argued that the

best test methods to evaluate the effects of aging mixtures include resilient modulus,

indirect tensile test, and dynamic modulus test, as well as tests on recovered asphalt.

Bell et al. (1994) demonstrated that the short-term procedure of exposing the mixtures in a

forced draft oven for 4 hours at 135 °C prior to compaction is adequate for the majority of

the field mixtures evaluated and conservative for some other mixtures. On the other hand,

Huber and Decker (1995) claimed that curing mixtures in an oven at 85 °C for 4 days could be

a procedure that represents the long-term aging occurred in projects of about 10 years old.

In addition, long-term oven aging of mixtures for 2 days at 100 °C was suggested specifically

for stiff mixes.

By taking into account the influence of UV radiations on the aging of SBS modified bitumen,

Durrieu et al. (2007) compared between laboratory and on site aging. They concluded that

the influence of UV radiation on the aging of the upper layers of surface courses of a

pavement cannot be totally ignored: it occurs rapidly and after 10 h of exposure to UV

Literature review

15


radiation the level of oxidation is the same as that reached after an RTFOT + PAV simulation

or that reached after one year of service in a pavement. Yet, another study (Liu et al., 2014)

was prepared to investigate the aging properties of the SBS modified bitumen from the

laboratory to the field. Results indicate that: (a) a 22-year field-aged binder had a higher

viscosity than the 9-day lab-aged (short-term) binder; (b) the field-aged binder had a similar

dynamic response with the 5-day lab-aged binder; (c) the Gel Permeation Chromatography

(GPC) result indicated that the applied lab aging produced have originated more asphaltenes

than the field aging.

2.4.2 Previous Methods to Evaluate Aging of Different Modified Bitumens

Araujo et al. (2013) studied the weathering aging of conventional asphalt binder and

styrene–butadiene–styrene (SBS), hydrated lime, reactive ethylene terpolymer (RET) and

polyphosphoric acid (PPA) modified asphalt binders. These modifiers represent the main

compounds used to obtain improved performance from asphalt binder. The degradation of

the samples was analyzed using Fourier transform infrared (FTIR) spectroscopy and thermal

analysis. The styrene–butadiene–styrene, polyphosphoric acid, and hydrated lime asphalt

binders showed a higher photo degradation resistance than the conventional asphalt binder

for aging times up to 200 h, considering the infrared spectroscopy results.

The ultraviolet (UV) aging properties of SBS modified bitumen appears to be affected by

organo-montmorillonite (OMMT). Zhang et al. (2011) observed that, as a result of UV aging,

both viscosity aging index and softening point increment (Figure 2-3) of OMMT/SBS modified

bitumen decrease significantly. There is a single phase trend in the morphology of the

bitumen after aging, which is accelerated by the existence of SBS.

They also found in another study, as a result of UV aging, that both viscosity aging index and

softening point increment of SBS modified bitumen decrease due to the introduction of

another additive (Na+-MMT), which can be further reduced under the influence of OMMT.

The micro-morphology of these types of binders becomes solid-like after UV aging (Henglong

Zhang, Yu, & Wu, 2012).

Literature review

16


Figure 2-3 Softening point increment of the binders after UV aging (H. Zhang et al., 2011)

B. Sengoz and G. Isikyakar (2008) examined the characteristics of the SBS polymer modified

bitumen aging using fluorescent microscopy and conventional test methods. The results

indicated that polymer modification improved the conventional properties (penetration,

softening point, among other) of the base bitumen and the mechanical properties (Marshall,

ITS, among other) of the corresponding mixtures. They also concluded that at low polymer

contents, the samples revealed the existence of dispersed polymer particles in a continuous

bitumen phase, whereas at high polymer contents a continuous polymer phase has been

observed. The aging indices decrease with increasing polymer content (Figure 2-4).

Figure 2-4 Aging indices corresponding to polymer content (B. Sengoz & G. Isikyakar, 2008)

Literature review

17


Expanded vermiculite (EVMT) clays modified bitumen can also be effectively used as a

modifier to improve the aging resistance of bitumen binders. EVMT modified bitumen may

form a phase-separated structure or an intercalated, and exfoliated nanostructure

(Henglong Zhang, Yu, & Kuang, 2012). As a result of the thin film oven test (TFOT) and situ

thermal aging, mass change rate and viscosity aging index are increased, while retained

penetration and ductility of binders decreased (Henglong Zhang, Xu, Wang, & Yu, 2013). The

variation of the different EVMT modified bitumen characteristics, like mass change rate

(MCR) and softening point increment Δ“ after in situ thermal aging comparing with

unmodified bitumen is shown in Figure 2-5.

Figure 2-5 MCR and Δ“ after in situ thermal aging (Henglong Zhang, Yu, & Kuang, 2012)

Moreover, flame retardant can also improve the aging resistance of asphalt binders

(Henglong Zhang, Shi, Han, & Yu, 2013). The flame retardancy of asphalt binder increased

after the RTFOT and PAV. The increasing amount of limiting oxygen index (LOI) decreased

with the flame retardants contents increasing (Figure 2-6).

The softening point and viscosity of asphalt binder increased and penetration and ductility of

asphalt binder decreased after two different types of aging procedures. Figure 2-7 shows the

decrease of penetration after these two types of short-term and long-term aging (Cong,

Chen, Yu, & Wu, 2010; Henglong Zhang, Shi, et al., 2013).

Literature review

18


Figure 2-6 LOI variation for different flame retardants contents (Henglong Zhang, Shi, et al., 2013)

Figure 2-7 Effect of aging on the penetration ratio of bitumens with different amounts of flame

retardant (Cong et al., 2010)

The effect of organic layered silicate on microstructures and aging properties of SBS

copolymer modified bitumen have also been investigated. Organic layered silicate SBS

modified bitumen shows the lower viscosity-aging index and the higher retained ductility. In

addition, the influence of organic layered silicate on these physical properties of SBS

modified bitumen before and after aging depends on its nature (Henglong Zhang, Zhu, Tan,

& Shi, 2014).

Literature review

19


Finally, a study concerning the use of crumb rubber modified bitumen (CRM) is also

presented. In general, the CRM binder partially loses its proportional elastic contribution at

higher temperatures, but such elastic contribution remains much higher than that of

unmodified binders (Mturi, O'Connell, Zoorob, & Beer, 2014). But with regard to the loss of

the penetration, softening point, ductility, viscosity, and weight loss, the crumb rubber

waste radiated by microwave and impregnated in epoxidized soybean oil (CRIMIESO)

modified asphalt was relatively less than CRM, indicating its relatively stronger performance,

namely concerning its resistance to aging (Yin, Wang, & Lv, 2013). The results of the viscosity

tests of the three modified asphalts are illustrated in Figure 2-8.

Figure 2-8 Viscosity ratio of three modified asphalt binders (Yin et al., 2013)

After presenting several previous works concerning the main topics of this research, it was

possible to define in more detail the materials to be studied and the test methods to be

used. That information is presented in the next Chapter of this thesis.

Materials and methods

21


3 MATERIALS AND METHODS

3.1 Basic Materials

3.1.1 Aggregates

The type of aggregates used in this study was a natural aggregate from granite rocks, which

is commonly used in the north of Portugal. Figure 3-1 shows the gradation curve of the

different sizes or fractions of aggregates (Error! Reference source not found.) used to

produce the studied mixture, as well as the AC 14 Surf specification envelope and the final

gradation used in the mixture.

Figure 3-1 Gradation curve for AC 14 Surf mixture produced in this study

Figure 3-2 Aggregates used to produce the asphalt mixture: (a) fraction 0/4; (b) fraction 6/14

0

10

20

30

40

50

60

70

80

90

100

0.01 0.10 1.00 10.00

Pa

ssin

g (

%)

Sieve size (mm)

AC14 Surf

envelopeFinal aggregates

mixtureFraction 10/14

Fraction 6/14

Fraction 4/6

Fraction 0/4

Fraction 2/4

Fraction 0.5/2

Filer


22


3.1.2 Binders

In this study, the following straight bitumen (B) and polymer-modified bitumens (PmB) were

used to study the short-term aging effect:

B1: a 35/50 penetration grade bitumen typically used in road construction supplied by

CEPSA company in Portugal.

PmB1: a 70/100 penetration grade bitumen supplied by CEPSA company in Portugal.

According to previous studies, this bitumen was modified by adding 5% of ethylene

vinyl acetate (EVA) polymer with a grain size of 4 mm (Figure 3-3). This was

manufactured in the laboratory by using a high shear mixer (Figure 3-4) at 7200 rpm

and a temperature of 165 °C for 20 minutes.

Figure 3-3 Polymers used to modify a 70/100 bitumen: (a) EVA; (b) HDPE

Figure 3-4 High shear mixer used to produce polymer modified binders


23


PmB2: a 70/100 penetration grade bitumen from CEPSA Company in Portugal. Again,

and according to previous studies, this bitumen was modified by adding 5% of

high-density polyethylene (HDPE) polymer with a grain size of 4 mm (Figure 3-3). This

was manufactured in the laboratory by using a high shear mixer (7200 rpm) at a

temperature of 170 °C for 20 minutes.

3.2 Methodology Overview

The properties of the three binders before aging (unaged binders) were characterized (B1,

PmB1, and PmB2) by carrying out the conventional binder specification tests, namely

penetration (EN 1426), ring and ball softening point (EN 1427), resilience (EN 13880-3), and

viscosity (EN 13302) tests according to EN 12591 and/or EN 14023 specifications (Figure 3-5).

Figure 3-5 Conventional tests specified for bitumen characterization: (a) Viscometer test; (b) Ring and

Ball softening point test; (c) Penetration test; (d) Resilience test

Subsequently, Rolling Thin Film Oven Test (RTFOT) was applied for 75 minutes at 163 °C to

age the three binders. Yet again, penetration, resilience, ring and ball, and viscosity tests

were carried out to characterize the rheological changes of the three aged bitumens.

Moreover, each one of the three different unaged bitumens (B1, PmB1, and PmB2) was used

to produce hot asphalt mixtures at 165 °C temperature. Six specimens of each asphalt

mixture were then compacted using the Marshall compactor (EN 12697-30), which were


24


later tested using the indirect tensile strength test (EN 12697-23) at 20 °C and 40 °C (three

specimens at each temperature). Afterwards, each type of binder used in the three asphalt

mixtures was recovered and, once again, the conventional binder specification tests were

conducted to obtain the changes of the basic properties of the three recovered bitumen.

Consequently, the rheological changes for all the states (unaged, RTFOT aged, and recovered

from mixtures after short-term aging) of the three studied bitumens were tested by using

the Dynamic Shear Rheometer (DSR) test (EN 14770).

The aging was additionally evaluated using Fourier transform infrared spectroscopy (FTIR)

for the three binders (B1, PmB1, and PmB2) for the unaged binders and after they are

exposed to RTFOT, as well as after the recovery process.

The differential scanning calorimetry (DSC) was also applied to determine the thermal

behavior (transition or melting temperatures) of B1, PmB1 and PmB2 in their different

states: unaged, after RTFOT, and after recovery process. However, it was essentially used to

determine the presence of the polymers in PmBs after the recovery process.

Finally, it is suggested to expose the same mixtures to an extended curing temperature of

163 °C for two hours (all their results are de oted ’ ). This method was recommended to

roughly characterize the long-term aging changes on the exposed binders. Six specimens

were compacted for B1, PmB1, and PmB2 after that curing time, following the procedures

previously presented for the mixtures without extended aging time. The voids ratios of the

specimens were obtained and they were also evaluated in the indirect tensile strength test.

3.3 Testing Programme

3.3.1 Specimens Preparation

A continuous grading Hot-Mix Asphalt (HMA) AC 14 Surf (Figure 3-1) was selected as being

the most common mixture in Portugal, to manufacture eighteen Marshall specimens using

the three different types of binders (B1, PmB1, and PmB2) mentioned previously (six

samples for each binder). The HMA had a maximum aggregate size of 20 mm and 2.5%

limestone commercial filler content (Figure 3-6).


25


Figure 3-6 Commercial filler used in the mixture

Asphalt specimens of 102 mm in diameter and an average height of 60.3 mm were

manufactured with binder content of 5% of the total weight of the mixture. The mixtures

were produced at a mixing temperature of 165 °C, being mixed for two minutes, and

compacted with a typical number of 75 blows on each side of the specimen (Table 3-1).

Table 3-1 Quantities of each material or aggregate fraction used to produce the asphalt mixtures

Fraction (mm) Material used (%) Weight (g)

10/14 10.5 × 95.0 1893

6/14 29.0 × 95.0 5227

4/6 11.0 × 95.0 1983

0/4 36.0 × 95.0 6489

2/4 8.0 × 95.0 1442

0.5/2 3.0 × 95.0 541

Commercial filler 2.5 × 95.0 451

Bitumen 5.0 949

Total 100.0% 18974

3.3.2 Volumetric Properties

The maximum theoretical density (��) and the air voids content (� ) for the all specimens

were obtained to study the volumetric properties of the specimens. These values were

found by using the saturated surface dry (SSD) water displacement method (EN 12697-6,

2012).


26


3.3.3 Indirect Tensile Strength (ITS) Test

The correlation between the deformation of the specimens and the indirect tensile strength

was assessed at two temperatures: 20 °C and 40 °C (in order to evaluate the performance at

medium and high in-service temperatures, at which cracking or rutting problems typically

occur). These values were obtained by using the Indirect Tensile Strength test (ITS) at a

loading rate of 50 mm/min since the specimens were laboratory-fabricated (Figure 3-7).

Figure 3-7 Indirect tensile testing frame (ITS)

Eighteen specimens were tested, being each six of them for one type of binder (B1, PmB1,

and PmB2), and then each three of the six were tested at each test temperature. In this case,

the deformation and the indirect tensile strength are denoted by def. and ITS respectively.

However, this process was then repeated in another eighteen specimens produced and

compacted after the mixtures were exposed to an extended curing temperature of 163 °C

for t o hours those results are de oted def.’ a d IT“’ . This ethod as re o e ded

to roughly assess the mechanical changes on the exposed binders after long-term aging of

the asphalt mixtures.

The reason why the ITS was carried out also at a temperature of 40 °C (not typically used in

this type of test) is that it could be interesting to assess the deformation and indirect tensile

strength for the mixtures with the polymer-modified binders (PmB1 and PmB2) at high


27


temperatures, because it might be significant to evaluate the rut resistance of the

corresponding HMA mixtures (HA, 2011). Furthermore, the temperature of 40 °C was

selected to represent the strength of the mixtures at high temperatures and below the

softening point of the conventional bitumen.

3.3.4 RTFOT Aging Method

As mentioned before, the Rolling Thin Film Oven Test (RTFOT) (Figure 3-8) was applied for

75 minutes to age the three binders, simulating the short-term aging according to the

standards (EN 12607-1, 2007). Many studies have claimed the validity of using RTFOT to age

unmodified bitumen. Yet, using RTFOT to age modified bitumen still open in doubt (Mouillet

et al., 2008). However, because it appears that there is no better method to simulate short-

term aging for modified binders, RTFOT was used in this study to simulate the short-term

aging of B1, PmB1 and PmB2. The mass loss of the binder, after it is exposed to RTFOT, was

determined by weighting two samples of binder before and after RTFOT.

Figure 3-8 Rolling thin film oven test (RTFOT)

The RTFOT was developed by the California Division of Highways and involves rotating eight

glass bottles each containing 35 g of bitumen in a vertically rotating shelf, while blowing hot

air into each sample bottle at its lowest travel position. During the test, the bitumen flows

continuously around the inner surface of each container in relatively thin films of 1.25 mm at


28


a temperature of 163 °C for 75 min. The vertical circular carriage rotates at a rate of

15 revolutions/min and the airflow is set at a rate of 4000 ml/min. The method ensures that

all the bitumen is exposed to heat and air and the continuous movement ensures that no

skin develops to protect the bitumen (G. D. Airey, 2003).

3.3.5 Binder Recovery Method

According to EN 12697-3 (2013), the extraction method used in this study was the

separation by centrifuge using the toluene as a solvent. Afterwards, the rotary evaporator

was used in the vacuum distillation process to separate the binder from the solvent at a

maximum temperature of 150 °C (Figure 3-9).

Figure 3-9 Rotary evaporator

These recovered aged binders were tested after that process to characterize viscosity,

penetration, ring and ball softening point, and resilience, as well as rheology in the DSR, DSC

and FTIR. These results will be used to understand the changes caused by aging in the

bitumen recovered from mixtures after the short-term phase of production and compaction,

which is also important for comparison with RTFOT results.


29


3.3.6 Dynamic Shear Rheometer (DSR)

According toEN 14770 (2012), this test in the DSR (Figure 3-10) is used to compare the

rheological behavior of the different binders before aging, after RTFOT aging, and after

asphalt binder recovery from the short-term aged mixtures produced in laboratory. The

temperature dependency (19 - 88 °C) of the phase angle, of the complex shear modulus

(G*), and of the complex viscosity of the several binders under evaluation was studied in this

phase of the work.

Figure 3-10 Dynamic shear rheometer (DSR) used in this work

This test applies the most commonly used method of fundamental rheological testing of

bitumen, which is the means of dynamic mechanical analysis (DMA) using oscillatory-type

test within the region of linear viscoelastic response (Luo & Chen, 2011). Measurements of

the rheological properties were conducted in a strain controlled rotational DSR with parallel

plate sample geometries of 25 mm diameter and 1 mm gap for the temperatures within the

range of 46 to 88 °C, and sample geometries of 8 mm diameter and 2 mm gap for the

temperatures within the range of 19 to 40 °C.


30


3.3.7 Fourier Transform Infrared Spectroscopy (FTIR)

FTIR is used to measure the infrared (IR) light absorbed by the material (Figure 3-11). The

samples should be prepared according to EN 12594 (2007). Five percent by weight solutions

of bitumens were prepared in carbon disulfide and tested in the spectral range between

4500 and 400 cm-1 with steps of approximately 1 cm-1 (BRRC, 2013).

Figure 3-11 Fourier transform infrared spectroscopy (FTIR) equipment

Results of FTIR were analyzed to evaluate the aging of the binders after RTFOT and after the

recovery process. Two peaks centered around 1,700 cm-1 and 1,030 cm-1 were determined

for the oxidation of bitumen because of aging: the first peak corresponds to carbonyl

functions, whereas the second one characterizes sulfoxides (Lamontagne, Dumas, Mouillet,

& Kister, 2001; X. Lu & Isacsson, 2002; Mouillet et al., 2008; S. p. Wu et al., 2009; F. Zhang,

Yu, & Han, 2011).

3.3.8 Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry (Figure 3-12) is a technique used to determine the change

of the difference in the heat flow rate (Höhne, Hemminger, & Flammersheim, 2003),

typically associated with transition temperatures of the material. DSC can be used to

characterize the thermal behavior of pure bitumen as well as the thermal behavior of


31


modified bitumens, by indicating the presence of specific crystalline components in the

PMBs (Gordon D. Airey, 2002).

Figure 3-12 Differential scanning calorimetry (DSC) equipment

However, in this study, this technique was mainly used to determine the presence or

absence of polymers in the binders (EVA and HDPE, respectively in PmB1 and PmB2) after

the recovery process. According to ISO 11357-4 (2014), the heating and cooling rate to apply

during the test should be 10 °C/min. It is also recommended to run a sample twice in DSC.

Each sample is heated and cooled, and then the sample is heated again to obtain the DSC

curve for analysis (Leng, 2013). From this technique, the values of temperature (°C) and heat

flow (mW) can indicate the presence of polymers in the binder after the recovery process

(only if the polymer melting-point in the DSC curve of the recovered bitumen is similar to

that of the polymer modified bitumen used to produce the corresponding mixture).

Tests results and discussion

33


4 TESTS RESULTS AND DISCUSSION

4.1 Mass loss in RTFOT

The mass loss of the binder was measured after exposing of two samples of binder to the

RTFOT test. This test does not evaluate the real performance of the binder after aging, and

thus it was decided to carry out this test only in binder PmB2 to have a general idea of its

value for a polymer modified binder (an average value of 0.27 % was found for the mass

loss). Some specifications recommended that the mass loss should not be more than 1.0 %,

and thus the obtained value is not considered high (HA, 2011). This means that this binder

might not be exposed to excessive age hardening, shrinkage and cracking since that a low

amount of light oil is being volatized during RTFOT (HA, 2011).

4.2 Volumetric Properties of Studied Mixtures

The volumetric properties of the asphalt mixtures are vital as they are related to the mixture

performance. It has been indicated that a higher air voids content lead to a higher rate of

aging process and water sensitivity and, consequently, a less durable mixture (Kandhal,

1996). This implies that volumetric properties have a significant influence on the service life

of asphalt mixtures.

As shown in Table 4-1, the results of the volumetric properties indicates a higher maximum

theoretical density (ρth) for polymer modified binder mixtures (PmB1 and PmB2) than the

unmodified binder mixture (B1). In addition, the average air voids for PmB2 mixture is the

highest in comparison to the PmB1 and B1 mixtures.

In fact, it has been presumed that a mixture of a high density implies a low air voids (Mallick

& El-Korchi, 2013), and this was generally observed in this work. In the case of PmB2

mixture, the air voids values are relatively high, and this may be caused by the higher

viscosity of this binder at higher temperatures due to the use of HDPE (the used polymer

with higher melting temperature), which may be hampering the compaction of this mixture.

Table 4-1 Volumetric properties of the studied mixtures


34


Asphalt mixture with binder: B1 PmB1 PmB2

ρth (kg/m3) 2501.7 2508.2 2508.5

ρ (kg/m3) 2361.6 2375.3 2342.9

ρ' (kg/m3) 2351.6 2337.6 2322.9

Average Vv (%) 5.6 5.3 6.6

Average Vv’ (%) 6.0 6.8 7.4

The density of the polymers (ρHDPE = 0.95 to 0.97 g/cm3 (Chen, Chen, & Hsu, 2006) and ρEVA =

0.90 g/cm3 (Simpson et al., 1997)) used to modify the binders have a small influence, due to

the small amount of this material in the final mixture (only 0.25 %).

The volumetric results indicate that the durability of the PmB1 mixture is expected to be the

best one in comparison with B1 and PmB2 mixtures, since it has the highest density and the

lowest air voids (at least before the extended curing time in the oven). In turn, the lower

density of the PmB2 mixture may increase the potential of aging and hence increase the

potential of fatigue deterioration, as mentioned by Mallick and El-Korchi (2013).

Table 4-1 also shows the specimens results of the voids ratio after they have been

additionally hardened at a temperature of 163 °C for an extended curing time of two hours.

Results show that the voids ratios were considerably increased when the mixtures become

stiffer. The highest rate of increase was in PmB1, even though it has only increased to a void

ratio value similar to that of PmB2 before the two-hour of hardening.

4.3 Indirect Tensile Strength (ITS)

ITS is a test that applies an axial force to characterize the stress-strain relation of an asphalt

material. It is typically used to characterize the resistance of the hot mix asphalt (HMA) to

the low-temperature cracking. However, it may also be used to evaluate the quality of the

mixtures and assess its potential for cracking and rutting (Christensen & Bonaquist, 2004).

There are some factors that may affect the test results: size and dimensions of the specimen,

composition and dimensions of the loading strip, rate of loading, load-deformation

characteristics of the material tested, and testing temperature. The first three factors are

considered constant in this study.


35


The most frequent modes of failure of each type of specimens after the two-hour hardening

(used to roughly simulate the long-term aging) are given in Figure 4-1.

Figure 4-1 Modes of failure (a) B1, single cleft failure (b) PmB1, ideal failure (c) PmB2, localized

crushing failure

These modes of failure indicated the way that the tensile stress distributed along the

sample. The failure in B1 mixtures occurred on the bottom side of the cylinder which was the

side loaded with the moving head of the machine. A shear failure is approximately

intersecting the loaded diameter in PmB1 (which is the ideal failure, with an additional

transversal contribution of the binder to the mixture strength), in addition to a localized

crushing with ultimate failure in tension in the case of PmB2 (Hudson & Kennedy, 1968).

As Figure 4-2 and Figure 4-3 sho , the results of IT“’ after extended aging (long-term aging),

either at 20 °C or 40 °C, are higher than those of ITS just after mixing (short-term aging) since

the mixtures were additionally hardened when exposed to a temperature of 163 °C for two

hours. When the mixtures were hardened, they become stiffer but more brittle.

Consequently, at 20 °C, the results of def.’ de reased after that additional hardening except

for PmB1. At 40 °C, the result of def.’ only decreased in the case of PmB2, hilst def.’

increased for B1 and PmB1. Whatever the case, it appears that the base binder used to

produce the PmBs is more decisive at the temperature of 20 °C, whereas the importance of

the polymer in ITS tests is mainly shown at higher temperatures (40 °C) or when the


36


mixtures are additionally hardened. In fact, this can be justified because ITS applies a tensile

stress to the specimen and the calculated deformation is the one that results indirectly from

the failure due to tension (Hudson & Kennedy, 1968).

Figure 4-2 Results of ITS testing of the several mixtures at 20 °C (with or without extended aging)

Figure 4-3 Results of ITS testing of the several mixtures at 40 °C (with or without extended aging)

PmB2 tends to have a tough behavior, since the more it becomes stiffer due to aging (i.e. ITS

value i reases to IT“’ value), the corresponding failure deformation decreases. Moreover, it

has high ratios of ITS stiffening due to aging (from 1476 to 1756 kPa and from 399 to 566 kPa

respectively at 20 °C and 40 °C). For instance, at 20 °C, when the value of ITS increased by

1878

1656

1476

2163

1686 1756

2.6

2.4

2.5

2.4

2.5

2.3

2.0

2.1

2.2

2.3

2.4

2.5

2.6

0

400

800

1200

1600

2000

2400

B1 PmB1 PmB2

20 °C

De

form

ati

on

(m

m)

ITS

(k

Pa

)

ITS (kPa) ITS' (kPa) Def. (mm) Def.' (mm)

399

457

393

589533

566

2.3 2.3

2.1

2.4

2.4

2.0 2.0

2.1

2.2

2.3

2.4

2.5

2.6

0

100

200

300

400

500

600

700

B1 PmB1 PmB2

40 °C

De

form

ati

on

(m

m)

ITS

(k

Pa

)

ITS (kPa) ITS' (kPa) Def. (mm) Def.' (mm)


37


nearly 20 % (from 1476 to 1756 kPa), the deformation decreased from 2.5 to 2.3 mm. In

contrary, PmB1 seems to have an elastic recovery tendency, considering that it has lower

ratios of ITS stiffening due to aging, while the failure deformation increases. It also appears

that the neat bitumen B1 has a tough behavior at a temperature of 20 °C, and some elastic

recovery tendency at a temperature of 40 °C.

When the effect of the polymer show up, i.e. at the temperature of 40 °C, it seems that

adding EVA to PmB1 protects the binder from hardening (ratio of IT“’ to IT“) more effectively

than HDPE did in PmB2 binder. In addition, the reduction in the stiffening ratio do to

extended aging between the ITS results at 20 °C or 40 °C are remarkably lower in PmB1

binder than in PmB2, thus showing the protective effect of EVA even at 20 °C.

However, it should be noticed that PmB2 has the highest void ratio, thus being less resistant

to deformation. On the other hand, PmB1 has a lower void ratio, which certainly improves

its capacity to resist deformation before failure. Moreover, when the mixtures were

hardened for two hours, the void ratio of PmB1 increased but its value (6.8 %) is only slightly

higher than that of PmB2 void ratio before the two-hour hardening (6.6 %).

4.4 Rheological Measurements

Generally, the rheological properties of the binders vary with the temperature. In the warm

weather, the binder becomes softer while in the cold weather it becomes harder. Thus,

bitumen has an elastic or viscous behavior, depending on temperature. At sufficiently low

temperatures, bitumen tends to behave as an elastic solid. As temperature increases, the

viscous property of bitumen becomes more dominant. Therefore, bitumen is essentially a

Newtonian liquid at sufficiently high temperatures (Lesueur, 2009; X. Lu & Isacsson, 2002).

However, it is noteworthy to mention that most of the rheological models were intended to

explain the unmodified bitumen (pure binder, such as B1 in this study) and not for PmBs (like

PmB1 and PmB2 in this study). Still, the conventional tendency of the pure (unmodified)

i ders’ eha ior ould e adapted to P Bs, but by adding new factors (Lesueur, 2009).

Figure 4-4, Figure 4-5, and Figure 4-6 show that the phase angle of the several binders

decreases with aging (after-RTFOT aging), while the complex modulus (G*) increases. This


38


implies that aging will make asphalt reveal more elastic and tough properties, and decrease

the permanent deformation of asphalt pavement (Tian, Zheng, & Zhang, 2004). It can also be

seen that the change of the phase angle and G* after-RTFOT aging is dissimilar at different

temperatures. In any case, X. Lu and Isacsson (2002) mention that aging after-RTFOT has a

minimal effect on phase angle and G* in comparison with other effects (e.g. temperature).

Figure 4-4 Rheological properties of B1 bitumen (phase angle and G*)

Figure 4-5 Rheological properties of PmB1 binder (phase angle and G*)


39


Figure 4-6 Rheological properties of PmB2 binder (phase angle and G*)

In the case of B1, after-recovery curves (phase angle and G*) show that the binder tends to

be less solid-like in its behavior comparing to its behavior after-RTFOT. The phase angle

curve in the low temperatures (15 to 35 °C) seems to be slightly inconsistent since the

behavior of the bitumen is considered as non-Newtonian fluid. It could also be caused by

test configuration problems of DSR at low temperatures, such as the possibility of the

sample to slip out in the 8 mm plate or the existence of micro cracks in the bitumen sample.

However, in the case of PmBs (PmB1 and PmB2), after-recovery curve surprisingly have

higher values than the unaged curve for phase angle and lower ones for G*. In fact, as the

short-term aging happened due to the production and compaction processes, the phase

angle is expected to decrease, while G* is expected to increase. This unexpected result is

discussed later in section 4.7 and 4.8. Anyway, at a temperature of nearly 20 °C, the phase

angle of PmB2 after-RTFOT (nearly 48°) is slightly higher than that of PmB1 (nearly 45°),

which means that the fatigue performance of PmB2 could be at least as good as that of

PmB1, and not as tough as previously observed. On the other hand, at a temperature of

nearly 50 °C, PmB1 has better permanent deformation properties than PmB2, since the

phase angle of PmB1 after-RTFOT (nearly 54 °C) is lower than that of PmB2 (nearly 67 °C).

Additionally, the plateau region of the phase angle can be determined more easily in PmB2

than in PmB1, and it started at a relatively lower temperature in PmB2 (nearly 76 °C). This

region could be used as an indication of the damage of polymeric network structure in the

bitumen (S. p. Wu et al., 2009), i.e., when the binder becomes more fluid.


40


4.5 Viscosity Results

The complex viscosity was obtained by testing the binders in DSR at lower temperatures (19

to 88 °C), while the dynamic viscosity was found in the rotational viscometer at high

temperatures (100 to 180 °C), as it can be observed in Figure 4-7, Figure 4-8 and Figure 4-9,

respectively for binders B1, PmB1 and PmB2.

Figure 4-7 Viscosity of B1 bitumen in the DSR and in the rotational viscometer

Figure 4-8 Viscosity of PmB1 binder in the DSR and in the rotational viscometer


41


Figure 4-9 Viscosity of PmB2 binder in the DSR and in the rotational viscometer

Results obviously show that when the binders are exposed to RTFOT, the viscosity increased

because of aging (hardening). Binders (B1, PmB1, and PmB2) become stiffer after exposed to

RTFOT, which decreased their flexibility and reversible deformation capacity. At traditional

mixing temperatures of nearly 160 °C, PmB2 has a higher viscosity value than PmB1 based

on the viscosity of base bitumen 70/100 grade penetration. This means that the amount of

aging effect on PmB2 was greater than on PmB1, confirming that PmB2 is stiffer than PmB1.

Likewise, at the regular in service temperature in the pavement (nearly 25 °C), PmB2 is

stiffer than PmB1 as the viscosity of PmB2 is slightly higher than viscosity of PmB1. Once

again, after-recovery results for B1 are higher than unaged results but lower than

after-RTFOT results. However, this is not the case regarding after-recovery results of polymer

modified binders. As said before, this will be explained in detail in sections 4.7 and 4.8.

A formula has been recommended, namely the Aging Index, with the purpose of evaluating

the effect of aging on binders. Aging Index is defined by the means of the ratio of

physical/rheological parameter of the aged bitumen to that of the original unaged bitumen.

Consequently, the viscosity aging index (VAI) is the evaluation of the change in the viscosity

after and before aging, in other words, evaluation of aging extent on the viscosity of bitumen

(Henglong Zhang, Yu, & Wu, 2012). The VAI value can be computed with Equation 1.

�� = � � � � −� � � �� × % (1)


42


In this study, the aged viscosity values (Figure 4-10) are considered as being the values of the

viscosity after the aging simulation in RTFOT, since their results are deemed sensible.

Figure 4-10 VAI values obtained with the viscosity results from DSR and from rotational viscometer

In fact, the values of recovered modified binders are considered unreasonable and senseless

si e the re o ered i ders’ is osit is supposed to e larger tha the u aged i ders’

viscosity for all types of bitumen. The process of mixing the binder with aggregates and

compacting the corresponding mixtures often hardens the bitumen, which leads to an

increase on its viscosity. Hence, this is what happened in the case of the recovered

unmodified binder B1. On the contrary, the results of the recovered modified binders (PmB1

and PmB2) show that their viscosity is lower than that of the unaged modified i ders’

viscosity. Consequently, it is concluded that there is a problem in the recovered process,

probably because the solvent used to recover the binders is not sufficiently efficient to melt

the polymers in the case of the modified binders (PmB1 and PmB2). In order to examine this

hypothesis, two tests were suggested: FTIR and DSC tests (section 4.7 and section 4.8).

According to Figure 4-10, VAI values resulting from the viscosity obtained by DSR is greatly

higher than VAI values resulting from the rotational viscometer for B1, PmB1, and PmB2.

This could mean that as the temperature (20 to 90 °C) decreases, the effect of aging is more

easily measured. This could be also refer to the fact that the change of the viscosity with

temperature is greater at low temperature than at high temperatures (Hraiki, 1974). It could

also result from using different test configuration (i.e. the parallel plates test could be more

450

328

125

5276 90

0

100

200

300

400

500

B1 PmB1 PmB2

VAI (%) by DSR VAI (%) by Viscometer


43


sensitive to aging than the rotating spindle apparatus). B1 has the greatest vulnerability to

aging in the lower temperature, whereas PmB2 has the greatest vulnerability to aging in the

higher temperature. In any event, PmB2 could be considered as the most resistant to aging

between the three studied binders, as the VAI value obtained in the DSR is significantly

lower than those of the other binders. Although the VAI value of PmB2 in the viscometer is

the highest one, it is noticed that it is only slightly higher than those of the other binders.

Based on this viscosity analysis, it seems that HDPE provided a higher extent of protection

from short-term aging to PmB2 than EVA did to PmB1. In fact, these magnitude of variations

has not a specific behavior, being dependent on the bitumen behavior and the evaluation

conditions (X. Lu & Isacsson, 2002).

4.6 Softening point, Penetration, and Resilience Results

The applications of the bitumen binders are classified depending on its consistency. For

example, it is recommended to use the higher penetration bitumen in cold climate whilst the

smaller penetration bitumen should be used in hot climate. In general, lower penetration

indicates a harder bitumen. Resilience of the binder is also a vital property to assess its

elastic recovery. As a matter of fact, higher softening point and higher resilience lead to

higher resistance to rutting and surface initiated cracks, as well as the reduction of fatigue or

reflection cracking (Mashaan, Ali, Karim, & Abdelaziz, 2012). Results for B1, PmB1, and PmB2

are summarized in Figure 4-11, Figure 4-12, and Figure 4-13, respectively.

Figure 4-11 Base properties of B1 bitumen

54.8

34.9

5.0

60.3

21.1 21.0

56.0

29.3

14.0

0.0

20.0

40.0

60.0

80.0

Ring & Ball (°C) Penetration (1/10 mm) Resilience (%)

B1Unaged Aged Recovered


44


Figure 4-12 Base properties of PmB1 binder

Figure 4-13 Base properties of PmB2 binder

For B1 results, it is obvious that the binder is aged after being exposed to RTFOT and after

recovering from the mixture production process. Hence, the softening point and resilience

increased, and the penetration decreased. Yet, the rate of aging after RTFOT is higher than

the rate of aging after mixture recovery. This can mean that the rate of aging in the field is

well simulated by RTFOT, but it is higher than the short-term rate of aging due to the

production of mixtures in laboratories (Lesueur, 2009). This could be happening because the

Marshall automatic impact compactor, which was used in this study, is relatively poor to

simulate the field compaction (Khan, Al-Abdul Wahab, Asi, & Ramadhan, 1998).

From Figure 4-12 and Figure 4-13, it seems, from the unaged PmB1 and PmB2 results, that

adding EVA (PmB1) or HDPE (PmB2) to 70/100 penetration grade bitumen had, to a certain

extent, the same effect on the softening point and penetration properties. However, the

48.7

75.3

0.0

61.5

43.0

28.0

67.5

27.0 30.0

56.0

42.1

13.0

0.0

20.0

40.0

60.0

80.0


PmB1Unaged unmodified 70/100 Unaged Aged Recovered

48.7

75.3

0.0

58.0

39.6

9.0

67.6

20.915.0

51.8 52.5

14.0

0.0

20.0

40.0

60.0

80.0


PmB2Unaged unmodified 70/100 Unaged Aged Recovered


45


percent of increasing of the resilience was considerably higher by adding EVA than HDPE.

Therefore, it could be assumed that PmB1 has more ability to resist the aging changes than

PmB2 (Campbell, 2008). Again, when the modified binders were exposed to RTFOT, the

binders aged, and thus, the softening point and resilience increased but the penetration

decreased. What could be noteworthy is that, based on the resilience results for PmB1 and

PmB2 after RTFOT, it could be mentioned that the global rate of aging effect on the case of

PmB1 is higher than PmB2.

Concerning on the results of the polymer-modified recovered binders properties (PmB1 and

PmB2), the results are supposed to indicate that the binders were aged after mixing process.

On the contrary, the results unexpectedly are not even in the range of after-RTFOT results

and unaged results. This could imply that the solvent was not efficient enough to extract the

polymer with the bitumen in the recovery process. Again, it was suggested to carry out DSC

and FTIR tests in order to examine this hypothesis, which is discussed later in sections 4.7

and 4.8. However, based on the unmodified 70/100 penetration grade bitumen (the base

bitumen for PmB1 and PmB2), it could be concluded that the addition of HDPE polymer may

be more protective from bitumen aging during the mixing process than the EVA polymer.

Based on the definition of Aging Index, Softening Point Index (SPI) is defined by the change

of the softening point property of a binder after and before the aging (Henglong Zhang, Yu,

& Wu, 2012). SPI can be computed with Equation 2.

SPI = Aged softening point value − Unaged softening point value (2)

The same concept is applied to evaluate the penetration effect. Hence, Penetration Index

(PI) is computed with Equation 3.

PI = |Aged penetration value − Unaged penetration value| (3)

Similar to the unaged viscosity values and for the same reason, the unaged values of the

softening point and penetration in this study are considered as the values of the softening

point and penetration for the binders after exposed to RTFOT aging.


46


Figure 4-14 illustrates the results of SPI and PI for the three different binders: B1, PmB1, and

PmB2. A smaller change in the SPI and PI indicates that the material has more resistance to

the effect of aging (Henglong Zhang, Yu, & Wu, 2012). Apparently, the lowest influence of

aging is in binder B1, which means that based on these two parameters (penetration and

softening point) B1 has more resistance to aging than both polymer modified binders PmB1

and PmB2. Still, this not imply that the added polymers (EVA to PmB1, and HDPE to PmB2)

were ineffective to protect the binder from aging, since the base bitumen for PmB1 and

PmB2 is a softer 70/100 penetration grade, different from B1 binder (35/50 penetration

grade). Furthermore, the differences between B1 and PmB1 results are relatively small.

Figure 4-14 SPI and PI values for B1, PmB1, and PmB2 binders

In spite of this, the effect of aging after adding EVA or HDPE to the same base binder (PmB1

and PmB2) could be compared. Based on these basic properties results, it appears that

PmB1 has more resistance to aging than PmB2, and thus adding EVA to the base binder

protects it from aging more effectively than adding HDPE. Thus, PmB1 could be considered

to have the best performance of resist aging comparing to B1 and PmB2. This result is

contradictory to that of the viscosity analysis, which means that aging assessment of

polymer modified binders is quite dependent on the type of test used.

4.7 Differential Scanning Calorimetry (DSC) Results

PmB1 and PmB2 were subjected to DSC testing in the three phases: unaged, after RTFOT,

and after recovery. From the resulting measurements (Figure 4-15), it is illustrated that the

5.5 6.0

9.6

13.8

16.0

18.7

0.0

5.0

10.0

15.0

20.0

B1 PmB1 PmB2

SPI PI


47


glass transition temperature (Tg) for the PmB1 and PmB2 started at a very low temperature

(nearly at -30 °C). Above Tg, more than one transition phase occurred (nearly at 30 °C),

which was considered due to the crystallization of species that have not crystallized during

cooling (Lucena, Soares, & Soares, 2004).

Figure 4-15 DSC curves for PmB1 and PmB2 binders

However, the critical evaluation here is to determine the presence of the polymer in the

binder (EVA and HDPE in PmB1 and PmB2 respectively) after the recovery process. In the

case of PmB1, it was generally shown that the EVA melting point is between a range of 48 to

70 °C (Gordon D. Airey, 2002; Brule & Gazeau, 1996). Consequently, Figure 4-15 shows that

the melting point occurred in DSC curves of unaged and after-RTFOT PmB1 at a temperature

of nearly 54 °C, whilst it did not occur in the after-recovery DSC curve. This implies that EVA

was absent in the PmB1 binder after recovery process.

With regard to PmB2, it is revealed that the melting point of HDPE is nearly 125 °C (Wei,

Thompson, Park, & Chen, 2010). Once again, this melting point occurred in DSC curves of the

unaged and after-recovery PmB2 at a temperature of nearly 123 °C and did not appear in the

after-recovery DSC curve, which means that there was no presence of HDPE in the binder

PmB2 after recovery process. Consequently, based on these facts, it seems that the solvent

is capable of extract the bitumen, but it is not able to extract the polymer from the asphalt


48


mixtures. It could obviously be concluded that the unexpected and extraordinary results

formerly obtained (i.e. penetration, softening point, resilience, G*, phase angle, and

viscosity) for the after-recovery behavior of PmB1 and PmB2 refers to the fact that these are

only the results of the bituminous part (based 70/100 binder after aging), which was

rejuvenated of PmB1 and PmB2 since the polymer was not recovered in the process.

It can be seen from Figure 4-15 that there are no conclusive effect of polymer aging after

RTFOT on polymers of PmB1 and PmB2 as their melting temperature almost remained the

same after RTFOT aging. Aging impact was clearly shown in the bituminous part of binders in

the previous results, with no robust evidence of impact on the polymers.

However, it can be noticed that the slope of the DSC curve of the after-RTFOT PmB2 binder

is not increasing, in contrast to the slope of the unaged PmB2. This should be most likely

caused by a technical matter related with the equipment, but roughly in the same trend of

the unaged curve of PmB2. Mainly, it should be observed that the melting point of HDPE

occurred almost in the same temperature of the unaged curve of PmB2.

Nevertheless, it has been shown that the key point of the recovering of the binders from the

asphalt mixture is the extraction process. This process has two basic stages: total separation

of the binder from the aggregate, and, then, using solvent to eliminate the fines inside the

bitumen. As an example, perchloroethylene was already used as a solvent to eliminate fines.

Yet, some studies have concluded in that the solvent efficiency was very low, and they tried

to develop new protocols or modify methods to extract binders from mixtures (Chitla, 1996;

Kano, Akiba, Kuriyagawa, & Kawai, 2005; Lopes et al., 2014; Ma, Mahmoud, & Bahia, 2010).

For instance, Kano et al. (2005) used high-temperature and high-pressure water to remove

the binder from the asphalt mixture. They found that this method is a valuable method to

recover oil resources and recycle aggregate from the asphalt mixture waste. Furthermore, a

modified technique, namely ARRB TR (Australian Road Research Board Transport Research)

was applied at elevated temperatures and the results showed that it recover bitumen with

negligible solvent concentration percent in the final product (Chitla, 1996).

It is also worth mentioning that a study was conducted by Nösler, Tanghe, and Soenen

(2008) to evaluate the effect of recovery process on the properties of the polymer-modified

bitumen. They used several solvents, namely methylenechloride, trichloroethylene, and


49


toluene, for three different asphalt mixtures manufactured using SBS-modified binder. Their

penetration results for recovered binders were sensible, but the results of softening point

were unreasonable. In any case, even opposing to the standard EN 12697-3 (2013), they

heated the mixtures to 160 °C before starting the separation step in the centrifuge and they

added the solvent (trichloroethylene or toluene) when the temperature of the mixture was

80 °C. Consequently, this could increase the aging of the binders before starting the

separation, and the volatilized percent of the solvents increased since the vapor pressure in

the case of toluene, as example, is significant (2900 Pa at 20 °C) (Arthurs, Stiver, & Zytner,

1995). Additionally, it can easily be noticed that different types of polymers used to modify

the bitumen could have a large effect on aging, as well as the recovery process.

4.8 Fourier Transform Infrared Spectroscopy (FTIR) Results

FTIR was applied to analyze the degree of oxidation as it indicates part of the binder aging.

The degree of oxidation is generally determined by two peak heights for carbonyl (ascribed

to C = O) and sulfoxide (ascribed to S = O) functions at wavenumbers of 1,700 and 1,030 cm-1

respectively (BRRC, 2013). The change of chemical structure of bitumen after aging could be

obtained by the calculation of functional and structural indices of these two functions, based

on Equations 4 and 5 (Lamontagne et al., 2001; S. p. Wu et al., 2009; F. Zhang et al., 2011):

IC=O = � ℎ � −1∑ A h w −1 (4)

IS=O = � ℎ � � −1∑ � ℎ � −1 (5)

The FTIR spectrums for B1, PmB1, and Pmb2 are given in Figure 4-16, Figure 4-17, and Figure

4-18. The peak height of the carbonyl band (C = O) at 1,700 cm-1and the peak height of

sulfoxide band (S = O) at 1,030 cm-1 are pointed out in the figures. It clearly appears that B1

and PmB2 have higher sulfoxide peak height than carbonyl peak height, in contrast to PmB1.

This refers to the tendency of sulfoxide to increase in the short-term aging more than the


50


carbonyl, which tends to increase due to the long-term aging (F. Zhang et al., 2011). It has

also been shown that in the three figures, there are no new peaks showed up after the

binders are exposed to RTFOT and after the recovery process, as well as any indication of

disappearing a peak (namely due to the unsuccessful process of binder recovery of both

PmBs studied in this work).

Figure 4-16 FTIR spectra analysis of B1 Binder before and after aging

Figure 4-17 FTIR spectra analysis of PmB1 Binder before and after aging

0

10

20

30

40

50

60

70

80

90

100

4009001400190024002900340039004400

Tra

nsm

itta

nce

(%

)

Wavenumber (cm-1)

B1unaged after RTFOT after recovery

0

10

20

30

40

50

60

70

80

90

100

4009001400190024002900340039004400

Tra

nsm

itta

nce

(%

)

Wavenumber (cm-1)

PmB1

unaged after RTFOT after recovery

� =

� =

� =

� =


51


Figure 4-18 FTIR spectra analysis of PmB2 Binder before and after aging

The chemical aging indices for all the binders were calculated and are presented in Table 4-2.

The main conclusion of these results is that PmB1 has the highest values of the carbonyl

(ascribed to IC=O) in its three states. It has been shown in many studies that EVA showed up

in a peak height of 1,740 cm-1 (BRRC, 2013; Jamroz, 2003; Williams, 1994), which is very

close and could overlap with the carbonyl peak height. Hence, these values, in this case,

could be an indication for both carbonyl and the polymer EVA in PmB1. What could support

this explanation is the decreasing from 0.05141 (after-RTFOT value) to 0.02659 (when the

binder was recovered), since DSC results showed the disappearing of EVA after the recovery

process. In addition, this evolution of PmB1 indices is unlike B1 and PmB2 evolution, where

the values increased.

Table 4-2 Changes of aging index before and after aging

Sample IC=O IS=O

B1 Unaged 0.00020 0.00317

After RTFOT 0.00080 0.01220

After recovery 0.00467 0.03703

PmB1 Unaged 0.01997 0.01124

After RTFOT 0.05141 0.01306


PmB2 Unaged 0.00020 0.01226

After RTFOT 0.00217 0.03160


0

10

20

30

40

50

60

70

80

90

100

4009001400190024002900340039004400

Tra

nsm

itta

nce

(%

)

Wavenumber (cm-1)

PmB2unaged after RTFOT after recovery

� =

� =


52


In fact, FTIR might be used as an indicator of the presence of polymers. A considerable effort

was spent trying to study this claim, i.e. to observe the presence of EVA in PmB1 and HDPE in

PmB2 after the recovery process on the binders. The previous studies have mentioned

various peak heights for EVA such as 1740, 1240, 1020, 610 cm-1 (Jamroz, 2003).

Nevertheless, some of the mentioned peaks were believed to be unreasonable in this study

as they designed to find VA content in EVA (Jamroz, 2003), or they were used to analyze EVA

as a copolymer in a different method (Williams, 1994). The peaks heights that are pointed

out as an indication of the presence/absence of the polymer in the spectrum of the binder

are at 1,740 and at 1,243 cm-1, using baselines between 1,770 and 1,714 cm-1 and between

1,280 and 1,196 cm-1 respectively (BRRC, 2013). Besides that, the described method is an

avoiding one because of the effect of the analyzed quantities (F. Zhang et al., 2011).

Essentially, the overlapping in the peaks between carbonyl (1,700 cm-1) and EVA (1,740 cm-1)

makes this method a little impractical. However, it seems that HDPE peak heights were not

formerly studied as an indication of presence/absence of that polymer or its contents.

Additionally, regarding the results given in Table 4-2, they can clearly show the chemical

effect of the aging in the after-recovery values of PmB1 and PmB2 binders. In spite of their

after-recovery physical results (e.g. G*, phase angle, viscosity, and penetration) have given a

preemptive indication of nonexistence of hardening in those binders, the aging index of

after-recovery results indeed demonstrate that the chemical aging has happened as a result

of mixing and compacting the binders. It is interesting to mention that in the case of PmB2,

the oxidation rate in the carbonyl functions due to mixing and compacting (i.e. after-

recovery) is higher than the oxidation rate due to the exposing to RTFOT. In the same way,

the oxidation rate in B1 due after recovery process is significantly higher than the oxidation

rate after exposing to RTFOT. This could shed light on the chemical aging that might be

caused by the recovery process itself due to the distillation in a high temperature and the

reaction with the solvent.

Conclusion

53


5 CONCLUSION

5.1 Final conclusions

In this study, two modes of bitumen aging were investigated, aging after exposing to RTFOT,

which is widely believed to simulate short-term field aging, and aging due to the production

of i tures’ sa ples i la orator i.e. i i g a d o pa ti g . Three differe t binders were

used, one unmodified 35/50 penetration grade binder, and two different polymer-modified

binders (70/100 pen grade modified with 5% of EVA – PmB1 and; 70/100 pen grade modified

with 5% of HDPE – PmB2).

It has been found that after-RTFOT aging, all binders could be characterized either by

conventional tests or by DSR testing, and the chemical structural indices of aging resulting

from FTIR analysis can also be easily obtained. On the other hand, it has been observed that

there is a significant complexity to characterize the aging after recovery process, especially in

PmBs, by conventional tests or DSR testing, since the DSC analysis clearly revealed that the

solvent failed to correctly extract the polymers from PmBs in the recovery process. This fact

made the properties of recovered PmBs (such as viscosity, penetration, G* and phase angle)

softer than those of the unaged PmBs, and only slightly harder than those of the unmodified

base binder of the PmBs, that is to say, the 70/100 penetration grade bitumen.

As the solvent did not recover the polymer, looking at the physical properties of the

recovered PmBs it seems that the binder was not aged during the process of asphalt mixture

production, compacting and recovery (instead, it looks like it has been rejuvenated). Yet, in

the FTIR analysis, it can be seen that the bituminous part of the binder was aged in the

process. FTIR spectra analysis actually indicated that after-recovery aging could be

characterized by its effect on the chemical structure of binders, which is reflected by the

increasing of oxidation rates for all binders. It is also remarkable to mention that the

oxidation rate due to after-recovery aging seems to be in some cases higher than that of

RTFOT aging. This could imply that the oxidation rate was higher due to the insufficiency of

Conclusion

54


the recover process and/or the higher impact of the process on the PmB binders. This could

be an interesting area for further analysis.

The behavior of PmB1 is another noteworthy area for consideration. It has been shown that

EVA gave a decent protection to PmB1 form aging effects in most cases. It reduced the aging

effects to be slightly similar to B1, as could be shown in the various aging indices. However,

it appears that this behavior was more easily observed during the assessment of mixtures

performance, more than with the binder evaluation, and ITS analysis (with or without

extended curing time) undoubtedly confirm this deduction. The reason for this behavior

could refer to the EVA ability to effectively protect the mixture by internally interacting with

the aggregate and the base bitumen, as well as due to the higher elastic recovery of the

bitumen after EVA modification.

It has also been found that FTIR test was sufficient to determine the chemical changes due

to aging effect to a decent extent. It is believed that further effort should be devoted to

spe if the odif i g pol ers’ a ds o FTIR spe tru a d deter i e their orrelatio

a d/or i flue e o o idatio ’s a ds.

Although it was argued, in some studies, that toluene could be used as a solvent in the

recovery process, this study indeed revealed that this cannot be generalized and depends on

the bitumen type and the modifying polymer. As the time of this study was limited, it is

recommended to additionally investigate the solvent efficiency on the recovery process,

namely by using other types of solvents.

5.2 Future works

The two-hour heated samples made from the three types of mixtures, which were tested in

ITS, are suggested to be recovered using an effective solvent and the properties of the

extracted binders could be tested. A comparison between these results with the previous

results could lead to interesting conclusions. In fact, it might be used as an indication to the

i ders’ eha ior after long-term aging.

Conclusion

55


Moreover, it is recommended to study the extent of the effect of aging on binders using FTIR

analysis. FTIR analysis was largely found to be a very promising method in aging studies. It

could be used to evaluate the effect of aging in the chemical structure of the bitumen by

calculating the height peaks of the related functions and determining its changes. It could

also be used as an indication to the presence or absence of the polymers in the binders after

recovery process. Consequently, determining the affected regions on the FTIR graphs

precisely becomes a needed area of investigation in the future.

The performance of the Dynamic Shear Rheometer test to assess the polymer-modified

i der’s properties is endorsed to be further studied in more detail. It was observed in this

study that some results of PmBs were inconsistent, especially in the low-temperature

ranges. As said before, all the rheological models were initially built to describe the

u odified i ders’ eha ior, but they need to be further developed to study adequately

the polymer modified binders.

References and bibliography

57


REFERENCES AND BIBLIOGRAPHY

Administration, U. S. F. H., Highway, A. A. o. S., Officials, T., Program, N. C. H. R., Board, N. R.

C. T. R., & Advanced Asphalt Technologies, L. (2011). A Manual for Design of Hot Mix

Asphalt with Commentary: Transportation Research Board.

Airey, G. D. (2002). Rheological evaluation of ethylene vinyl acetate polymer modified

bitumens. Construction and Building Materials, 16(8), 473-487.

Airey, G. D. (2003). State of the Art Report on Ageing Test Methods for Bituminous

Pavement Materials. International Journal of Pavement Engineering, 4(3), 165-176.

Araujo, M. d. F. A. d. S., Lins, V. d. F. C., Pasa, V. M. D., & Leite, L. F. M. (2013). Weathering

aging of modified asphalt binders. 115, 19–25.

Arega, Z. A., Bhasin, A., & Kesel, T. D. (2013). Influence of extended aging on the properties

of asphalt composites produced using hot and warm mix methods. Construction and

Building Materials, 44(0), 168-174.

Arthurs, P., Stiver, W. H., & Zytner, R. G. (1995). Passive volatilization of gasoline from soil.

Soil and Sediment Contamination, 4(2), 123-135.

Banerjee, A., de Fortier Smit, A., & Prozzi, J. A. (2012). The effect of long-term aging on the

rheology of warm mix asphalt binders. Fuel, 97(0), 603-611.

Bell, C. A. (1989). Summary report on aging of asphalt-aggregate systems.

Bell, C. A., Wieder, A. J., & Fellin, M. J. (1994). Laboratory aging of asphalt-aggregate

mixtures: field validation.

Brovelli, C., Hilliou, L., Hemar, Y., Pais, J., Pereira, P., & Crispino, M. (2013). Rheological

characteristics of EVA modified bitumen and their correlations with bitumen concrete

properties. Construction and Building Materials, 48(0), 1202-1208.

BRRC, B. R. R. C. (2013). Bitumen analysis by FTIR spectrometry: testing and analysis protocol

(BRRC method of measurement – ME85/13). Brussels: Belgian Road Research Centre.

Brule, B., & Gazeau, S. (1996). Characterization of rheological and thermal behavior of

asphalt cements modified by ethylene copolymers. Preprints of Papers, American

Chemical Society, Division of Fuel Chemistry, 41(CONF-960807--).

Campbell, F. C. (2008). Elements of Metallurgy and Engineering Alloys: ASM International.

Chen, H., Chen, T., & Hsu, C. (2006). Effects of wood particle size and mixing ratios of HDPE

on the properties of the composites. Holz als Roh-und Werkstoff, 64(3), 172-177.


58


Chitla, S. R. (1996). Part 2. Binder recovery using a modified procedure Research Report ARR

(pp. 30-33).

Christensen, D. W., & Bonaquist, R. F. (2004). Evaluation of indirect tensile test (IDT)

procedures for low-temperature performance of hot mix asphalt: Transportation

Research Board.

Cong, P., Chen, S., Yu, J., & Wu, S. (2010). Effects of aging on the properties of modified

asphalt binder with flame retardants. Construction and Building Materials, 24(12), 2554-

2558.

Cuadri, A. A., Carrera, V., Izquierdo, M. A., García-Morales, M., & Navarro, F. J. (2014).

Bitumen modifiers for reduced temperature asphalts: A comparative analysis between

three polymeric and non-polymeric additives. Construction and Building Materials,

51(0), 82-88.

Durrieu, F., Farcas, F., & Mouillet, V. (2007). The influence of UV aging of a

Styrene/Butadiene/Styrene modified bitumen: Comparison between laboratory and on

site aging. Fuel, 86(10-11), 1446-1451.

EN 12594, B. E. (2007). Bitumen and bituminous binders. Preparation of test samples: BSI.

EN 12607-1, B. E.-. (2007). Bitumen and bituminous binders. Determination of the resistance

to hardening under influence of heat and air. RTFOT method: BSI.

EN 12697-3, B. E.-. (2013). Bituminous mixtures. Test methods for hot mix asphalt. Bitumen

recovery: Rotary evaporator: BSI.

EN 12697-6, B. E.-. (2012). Bituminous mixtures. Test methods for hot mix asphalt.

Determination of bulk density of bituminous specimens: BSI.

EN 14770, B. E. (2012). Bitumen and bituminous binders. Determination of complex shear

modulus and phase angle. Dynamic Shear Rheometer (DSR): BSI.

García-Morales, M., Partal, P., Navarro, F. J., & Gallegos, C. (2006). Effect of waste polymer

addition on the rheology of modified bitumen. Fuel, 85(7-8), 936-943.

Gar ıa-Morales, M., Partal, P., Na arro, F. J., Martı ez-Boza, F., Gallegos, C., González, N., . . .

Muñoz, M. E. (2004). Viscous properties and microstructure of recycled eva modified

bitumen. Fuel, 83(1), 31-38.

Go zález, O., Muñoz, M. E., “a ta arıa, A., Gar ıa-Morales, M., Navarro, F. J., & Partal, P.

(2004). Rheology and stability of bitumen/EVA blends. European Polymer Journal,

40(10), 2365-2372.


59


Haddadi, S., Ghorbel, E., & Laradi, N. (2008). Effects of the manufacturing process on the

performances of the bituminous binders modified with EVA. Construction and Building

Materials, 22(6), 1212-1219.

Hı ıslıoğlu, “., & Ağar, E. 200 . Use of aste high de sit pol eth le e as itu e odifier in asphalt concrete mix. Materials Letters, 58(3–4), 267-271.

Höhne, G., Hemminger, W., & Flammersheim, H. J. (2003). Differential Scanning Calorimetry:

Springer.

Hraiki, S. (1974). Rheological properties of bituminous materials. Rheologica Acta, 13(3),

567-570.

Huber, G. A., & Decker, D. S. (1995). Engineering Properties of Asphalt Mixtures and the

Relationship to Their Performance: ASTM.

Hudson, W. R., & Kennedy, T. W. (1968). An indirect tensile test for stabilized materials.

ISO 11357-4, B. E. I.-. (2014). Plastics. Differential scanning calorimetry (DSC). Determination

of specific heat capacity: BSI.

Jamroz, N. (2003). Determination of vinyl acetate (VA) content of ethylene-vinyl acetate

(EVA) copolymers in thick films by infrared spectroscopy. Jour. Chem. Soe. Pak. Vol,

25(2).

Kandhal, P. S. (1996). Evaluation of voids in the Mineral aggregate for HMA Paving Mixtures.

Kano, Y., Akiba, S., Kuriyagawa, Y., & Kawai, T. (2005). Removal of binder from asphalt

mixture using high temperature and high pressure water. Journal of the Japan

Petroleum Institute, 48(6), 358-364.

Khan, Z. A., Al-Abdul Wahab, H. I., Asi, I., & Ramadhan, R. (1998). Comparative study of

asphalt concrete laboratory compaction methods to simulate field compaction.

Construction and Building Materials, 12(6–7), 373-384.

Krishnan, J. M., & Rajagopal, K. R. (2005). On the mechanical behavior of asphalt. Mechanics

of Materials, 37(11), 1085-1100.

Lamontagne, J., Dumas, P., Mouillet, V., & Kister, J. (2001). Comparison by Fourier transform

infrared (FTIR) spectroscopy of different ageing techniques: application to road

bitumens. Fuel, 80(4), 483-488.

Lee, S.-J., Amirkhanian, S. N., & Kim, K. W. (2009). Laboratory evaluation of the effects of

short-term oven aging on asphalt binders in asphalt mixtures using HP-GPC.

Construction and Building Materials, 23(9), 3087-3093.


60


Lee, S.-J., Amirkhanian, S. N., Shatanawi, K., & Kim, K. W. (2008). Short-term aging

characterization of asphalt binders using gel permeation chromatography and selected

Superpave binder tests. Construction and Building Materials, 22(11), 2220-2227.

Leng, Y. (2013). Materials Characterization: Introduction to Microscopic and Spectroscopic

Methods: Wiley.

Lesueur, D. (2009). The colloidal structure of bitumen: Consequences on the rheology and on

the mechanisms of bitumen modification. Advances in Colloid and Interface Science,

145(1–2), 42-82.

Liu, G., Nielsen, E., Komacka, J., Greet, L., & Ven, M. v. d. (2014). Rheological and chemical

evaluation on the ageing properties of SBS polymer modified bitumen: From the

laboratory to the field. Construction and Building Materials, 51(0), 244-248.

Lopes, M., Zhao, D., Chailleux, E., Kane, M., Gabet, T., Petiteau, C., & Soares, J. (2014).

Characterisation of ageing processes on the asphalt mixture surface. Road Materials and

Pavement Design.

Lu, X., & Isacsson, U. (2000). Artificial aging of polymer modified bitumens. Journal of Applied

Polymer Science, 76(12), 1811-1824.

Lu, X., & Isacsson, U. (2002). Effect of ageing on bitumen chemistry and rheology.


Lucena, M. d. C. C., Soares, S. d. A., & Soares, J. B. (2004). Characterization and thermal

behavior of polymer-modified asphalt. Materials Research, 7(4), 529-534.

Luo, W.-q., & Chen, J.-c. (2011). Preparation and properties of bitumen modified by EVA

graft copolymer. Construction and Building Materials, 25(4), 1830-1835.

Ma, T., Mahmoud, E., & Bahia, H. U. (2010) Estimation of reclaimed asphalt pavement binder

low-temperature properties without extraction: Development of testing procedure.

Transportation Research Record (pp. 58-65).

Mallick, R. B., & El-Korchi, T. (2013). Pavement Engineering: Principles and Practice, Second

Edition: Taylor & Francis.

Mashaan, N. S., Ali, A. H., Karim, M. R., & Abdelaziz, M. (2012). An overview of crumb rubber

modified asphalt. International Journal of Physical Sciences, 7(2), 166-170.

Mastrofini, D., & Scarsella, M. (2000). The application of rheology to the evaluation of

bitumen ageing. Fuel, 79(9), 1005-1015.

Mouillet, V., Farcas, F., & Besson, S. (2008). Ageing by UV radiation of an elastomer modified

bitumen. Fuel, 87(12), 2408-2419.


61


Mturi, G. A. J., O'Connell, J., Zoorob, S. E., & Beer, M. D. (2014). A study of crumb rubber

modified bitumen used in South Africa. Road Materials and Pavement Design.

Nösler, I., Tanghe, T., & Soenen, H. (2008). Evaluation of binder recovery methods and the

influence on the properties of polymer modified bitumen. Paper presented at the E&E

conference, Copenhagen.

Pan, T., Lu, Y., & Lloyd, S. (2012). Quantum-Chemistry Study of Asphalt Oxidative Aging: An

XPS-Aided Analysis. 1, 9 − 9 .

Pang, L., Liu, K., Wu, S., Lei, M., & Chen, Z. Effect of LDHs on the aging resistance of crumb

rubber modified asphalt. Construction and Building Materials(0).

Pérez-Lepe, A., Martínez-Boza, F. J., & Gallegos, C. (2005). Influence of Polymer

Concentration on the Microstructure and Rheological Properties of High-Density

Polyethylene (HDPE)-Modified Bitumen. Energy & Fuels, 19(3), 1148-1152.

Pérez-Lepe, A., Martínez-Boza, F. J., Gallegos, C., González, O., Muñoz, M. E., & Santamaría,

A. (2003). Influence of the processing conditions on the rheological behaviour of

polymer-modified bitumen. Fuel, 82(11), 1339-1348.

Qin, Q., Schabron, J. F., Boysen, R. B., & Farrar, M. J. (2014). Field aging effect on chemistry

and rheology of asphalt binders and rheological predictions for field aging. Fuel, 121(0),

86-94.

Sengoz, B., & Isikyakar, G. (2008). Analysis of styrene-butadiene-styrene polymer modified

bitumen using fluorescent microscopy and conventional test methods. Journal of

Hazardous Materials, 150(2), 424-432.

Sengoz, B., & Isikyakar, G. (2008). Evaluation of the properties and microstructure of SBS and

EVA polymer modified bitumen. Construction and Building Materials, 22(9), 1897-1905.

Simpson, R., Urtiew, P., Ornellas, D., Mood , G., “ ri er, K., & Hoff a , D. 3997 . CL‐20 performance exceeds that of HMX and its sensitivity is moderate. Propellants,

Explosives, Pyrotechnics, 22(5), 249-255.

Tian, X., Zheng, J., & Zhang, Q. (2004). Effect of aging on viscoelastic performance of asphalt

binder. SATC 2004.

Wei, H., Thompson, R. B., Park, C. B., & Chen, P. (2010). Surface tension of high density

polyethylene (HDPE) in supercritical nitrogen: Effect of polymer crystallization. Colloids

and Surfaces A: Physicochemical and Engineering Aspects, 354(1–3), 347-352.

Williams, K. R. (1994). Analysis of Ethylene-Vinyl Acetate Copolymers: A Combined TGA/FTIR

Experiment. Journal of chemical education, 71(8), A195.


62


Wu, S., Pang, L., Liu, G., & Zhu, J. (2010). Laboratory study on ultraviolet radiation aging of

bitumen. Journal of Materials in Civil Engineering, 22(8), 767-772.

Wu, S. p., Pang, L., Mo, L. t., Chen, Y. c., & Zhu, G. j. (2009). Influence of aging on the

evolution of structure, morphology and rheology of base and SBS modified bitumen.


Yin, J., Wang, S., & Lv, F. (2013). Improving the short-term aging resistance of asphalt by

addition of crumb rubber radiated by microwave and impregnated in epoxidized

soybean oil. Construction and Building Materials, 49(0), 712-719.

Zhang, F., & Yu, J. (2010). A Study on the Aging Kinetics of PPA Modified Asphalt. 28(13),

1338-1344.

Zhang, F., Yu, J., & Han, J. (2011). Effects of thermal oxidative ageing on dynamic viscosity,

TG/DTG, DTA and FTIR of SBS- and SBS/sulfur-modified asphalts. Construction and

Building Materials, 25(1), 129-137.

Zhang, H., Shi, C., Han, J., & Yu, J. (2013). Effect of organic layered silicates on flame

retardancy and aging properties of bitumen. Construction and Building Materials, 40(0),

1151-1155.

Zhang, H., Xu, H., Wang, X., & Yu, J. (2013). Microstructures and thermal aging mechanism of

expanded vermiculite modified bitumen. Construction and Building Materials, 47(0),

919-926.

Zhang, H., Yu, J., & Kuang, D. (2012). Effect of expanded vermiculite on aging properties of

bitumen. Construction and Building Materials, 26(1), 244-248.

Zhang, H., Yu, J., Wang, H., & Xue, L. (2011). Investigation of microstructures and ultraviolet

aging properties of organo-montmorillonite/SBS modified bitumen. Materials Chemistry

and Physics, 129(3), 769-776.

Zhang, H., Yu, J., & Wu, S. (2012). Effect of montmorillonite organic modification on

ultraviolet aging properties of SBS modified bitumen. Construction and Building

Materials, 27(1), 553-559.

Zhang, H., Zhu, C., Tan, B., & Shi, C. (2014). Effect of organic layered silicate on

microstructures and aging properties of styrene–butadiene–styrene copolymer modified

bitumen. Construction and Building Materials, 68(0), 31-38.

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