wma report

8/19/2019 WMA Report

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Warm Mix Asphalt Lecture Dr.Abdulhaq Hadi Abedali

What is Warm Mix Asphalt -WMAWarm-mix asphalt (WMA) is a group of technologies that allow a reduction in the temperatures at

which asphalt mixes are produced and placed . These technologies tend to reduce the viscosity of the

asphalt and provide for the complete coating of aggregates at lower temperatures.

The benefits of WMA technologies include;

Reduced fuel usage,

Emissions in support of sustainable development,

Improved field compaction, which can facilitate longer haul distances,

Cool weather pavement, and

Better working conditions.

1- Background History of Warm Mix Asphalt DevelopmentFrom historical point of view, the concept of using lower production and compaction temperature is

not completely new. The earliest work started by professor Ladis Csanyi in 1956 at Iowa State

University when the potential of foamed bitumen was investigated for use as a soil binder. From that

time, successful foamed asphalt technologies are carried out in many countries (Chowdhury &

Button 2008). However, despite the fact that the concept of introducing steam into hot bitumen was

successful, the work was impractical for in situ foaming operations. It is therefore that, in 1968,

Mobile Oil Australia had obtained the patent rights for Csanyi’s invention and made modification to

the original process by supplying cold water instead of steam in to the hot bitumen(Kristjansdottir

2006; Muthen 1998).

Further advancement in this technology was introduced to the market in the USA as the Conoco

product that was evaluated as a base stabilizer both in the field and the laboratory(Chowdhury &

Button 2008; Little, Button & Epps 1983). Back to the early 1970s, new methodologies of pavement

mixtures stabilized with emulsified asphalt was successfully developed by Chevron who published

‘Bitumuls Mix Manual’ as a practical guideline in 1977(Chowdhury & Button 2008; Zettler 2006)

In terms of producing mixture in an ambient temperature, Maccarone et al in 1994 investigated and

studied Cold-mixed asphalt-based foamed, which is produced approximately at 68℉ to 120℉, and

highlighted that due to lower emissions and energy efficiency of such use of this system, Cold mixwas broadly gaining acceptance(HoUeran & MaCCarrone 1994). Indeed, it was stated that “Cold

technologies represent the future in road surfacing” (Chowdhury & Button 2008). However, despite

the fact that Cold mixes have many good properties, it is not affected to the position of hot mix

therefore, CAM would not apparently be able replace hot asphalt mixture as the primary road

surfacing materials because of the requirement of curing time and long period to open to traffic and

also inadequate achievement of the same overall long term performance in comparison with HMA,

(Gandhi 2008). But rising fuel prices, global warming and more stringent environmental regulations

have resulted more demand to reduce production and compaction temperature. I t is therefore

requi red at least to heat the aggregate above the ambient temperature so that appropr iate coatings

happen between the aggregate and bi nder . From this idea, in 1999, Jenkins et al introduced a new

concept of half-warm foamed bitumen treatment which can enhance mix cohesion, tensile strengthand compaction (Jenkins et al. 1999).

A warm asphalt mixture process has been recently developed in Europe. Between 1996 and 1999,

several road trials in Europe were conducted to study and demonstrate the warm mixture

performance in the field with three major asphalt companies in Norway, the UK and the Netherlands

and were firstly reported by Harrison and Christodulaki at the First International Conference of

Asphalt Pavement in Sydney, 2000. And then after a more comprehensive and complete report was

introduced by Koenders et al. at the Eurobitume congress in 2000, which described an innovation of

warm asphalt mixture and its performance based on laboratory tests and large-scale field

evaluation(Jones 2004; Koenders et al. 2000). It can therefore be said that some today’s versions of

warm asphalt technologies are the brainchild resulting from European countries to lower

mixing/compaction temperatures.


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In recent years, and despite the fact that the innovation of warm asphalt technologies remarkably

started in Europe, strong interest in these innovations is gaining in the USA. In May 2007, a team of

13 materials experts from the United State visited four European countries Belgium, France,

Germany and Norway to assess and evaluate various WMA technologies(D'Angelo et al. 2008).

From that time, extensive researches have been carried out to establish potential benefits of using

WAM and evaluating the performance compared to the traditional HMA and up to date, no negative

performance of WMA has been reported in terms of field evaluation.

2-Available Warm TechnologiesIn general, despite the fact that WAM technologies have different behaviours to reduce the

manufacturing and paving temperature, they obviously tend to follow the same patterns. Different

classifications can be used in order to classify the WAM technologies. One is to classify the

technologies based on the degree of temperature reduction. Warm-mix signifies an asphalt mix that

can practically be achieved at temperatures around 30oC or cooler than the typical temperature used

in HMA production and slightly above 100℃ and for some technologies even below the boiling

point of water. The next figure illustrates the different production temperature of flexible pavement

mixtures

Figure 2- 1 Production Temperatures of Asphalt Mixtures(Bueche 2009)

But, for a more destructive and comprehensive definition, warm technologies can be classified based

on its products to foaming process which could be sub-divided into water-containing and water-

based process, organic additives such as Fisher-Tropsch synthesis wax, fatty acid amides and Montan

wax and addition of chemical additives which can be either emulsification agents or polymers(Rubio

et al. 2012). This section of literature of the research mainly focuses on the most well-known

technologies that are extensively studied by the researchers. However, more attention will be paid to

the performance of Sasobit and Rediset as considered in this research.

Table 1 Available Warm Technologies & CompaniesProduct Company

Low Energy Asphalt Advanced Concepts Engineering Co.

Rediest WMX & Liquid Akzo Nobel

CECABASE RT Arkema Group

Double Barrel Green Astec Industries

Aspha-Min Eurovia Services

Ultrafoam Gx Gencor Industries

Aquablack WMA Maxam Equipment Inc.

Low Emission Asphalt McCnnaughay Technologies

Evotherm MeadWestvaco Asphalt Innovations

Advera PQ Corporation

Sasobit Sasol Wax Americas

WAM Foam Shell BitumenWarm Mix Asphalt System Terex Roadbuilding


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3 Foam TechnologyIn this technology, small amount of water is injected into the preheated asphalt binder or could be

injected directly in asphalt mixing chamber. This will result to evaporative the water and the

liberated steam is encapsulated in the binder which can then produce large volume of foam. It is

therefore that this action will rapidly and considerably lower the viscosity of the binder by increasing

the surface area of the bitumen leading to a better distribution of the binder with the mixture which

enhances coating and workability. However, much attention should be paid in this process because

just enough water to produce foam must be added otherwise stripping problems may well happen. Toovercome this problem, antistripping additives can act as a bridge between the aggregate surface

and the asphalt binder so that moisture susceptibility is minimised. Having mentioned that , foaming

technologies is sub-categorised into two groups: water based and water containing .

3-1 Water Bearing/Containing AdditivesFrom the point of perspective work of warm technology water-based containing, there are two

synthetic zeolite of warm technology Aspha-Min and advera which both works in smaller manner

1-Aspha-Min

Aspha-Min is finely white powdered synthetic zeolite. Zeolite is crystalline hydrated aluminium

silicates which exist in the natural environment and is also produced artificially. In general, natural

synthetic zeolite has the ability to hold different quantities of water , therefore in order to utilise this

advantage to lower the production temperature of asphalt mixture, Eurovia Services GmbH, based inBottrop, Germany developed Aspha-Min which is a manufactured synthetic sodium aluminium

silicate (Hurley & Prowell 2005a). From the chemical structure point of view, Zeolite has generally

framework of silicates with large empty spaces in its structure that allow providing large cations

sodium, barium and calcium, for example, and large cation groups, such as water molecule can also

available. The available water can be driven off from the zeolite structure by heating therefore; the

available spaces can be interconnected and formed long wide channels of varying sizes depending on

the mineral. These channels allow the easy movement of the resident ions and molecules into and out

of the zeolite, therefore zeolite acts as a delivery system for the new fluid(Button, Estakhri &

Wimsatt 2007; Corrigan 2005). The released water, which is typically up 20% by mass, will

evaporative and the liberated steam is encapsulated in the binder leading to a volume expansion of

the binder which results in asphalt foam and allows enhancing the workability of the mixture as wellas aggregate coating at lower temperatures. The recommended dosage of adding Aspha-Min is 3.0%

by the total weight of the asphalt mixture mass which can yield and promote a reduction in the

production temperature of approximately more than 30℃ and save 30% energy (Kristjánsdóttir

2007) and as declared by Eurovia, it accommodates addition of RAP and uses different polymer-

modified binders. The foaming can effectively stand up to six hours(DTU 2010).

In terms of Aspha-Min performance, in 2005, Hurley and Prowell studied the influence of Aspha-

Min extensively at the National Centre for Asphalt technology (NCAT). It was highlighted that

Aspha-Min decreased the air voids by 65% on average and in parallel the compaction was improved

at temperature as low as 88℃. Moreover, resilient modulus was not adversely affected at any

compaction temperatures by adding Aspha-Min but the compactability improvement of Aspha-Min

mixtures led to improve the measured resilient modulus at this research. In terms of permanent

deformation, rutting potential was not increased by the addition of zeolite, on the other hand,

apparently incomplete drying of the aggregate caused by decreasing production and compaction

temperature and water enclosed in the coated aggregate attributed to the decreased the tensile

strength, therefore the visual stripping was noticed in WMA mixes manufactured at 121℃. In order

to mitigate the problem of the moisture damage, 1.5% of hydrated limed was accepted to enhance the

cohesion and moisture susceptibility of WMA in comparison with mixtures without the hydrated

lime. This was remarkable in enhancing the results obtained by Hamburg Wheel Tracking that

confirmed the hydrated improved the rutting resistance of warm mixtures compacted at lower

temperatures.

They concluded that the addition of Aspha-Min should not be taken in account during thedetermination of the optimum asphalt content. Furthermore, if the manufactured temperature is


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higher than 135℃, the same binder could be used in the design otherwise the high temperature grade

has to be increased by one grade or it is possible to minimise the tendency of decreasing rutting

resistance by adding a hydrated lime. It is also recommended that tensile strength ratio testing has to

be determined at the expected field production(Hurley & Prowell 2005a). It is however concluded by

Gandhi et al that the moisture susceptibility of warm asphalt additives was improved when sasobit

and aspha-min were evaluated at this study. They showed that tensile strength ratio values of the

unaged mixes increased(Gandhi, Rogers & Amirkhanian 2010). But, more importantly, according to

(Kheradmand et al. 2014), warm asphalt mixtures containing Aspha-Min have the worst moisturesusceptibility in comparison with other warm additives.

Gandhi and Goh et al. also highlighted that the use of Aspha-Min has no influence on the dynamic

modulus(Goh, You & Van Dam 2007). It is also demonstrated that the addition of Aspha-Min does

not significantly affect the asphalt binder grading (Barthel, Marchand & Von Devivere 2004;

Wasiuddin et al. 2007). At temperature of 135℃ and 120℃ , Aspha-Min has no significant effect on

the viscosity of the binders in comparison with base binder and more importantly the viscosity is

remarkably higher than the viscosity of conventional binders after 60 to 90 minutes (Gandhi 2008).

This is surly because of the addition of fine solid material to the binder. This issue was also

confirmed by another study. In 2009, in terms of asphalt recycling materials, it was also shown that

Aspha-Min has a negative effect to the viscosity of recycled binders as the viscosity increases when

Aspha-min is used and also it is considered that it has no positive effect on the resistance to fatiguecracking of recycled binders(Lee et al. 2009).

2-Advera

Another type of synthetic zeolite is Advera which is developed and manufactured by PQ Corporation

in Malvern, PA, USA. Advera has the ability to store approximately 20 percent of water in its

chemical structure (Hanz, Mahmoud & Bahia 2011) and the water is released at temperature of

210℉ which allowes a reduction in the production temperature approximately 50-70℉ (Perkins

2009). It is Worth mentioning that although, the mechanism of working Advera with asphalt binder is

significantly similar to the Aspha-min, there is no remarkably effects on the rheological properties of

the mix because the zeolite will reabsorb the water again (Kheradmand et al. 2014). Several studies

have been carried out to investigate physical and mechanical properties of WMA containing Advera.

A study conducted by (Mogawer et al. 2011a) showed that in terms of moisture resistance, as theaging time increased, the moisture susceptibility of the warm mixtures including Advera mix’s

improved significantly and the most improvement of the Avdvera performance was observed with the

addition of hydrated lime over the use of liquid antistrip.

Another study conducted by (Mogawer et al. 2011b) showed, based on foaming process, Advera was

more susceptible to moisture damage in comparison with other warm technologies, Evotherm,

Sasobit and Sonnewarmix. This issue may seemingly result from some enclosed water into aggregate

leaded to stripping problems. It is however that a study conducted by other researches revealed that

the addition of Advera did not make the mixture prone to moisture damage and also concluded, there

were not favourable properties of mixtures containing Advera with highly acidic aggregates such as

granite (Ghabchi et al. 2013). In 2011, Goh and You demonstrated that warm mixtures Sasobit and

Advera had the lower values of dynamic modulus at most of the temperatures mixed and compacted

at (100℃, 115℃ and 130℃) and frequencies tested (from 0.1 Hz to 25Hz). This issue wassignificantly at higher testing temperatures. In terms of WMA fatigue life, most WMA performed

similar or even better the control HMA apart from warm mixtures manufactured at 130℃. More

importantly, the WMA’s fatigue life of mixtures tested at 115 ℃ had the highest fatigue life as

compared with other WMA(Goh & You 2011).

3-2 Water Based

1-Double Barr el Green

The concept of this technology is to use some type of nozzle to inject small amount of water into

asphalt binder stream. The nozzle should be computerized to control the amount of water and the

foaming rate(Button, Estakhri & Wimsatt 2007). The addition water, which is delivered to the systemusing a positive displacement piston pump capable of accurately rating water into the system, will


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microscopically foam the binder which creates encapsulated steam in the binder leading to force

enlarging the volume of the binder and decrease the viscosity of the binder .

G1 and G2 are two generations of this technology which have been designed since 2007 and

developed by Astec Industries in the USA. The main difference between these two types is the nozzle

system functionality. However, there is typically no need to make any changes in mixture design

process but foaming device should be used in the laboratory in order to simulate plant mixing.

(Middleton & Forfylow 2009) reported that the properties of asphalt binder and mixtures performed

as same as HMA. The rutting susceptibility of mixtures produced with process of Double BarrelGreen was identified to be adequate, moreover in terms of moisture susceptibility, this technology

has no negative influence on the moisture susceptibility of mixtures. Environmentally, a 10%

reduction in nitrogen oxide, carbon monoxide and carbon dioxide was determined and reported in

this process as well as a 24 percent reduction in energy consumption.

It is thought that this technology may eliminate the need for expensive additives because it is only

required small amount of water to be injected to the stream of the binder but, however having

mentioned that the water should be accurately injected to avoid having stripping problem. Despite the

fact that this technology has gained more popularity in the USA, not many researches have been

conducted in this area compared with other technologies such as Advera and Aspha-Min. the

following figure illustrates the process of this technology.

Figure 2 Double Barrel Green(Equipment & Lounge ; Jenkins et al. 1999)


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2-Low Energy Asphalt

Low Energy Asphalt (LEA) WMA technology is developed by Advanced Concepts Engineering&

Design LLC. and distributed in the USA by McConnaughay Technologies. This technology has

different process in comparison with double barrel green. The process involves mixing the hot

bitumen’s (140℃ 180℃ ) with hot coarse aggregate at temperature around 290℉/145℃ and then

incorporating wet fine aggregates at ambient temperature which are not submitted to heating . This

process leads to liberate the moisture of the fine aggregates as steam and therefore, foaming action

will be resulted which facilities the fine aggregate coating (D'Angelo et al. 2008; Perkins 2009;Rubio et al. 2012). This technology is reported to reduce the production mixing temperature to

approximately 90℃ which significantly yields reduction in energy savings and gas emissions.

However, the author thinks that coating and adhesion promoter should be introduced in this

technology to enhance the performance of the asphalt mixtures by minimising stripping problems.

Despite the fact that this technology has a great advantage in reducing the production temperature, it

requires a major plant modification. In 2006, Romier et al developed a kit which can be attached to a

batch plant. The kit can control the amount of cold sand by a specific hopper and also is integrated

with an advice for adding water to the fine aggregate. The RAP can also allowed to introduce

directly into the mixer(Chowdhury & Button 2008; Romier et al. 2006) . They are also interestingly

highlighted reduced soiling of production equipment because of available moisture which results in

minimising the requirements of cleaning and corresponding use of solvents.Between 2005 and 2010, more than 400,000 tons of LEA were manufactured on 40 plants (LEA-CO)

and it is reported that specific multifunctional were mostly used to enhance the foam-ability and the

coating ability of the binder. This technology was conducted successfully mainly in France by

EIFFAGE and FAIRCO and the USA by Suit Kote and to least extent in the UK by PetroPlus, in spin

by EIFFAGE Infrastructures and Newszland by Fulton Hogan. However, indeed few literatures have

been published in this area, therefore further concern is highly recommend in order to gain more

understanding about the properties of asphalt mixtures and also to check the validity of this process

with other materials, climates and mix design methods in order to discriminate the process with other

warm technologies as (Gaudefroy et al. 2007) believes, it is fertile WAM process.

Figure 2 functional Diagram Low Energy Technique, (Chowdhury & Button 2008)


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3-Warm Asphalt M ix-F oam (WAM -Foam)

WAM-foam is a water-based foaming technology which was presented for the first time at the Euro-

asphalt & Euro-bitumen congress in 2000 and it was a result of work from a cooperation between

Kolo Veidekke and Shell initiated work on Warm Asphalt Mixtures with laboratory experiments

back in 1995(Koenders et al. 2000; Koenders et al. 2002). From the practical work point of view,

WAM- foam is slightly different from others technologies of water-based because soft binder and

hard are introduced at different time in the mixing cycle. The first stage involves heating up the

aggregate to around 130℃ and then coated with the soft binder which is accounted about 20% to30% of the total binder. At the second stage, the hard binder is foamed by introducing water at 2 to 5

percent of mass of the hard binder at temperature about 180℃. The main advantage of this process is

to ensure adequate bitumen absorption of the coarse aggregate by the use the soft binder which may

not satisfy or occur with hard binder at lower temperature which then leads to sufficient distribution

of the binder in the mixture and an adequate workability through paving.

In spite of reporting 30% plant fuel reduction and 30% reduction in emission rates (Larsen et al.

2004), it still needs to heat the hard binder to the required temperature of HMA, and stripping

problem may also happen because of uncompleted water evaporation. It is however that some

researchers demonstrated WAM-foam can successfully be used in the base course and wearing

course and it has performance, in terms of volumetric properties, very similar to the compassion of

HMA using the same materials. Consequently, the mechanical properties of WAM-foam maycorrespond to those of HMA. Furthermore, field studies reported that the paved sections of WAM-

foam are equivalent in terms of permanent deformation and surface texture(Larsen et al. 2004).

Another study by (Losa et al. 2009) confirmed good results in terms of fatigue life and permanent

deformation of this process.

3-4 Chemical Technology

Another technology which is utilised to reduce manufactured and compaction temperature is

Chemical additives which has a different behaviour to produce WMA when added to the mix. This

technology involves different packages such as surfactants, emulsification agents, aggregate coating

enhancers and anti-stripping additives. The revision of the research focuses on the most important

chemical additives such as Evotherm and Rediset.

3-4-1 Evotherm

Evotherm is a chemical package which has been manufactured by MeadWestvaco Asphalt

Innovations and introduced to the market in 2005, included materials to improve workability,adhesion promoters and emulsification agents. It is currently delivered with relatively high asphalt

residue (around 70%)(Bennert et al. 2010; Hurley & Prowell 2006). MeadWestvaco has developed

and distributed three kinds of Evotherm to the markets, Evotherm DAT, ET and 3G (Kheradmand et

al. 2014). It is reported by manufacture that no special requirements or modifications are needed to

pump the Evotherm to the asphalt plant. From the field paving up to date, Evotherm has directly been

pumped off a tanker truck. When Evotherm is mixed with the hot aggregate, the water in the emulsion

will be liberated in the form of steam enhanced mixture workability and aggregate coating . This

process allows asphalt application at a temperature 50℃ to 70℃ lower than traditional HMA. It was

reported that a production temperature was successfully dropped by up to 56℃ as demonstrated in

the fields test. This allowed energy savings of up to 55% in which 45% reduction in Co 2 and So2

emission as well as 50% reduction in Nox and 41% reduction in the total organic materials were

achieved(Sampath 2010).

In terms of Rheological properties, one can say that Evotherm has a minor effect on the bitumen

rheological properties. (Xiao, Punith & Amirkhanian 2012) identified the performance of different

warm additives including Evotherm. It was showen that Evotherm did not exhibit remarkably a

different failure temperature in comparison with control binder. Moreover, in spite of increasing m-

value of Evotherm modified binder which can enhance low temperature properties, amplitude sweep

tested at 60℃ in terms of strain response did not reveal any different in the complex modulus and

phase angle of evaluated warm additive apart from Sasobit in this study, in addition, Evothermexhibited the highest value of creep compliance. It is therefore thought that Eovtherm may be more


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prone to deformation due to the reduction of compliance value. It is also important mentioning that

Evotherm has generally no influence on the viscosity properties of asphalt binder when investigated

based on the both rotational viscosity and NCHRP 9-39 Method(Bennert et al. 2010). As a matter of

fact, Evotherm only enhances workability of asphalt mixtures in which mixtures can be compacted at

lower temperatures.

In 2006, Hurley and Prowell highlighted that the addition of Evotherm reduced air voids measured in

the Gyratory Compactor for given asphalt content. This issue may need to reduce the optimum

asphalt content. However, as their recommendation, further research is required to profoundly

investigate this issue because favourable performance, in terms of compaction, resulting from the

addition of Evotherm may be negated by reducing the optimum asphalt content(Hurley & Prowell

2006). Despite the fact that Evotherm has a potential to decrease rutting or similar performance as

controlled HMA as revealed by (Hurley & Prowell 2006; Mogawer et al. 2011b; Sampath 2010;

Xiao, Amirkhanian & Putman 2010), visual stripping problems were observed. Consequently, liquid

antistrip or hydrated lime could be utilised in order to remediate the WMA mixture susceptibility to

moisture damage. Having mentioned that, there is a high demand to simulate the required aging time

in the Laboratory because in fact up to date no such problem of WMA moisture damage hashighlighted in the field so far.

3-4-2 Rediset WMX and LQ

Rediset is a product delivering significant advantages to the road construction in one very convenient

chemical package. This is the most recent innovation of AkzoNobel Corporate introduced in 2007.

Two kinds of Rediset have been supplied by AkzoNobel, Rediset WMX and Rediset LQ which does

not significantly differ between each other. Rediset WMX is a solid pelletized additive and designed

in such a manner that it does not have a negative effect on the binder in its high-temperature or low-

temperature properties of bitumen at a wider dosage level(AkzoNobel). This additive is classified as

both a viscosity reducer and a surfactant. The letter type is Rediset LQ which is a surfactant,

compaction aid and active adhesion as this additive enables the bitumen to displace residual water

from the incomplete dried aggregate surface and creates a strong chemical bond between the

aggregate and the bitumen that is resistant to moisture damage. It is reported by the manufacturer that

Rediset LQ does not alter the binder properties and bitumen grade at the recommended dosage as the

recommended dosage is verifying between 0.4-0.75 percent of the total effective binder weight.

Having mentioned that, the Rediset LQ also functions as adhesion promoter, therefore the potential

need for the additional anti-strip is eliminated. Moreover, Rediset LQ could potentially improve the

stress characteristics of asphalt concrete(Hill et al. 2012). In spite of superior performance of the

innovation of AkasNobel, Rediset has not been extensively studied so far.

1- Ef fect of Rediset on the asphalt binder properties

Studies conducted by (Xiao, Amirkhanian & Zhang 2011a, 2011b; Xiao, Punith & Amirkhanian

2012) to investigate the rheological properties of non-foaming additives revealed that the viscosityvalues of all asphalt binder modified with Rediset WMX decreased as the test temperature increased

Figure 3 Creep Compliance values of modified WMA binder in terms of various loading times

at 60℃.(Xiao, Punith & Amirkhanian 2012)


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and it should also be mentioned that no negative effect of storage duration on viscosity was found.

Therefore, the modified binder could be stored for a certain period if it is required. This is also

confirmed by (Arega et al. 2011) but they highlighted during their study that some warm additives

involved Rediset WMX reduced the binder viscosity measured at 135 ℃ with minor exceptions. An

attention should be drawn to the performance of Rediset in terms of permanent deformation because

researches manifested the modified binder with Rediset WMX exhibited high value of compliance in

terms of creep and creep recovery test and more stress sensitive relative to the virgin binder but

without adversely significant effect on High-Temperature continuous grade (Hanz, Mahmoud &Bahia 2011). This means that asphalt binder modified with Rediset is more prone to rutting issue, on

the other hand, it has a high m-value in comparison with virgin binder, and therefore the addition of

Rediset WMX may well lead to better thermal cracking and fatigue life performance and short-term

aging of warm modified binder plays an important role in determine the rheological properties of

asphalt binder. This mater is highlighted by (Arega et al. 2011) who also reported that the

recommended strategies such as addition of RAP to compensate the reduced initial stiffness in WMA

must be tailored to the specific kind of WMA mixture because of subjecting the short-term aged

modified binder to PAV had low temperature and fracture properties similar or lower than the PAV

residues of conventional or control asphalt binder which means the long-term aging may erase the

variation of reduced short-term aging influence in WMA. Consequently, the incorporation of RAP

materials or any other strategy to overcome the reduced initial stiffness in WMA may adverselyaffect low temperature behaviour of warm asphalt mixtures.

Conversely, this issue is not corresponding with another study carried out by (Banerjee, de Fortier

Smit & Prozzi 2012) who studied the effect of long-term aging on the rheology of mix asphalt

binders. Results suggested that warm modified binder not only reduce short-term aging influence on

the rheological properties but can also retard the rate of aging in which the stiffness raises over time.

Surprisingly, more importantly, the Rediset WMX exhibited the lowest rate of aging compared with

adopted additives in this study.

During all aforementioned studies, not surprisingly, the binder source also significantly affected the

viscosity values and rheological properties of same binder grade. This fact brains in mind that the

chemical interaction between warm additives and different asphalt binder sources should be

profoundly investigated in order to select the appropriate additive dosage in which warm mixture hassimilar or better performance of HMA. Rediset LQ has not been investigated deeply in the literature;

therefore this project will deeply investigate the effect of both Rediset WMX and LQ.

2- Ef fect of Rediset on the Asphalt M ixture Properties

Some researchers have investigated the effect of Redsiet as WMA technologies to reduce the

manufactured and placement temperatures. In terms of workability and compactability, it is reported

that the recommended dosage of Rediset WMX which is 2% of binder weight exhibited the best

workability and compactability compared with 1% (Bennert et al. 2010). This certainly achieved by

the action of Rediset to reduce binder viscosity and enhance wetting of aggregate surface. Recently,

this has been confirmed by a study carried out by (Hamzah, Golchin & Tye 2013) who proclaimed

that there is a slight decrease in the marshal stability by using 3% Rediset over 2%, therefore one can

approach to the fact the 2% of Rediset give the desired and adequate performance. In addition, the

higher Rediset content the higher softening role in the asphalt mixtures will be.

Consequently, the WMA’s modified with Rediset WMX exhibited superior performance in terms of

low-temperature mechanical properties. In fact, the susceptibility of chemical additives to thermal

cracking was explored by (Hill et al. 2012). As mentioned previously, the chemical additive has the

ability to emulsify the conventional binder which in result leads to softer mixes. Therefore, Hill et al

found the fracture energy of chemical modified WMA mixtures included Rediset LQ and Evotherm

slightly increased by 7% in comparison with control HMA and displayed the greatest creep

compliance whereas the addition of the organic additive (Sasobit) and foaming (Advera) decreased

the fracture energy by 12.7% and 11.1% respectively. It can therefore be demonstrated that low-

temperature characteristics are sensitive to the kind of warm technology used because the influenceof manufactured temperature was not clear as two system of WMA had higher fracture energy


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whereas others had lower values. It should also be mentioned that the above study has not addressed

the aging issue as the NCHRP 9-43 recommended at least 2 hours aging time to simulate the

performance of warm mixture that will undergo in the field. Subsequently, study the performance of

inclusion RAP materials in WMA is highly required to offset potential low-thermal cracking issues

and achieve adequate level of rutting performance.

2-5 Organic AdditivesThis technology is based in using waxes asphalt mixture because when temperature reaches the

melting point of waxes, which contain high molecular hydrocarbon chains; waxes will be meltedleading to viscosity reduction in asphalt binder . However when mixtures cools these additive will

solidify into microscopically small and uniformly distributed particles in the bitumen (Rubio et al.

2012). This phenomenon leads to stiffen the binder in the smaller manner of fibre-reinforced

materials. Some researchers highlighted that complicated problems exist when the melting point of

wax is below than in-service temperature and careful selection of wax type is needed to avoid

potential temperatures problems (Shang et al. 2011; Silva et al. 2010). As a matter of fact not only the

kind of wax but also the type of binder also plays an important role in determining the performance

of inclusion synthetic waxes as the internal crystallizing fraction depends on the bitumen type and

source (Edwards & Redelius 2003). In general, the introduction of synthetic waxes to the asphalt

mixture will boost the permanent deformation resistance by increase the mixture stiffness properties

on the other hand the adversely effect on the fatigue response may exist because stiffer materialsexhibit less ductile behaviour of the mixture(Barbati et al. 2009).

Three well-known technologies of synthetic waxes are available the Fischer-Tropsch wax, fatty acid

amide and Montan wax. The author in this research will only focus on the more use wax in the WMA

whether in filed or laboratory performance, Fischer-Tropsch wax, as Sasobit is considered in the

project as the main additive.

Sasobit is a Fisher-Tropsch synthetic wax which is produced by Sasol Wax GmbH in Germany.

From the industrial point of view, when coal or natural gas is partially oxidized to carbon monoxide

and then converted into higher hydrocarbons when it is reacted with hydrogen under catalytic

conditions, the high length of carbon C 5 to C 100 plus carbon atoms will be generated. After that the

generation of synthesis gas is reacted with cobalt or iron catalyst to form products such as kerosene,

gasoil, synthetic naphtha and waxes. Finally, recovered Sasobit is carbon chain length range of C 45 to C 100 plus which is longer than microcrystalline bituminous paraffin wax chain length from C 25 to

C 50. (Butz, Rahimian & Hildebrand 2001; Hurley & Prowell 2005b; Wasiuddin, Saltibus &

Mohammad 2011).The chemical reaction is presented in the equation 2-1:

(2n+1)H2 + nCO2 CnH2n+2 + nH2O (1)

Sasobit is supplied in the form of Greyish-white to yellowish Pastilles and pills (Jamshidi, Hamzah &

You 2013). It is also reported that Sasobit does not require higher shear mixing apparatus and can be

easily blended manually and /or mechanically and type of method use has no effect on the properties

of Sasobit-modified asphalt binder(Ji & Xu 2010; Sasolwax). Therefore no major modification is

required to introduce Sasobit in the aspfalt plant because it can be either mixed with hot bitumen or

added directly to the aggregate. The recommended dosage of adding Sasobit is 0.8-4% of binder

mass. More than 4% has a negative effect in terms of low-temperature properties of

bitumen(Edwards & Isacsson 2002).

3-5-1 Performance of Asphalt Binder Containing Sasobit

1- Ef fect of Sasobit on Asphalt Binder Rheological Properties

Having mentioned that Sasobit has a predominant range of hydrocarbons chain length from 45 to 100

carbon atoms while the natural asphalt paraffin waxes is normally in the range of 25 to 45 carbon

atoms. The long chain of carbon atoms increase the plastic limit and also increase the domain of

melting temperatures of asphalt binders (Wasiuddin, Saha & King 2011; Wasiuddin, Saltibus &

Mohammad 2011). It is determined that the melting point of Sasobit is approximately 100℃

therefore above this temperature Sasobit liquefies the asphalt binder resulted in a reduction of asphalt

binder, thereby the manufactured temperature of asphalt mixture at which mixture should be produced decreases. However, below the melting point of wax, Sasobit forms a lattice structure


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11

which acts as a bridge between molecules and prevents their movements; consequently, it increases

the viscosity of asphalt binders at lower temperatures. It should also mention Sasobit exhibits

Newtonian behaviour at lower temperature and Non-Newtonian below its melting point(Jamshidi,

Hamzah & You 2013). Based on the manufacturer the production temperature can be approximately

depressed by 20-30℃. However this is not always true because the reduction in the production

temperatures is also highly affected by the binder source and grade. (Silva et al. 2010; Silva et al.

2009) reported that in order to maximise such benefit of using Sasobit, softer base bitumen should be

used and it was found that a maximum temperature reduction of 15 ℃ was achieved by using 4% ofSasobit with a softer binder.

Many researchers investigated the rheological properties of Sasobit-modified asphalt binder. In all

seniors, Sasobit increases the complex shear modulus (G*) of asphalt binder while decreases the

phase angle (°) regardless of binder type and grade. Moreover, the addition of Sasobit increases the

failure temperatures of all binders and exhibits lower creep compliance and high creep stiffness with

lower m-value, subsequently enhanced the permanent deformation of asphalt binder but may

adversely affect the low-temperature properties of asphalt binder(Gandhi, Rogers & Amirkhanian

2010; Xiao, Amirkhanian & Zhang 2011a, 2011b; Xiao, Punith & Amirkhanian 2012).

However, in terms of long term aging, a study conducted by (Banerjee, de Fortier Smit & Prozzi

2012) showed that Sasobit gains a slow rate of stiffness increase over time, therefore Sasobit retards

the rate at which binder stiffness raises overtime in comparison with the conventional asphalt binder.Moreover 2% of Sasobit increases the cohesive strength of asphalt binder evaluated by Surface free

measurements(Wasiuddin, Saha & King 2011). It is also must be mentioned that the interaction

between Sasobit and asphalt binder is only physical because a study conducted by (Menapace et al.

2014) outlined that NMR (Nuclear Magnetic Resonance) did not detect any chemical interaction due

to the addition of Sasobit.

From Sustainable engineering point of view, not surprisingly, the content and Sasobit dosage should

be carefully selected because it was reported that low-temperature cracking resistance of both unaged

and long-term aged binder decreases as the Sasobit dosage increases. In other words, asphalt binder

containing high percentage of Sasobit will be more prone to cracking issues(Liu et al. 2012). It is

therefore that more challenging may be when RAP materials are included in the mixtures.

2-

Ef fect of Sasobit on the Topography of Asphal t binder Structur e

With recent and sophisticated technology, the surface of the asphalt binder can be investigated by

using AFM (Atomic Force Microscopy) in order to subsequently bridge and link the observed

behaviour of asphaltic binder to the chemical makeup and bulk properties of asphalt binders

(MASSON, Leblond & Margeson 2006; Menapace et al. 2014; Rebelo et al. 2014). Briefly, it is

revealed that the bitumen can be separated into four fractions Saturates, Aromatics, Resins and

Asphaltenes (MASSON et al. 2007; Nahar et al. 2013b). The more aphaltenes there are in the asphalt

binder, the more viscous and harder that bitumen likely to be because molecules could form easily as

they carry positive and negative charge at different points therefore bonds between molecules are

easily linked. At other end of scale, the more saturates, the softer binder will be. Saturates are a non-

polar fraction and they form a soup surrounding the other molecules. However, the other molecule

kinds, aromatics and resins are intermediate components in the soup. Resins are similar to the

asphatenens and are highly polar which influence the degree to which asphaltenes are readily

dispersed within the bitumen whereas Aromatics behaves as a solvent to both resins and

asphaltenes(Thom 2008).

These components are explained by bee-structure which consist of from catana phase which is

assigned to the most rigid and polar bitumen, the asphaltenes. The peri phase is attributed to the less

polar aromatics and resins while the para phase is referred to non-polar saturates. It was therefore

possible made to investigate the effect of different polymers to the components of asphalt binder and

link between the morphology of bitumen structure and its rheological properties.

It is reported that Sasobit highly affects the morphology of asphalt binder. (Menapace et al. 2014)

found Sasobit enlargers the bee-like stratures of bitumen. In other words, Sasobit caused the catana


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phase and the peri phase to grow which can reflect the presence of Sasobit in the asphalt binder. The

next figures illustrate the effect of Sasobit on 60/70 Pen and PG 76-22

Figure 2- 4 Height (left) and Phase (right) images with scan size 10um and 25 µm

Figure 2- 5 Height (left) and phase (right) images with scan size of 25 µm

3-5-2 Performance of Asphalt Mixture Containing Sasobit

1- Ef fect of Sasobit on M ix Design and Volumetric Properties

Sasobit is a flow modifier and viscosity reducer therefore it is expected to have influence to the

volumetric properties and mix design. (Hurley & Prowell 2005b) found that air voids of asphalt

mixtures decreased when Sasobit was added which may result in reduction in the optimum asphalt

content. It was found that using of 2.5% of Sasobit improved the compactability of the mixtures in

both the SGC (Super-pave Gyratory Compacter ) and vibratory compactor in which reduced in air

voids up to 0.87%. However, another study highlighted that addition of Sasobit has no significantinfluence on optimum asphalt binder content and 3% of Sasobit resulted in energy saving up to

12%(Hamzah et al. 2010). This is could be confirmed because achieving the required density is

quicker for Sasobit-WMA mixtures than for HMA even at lower compaction temperatures as the as

study by (DTU 2010) reported the modified asphalt mixtures with Sasobit reached the final density

after 100 gyrations at 135℃, whereas, HMA reached thefinal density after 170 gyration at 155℃. In

fact, one can say that Sasobit generally has on negative effect in terms of mix design and volumetric

properties.

2- Ef fect of Sasobit on Rutting Susceptibi li ty

In terms of lower production temperature, warm mixtures may be softer because of reduced oxidative

aging and incomplete drying aggregate. The performance of Sasobit with particular reference to

rutting susceptibility has been investigated by many researchers. Testing conducted using HomburgWheel tracking Test (HWTT) showed that Sasobit modified mixtures were within the allowable

rutting limit after 10,000 loading cycles(Estakhri, Button & Alvarez 2010; Hurley & Prowell 2005b;

Kim et al. 2012). The superior performance of Sasobit also was confirmed by using APA ( Asphalt

Pavement Analyser ). It was reported that the controlled HMA and Sasobit – WMA performed

similarly and met the criterion for rutting resistance. In other words, warm mixtures containing 1.5%

Sasobit had as similar as performance of HMA after 8000 loading cycles (Goh & You 2009; Hearon

& Diefenderfer 2008).

Moreover, despite the fact that (Mohammad, Saadeh & Cooper 2008) reported Sasobit modified

mixtures presented lower modulus values, other researcher (Haggag, Mogawer & Bonaquist 2011;

Petit et al. 2012; Yang, Zhang & Wu 2009) showed that Sasobit modified mixtures had a higher |∗|

and also it is revealed that Sasobit-WMA exhibited an added stiffness, particularly at higher reduced

frequencies and/or lower temperatures because the addition of synthetic wax resulted a more stable

60/70 Pen PG 76-22

60/70 Pen + Sasobit PG 76-22 + Sasobit


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asphalt binder and consequently leads to a more stable asphalt mixture due to its crystallized

form(Petit et al. 2012).

Sasobit modified mixture containing moisture aggregate has investigated by (Xiao, Amirkhanian &

Putman 2010) who declared using Sasobit in the mixtures involved moisture aggregate did not

require additional treatment to satisfy the required pavement performance in terms of rutting and

concluded that the mixture with Sasobit exhibited the best rutting resistance. This coincides with a

another study undertaken by (Bennert, Maher & Sauber 2011) to study the effect of production

temperature and aggregate moisture content which revealed that as the mixing temperature reduced,the FN (Flow Number) also decreased but it was not in the case of Sasobit-modified mixture which

was able to maintain FN values at the 270℉ production temperature at the 1.0% and 1.5% dosage

rates and achieved high-temperature stiffness and permanent deformation that surpassed the baseline

mixture.

In general, as (Edwards, Tasdemir & Isacsson 2006a) and (Edwards, Tasdemir & Isacsson 2006b),

Sasobit-modified mixture offered the smallest strain in dynamic creep testing, it can be concluded

that rutting performance of Sasobit-WMA is smaller or even better than HMA.

3- Ef fect of Sasobit on Low-Temperature Performance and Fatigue L ife

Asphalt mixture fatigue performance can be generally affected by a number of factors such as an

inadequate structural design, repeated heavy loads, poor drainage and construction and asphalt binder

stiffening due to aging at low and intermediate temperatures (Jamshidi, Hamzah & You 2013).Having highlighted that Sasobit stiffens the asphalt binder consequently leads to a stiffer asphalt

mixture. However, the lower production temperature may offset the negative effect of addition

Sasobit in terms of low-temperature properties and fatigue life because it expected that binder will be

less oxidative in which results a more ductile mixture. This thought may not be true because (Hill et

al. 2012) found that the effect of manufactured temperature was not as conclusive and the selection of

warm additive affects the low-temperature properties. In that study, organic additive presented in

Sasobit reduced fracture energy by approximately 12.7% in comparison with chemical technologies

which were able to increase the fracture energy around 7% because chemical technologies may have

had a tendency to emulsify the neat asphalt binder whereas Sasobit resulted in stiffer asphalt

mixtures. This is corresponding with another study which indicated the inclusion of Sasobit increased

the chances for low-temperature cracking as lower tensile strength and failure strain reported toSasobit modified binder especially at lower temperatures(Liu et al. 2012)

In fact, the effect of warm additives including Sasobit on fatigue performance is not clear as some

studies showed that the fatigue life of Sasobit-modifed mixtures were similar or even better than the

control HMA when evaluated based on four-point beam fatigue testing and cyclic direct tension test

(Goh & You 2011; Haggag, Mogawer & Bonaquist 2011). Whereas the substantial effect of the

synthetic wax additive is detrimental for the fatigue cracking resistance as highlighted by (Silva et al.

2010) who also recommended that the fatigue resistance may only improve without compromising

the rutting resistance by using softer binders due to the brittle behaviour of wax additives. Therefore

the issue may be more challenge when RAP materials are considered as stiffer materials make the

mixtures more prone to fatigue deterioration.

It is therefore that one of the most important objectives of this project is to investigate and identify

the performance of warm mixtures in terms of fatigue life and low-temperature properties containing

organic and chemical additives with inclusion RAP materials in order to gain more understanding

about the behaviour of likely brittle mixtures with particular reference to different aging times.

4- Ef fect of Sasobit on M oisture Susceptibi li ty

Loss of bonding between the asphalt binder and aggregate, known as stripping, is a major problem

that pavement engineers are concerned about because it causes surface manifestations such as rutting,

corrugations, shoving, revelling and cracking(Caro et al. 2008; Kim & Amirkhanian 1991; Xiao &

Amirkhanian 2009; Xiao et al. 2012). Moisture damage is generally affected by a number of factors

such as the cohesive bond between the aggregate and the asphalt binder, the cohesive resistance of

the binder and the frictional resistance and interlock between aggregate particles(Jamshidi, Hamzah& You 2013). Several mechanisms have been proposed to explain the moisture damage reasons


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included detachment which is the microscopic segregation of an asphalt film from the aggregate

surface without obvious breaking in the asphalt film and displacement which is defined as a removal

of aggregate from asphalt film by water. Moreover, Spontaneous Emulsification, Film Rupture, Pore

Pressure, Hydraulic Scouring and also pH instability mechanisms can also influence the durability of

asphalt pavement and cause a premature failure (Kiggundu & Roberts 1988; Little & Jones 2003).

The low production temperature of WMA asphalt will result incomplete drying of entrapped water in

the aggregate which make the WMA more prone to stripping issues.

wma report

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