EVALUATION OF RUTTING IN WARM MIX ASPHALT INCOPORATING
AT UNIVERSITI TUN HUSSEIN ONN MALAYSIA
DR. MUHAMMAD YUSRI
Faculty of Civil and Environmental Engineering
University Tun Hussein Onn Malaysia
TABLE OF CONTENTS
TABLE OF CONTENTS ii
LIST OF TABLES iii
LIST OF FIGURES iv
CHAPTER 1 INTRODUCTION 9
1.1 Background of the research 9
1.2 Problem Statement 11
1.3 Objectives 12
1.3.1 Aim 12
1.3.2 The objectives are as follows 13
1.4 Scope of research 13
1.5 Organization of the thesis 14
CHAPTER 2 LITERATURE REVIEWS 15
2.1 Introduction 15
2.2 Warm-mix asphalt 16
2.2.1 Benefits of utilizing WMA 18
184.108.40.206 Environmental Benefit 19
220.127.116.11 Paving Benefit 22
18.104.22.168 Economic Benefit 24
2.3 Warm Mix Asphalt Technologies 24
2.3.1 Organic-based WMA technologies 25
2.3.2 Chemical Additive-based
2.3.3 Water-based WMA Technologies 26
2.3.4 Water Bearing Additive
2.4 Basic Materials in Warm Mix Asphalt 27
2.4.1 Aggregate 27
2.4.2 Binder 28
Types and Grades of Bitumen
Characteristics of Bitumen
2.5 Problems Related with Warm Mix Asphalt 30
2.5.1 Moisture Susceptibility of WMA 31
2.5.2 Rutting 31
Insufficient data for evaluation
Long term performance
Low temperature behavior
Life cycle assessment
Use with SBS polymer modified
2.6 Anti-stripping agents 35
2.6.1 Hydrated lime 35
2.6.2 Liquid Anti-Stripping Agents
2.10.1 Types of Rutting 42
Causes of Rutting
Factor Affecting rutting
Mechanism of rutting
Laboratory Test Related to Rutting
Wheel Tracking device
2.11 Other test Related to rutting 49
2.11.1 Homburg wheel tracking device 49
2.12 Summary 50
CHAPTER 3 METHODOLOGY 52
3.1 Introduction 52
3.2 Laboratory tests procedures 54
3.3 Materials selection
3.3.1 Asphalt binder
3.3.2 Softening Point
3.3.3 Penetration Test
3.3.4 Rational viscosity test
3.4 Dynamic Shear Rheometer 56
3.5.1 Aggregate impact value test
3.5.2 Sieve analysis test
3.5.3 Flakiness and Elongation Index Test 59
3.6 Sample Preparation 60
Warm mix asphalt additive
Design of binder content
Moisture Susceptibility test
3.10.1 Wheel tracking test 63
3.10.2 Compaction of specimen for wheel
3.11 Analysis and discussion
CHAPTER 4 EXPECTED RESULTS
4.1 Expected Result 65
LIST OF TABLES
2.1 Recommended amount of some available WMA
additive (Oliveira j, et al, 2010).
2.2 Emission reduction Measured from WMA
Projects (Gandi, 2008)
2.3 Placement and compaction temperature, (Gandhi
2.4 Emission reduction in plants with WMA (%)
(D’angelo et al., 2008)
2.5 physical Properties of the Mineral Fillers 37
2.6 (Kandahar, et al, 2003) 46
3.1 Gradation limit for AC 14 according to
3.2 Standard specification test for bituminous
LIST OF FIGURES
2.1 Classification of Asphalt Mixture Types
According to Production Temperature and Fuel
Usage (D’ Angelo et al, 2008).
2.2 Modification of binder Temperature/viscosity
relationship (Jean-Martin et al, 2008)
2.3 Temperature-viscosity relationship 25
2.4 Stripping in pavement (pavement
2.5 Rutting pattern on road 42
2.6 Determination of rutting depth (highway
2.7 Characterization of downward and total rutting,
(Williams and Romero, 2009)
2.8 Wheel Tracker Solid Rubber Tyre (After
2.9 Hamburg Wheel-Tracking device (Hans,2006) 50
3.1 Research methodology flow chart 53
1.1 Background of the Research
Conventional hot mix asphalt (HMA) has been the primary material used in asphaltic
paving in past decades. Recently, compared to conventional HMA mixtures, warm mix
asphalt (WMA) mixtures have shown great potential and offer benefits not given by
HMA mixtures, since the WMA mixtures can produce asphaltic layers at lower
temperatures.WMA additives can reduce the viscosity of the binder or mixture; thus, the
production and compaction temperatures can be lower, compared to those needed for
conventional HMA (Kim, 2011). WMA originated in Europe and has been used only
recently in the United States (Wasiuddin et al. 2007).
Warm Mix Asphalt (WMA) is mixes that are manufactured and spread at lower
temperatures than Hot Mix Asphalt. This temperature reduction of 20-40 0
C has led to
the following temperature based classification of asphalt mixes: Hot Mix Asphalt or
C);Warm Mix Asphalt or WMA(100-140o
C);Half-Warm Mix Asphalt
or HWMA (60-100O
C)(The use of Warm Mix Asphalt, 2010; Vaitkus et al, 2009).The
WMA temperature reduction is the result of recently developed technologies that
involve the use of organic additives, chemical additives, and water-based or water
containing foaming processes (You and Goh, 2008;Zaumanis, 2010).Even though these
technologies quite different, but they have the same function to lower the bitumen
viscosity, improve workability and emission condition.
One of the causes of pollution associated with the construction of transportation
infrastructure is the emission of greenhouse gases into the atmosphere (Rubio,
2011).Curtis (2009) reported that greenhouse gases emission (CO2) produced
anthropogenic climate change and raised global concern on global warming. The
elevated daily temperature, rising sea level, more frequent intense precipitation events,
and increases in hurricane intensity has a physical impact related to both infrastructure
and the operations of various transport modes. So the used of WMA technologies can
help improve the environment because it produces asphalt t temperature 20-40o
in comparison to Hot Mix Asphalt. Even though the use of Warm Mix Asphalt
technology has many advantages, Kim et al., (2012) reported that asphalt mixture
prepared using the WMA additives suffered the increasing tendencies to rutting, in
contrary decreasing the aging of asphalt binder due to mixing and compaction at lower
Rutting is one of the most important distresses for asphalt pavement. It is caused
by material consolidation and lateral movement due to repeated heavy wheel loadings
on the various pavement layers/subgrade. The distress is manifested by a depressed rut
along the wheel path on the pavement surface. The rutting distress is viewed as not a
structure failure, but a serious safety hazard to vehicles because hydroplaning can occur
in the presence of rutting in rainy weather, resulting in serious traffic accidents.
Moreover, vehicles tend to be pulled towards the rut path, making it difficult to drive.
Many factors can contribute to the rutting distress of pavement, such as environment
(high temperature), truck speed and tire contact pressure, the method to prevent the
rutting are primarily though engineering an asphalt mixture with improved shear
resistance to withstand problems posed by the environment and traffic loadings.
However, the addition of warm mix additives into asphaltic mixture can complicate the
engineering process; more knowledge is needed to assess the influence of the warm
additives to the pavement rutting performances (Mallick et al, 2009).
1.2 PROBLEM STATEMENT
Conventional hot-mix asphalt (HMA) has been the primary material used in
asphaltic paving in past decades. However, compared to conventional HMA mixtures,
warm-mix asphalt (WMA) mixtures have shown great potential, and offer benefits
not given by HMA mixtures, since the WMA mixtures can produce asphaltic
layers at lower Temperatures, without compromising pavement performance. WMA
materials can reduce the viscosity of the binder by the addition of warm-mix
additives; thus, the production and compaction temperatures can be lower,
compared to those needed for conventional HMA. One of the primary benefits of
WMA is the opportunity to reduce carbon dioxide emissions during the production
and compaction of asphalt mixtures. This could support the objective of reducing
greenhouse gas emissions set by the Kyoto Protocol, as well as allowing asphalt mixture
plants to be located in some areas with strict air regulations. In addition, WMA
technology presents other obvious advantages, such as less fuel usage, greater distances
that asphalt mixtures can be hauled to paving sites, better working conditions, an
extended paving season, and the potential use of more Reclaimed asphalt pavement
(RAP) materials ( Mallick et al,2008). By heating and dry at lower temperature will lead
moisture content incomplete dryness and will affect aggregate-bitumen bonding and
potentially will reduce the durability of mixes. Also lower production temperature will
cause rutting and reduce the asphalt binder oxidation, which results in a mixture with
lower stiffness, lesser aggregate drying and possible create a mixture more sensitive to
rutting. The decrease of mixing temperature results in increasing binder viscosity makes
the asphalt mixture difficult to compact, which results in high air voids, which affects
the aggregates and bitumen bonding and easily raise the problem ofrutting(Bennert
2012). Anti-stripping agent, namely hydrated lime is commonly used in asphalt mixes
to increase physical-chemical bond between the bitumen and aggregate and improve
wetting by lowering the surface tension of bitumen.
The aim of the research is to determine the effect of anti-stripping agents on the
pavements under different loading and its resistance to rutting.
1.3.2 The objectives are as follows:
(i)To evaluate and determine the rutting potential of compact mixture containing
different types of anti-stripping additive using wheel tracking test.
1.4 Scope of research
The study focus on the rutting resistance of warm asphalt mix by incorporating
SasoBit®.The different behavior and properties will be study under the experimental
results. the asphalt mixture used for the proposed study will be consist of granite
aggregate and conventional bitumen grade 80/100,along with hydrated lime,PMD and
ordinary Portland cement as a filler.
The different experiments on specimens such as aggregate properties, sieve
analysis, and binder content determination tests will be conducted. Binders with
stipulated SasoBit®. contents will be evaluated using the dynamic shear rheometer to
investigate rheological behaviors after being conditioned in a rolling thin film oven
(RTFO).The effectiveness of anti-stripping additives will be evaluated through the
wheel tracking test, indirect tensile strength test to evaluate the effectiveness of anti-
1.5 Organization of the Thesis
A general introduction to the research project is presented in chapter 1. Chapter 2
provides a literature review of recent WMA implementation and technologies globally.
This chapter also describe in detailed the different technologies used for WMA
production and the behavior of anti-stripping agent and their role in minimizing the
binder viscosity. The methodology used to conduct the research is given in chapter
3.this chapter also discuss and evaluates the properties of the materials used in
accordance to test standards.
In addition, detailed explanations on additives used were included in this
chapter. Moisture damage, temperature reduction effects, use of mineral fillers to
improve rutting and stripping resistance were highlighted as well. the chapter 4 discuss
the results analysis, and different tests auto comes for the rutting resistance of the
asphalt mixes incorporating anti-stripping agents and pavement modifier in optimum
quantity. Chapter 5 concludes the outcome of the research project and highlights some
recommendations for future studies. The schematic diagram summarizing the overall
experimental approach is shown in figure.
The rapid construction of new asphalt pavements, the asphalt industry has been
contributing to greenhouse gas emissions released into our atmosphere. Greenhouse gas
emissions cause many environmental problems for our earth. Many gas emissions soak
up infrared radiation from the atmosphere, trapping heat in our lower
atmosphere.(EnergyInformation Administration, 2005).According to computer-
stimulated models, the increase in gases will always result in Earth’s temperature rising.
Although these are just computer models, the actual temperature of the Earth has
increased 0.6ºC over the past 100 years (Energy Information Administration, 2005).
The asphalt sector emitted 830,000 tones of CO2 (CO2) in 2007 from the manufacture
of 26 million tons (Mt) of product in 350 plants (Mineral Products Association, 2007).
On average 30-50% of the costs at an asphalt plant are for emission control (Energy
The Hot Mix Asphalt Concrete Industry has produced around 1600 million
metric tons of Hot Mix Asphalt (HMA) during 2007 all around the world (European
Asphalt Pavement Association, 2007).Thus to produce one metric ton of HMA need
Around 85 kWh of energy (European Asphalt Pavement Association, 2007). This
means that the whole industry of HMA consumed 0.28% of the world’s crude oil
production. The aggregate moisture content is the main deciding factor for the level of
energy consumption during the whole production process of HMA (ANG et al.1993).
To reduce and avoid the huge amount of GHS gases and energy consumption
the warm mix asphalt techniques are introduced. Warm Mix Asphalt (WMA) additives
and technologies allow asphalt to be mixed and placed with mineral aggregates at
relatively lower temperatures, 20 to 55°C (35 to 100°F) lower than typical HMA
(Mallick et al., 2009).Recently, there have been products developed, such as Sasobit®,
that decrease viscosity of asphalt at a lower than conventional mix temperature, which
can in turn reduce greenhouse gas emissions and energy consumption. These
technologies reduced asphalt binder viscosity and enabling the coating of aggregates
particles completely at lower temperatures. The incorporation of WMA also tends to
improve Compaction reducing the permeability and binder hardening caused by aging,
improving the performance of the asphalt mix in terms of cracking resistance and
susceptibility to moisture.
2.2 Warm-mix asphalt
Warm asphalt mixtures is currently used throughout the world, aiming to save energy
and reducing emission during production process, without decreasing the in-service
properties and field performance of asphalt mixture. These properties can be achieved
by incorporating the chemical additives, which works to reduce the moisture level
without disturbing the physical properties of mixture. There is a lot of additive and anti-
stripping agents are used nowadays to reduce the fuel and emission during preparation
process.WMA are generally produced in a temperature range from 100 to140 C, while
half-warm mix asphalt (HWMA) are fabricated between 70 and 100 C. The temperature
decrease is around 30C for the first case and can attain up to 80 C for the second case
(World Road Association, 2008).
The evaluations carried out in Europe, show it clear the decrease of different
emission throughout the production process in plant, as follows: 30–40% for
CO2(carbon dioxide) and SO2(sulfur dioxide), 50% for VOC (volatile organic
compounds), 10–30% for CO (carbon monoxide), 60–70% for nitrous oxides, and 25–
55% for dust. Reductions from 30% to 50% for asphalt aerosols/fumes and polycyclic
aromatic hydrocarbons (PAHs) have also been reported, which have a substantial
influence on the exposure of the workers and the surrounding area of construction sites
to those products (European Asphalt Pavement Association,2010).
There are some concerns related to WMA cost in its whole lifecycle, as the technologies
available for WMA generally increase the initial production cost. On the one hand, this
can be connected to the additional equipment needed for plants, allowing the use of
specific technologies or additives. On the other hand, the use of additives brings some
supplementary cost, which could be only partially compensated by lowering the
operating temperature. (Button, et al, 2007)
There is some danger related to the WMA because the production of additives
also emits carbon (Zaumanis, 2010). Warm-mix asphalt (WMA) is much like Hot-Mix
Asphalt(HMA), but it is produced at lower plant temperatures than conventional HMA.
The key benefits of the reduced production temperature of WMA include the reduction
of fuel consumption and emissions (Hurley and Powell 2006)
The WMA technology can be classified in three main groups’ organic additives,
chemical additives and foaming technologies. Reediest™ WMX and Casabas RT are
both chemical additives. Those types of products chemically enhance active adhesion
and improve the wetting of aggregates by bitumen without changing considerably the
binder performance (Silva and Almeida, 2009).
Table 2.1: Recommended amount of some available WMA additive (Oliveira, et al,
2.2.1 Benefits of utilizing WMA
Warm-mix asphalt has a lot of benefits over the conventional HOT. These benefits
depend upon which method and approach of WMA is used for production of WMA.
There is a lot of approaches are used, which all have different perceptive benefits and
concern. The most common and visible benefits of WMA are the following:
Additive Additive rate range Typical additive rate
Astec PER 0.5%-0.75 by total weight of
RAP( only for high level of
Asphaltan- B 2-4% by weight of total
2.5% by weight of binder
sasobit 0.8-4% by weight of total
binder 1.5% by total weight of total
Sonne warmix 0.5-1.5% by weight of total
binder 0.75% -maximum
recommender for unmodified
Cesa base RT 0.3-0.5% by weight of binder ---
Rediset WMX 1.5% -2.5% by weight of
Evotherm About 5% of diluted
chemical packed by weight of
22.214.171.124 Environmental Benefit
The idea of WMA arises as a challenge to the emissions during production and
compaction which directly affects the health of workers and a key element for
environmental degradation. The HMA plants emit a variety of particulate matters and
gaseous pollutants. The gaseous emissions include sulfur dioxide, nitrogen oxides,
carbon monoxide, and volatile organic compounds. The Environmental Protection
Agency (EPA) has offered an example to illustrate the emissions estimates. If a
natural gas-fired drum mixing dryer produced 200,000 tons per year, the
estimated emissions during that period would be 13 tons of carbon Monoxide, 5
tons of volatile organic compounds, 2.9 tons of nitrogen oxides, 0.4 tons of sulfur
oxides, and 0.65 tons of hazardous air pollutants (U.S. EPA Report 2000).One of main
benefits of WMA is significant emission reduction during the mixing and
Compacting.(Mallick et al. (2009) did the assessments on the WMA additives and
concluded that temperature seems to be the main driving factor for carbon dioxide
emissions. Hence reducing temperature during production and compaction of asphalt
mixing can significantly reduce the carbon foot print. Gandhi (2008) did the field
demonstration of WMA projects in India and compared to the HMA and concluded the
Table 2.2: Emission reduction Measured from WMA Projects (Gandi, 2008)
2.2 Ashpa -min Sasobit Evotherm WMA -foam
Sulfur Dioxide 17.60% --- 81% N/A
Carbon 3.20% 18% 46% 31%
Carbon monoxides N/A N/A 63% 29%
Gandhi (2011) warm and conventional hot mix evaluation on two different projects on
roads in India. The ambient air temperature was around 37 °C at the start of the day,
rising to a maximum of 42°C.The field experimental data is presented in the following
Table 2.3 Placement and compaction temperature,(Gandhi2011)
The use of WMA has three benefits: air pollution, fossil fuel depletion, and smog
formation. Further WMA could reduce 24% of impact of air pollution, and 18% in
fossil fuel depletion caused by HMA.It can also reduce smog formation reduction of
10%. The use of WMA could provide a reduction of 15% to the environmental impacts
induced by HMA.( Hassan 2009)At temperatures above the melting point, they reduce
the viscosity of the binder to make it possible to reduce the production temperature
whereas, below the melting point, they tend to increase the stiffness of the binder
Nitrogen Oxide 6.10% 34% 58% 62%
Total particular matter 35.30% N/A N/A N/A
N/A 8% 25% N/A
2.3 Conventional hot mix Warm mix
Production temperature (C) 160 130
Mix delivery temperature (C) 140-150 125-130
Mix Temperature behind paver (C) 130-145 120-125
Break down compaction temperature (C) 130-145 110-115
Finished PTR compaction temperature
Mix haul time 15-25 15-25
Core area voids after compaction (%) 5-7 3.99
Figure 2.1: Classification of Asphalt Mixture Types According to Production
Temperature and Fuel Usage (D’ Angelo et al, 2008).
Another notable benefit of WMA usage instead of HMA in road pavements is
the reduced emissions produced from the asphalt producing plants Based on processing
conditions and production temperature, WMA plant emissions were reported to
represent 30 to 98% of HMA emissions (Hossain et al., 2009). A considerable reduction
in fume emissions was reported between HMA produced at 165°C and WAM-Foam
prepared at 115°C, from 0.2-0.5 mg/m3 range to below 0.05 mg/m3 . Button et al.
reported that a production temperature reduction of 47°F using Aspha-Min resulted in a
75% reduction in fume emissions (Button et al., 2007)
Table 2.4: Emission reduction in plants with WMA (%) (D’angelo et al., 2008)
Emission Norway Italy Netherland France 2.4
CO2 31.5 30-40 15-30 23
SO2 N/A 35 N/A 18
VOC N/A 50 N/A 19
CO 28.5 10-30 N/A N/A
NOX 61.5 60-70 N/A 18*
Dust 54 N/A N/A N/A
126.96.36.199 Paving Benefit
The basic mechanism that make suitable WMA to reduce the binder viscosity and in
return it cover easily the aggregates as compare to conventional HMA where intensive
heat required to reduce the binding viscosity, is the techniques of WMA. WMA can
improve mixture compatibility in both the Super pave gyratory compactor and the
There is many benefits of WMA including facilitating
compaction,transportation,recycling at higher rates, placement of multiple lifts within a
short time window and placement of Bituminous materials on crack-sealed substrates
without the occurrence of bumps:
Warm mix technologies improve compaction. The WMA objectives include
temperature/viscosity relationship modification in such manner that, suitable mixing
and compaction viscosities are achieved at lower temperatures, while adequate viscosity
is maintained at service temperatures.( Jean-Martin et al, 2008).
(ii) Lower Viscosity
WMA technologies have the ability to reduce the binder viscosity. Several advantages
are gained from the lower viscosity as the workability of the asphalt mixture is
improved. Better compaction can be achieved and a lower number of roller passes are
needed to reach the targeted density .Hence, WMA can help extend the paving season
and enable hauling the asphalt mix for longer distances and preserve sufficient
workability for placement and compaction (Hossain et al., 2009).
Figure 2.2: Modification of binder Temperature/viscosity relationship (Jean-Martin et
(iii) Oxidative Hardening
Oxidation of the asphalt binder starts during its mixing with hot aggregates and
continues throughout the pavement life. Age hardening takes place due to oxidation
resulting in the stiffening and the hardening of the binder with the temperature of the
asphalt oxidation reaction a significant factor that determines the rate of formation and
the type of oxidized species formed (Hossain et al., 2009). Hence, theoretically, using
WMA technologies can possibly reduce the susceptibility of an asphalt mixture to aging
and cracking as the mix is not exposed to the elevated production and placement
temperatures which can lead to a longer pavement service life.
188.8.131.52 Economic Benefit
WMA can usually lower asphalt-mixing temperatures by 15 °C to 30 °C
compared to Conventional HMA. This could reduce burner fuel costs by 20% to 35%.
Fuel savings could be 50% or more when producing low-energy asphalt concrete
and low-energy asphalt in which the aggregate is not heated above the boiling of
water. However, Additional costs could be necessary for equipment and additives
(D’Angelo et al. 2008).
Based on the WMA technique used and conditions; the energy consumption
range is 20 to 75% of HMA, and the burner fuel savings range from 20 to 35% (Hossain
et al., 2009). For processes such as low-energy asphalt concrete, and low energy asphalt
(LEA), fuel savings could reach more than 50%. Previous studies showed that the
WAM-Foam WMA plant processing can be implemented with 40% lower energy
consumption than HMA. Moreover, a 30% in energy consumption reduction was
reported in measurements conducted for Eurovia when using Aspha-Min because of a
54 to 63°F decrease mix temperature (Button et al., 2007). The true economic gain from
the reduced energy consumption relies on the type of energy and its cost at the time.
With continuous surges in the prices of energy sources, the non-renewable sources
specifically, WMA could turn into an economically attractive alternative to HMA in the
near future (Hossain et al., 2009).
2.3 Warm Mix Asphalt Technologies
There are many different products and processes that are used to achieve this reduction
in temperature but the technologies can generally be grouped into four main categories.
2.3.1 Organic-based WMA Technologies
Organic additives are waxes that are used to reduce the viscosity of asphalt binder at
lower temperatures. Sasobit®, produced by Sasol Wax Americas, Inc. is an example of
a wax based Organic additive and is the most often used organic additive in the United
States.( Sasol Wax North America Corporation,2011).
Figure 2.3: Temperature-viscosity relationship with addition of organic additive
(Anderson, et al., 2008)
2.3.2 Chemical Additive-based Technologies
Chemical additives, which are also known as surfactants, are an emerging group of
additives for WMA. Surfactants help the asphalt binder coat the aggregate at a lower
temperature. Evotherm™ Emulsion Technology (ET) which is produced by
MeadWestvaco Asphalt Innovations is an example of a chemical additive. The process
consists of the additive being blended with asphalt that is mixed with the aggregates to
produce asphalt mixtures with a 55⁰C (100⁰F) reduction in production temperature.
Evotherm™ requires no plant modification and the majority of the water in the
emulsion flashes off when the emulsion is mixed with hot aggregates (MeadWestvaco
Asphalt Innovations ,2011).
2.3.3 Water-based WMA Technologies
Small amounts of water are introduced into the heated asphalt binder to form a
controlled foaming effect that results in a small increase in binder volume and a
reduction in viscosity. Water-bearing additives such as synthetic zeolites are used to
enhance aggregate coating by asphalt at lower temperatures. Zeolites have porous
structures that include approximately 20% water. When heated to a specified
temperature, the water is released and foamed asphalt is produced (5). Advera®,
produced by the PQ Corporation, is an example of a water-bearing additive. Advera® is
a hydrated zeolite powder that can be added to reduce the production temperature of
asphalt mixtures by 10⁰C to 21⁰C (50⁰F to 70⁰F). Advera® can be added to asphalt
mixtures without any mixture design changes. (PQ Corporation, 2011).
2.3.4 Water Bearing Additive Technologies
Foamed asphalt is produced by adding a small amount of water to the heated asphalt
through the means of a nozzle or damped aggregate. Introducing the moisture into a
stream of hot asphalt causes spontaneous foaming of the asphalt which increases the
surface area of the asphalt while lowering its viscosity. This technology is believed to
be the most cost effective from among the WMA technologies since it does not require
any costly additives to be added to the mixture(Ala, et al, 2011)
2.4 Basic Materials in Warm Mix Asphalt
Aggregate is the main component of any asphalt pavement. American Society Testing
Materials (ASTM) had define aggregates as a granular or coarse material in the form of
mineral such as crushed stone, sand and gravel. Aggregates can be used with
cementing medium to form mortars or concrete or alone as in base courses, in the
presence of medium like water. Aggregate can generally be described as the rigid, static
mineral material component of the mixture, which provides a stable, structural skeleton
to the mixture. This mechanically stable skeleton/framework primarily contributes to
the load-supporting capacity of the pavement mixture. Consequently, the performance
of a mixture is heavily influenced by the aggregate. Aggregate is the main component
of an asphalt mix, generally consists of 90-95% by Weight and 75-85% by volume.
(Asphalt Institute, 2007). The aggregates have significant influence on the mixture
performance since the mixture consists mostly of aggregates. Brown et al (1996)
classify these different sized aggregates as coarse and fine aggregate as well as filler
According to their size. The coarse aggregate is described as particles retained on a No.
4 sieve (4.75 mm), fine aggregate as particles passing the No. 4 sieve (4.75 mm) But
retained on the No. 200 sieve (0.075 mm) and the mineral filler as at least 70% of The
material passing the No. 200 sieve (0.075 mm).furthermore, aggregates are also used in
sub-base layers for rigid and flexible pavements. The aggregates either will be natural
or obtained by some mechanical process.
The natural aggregates are obtained from open excavation of Rocky Mountains
which have specific quality of rocks capable of engineering properties. Broadly the
natural aggregates can be classified as igneous, metamorphic and sedimentary. Crushed
stone, sand and gravel are three types of the aggregates. Crushed stone also known as
crushed rocks and mostly crushed stone is excavated from the bedrock. The second type
of rock is gravel; it is the result from the erosion and destruction of bedrock and surface
resources. Gravel also can be crushed, since it has a large contribution in
constructing asphalt pavement or bases. The formation of sand is either from the
erosion of bedrock or mechanically crushed.
The different names are used for binder in different countries like binder, bitumen, and
asphalt. The Asphalt Institute (2007) describes binder as viscous Liquids or solids
mainly consisting of hydrocarbons and their derivatives, which are soluble in carbon
disulphide. At room temperature the binder is nonvolatile but with heating it’s become
softens. The binder is also called visco-elastic material; it means the binder behavior
changes with change in temperature or loading time. Modified binder such as
polymer modified binder are recommended to improve resistance of asphalt binder
against rutting and thermal cracking (Moghaddam, et al, 2011).This is class of black
or dark-colored (solid, semi-solid or viscous) cementations substances, natural or
manufactured, composed principally of high molecular weight hydrocarbons, of which
asphalts, tars, pitches, and asphaltenes are typical. In other words, it acts as the glue
that holds the road together ( Youtcheff,et al, 2000).Bitumen or asphalt is a
constituent of petroleum with most crude petroleum containing some asphalt.
Crude petroleum from oil wells is separated into its fractions in a refinery by a
process called distillation. During the process, crude petroleum is fed into a tube still,
where its temperature is quickly raised for initial distillation processes. It then enters a
fractionating tower where the lighter or more volatile fractions vaporize and are drawn
off for further refining. Residue from this fractionating process is the heavy component
of crude petroleum, which includes asphalt. However, further refinement is necessary to
produce bitumen cement.
184.108.40.206 Types and Grades of Bitumen
The two main types of binders are conventional (or penetration grade) and modified (or
polymer-modified) bitumen. According to Sabita, (2007) other types of bitumen
included cutback bitumen, bitumen emulsions and bitumen rubber.
Modified binders are typically used for
(i) To increase the mixture’s resistance to rutting of mixture.
(ii) To increase resistance to thermal cracking of mixture
(iii) To increases durability of mixture
220.127.116.11 Characteristics of Bitumen
Bitumen has the ability to adhere to a solid surface in a fluid state depending on the
nature of the surface. The presence of water on the surface will prevent adhesion.
b) Resistance to Water:
Bitumen is water resistant. Under some conditions water may be absorbed by minute
quantities of inorganic salts in the bitumen or filler in it.
To measure the hardness of bitumen, the penetration test is conducted, which
measures the depth of penetration in tenths of mm. of a weighted needle in
bitumen after a given time, at a known temperature. Commonly a weight of 100
gm is applied for 5 sec at a temperature of 77 °F.
The penetration is a measure of hardness. Typical results are 10 for hard coating
asphalt, 15 to 40 for roofing asphalt and up to 100 or more for water proofing bitumen.
d) Viscosity and Flow
The viscous or flow properties of bitumen are of importance both at high
temperature during processing and application and at low temperature to which
bitumen is subjected during service. The flow properties of bitumen vary
considerably with temperature and stress conditions. Deterioration, or loss of the
desirable properties of bitumen, takes the form of hardening. Resultantly, decrease in
adhesive and flow properties and an increase in the softening point temperature and
coefficient of thermal expansion.
2.5 Problems Related with Warm Mix Asphalt
A large number of questions regarding the implementation of this technology,
especially about the specifications and quality control need to be answered. Potential
drawbacks should be considered in context with the specific technology as different
methods have particular flaws, but to generalize, there are some concerns about the
performance and implementation of WMA. They are listed below
2.5.1 Moisture Susceptibility of WMA
The most major concern for WMA is the potential moisture susceptibility of the
pavement since significantly reduced production and compaction temperatures might
lead to incomplete drying of aggregates, and therefore presence of residual moisture,
which could have negative influence on pavement performance, such as rutting,
stripping and fatigue cracking. On one hand, given the limited drying time and
relatively low temperatures, aggregates may not dried sufficiently, leading to certain
amount of moisture trapped in the mixture; on the other hand, to reduce binder
viscosity, additives or foaming technologies may be introduced into asphalt binder.
Furthermore, these pavements could be subjected to moisture during rainy seasons. Any
moisture remaining in or on the aggregates would affect aggregate coating and
exacerbate the loss of bond between asphalt binder and aggregates, causing asphalt
stripping and premature pavement failure. Typically the loss of bond begins at the
bottom of the pavement layer and progresses upward ( Hossain., et al,2009).
Premature rutting has been reported for surface asphalt concrete in different studies.
This has been mostly related to decreased ageing at lower production temperatures and
increased moisture content for foaming technologies.
2.5.3 Insufficient data for evaluation
Since the field test sections constructed in United States are less than seven years old
and the sites in Europe (Germany and Norway) are somewhat over ten years old, it is
too early to comment on long term performance. To date, in US no notable negative
long term performance has been reported (Arif and Button,2008). and in Europe the
trial sections of WMA have performed the same or better than HMA overlays (John, et
al,2008,). It must be noted that in the US there are number of government programmers’
for WMA evaluation, whereas in Europe examinations mostly depend on private
companies which means significantly less independent review of different WMA
2.5.4 Long term performance
Theoretically, because the better compaction possibilities may result in higher density
for WMA, this could result in problems due to insufficient number of air voids in the
mixture to ensure desirable bitumen content. This may lead to problems with moisture
susceptibility, cracking and oxidative ageing. A similar problem is connected with
lower mixing temperatures indicates less binder absorption into the aggregates,
which may lead to the same faults as described above.
2.5.5 Water presence
Foaming and some of the chemical WMA technologies are somewhat connected
with the introduction of water in the initial mixing process. Because of possible
incomplete vaporization of water during the mixing and laying process residual water in
the mixtures may cause problems of premature rutting and stripping of pavements.
Therefore special attention must be paid to the evaluation of potential moisture damage
in the laboratory. This is especially important with any foaming technologies and
although most of them use chemical anti -stripping additives to improve coating and
adhesion different initial material moisture content together with poor water resistant
mix formula may cause some coating problems.
There are some concerns about the implementation of WMA production technology
because of its cost. It is necessary to prove the potency of WMA compared to
HMA so that the use of this technology becomes widespread. It must be
established whether reduced energy consumption will reduce the overall costs of
WMA production. If no proof of lower production costs are established, it may be
possible that contractors will not choose this technology for its other benefits
alone, and if no stricter emission regulations are obligated, the WMA technology
could not become widespread. Increase in costs may arise from:
(i) The investment and the depreciation of plant modification;
(ii) The costs of additives;
(iii) Possible costs for technology licensing
2.5.7 Low temperature behavior
The low temperature properties of bitumen used in organic WMA technologies can be
slightly different than expected for conventional HMA. Through this attention should
be given to change in low temperature behavior if it is relevant for the given
climate conditions. This change in performance can be explained through the
crystallization of waxes thattend to increase the viscosity and stiffness of the binder.
Therefore low temperature binder properties should be evaluated to predict the possible
changes of bitumen in WMA.
2.5.8 Life cycle assessment
Good and easy to use life cycle assessment tool would be necessary to verify the
statement of potential environmental benefits. There are concerns that some of the
environmental benefits may be offset due to the carbon footprint embodied for
producing additives and/or any additional equipment supporting the production of
WMA. Since there are still some concerns about the WMA long term performance
compared to Hot Mix Asphalt (HMA), life cycle assessment would require information
on the longevity of WMA.
2.5.9 Use with SBS polymer modified bitumen
Although WMA technologies are fully compatible with Styrene-Butadiene-Styrene
(SBS) modified bitumen. ( Michael,et al,2008) states, that modification of bitumen with
both SBS polymer and Fischer Tropsch (FT) wax might not be reasonable for
performance improvement as the benefit from adding wax to SBS modified bitumen is
less than when adding it to pure bitumen, but the results achieved in super-pave
applicable temperature range Penetration Grade (PG) are almost the same, thus
somewhat “overlapping” the benefits and increasing the costs. However it does not
reduce the effects of lower temperature production and paving so it still might be
beneficial to use FT-wax with modified binders.
2.6 Anti-stripping agents
2.6.1 Hydrated lime
The use of hydrated lime for moisture reduction in HMA are well recognized and
widely used in industry. The WMA also show the same results of reduction in moisture
reduction by gradually increasing the amount of hydrated lime. The moisture content in
WMA leads to the problem of stripping. The phenomenon of breaking of the bond
between aggregate and bitumen is known as stripping (Amirkhanian, 2010). Moisture
damage of asphalt pavement can lead to serious distress, reduced performance, and
increased maintenance of asphalt pavements.
Localized bleeding, particle degradation, disintegration, potholes, shoving, and
structural failure of pavement due to permanent deformation and cracking are examples
of moisture-induced damage.(Kennedy TW,2009)Detachment, displacement,
emulsification, pour water pressure, hydraulic scoring, and bitumen–aggregate
interfacial physical–chemical processes have been identified as the cause of moisture
susceptibility problems.( Little DN, Epps JA,2011).the moisture susceptibility is one of
the potential disadvantages of WMA mixtures (Roshani,2012).thus to prevent moisture
susceptibility ,proper mix design and use of anti-stripping agent is required. one of the
most commonly used anti-stripping agents in the world is aggregate coating with
suitable agents such as hydrated lime and polymer.(Zhao W,2010).The Mixes
containing hydrated lime and liquid anti-stripping agent are stiffer, less susceptible to
rutting, moisture damage and cracking. (Tahmoressi, Sebaaly, 2005).the research
carried out shows that apart from the sources of aggregates and bitumen, hydrated lime
has the most effect on moisture resistance increase (Zhao W et al, 2005).Three forms of
lime are used: hydrated lime (Ca (OH) 2), quick lime (CaO), and Dolomitic limes (both
types S and N) (Roberts et al, 1996). Several methods exist for adding lime to mixtures.
Dry hydrated lime is added prior to the asphalt cement. Georgia DOT adds the dry
hydrated lime immediately before the asphalt cement is added (Roberts et al. 1996).
2.6.2 Liquid Anti-Stripping Agents
The most common liquid ASAs such as amines, demines, liquid polymers, and solids
like Portland cement, fly ash, flue dust, etc. are currently used .Pavement contractors
usually prefer liquid ASAs as they are relatively easy to use. (Lu and Harvey,2006).
Most anti -stripping agents reduce surface tension between the asphalt and aggregate in
a mixture (Tunnicliff et al. 1984).the liquid anti-stripping agents reduce surface tension,
and increase the adhesion between aggregates and asphalt. Thus, most liquid anti -
stripping agents are surface-active agents (Roberts et al. 1996). The liquid asphalt
commonly is mixed with the liquid anti stripping agent prior to adding aggregate to the
mix. (Roberts et al.1996).
2.7 Mineral Filler
Mineral filler consists of very fine, inert mineral matter that is added to the mixtures to
improve the density and strength of the mixture. Mineral fillers have traditionally been
used in asphalt mixtures to fill the voids between the larger aggregate particles.
Generally, the aggregate material passing the No.200 sieve is referred to as filler. Filler
defined as “finely divided mineral matters such as rock dust, slag dust, hydrated lime,
hydraulic cement, fly ash, or other suitable mineral matters, such as carbon black and
sulfur, have been used primarily to modify asphalt binder properties, but they do have a
role as filler.(ASTM D 242,1995).This specification further requires that 100 percent of
the particle shall be finer than 600-gm, 95-100 percent shall be finer than 300-gm, and
70-100 percent shall be finer than 75-gm.
Filler may be used for the following purposes. The use and the application of mineral
filler in asphalt mixtures are intended to improve the properties of binder by reducing
the binder’s inherent temperature susceptibility. (Ratnasamy, 2009). Two theories had
been proposed regarding the functions of fillers. The" Filler Theory "presumed that
particles coated with bitumen fill the voids in the aggregates."Mastic Theory"
proposed that the filler and bitumen combined to form mastic which fills the voids
and binds the aggregates.( Csanyi and Cox,1964).
(i) Fill the voids
(ii) Increase stability and strength
(iii) Improve the bond between asphalt cement and aggregate
(iv) They stiffen the mixture at the upper range of pavement temperatures with little
stiffening at lower temperatures. At low temperatures they appear to toughen
the asphalt binder increasing resistance to cracking.
(v) Not all mineral fillers are the same or affect mixtures in the same manner. A
May extend the asphalt cement or may stiffen the asphalt cement. Gradation
parameters alone are not reliable predictors of filler behavior in a mix.
The mineral filler shall also be treated as an anti-stripping agent. (JKR, 2008)
Table 2.5: physical Properties of the Mineral Fillers
Filler Specific Gravity % passing sieve No.200
Portland Cement 3.15 96
Lime stone Powder 2.78 94
Glass Powder 2.65 92
2.8 Pavement modifier
Asphalt cement requires modification to meet the specifications under certain
circumstances. Asphalt cement modification has been in practiced from 50 years.
Polymer-modified binders helped to improve the performance of HMA asphalt
pavement, but a problem occurs when WMA was introduced. WMA is to be produced
and compacted at lower temperatures than HMA but still perform comparably to the
HMA. Simply modifying the binder with polymers will only improve the performance
of the mixture at high temperatures and this alone will not be enough to lower the
production and compaction temperatures and still achieve equal or better performance
than HMA mixes. Thus WMA technologies were developed to create an additive or
process which would reduce the production/compaction temperatures of the mix and
still maintain the desired performance criteria required.WMA technologies generally
reduce the binder viscosity and provide complete coating of the aggregate at lower
According to the European Roads Review 18 (ERR, 2011) these WMA
technologies can reduce production temperatures by as much as 40%. WMA
technologies are classified by type with regard to how they are implemented. Two main
types of WMA technologies are classified, namely foaming technologies and additive
technologies. Foamed asphalt is formed by combining hot asphalt binder with cold
water. When the cold water comes in contact with the hot asphalt binder, it turns into
tiny steam bubbles trapped inside the asphalt binder. This leads to an expansion in the
volume of the binder and improves the coating potential of the binder. Warm asphalt
mix using foamed asphalt technology (WAM-foam) is a patented process developed
jointly by Shell Global Solutions and Kolo Veidekke in Norway. In the WAM-foam
production process, two different bitumen grades, soft bitumen and hard bitumen, are
combined with the mineral aggregate. The aggregate are first mixed with the softer
binder, which is fluid enough at lower temperatures, and then the harder binder is
foamed and mixed with the aggregates pre-mixes with the softer binder. However,
selecting the right grades of the soft and hard binders is critical to this process. This
process makes it possible to produce the asphalt mixture at temperatures between 100°C
and 120°C (212 and 250 °F) and compact it at 80 to 110°C (175 to 230 °F) (Koenders et
al. 2000). Recently, Astec Inc. in Chattanooga, TN also developed a Double Barrel
Green System, where a multi-nozzle device is fitted to a double barrel drum plant. The
multi-nozzle device is used to produce microscopic bubbles in the asphalt binder by
combining a small amount of water with the asphalt binder before it is introduced to the
aggregate. The manufacture claims that this process can reduce the fuel consumption by
as much as 11% (Astec Inc, 2007).
Generally the asphalt cement is modified to achive the following(Roberts et al, 1996).
(i) Lower stiffness (or viscosity) at the high temperatures associated with
(ii) Higher stiffness at high service temperatures. This will reduce rutting and
(iii) Lower stiffness and faster relaxation properties at low service temperatures.
This will reduce thermal cracking.
(iv) Increased adhesion between the asphalt binder and the aggregate in the
presence of moisture.
WMA mixtures are more prone to moisture damage then HMA mixtures, designed
using the same aggregates and binder. The premise of employing WMA technology is
to guarantee that WMA pavement must possess similar workability, durability and
performance characteristics as HMA using substantially reduced temperature.
(Bonaquist, 2011). The major problem with WMA is the potential moisture
Susceptibilityof the pavement since the temperature for production and compaction is
lower as compared to HMA and it might lead to incomplete drying of aggregates.The
presence of residual moisture which could have negative influence on pavement
Performance. Moisture content leads to rutting, stripping and fatigue cracking in the
WMA. On one hand, given the limited drying time and relatively low Temperatures,
aggregates may not dried sufficiently, leading to certain amount of Moisture trapped in
the mixture; on the other hand, to reduce binder viscosity, additives or foaming
technologies may be introduced into asphalt binder. Stripping is one of the most
occurring modes of pavement failure. Stripping is defined as bonding failure between
aggregates particles and bitumen and either failure within bitumen structure (Xiao and
Zhao,2010).the failure mechanisms of this phenomenon are very complicated.(khodaii,
Figure 2.4 Stripping in pavement (pavement interactive, 2010)
Stripping causes a reduction of materials strength over time, manifesting itself in terms
of rutting, corrugation, shoving, raveling and cracking distresses (Juang, et al,2007).
Some researchers believe that the low mixing and compaction temperatures can lead to
increased stripping potential in mixes, as a result of retained moisture in aggregate
particles (Kazemi and tehrani, 2012). Furthermore, these Pavements could be subjected
to moisture during rainy seasons. Any moisture remaining in or on the aggregates would
affect aggregate coating and exacerbate the loss of bond between asphalt binder and
aggregates, causing asphalt stripping and premature pavement failure. Typically the loss
of bond begins at the bottom of the pavement layer and progresses upward (Hossain,
The roads are mostly consists of flexible pavements. Road pavements are exposed to
various traffic loads, changeable climatic cycles, and different soil characteristics of
roadbed, which may result in distortion of pavement layers. These distortions either will
be cracks, deformations, deterioration, and, failure and are located underneath the wheel
tracks especially where the soil bearing capacity has been weakened during highly
varied climatic temperatures. The most common pavement distress involved cracking,
and rutting (permanent deformation). Rutting is known as longitudinal depression,
which follow the line of wheel paths. The deterioration of pavements due to rutting is
the result of heavily travelled flexible pavements. Rutting is the result of permanent
deformation due to traffic loading in one or more layers of pavements. Rutting leads to
decrease in riding quality. Rutting in pavements causes hydroplaning, severe
physiological and safety concern for users. Rutting can be the result of permanent
reduction in volume (consolidation/traffic densification), permanent movement of the
materials at constant volume (plastic deformation/shear), or combination of both.
(Christos and Drakos, 2004).Bituminous concrete plastic properties contribute to
permanent deformation under repeated loading. Development of rutting is caused by a
combination of densification and shear-related deformation with an increasing number
of load applications and may occur in any layer of a pavement structure. (Wang, H.,
Zhang, Q., and Tan, J. (2009).The deterioration may occur due to lateral plastic
deformations especially in high temperature in unstable wearing course or sub grade
soil (O Flaherty,1988). Field studies indicated that the rutting is usually influenced by
the use of excessive binder content and improper aggregate gradation (Brown and
Mahrez, 2008). This excessive binder essentially results in low air void and causes a
loss of mechanical friction in the mineral skeleton and eventually leads to a greater level
of plastic flow in bituminous pavement matrix(Mahrez, 2008). Varied temperature,
adhesion of bitumen with aggregate, speed of vehicle, amount and distribution of
traffic, and surface contour are important factors to create rutting in pavements. Shear
deformations resulting from high shear stresses in the upper portion of bituminous layer
appear to be the primary cause of rutting in flexible pavements. Repeated applications
of these stresses under conditions of comparatively low mix stiffness lead to the
accumulation of permanent deformations at the pavement surface (Katman,
2006).Rutting or channeling, could be classified in three types: 1) mechanical
deformation (rutting in sub grade or base), 2) plastic flow (unstable asphalt layer), and
3) wheel path consolidation ( The Asphalt Institute, 2003).
Figure 2.5: rutting pattern on road(Asphalt institute, 2007)
Figure 2.6: Determination of rutting depth (highway association, 1999)
2.10.1 TYPES OF RUTTING
Rutting can be divide into three types, based on the cause and layers in which rutting
occurs, and it can be characterized by two components of the original (initial) Pavement
profile change which are direct consequences of permanent deformation: uplift and
downward deformation (Kandhal and Cooley,2003).
Figure 2.7:Characterization of downward and total rutting, (Williams and Romero,
(i) One-dimensional densification (vertical compression)
A rut depth caused by material densification is a depression near the centre of the
Wheel path without an accompanying hump on either side of the depression. Generally,
The densification of material is caused by excessive air voids or inadequate compaction
after placement of asphalt material, thereby allowing the material or underlying layers
to Compact when subjected to traffic loads This type of rut depth usually results in a
low-to moderately-severe level of rutting(Cooley, 2003).
(ii) Lateral flow or plastic movement
Such longitudinal or lateral distortion of asphalt mixtures is caused by the localized
shear failure resulting from overstressing the mixture with high tire pressure (NCHRP
Report, 2003). Rutting depression occurs by the lateral flow of material near the centre
of the wheel path with humps on either side of depression. This type of depression in
pavement usually results in a moderate to highly severe level of rutting. Displacement
of materials will occur in those mixtures with inadequate shear strength or an
insufficient amount of total voids in the asphalt layer. Low voids after construction can
make asphalt to act as a lubricant rather than a binder during hot weather.
For visco-elastic materials, such as asphalt mixtures, the time of load affects the
amount of deformation that occurs in the material, so distortions will be less on
highways with higher speeds than on highways with lower speeds, given the same
truckloads. Also this deformation at the constant load conditions will be higher at higher
temperatures. Rutting caused by lateral flow is difficult to accurately predict with
repeated load tri-axial testing equipment, especially when the asphalt mixture is highly
anisotropic, i.e. properties vary with direction ( Transportation Research Board,
Washington, DC, 2003).
(iii) Mechanical deformation
The mechanical deformation or rutting is the consolidation (compaction),or the lateral
movement of the unbound materials below the asphalt surface. This type of rutting has
been referred to as "mechanical deformation". Mechanical deformation is a result of
subsistence in the base, sub base, and/or sub grade and is usually accompanied by a
longitudinal cracking pattern at the pavement's surface when the asphalt mixture is too
stiff (high elastic modulus). These longitudinal cracks generally occur in the centre and
along the outside edges of the ruts(Asphalt Institute, Lexington,A. Cooley, KY, 2003).
2.10.2 Causes of rutting
Rutting in asphalt pavements has become one of the major distress forms with the
increase in traffic volume, tire pressure and axial load. It often happens within the first
few years after opening to traffic. (Suo and Wong, 2008).according to the national
cooperative Highway Research Program, permanent deformation was selected as the
most serious problem for highways and runways in the united states among all the
distresses in asphalt pavements.(Witezak,1998).fatigue cracking was rated the second
serious problem and thermal cracking the third serious problem with asphalt pavement
Major rutting is attributed to the decrease in thickness of middle and lower layer,
and the driving lane shows a severer rutting. Inadequate compaction is a major cause of
the final depth of rutting. The aggregate gradation is also a major contribution to the
rutting distress of pavement.
The gradation Between 1.18 and 4.75 mm in sieve size becomes finer for the
three layers. Show an increase in asphalt content, but the lower layer presents a decrease
in asphalt content.
The rutting principally occurs due to repetitive shear deformation under a
variety of traffic loading. (SHRP, 1991).loading conditions in the form of magnitude,
tire pressure, and traffic volume; environmental conditions in the form of temperature;
and WMA properties in the form of aggregate characteristics (shape, texture, and
structure), and binder type are among the major contributors to rutting resistance.
2.10.3 Factors Affecting Rutting
Table2.6:(Kandahar, et al, 2003)
2.10.4 MECHANISM OF RUTTING
Rutting in asphalt pavements develops because of the densification (compaction) and
shear flow in asphalt concrete layers and due to permanent deformations in the
aggregate base, sub base and soil sub-grade. Rutting in asphalt concrete pavement
usually appears as a longitudinal Depression under the wheel paths of vehicles and a
small bulging on the sides. The extent of rutting gradually accumulates with increasing
numbers of wheel load applications on the pavement .Two major phenomena
contributing to rutting of asphalt concrete pavements are densification (decrease in
volume and hence increase in density) and shear plastic Deformation (Collop et al.,
These two phenomena contribute in varying degrees to the permanent
deformations in all pavement layers including asphalt concrete surface course, asphalt
base course, aggregate base and sub base and sub-grade. Studies on asphalt mixtures
indicated that shear deformation rather than densification was The primary rutting
mechanism (Highway Research Board, 1962) and (Hofstra et al., 1972). (Eisenmann et
al., 1987) also concluded that if the Pavement has been compacted to higher density
during construction, their densification during the application of wheel loads is unlikely,
and rutting is induced predominantly due To shear flow of the asphalt mixture.
Thicker asphalt concrete layers exhibit more permanent deformation within the
asphalt Concrete layer, but the amount of permanent deformation does not increase
directly with the increasing layer thickness beyond a certain threshold thickness of the
asphalt layer. Any increase in the depth of the asphalt layer beyond this threshold will
not influence the Total rut depth within the asphalt layer.(Uge and Van de Loo,1974)
demonstrated that the rut depth reaches a limiting value for An asphalt concrete layer
thickness of 13 cm to 25 cm and any further increase in the depth Has a negligible
effect on the total amount of rutting in the asphalt layer. Similar findings were made
during the AASHO road test, Highway Research Board (1962). This is due to the
decrease in shear stresses at greater depth in the asphalt layers.(Hofstra and Kiomp,
1972) observed during laboratory test track studies on asphalt Pavements that the
permanent deformation within the asphalt layer increases relative to the thickness of the
However, by increasing the thickness of the asphalt layer beyond 10 cm. further
increases in permanent deformation of the asphalt layer was insignificant. (Hofstra et
al., 1972) shows that by increasing the thickness of the asphalt layer from 10 to 20 cm.
the increase in permanent deformation is Negligible. However, a significant increase in
permanent deformation within the asphalt Layer can be noticed when the layer
thickness is increased from 5 to 10 cm. This also strengthens the belief that the larger
portion of the total rut depth is contributed by the Asphalt layer near the surface due to
high shear stresses under the wheel load. These Results reveal that if the supporting
material under the asphalt concrete layer is reasonably stiff, most of the total pavement
rutting develops within the asphalt concrete layer(Ce’lard, 1977).
18.104.22.168 Laboratory Test Related to Rutting
22.214.171.124 Wheel Tracking Device
Wheel Tracker typically measures the rut, created by repeated passage of a wheel over
Prismatic asphalt concrete samples. It will be used to assess the resistance to rutting of
theAsphaltic material, under standard defined conditions of load and temperatures. the
wheel speed is maintained during the test. The rut resistance can be quantified as the
rate of rutting during the test or the rut depth at the conclusion of the test, measured
with Linear Variable Displacement Transformers (LVDT) 25mm (min). Slab specimens
were prepared in the laboratory for research study. The susceptibility of an asphaltic
material to deform is assessed by measuring the rut formed byrepeated passes of a
loaded wheel at specified temperatures. The wheel tracking apparatusconsists of loaded
wheel which bears on a sample held on a moving table. The moving table reciprocates
with simple harmonic motion with a frequency of 26.5passes per minutes (European
Standard- EN 13108/12697-22, 2002).
Figure 2.8: Wheel Tracker Solid Rubber Tire (After Cooper, 2006)
The wheel is fitted with solid rubber tire of outside diameter 200 mm. The tire is a
rectangularsection 50 ± 1 mm wide and 10mm to 13 mm thick. The wheel tracker is
fitted with atemperature controlled cabinet with a maximum temperature up to 65Co
. Square slabspecimens (305x305mm) of asphalt mixes with typical asphalt wearing
course thickness of50mm thick, fitted with wheel tracker (WT) table, clamps for
securing specimen holders. Mixes were evaluated under a loaded wheel (700 ± 20 N)
tracked with simple harmonic motion through a distance of 305mm on specimens under
specified conditions i.e. 53 passes perminute at temperatures 25Co
(European Standard- EN 13108/12697-22,2002).
The operational software run under Windows to start and stop the WT, control
speed and acquire deformation and temperature data. An on-screen display provides a
continuously updated graph of time versus deformation as shown in Figure 6.3. The test
data are stored in a text file for subsequent analysis using a spreadsheet.
2.11 Other Test Related to Rutting
2.11.1 Hamburg Wheel-Tracking Device
The HWTD, was developed by Helmut-Wind incorporated of Hamburg, Germany
(Aschenbrener, 1995).it is used as a specification requirement for some of the most
traveled roadways in Germany to evaluate rutting and stripping. Tests within the
HWTD are conducted on a slab that is 260 mm wide,320 mm long, and typically 40 mm
high( 10.2 in x 12.6 in x 1.6 in).
Figure 2.9: Hamburg Wheel-Tracking device (Hans, 2006)
(i) The warm mix asphalt is an alternative solution to the problem of global
warming and preservation to the economy of the country. It has significant
benefits to the working environment because it’s significantly reduced the
emission and heat from the mix.
(ii) As compare to HOT, WMA is largely adopted by many countries for their
highway constructions. Many technologies and techniques are in-cooperated
with WMA to improve its resistance to pavement distress.
(iii) The problem with WMA as pointed out is moisture content, because of their
preparation at lower temperature as compare to HOT. To overcome the
problems of moisture Susceptibility, additives are used. Additives function is
to reduce moisture and increase the binder viscosity.
(iv) The common pavement distress is cracking, rutting, and stripping.
(v) The rutting can be minimized by the use of anti-stripping agents and
(vi) Hamburg Wheel Tracking Test and other laboratory tests will be used to
assess and evaluate the rutting resistance under different loading conditions.
(vii) The stripping will be assess and anti-stripping agents namely hydrated lime,
Portland cement and PMD effects will be study and its effects on stripping
will be evaluate.
(viii) The purpose of the study is to enhance the rutting resistance of warm asphalt
mixes, and study the effects of Sasobit®
. on rutting resistance.
This research methodology was developed to achieve the aim and objectives of this
research. The aim of this study is to evaluate the rutting resistance of warm Mix asphalt
incorporating anti-stripping agents namely Sasobit®
.The first step will be the
background information and study of the proposed research, to explore in detail the
information before going to the actual laboratory tests.
After the primary data search the next step will be laboratory tests and data
evaluation. The test is conducted according to the required specifications, laboratory
test procedure and information on the materials used and also based on the sample
properties. The laborites’ tests are starting from selection of proper materials for warm
asphalt mix design. After selection of materials the material test for bitumen,
aggregates. Then the addition of additives and anti-stripping agents to improve the
asphalt mix viscosity at lower temperature. The wheel tracking test will be conducted
under different loading and temperature, and the rutting resistance will be noticed.
Figure 3.1: Research methodology flow chart
(Aggregate, asphalt binder)
Aggregate Properties Evaluation
Aggregate Impact Value
Flakiness and Elongation
(Aggregate and asphalt binder)
Asphalt Binder Properties Evaluation
Rational viscosity Test (RV)
Dynamic Shear Rheometer test
Anti-Stripping Agents Use
Data and Analysis
Discussion and Conclusion.
Wheel tracking test
Moisture Sensitivity Test
Moisture sensitivity test (AASHTO T283)
3.2 Laboratory tests procedures
The study will be conducted base on laboratory testing as the main testing procedure to
obtain the required results and estimates. The entire test will be conducted in the
highway laboratory. The laboratories tests are divided into several stags begin with the
aggregates preparation. Crush aggregate granites will be washed, dried and sieved into a
selected size range according to standard specifications (ACW 14) as requirements by
the Public Works Department (JKR, 2008).
3.3 Materials selection
3.3.1 Asphalt binder
The binder used in this research study is grade PEN 80/100 . Type of asphalt
cement binders is classified based on their depth of penetration at Various
temperatures. Thebinder classification tests performed include Penetration test (ASTM
D5097) and Softening Point test (ASTM D-3461). The asphalt binder selection depends
on temperature and traffic loading conditions in the project area. Penetration Grade
Bitumen is commonly used in road surfacing, and some industrial applications.
3.3.2 Softening Point
The objective of softening test is to determine the softening point of bitumen within the
range 30 to 157 º C by means of the Ring-and-Ball apparatus. The procedure of this test
is the specimen will be carried out according to ASTM D36 (ASTM, 2005b)
procedures, precisely. Dimensioned brass rings and will be maintained at a temperature
of not less than 10’C below the expected softening point for at least 30 minutes before
the test. Then, the rings and assembly and two ball bearings will be placed in a liquid
bath filled to a depth of 105 ± 3mm and the temperature of 5 ± 1’C for 15 minutes will
3.3.3 Penetration Test
The objective of a penetration test is to examine the consistency of a sample of
bitumen by determining the distance in tenths of a millimeter that a standard needle
vertically penetrates the bitumen specimen under known conditions of loading, time and
temperature. The procedure of this test is the specimen will be prepared in sample
containers exactly as specified ASTM D5 (ASTM, 2005c) and placed in a water bath at
the prescribed temperature of the test for 1 to 1.5 hours before the test. Next, for normal
tests the precisely dimensioned needle, loaded with 100 ± 0.05 grams will be brought to
the surface of the specimen at right angles, allowed to penetrate the bitumen for 5 ±
0.1s, while the temperature of the specimen is maintained at 25 ± 0.1’C. The penetration
will be measured in tenths of a millimeter (deci-millimeter, dmm).
.3.3.4 Rational viscosity test
Viscosity is a fundamental characteristic of bitumen that describes the resistance of
fluids to flow.The Rotational Viscometer (RV) is used to determine the viscosity of
asphalt binders in the high temperature range of manufacturing and construction. The
RV test can be conducted at various temperatures, but since manufacturing
andconstruction temperatures are fairly similar regardless of the environment, the test is
conducted in the range of 120 C to 160 C.
The characteristic of bitumen will be tested using a Brookfield Viscometer and
will be conducted according to ASTM D4402 (ASTM, 2005d) procedures. According
to Asphalt Institute (2007), the ideal laboratory mixing and compaction temperature of
asphalt concrete and other hot-mix type using conventional binder are the temperature
at which the binder achieves a viscosity of 0.17 ± 0.02 Pa.s and 0.28 ± 0.03 Pa.s,
respectively. However,Yildrim et al. (2006) established the ideal mixing and
compaction temperatures for asphalt mixes using modified binder at a viscosities
equivalent to 0.275 ± 0.03 Pa.s and 0.550 ± 0.06 Pa.s, respectively.
3.4 Dynamic Shear Rheometer
In order to resist rutting, an asphalt binder should be stiff and it should be elastic (it
should be able to return to its original shape after load deformation).Therefore, the
complex shear modulus elastic portion, G*/Sin δ. When rutting is of greatest concern, a
minimum value for the elastic component of the complex shear modulus is specified.
Intuitively, the higher the G* value, the stiffer the asphalt binder is, and the lower the δ
value, the greater the elastic portion of G*. Rutting is basically a cyclic loading
phenomenon. With each traffic cycle, work is being done to deform the pavement
surface. Part of this work is recovered by the elastic rebound of the pavement surface,
while part is dissipated in the form of permanent deformation, heat, cracking and crack
propagation. Therefore, in order to minimize rutting, the amount of work dissipated per
loading cycle should be minimized.
The dynamic shear rheometer (DSR) is used to characterize the viscous and
elastic behavior of asphalt binders at medium to high temperatures. The test will be
conducted in accordance to super pave requirements (Asphalt institute, 2007) to
characterize bitumen rheology, both viscosity and elastic behavior, by measuring the
complex modulus (G*) and phase angle (δ) of the asphalt binders at different
temperatures. G* is considered as the total resistance of the binder to deformation when
repeatedly sheared, whereas δ is an indicator of the relative amounts of recoverable and
non-recoverable deformation (Roberts et al.,1996).The basic DSR test uses a thin
asphalt binder sample sandwiched between two circular plates. The lower plate is fixed
while the upper plate oscillates back and forth across the sample at 10 rad/sec (1.59 Hz)
to create a shearing action. DSR tests are conducted on un-agedand aged asphalt binder
samples. A frequency of oscillates that simulates the shearing stress corresponding to
traffic speed about 100km/h. The test is largely software controlled.
Aggregates are the main constituent of asphalt mixture. Aggregates used in the
asphalt mixture include various particle sizes which arecoarse and fine aggregates.
The selection of aggregates is necessary because it affects the performance of WMA
The propose of this study is to identify and determine the properties of different
types of aggregates, so aggregate have to be sieved to achieve a better gradation of
coarse and fine aggregate. Several size of sieve is needed to be use in order to get the
size of aggregate required such as size of 20mm, 14mm, 10mm, 5mm, 3.35mm,
1.18mm, 0.425mm, 0.15mm, 0.075mm,. Then aggregates are mixed together following
the required total weight of each size of the aggregate to prepare sample of bituminous
3.5.1 Aggregates impact value test
The aggregate impact value gives a relation measure of the resistance of an aggregate to
sudden shock or impact, which in some aggregates differs from their resistance to a
slowly applied compressive load refer to MS 30: Part 10 (MS, 1995).The objective to
determine the aggregate impact value in the laboratory. Firstly, the aggregate will sieve
and will obtain in the portion passing 12.5mm and will be retained on 10mm sieve. The
aggregate will be washed and dry at a constant temperature of 105’C to 110’C and then
the aggregate will be cooled. The aggregate will be filled with the cylindrical measure
in 3 layers, tapping each layer 25 times with the tamping rod. The surface tamping road
will be level using the straight edge. The aggregate will be taking the weight and will be
used for the duplicate test on the same material. The aggregate from the cylindrical will
be transferred to the cup in 3 layers and will be compact each layer by tamping in 25
strokes with the tamping road. The hammer will be released in fall freely on the
aggregate. The test sample is subjected to a total of 15 blows. The aggregate sample
will be removed from the cup and sieve through a 2.36 mm sieve. The fraction passing
the sieve will be taking the weight.
3.5.2 Sieve analysis test
Sieve Analysis (ASTM C136) is a procedure to analyze the grading of a stock of
aggregate. This is to ensure that the proportions of aggregate that are going to be used in
the mixture are within or fulfill the limitation of the JKR/SPJ/2008 specification. The
grading of the aggregate that used is ACW 14 (Asphaltic Concrete Wearing). Table
below show the gradation limit for ACW 14 according to JKR/SPJ/2008.
Table 3.1 Gradation limit for ACW 14 according to JKR/SPJ/2008
% Passing By Weight
3.5.3 Flakiness and Elongation Index Test
The particles shape of aggregates is determined by the percentage of flakey and
elongated particles contained in it. The presence of flakey and elongated particles is
considered undesirable as they may cause inherent weakness with possibilities of
breaking down under heavy loads. The angularity number is considered important for
various types of mixes.
The flakiness and elongation index test will carried out in accordance with
procedures stated in MS 30:Part 5 (MS, 1995) and MS 30:Part 3 (MS, 1995),
respectively. The particle shape of aggregates is determined by the percentages of flaky
and elongation particles. Flaky and elongation particles are considered undesirable as
they cause weakness of the pavement. The objective of this test is to determine the
flakiness and elongation indices of the given aggregate sample. Generally, the sieve
sample will take the weight every each of the individual size fractions that retained on
these sieve, other than the 63.0 mm sieve and will be stored in separated trays marked
with their size. Gauge each fraction from the respective slots in the thickness gauge will
be the weight which pass through the slot.
3.6 Sample Preparation
Crush aggregate granites will be washed, dried and sieved into a selected size range
according to standard specification (ACW 14) as requirements by the Public Works
Department (JKR, 2008). Conventional bitumen 80/100 penetration grade will be used
for the whole specimen preparations as well as Ordinary Portland Cement and
Pavement Modifier.The crush aggregate will be supplied by Quarry Minyak Beku, Sdn.
Bhd. while Sasobit®
will be supplied by Asa Infratech (M) Sdn. Bhd.
In this study, two asphalt mix designs will be evaluated consisting of 2%
Ordinary Portland cement and 2% Pavement modifier, respectively. The different of
contents will used by mass of bitumen.The effects of Sasobit®
bitumen at different temperature were evaluated. The bitumen will be heated at 1200
and pour into the container. A propeller mixer will be used to blend the Sasobit®
binder at 150°C. The asphalt binders will be tested for viscosity. Each material will be
through several tests to ensure conformity to the specifications. A sample of HMA
mixtures is prepared as a control sample.
3.7 Warm Mix Asphalt addtive
To characterize the rutting performance of warm mix asphaltic mixtures, 2 different
samples are needed, which is with or without WMA additive for further inductive
reasoning with respect to more general inference. The Sasobit® content will be used 1%
and 2% respectively based on earlier studies conducted by Biro et al, (2009) and Lee et
The additives are not involved in foaming technology/mechanism. The additives
are in viscous liquid state at the room temperature. The warm additives were selected in
such a way that the characterization of the products from these categories (chemical)
could be possibly investigated.
3.8 Design of binder content
In binder determination, the method that will be used is Marshall test. The Marshall
method seeks to select the binder content at a desired density that satisfies minimum
stability and range of flow values. The Marshall test was conducted in accordance with
BS 598:1985 as shown in Table 3.3. The procedure to obtain the stability and flow were
started with conditioning the specimen in a 60°C water bath for 30-40 minutes. The
Marshall stability and flow test provides the performance prediction measure for the
Marshall mix design method. The testing was conducted using a Marshall testing
Table 3.2Standard specification test for bituminous mixture
Laboratory Test Standard Test Objective
Marshall Test ASTM D1559 To determine the optimum bitumen
The mix design conduct with the coarse aggregate, fine aggregate, and the filler
material should be proportioned. The quantity of the mix is taken so as to produce
compacted bituminous mix specimens of thickness 63.5 mm approximately. 1200 gm of
aggregates and filler are required to produce the desired thickness. The aggregates will
heated to a temperature of 175° to 190°C the compaction mold assembly and rammer
are cleaned and kept pre-heated to a temperature of 100°C to 145°C. The bitumen are
heated to a temperature of 121°C to 138°C and the required amount of the first trial of
bitumen is added to the heated aggregate and thoroughly mixed. The mix is placed in a
mold and compacted with 75 numbers of blows . The sample is taken out of the mold
after a few minutes using sample extractor. According to ACW 14, the design of
bitumen content ranged from 4.0% to 6.0%.
3.9 Moisture Susceptibility test
Currently tensile strength Ratio method (TSR) is widely used and accepted or AASHTO
T283 is used to determine moisture susceptibility of WMA mix. the asphalt institute
(1987),reported that AASHTO T283 test method is better than the immersion-
compression test (ASTM D1075) or Marshall-immersion method because these two
methods failed to effectively predict the moisture susceptibility of the mixtures.
Approximately 1200g batch weight was used to prepare specimen of 100 mm in
Diameter and 71 ±3 mm in height. Initially, the trial and error method was practiced at
the beginning to determine the appropriate weight of specimens at the desired air voids
level. The number of gyrations needed to prepare the specimens was also determined
after several trials using the SGC.
To determine moisture susceptibility, all WMA specimens were compacted to
approximately 7±0.5% air voids at optimum binder content that allows for the air voids
of the specimen to be measured according to AASHTO T166. Any specimens outside
the specified air voids range were not considered. For each specimen, the bulk specific
gravity was determined and percent air voids were calculated as follows:
Air voids (%) = 100 x (1-A/B)
A = bulk specific gravity
B= theoretical maximum specific gravity
Compacted specimens were divided into two subsets each having the same
average Air voids, the dry subset (control group) was placed in a plastic bag submerged
in Water bath and conditioned for two hours at 25°C prior to testing. The saturated
specimens that are within the specification were then placed in a freezer at -18 Co
hours. Then placed in a water bath at 60°C for another 24 hours and finally at 25"C two
hours before testing.
3.10 Rutting tests
The tests used to determine the rutting potential of WMA is Wheel tracking test.Wheel
tracking test is used to assess the resistance to rutting of asphaltic materials under
conditions which stimulate the effect of traffic.A loaded wheel tracks a sample under
specified conditions of load,speed and temperature while the developement of the rut
profile is monitured continuosly during the test.
3.10.1 Wheel tracking test
Laboratory scale test is normally conducted at the temperature of 45o
C and 60o
the load of 300 N and 700N applied by the wheel to the surface of asphalt material.The
performance of the material under wheel tracking test is assessed by measuuring the rut
depth after a standard number of tracking.The wheel tracking machine was contrived
for testing a cylindrical sample,150mm in diameter and 65mm of depth, manufactured
using a gyratory compactor.A standard air voids content (5%) is used when comparing
The tyre have an outer diameter of 20mm and cross section of 50x10-13
tyre travel for distance of 230mm. The rate of tracking is 42 passes/minute. For the test
duration,the test is continues until a rut depth of 15mm is achieved or for 45
minutes,whichever that comes first.Results obtained by plotted vertical displacement
3.10.2 Compaction of specimen for wheel tracking test
Sample dimension of 150mm in diameter and 65mm height compacted using Super
pave Gyratory Compactor. Super pave Gyratory Compactor consists of these
components such as reaction frame, rotating base, motor, loading system, loading ram
pressure gauge, height measuring and recordation system, mold, base plate and
specimen extruding device. A loading mechanism presses against the reaction frame
and applies a load to the loading ram to produce a 600-kPa compaction pressure on the
specimen. A pressure gauge measures the ram loading to maintain constant pressure
during compaction. TheSuper pave Gyratory Compactor mold has an inside diameter of
150mm and a base plate in the bottom of the mold provides confinement during
compaction. The Super pave Gyratory Compactor base rotates at constant rate of 30
revolutions per minute during compaction, with the mold positioned at a compaction
angle of 1.25 degrees. Specimens height measurement is an important function of the
Super pave Gyratory Compactor Specimen density can be estimated during compaction
by knowing the mass of material placed in the mold, the inside diameter of the mold,
and the specimen height. Height is measured by recording the position of the ram
throughout the test.
3.11 Analysis and discussion
In this study, the performance of WMA by using anti-stripping agents will be analyzed.
The performance graph and bar chart will be used to analyze the performance of each
specimen under different concentration of pavement modifier in terms of rut depth. The
actual test data will be summarized in result and discussion section. The result will be
analyzed the effectiveness of rut potential of asphalt mixes between neat binder and
4.1 Expected Result.
The two types of asphalt currently widely used are porous and dense asphalt, the dense
asphalt structure provide less water penetration and high resistance to impact tire
loading, andincreased road safety in wet weather. But the problem with asphalt is the
production of greenhouse gases.In recent years, the asphalt industry has been exploring
alternatives to reduce the greenhouse gases and environmental pollution. The WMA to
a large extent improves the greenhouse emission from asphalt production. The problem
with WMA is the rutting and other pavement related distress as extensive as compare to
The use of anti-stripping agents has shown remarkable improvement in rutting
resistance and lowers the emission of toxic and hazardous gases. The rutting and other
pavement distress affects the service life of pavement and makes it undesirable for
future adaptation. Therefore,this study aims to improve the resistance of warm mix
asphalt incorporating anti-stripping agents, and increase the service life of pavement to
make it more economically attractiveand applicable. In this study detail tests will be
carried out for aggregates and binder and their properties will be evaluate for rutting
resistance. Next, the effect of anti-stripping agents will be investigated on rutting
resistance of warm mix asphalt. Finally the results will be evaluated in statistical and
graphical forms to enhance the rutting resistance with future improvements.
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