WMA Report

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

What is Warm Mix Asphalt -WMA Warm-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 Development From 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 mix was 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. It is therefore required at least to heat the aggregate above the ambient temperature so that appropriate coatings happen between the aggregate and binder. From this idea, in 1999, Jenkins et al introduced a new concept of half-warm foamed bitumen treatment which can enhance mix cohesion, tensile strength and 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.

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 Technologies In 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 waterbased 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 & Companies Product Low Energy Asphalt Rediest WMX & Liquid CECABASE RTR Double Barrel Green Aspha-Min Ultrafoam GxTM Aquablack WMA Low Emission Asphalt EvothermR Advera Sasobit WAM Foam Warm Mix Asphalt System

Company Advanced Concepts Engineering Co. Akzo Nobel Arkema Group Astec Industries Eurovia Services Gencor Industries Maxam Equipment Inc. McCnnaughay Technologies MeadWestvaco Asphalt Innovations PQ Corporation Sasol Wax Americas Shell Bitumen Terex Roadbuilding

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

3 Foam Technology In 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. To overcome 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 Additives From 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 in Bottrop, 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 well as 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 polymermodified 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 AsphaMin 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 the determination of the optimum asphalt content. Furthermore, if the manufactured temperature is

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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 moisture susceptibility 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 fatigue cracking 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 the aging 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 was significantly 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 Barrel 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 system using a positive displacement piston pump capable of accurately rating water into the system, will

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 Barrel Green 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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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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℃ 𝑡𝑜 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)

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

3-Warm Asphalt Mix-Foam (WAM-Foam) WAM-foam is a water-based foaming technology which was presented for the first time at the Euroasphalt & 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% to 30% 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 may correspond to those of HMA. Furthermore, field studies reported that the paved sections of WAMfoam 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 mvalue 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, Evotherm exhibited the highest value of creep compliance. It is therefore thought that Eovtherm may be more

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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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.

Figure 3 Creep Compliance values of modified WMA binder in terms of various loading times at 60℃.(Xiao, Punith & Amirkhanian 2012) 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 has highlighted 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 lowtemperature 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. 1Effect 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 viscosity values of all asphalt binder modified with Rediset WMX decreased as the test temperature increased

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 adversely affect 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 has similar 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. 2Effect of Rediset on the Asphalt Mixture 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 lowtemperature characteristics are sensitive to the kind of warm technology used because the influence of manufactured temperature was not clear as two system of WMA had higher fracture energy

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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 Additives This 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 melted leading 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 materials exhibit 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 C5 to C100 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 C45 to C100 plus which is longer than microcrystalline bituminous paraffin wax chain length from C25 to C50. (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 1Effect 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

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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% of Sasobit 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 (𝛿°) 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. 2Effect of Sasobit on the Topography of Asphalt binder Structure 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 nonpolar 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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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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 60/70 Pen

PG 76-22

Figure 2- 4 Height (left) and Phase (right) images with scan size 10um and 25 µm 60/70 Pen + Sasobit

PG 76-22 + Sasobit

Figure 2- 5 Height (left) and phase (right) images with scan size of 25 µm 3-5-2 Performance of Asphalt Mixture Containing Sasobit 1Effect of Sasobit on Mix 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 significant influence 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. 2Effect of Sasobit on Rutting Susceptibility 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 Homburg Wheel 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 |𝐸 ∗ | 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

Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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. 3Effect of Sasobit on Low-Temperature Performance and Fatigue Life 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 to Sasobit 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. 4Effect of Sasobit on Moisture Susceptibility 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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Warm Mix Asphalt Lecture

Dr.Abdulhaq Hadi Abedali

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.