Int J Civ Eng DOI 10.1007/s40999-017-0188-5

RESEARCH PAPER

Evaluation of Rutting Performance of Warm Mix Asphalt Ali Topal1 · Julide Oner2 · Burak Sengoz1 · Peyman Aghazadeh Dokandari3 · Derya Kaya3 

Received: 11 May 2016 / Revised: 23 August 2016 / Accepted: 28 December 2016 © Iran University of Science and Technology 2017

Abstract  In recent years, environmental protection is increasingly becoming a major issue in transportation including asphalt production. Despite the fact that hot mix asphalt (HMA) is widely used around the world, some recent studies suggest that using warm mix asphalt (WMA) technology reduces the production and placement temperature of asphalt mixes. Currently, a common way of producing WMA is through the utilization of additives. This paper firstly characterizes the effect of WMA additives (organic, chemical, water-containing additives) on base bitumen properties. Following the determination of optimum bitumen content of the mixtures with different WMA additives through Marshall test, Hamburg wheel-tracking device is used to measure the permanent deformation characteristics of WMA mixtures. Based on the findings of this study, the utilization of WMA additives helps in the reduction in viscosity values which in return decreases mixing and compaction temperature leading to the reduction in energy costs as well as emissions. Besides, it can be concluded that all WMA mixtures performed better than HMA mixtures in the matter of rut depth. Keywords  Warm mix asphalt · Organic additive · Chemical additive · Water-containing additives · Hamburg wheel-tracking device * Burak Sengoz [email protected] 1

Department of Civil Engineering, Faculty of Engineering, Dokuz Eylul University, 35160 Izmir, Turkey

2

Department of Civil Engineering, Faculty of Engineering, Usak University, Usak, Turkey

3

Graduate School of Natural and Applied Sciences, Dokuz Eylul University, Izmir, Turkey



1 Introduction Asphalt stands as one of the oldest engineering materials which leads to investigate related technologies and seeks solutions in order to increase construction efficiency, improve pavement performance and conserve resources through years [1, 2]. The utilization of warm mix asphalt (WMA) is not a new technology. The world focuses on the development of WMA technologies that may be traced back to two distinctive events [3]. The first time, Csanyi produced asphalt with bitumen that was foamed by steam in 1956 at Iowa State University, USA [4]. Then, foaming technology started to spread out in different countries such as Australia, USA, Germany and France. Scientists have introduced the utilization of waxes as viscosity modifier for the last twenty years [5]. Initially, waxes were used for efficient workability of asphalt, not for lowering the temperature purpose. On the other hand, the world focuses on the development of WMA technologies due to two distinctive events such as the 1992 United Nations’ discussions on the environment and the 1996 Germany’s consideration to review asphalt emissions exposure limits. Reduction in mixing and placement temperatures became the obvious answer and triggered the development of WMA concepts and technologies [6]. In conjunction with developing modern WMA technologies, laboratory studies have been conducted to show potential benefits of WMA and to evaluate the performance compared to traditional hot mix asphalt (HMA). First research reports are from Europe in mid-1990s; then, a lot of testing and field trials have been conducted in USA with publically available reports [5]. The concept of ecologically conscious and energy saving roads must be expanded to the performance of the asphalt mixtures [7]. The conventional HMA is produced

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at temperatures ranging from 138 to 160 °C. This high temperature is used to decrease the viscosity of bitumen and dry the aggregates in order to cover them by bitumen. However in WMA, the mixing and compaction temperatures range from 100 to 140 °C temperature and viscosity are decreased by the addition of chemicals or lubricants in mixing processes [8]. The additives are simply an adhesion agent, which plays a significant role in WMA technology. The mixing of additives reduces viscosity of bitumen and also increases workability of mixture. Besides these, evaporation of the less heavy components of bitumen occurs less than conventional applications and causes less odors in asphalts plants and therefore provides more pleasant working conditions [9]. Based on discussions with industry experts and a scan of the available literature, these WMA additives are the most predominantly specified and utilized both nationally and regionally in northeast of USA for field trials [10]. All of the current WMA additives in use facilitate lowering of production temperature by either lowering the viscosity or expanding the volume of the bitumen at a given temperature [11, 12]. By lowering the viscosity or expanding the volume of the bitumen, the aggregates are completely coated in the bitumen at lower temperature than conventional mixtures [10]. Lowering of mixing and compaction temperatures reduces energy consumption because of saving fuel. Decreasing asphalt production emissions at the plant and lowering placement emissions in the field are the most important benefits of utilizing WMA. WMA technology can be classified based on organic as well as chemical additives and water-containing additives. Organic additives are used to improve bitumen flow by reducing viscosity of bitumen [13]. A decrease in viscosity produces asphalt mixtures at low temperatures. After crystallization, they tend to increase the stiffness of the bitumen and asphalt’s resistance against deformation [5]. Chemical additives are combination of emulsification agents, polymers and additives to enhance workability, compaction and adhesion. The contents of chemical additive used in bitumen were generally based on the recommendations by the suppliers as well as literatures [14–17]. Utilization of water for WMA can be classified into two major groups, mainly the direct injection of water to the bitumen and the utilization of hydrothermally crystallized minerals such as zeolites. Synthetic zeolite is a finely powdered hydrated sodium aluminum silicate that is hydrothermally crystallized, and it holds 18–22% (by mass) of water. Theoretically, the zeolite releases water with the interaction of the asphalt mixture’s temperature which creates foam that reduces the viscosity and increases the workability. It facilitates better coatings of the bitumen on aggregates [18].

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In spite of all WMA advantages, there may be still possible drawbacks of WMA technology like any other new technology [19]. The first issue is that this technology is considered as a relatively new technology, and there is still no sufficient evaluation of field problems. Since WMA additives lower the mixing and compaction temperatures, the performance of WMA throughout the service life of the pavement has recently been gathered the attention of researchers. The process used in this research treated four types of WMA additives at recommended contents (organic additive at a dose of 3%, chemical additive at a dose of 2%, watercontaining additives at a dose of 5% by weight of the bitumen) within 50/70 penetration grade bitumen. Following the determination of conventional bitumen properties of WMA additive-bitumen samples, the mixture properties of WMA samples have been evaluated through Marshall test. Hamburg wheel-tracking device has also been used to determine the rutting performance of the mixtures.

2 Experimental 2.1 Materials The base bitumen with a 50/70 penetration grade has been obtained from Aliaga/Izmir oil terminal of the Turkish Petroleum Refinery Corporation. In order to characterize the properties of the base bitumen, conventional test, such as penetration test, softening point test, thin-film oven test (TFOT), penetration and softening point after TFOT, was performed. These tests were conducted in conformity with the relevant test methods that are presented in Table 1. A mix of basalt and limestone aggregates provided from Dere Madencilik Inc. (Quarry located in Belkahve—Izmir) was used in this study. In order to find out the properties of basalt and limestone aggregate used in this study, sieve analysis (ASTM C136), specific gravity (ASTM C127-07, ASTM C128-07), Los Angeles abrasion resistance test (ASTM C131-01), sodium sulfate soundness test (ASTM C88-05), fine aggregate angularity test (ASTM C1252-06) and flat and elongated particle tests (ASTM D4791-10) were conducted on basalt and limestone aggregates. Physical properties of each kind are given in Table 2. Based on the associated test results, a mix gradation of basalt and limestone was intentionally chosen to provide desired performance in conformity with Turkish specifications concerning the type 1 wearing course. Basalt plays the role of strengthening constituent as coarse aggregate, while limestone participates in the fine aggregate framework. The gradation is given in Table 3. The organic WMA additive is S ­ asobit®, which is made of Sasol Wax is a long-chain aliphatic polymethylene

Int J Civ Eng Table 1  Properties of the base bitumen

Test

Specification

Results

Specification limits

Penetration (25 °C; 0.1 mm)

ASTM D5-97 EN 1426 ASTM D36-95 EN 1427 ASTM D4402-06 ASTM D1754-97 EN 12607-1

55

50–70

49.1

46–54

0.413

–

0.04 75

0.5 (max.) –

5

7 (max.)

100 1.030 260+

– – 230 (min.)

Softening point (°C) Viscosity at (135 °C), Pa.s Thin-film oven test (TFOT); (163 °C; 5 h) Change of mass (%) Retained penetration after TFOT (%) Softening point difference after TFOT (°C) Ductility (25 °C), cm Specific gravity Flash point (°C)

Table 2  Physical properties of used aggregates

Test

Specification

Results Limestone

Specific gravity (coarse agg.)  Bulk  Saturated surface dry  Apparent Specific gravity (fine agg.)  Bulk  Saturated surface dry  Apparent Specific gravity (filler) Los Angeles Abrasion (%) Flat and elongated particles (%) Sodium sulfate soundness (%) Fine aggregate angularity

Table 3  Gradation of the aggregates

ASTM D5-05 EN 1426 ASTM D36-95 EN 1427 ASTM D113-07 ASTM D70-03 ASTM D92-01 EN 22592

ASTM C 127-07

ASTM C 128-07

ASTM C 131-01 ASTM D 4791-10 ASTM C 88-05 ASTM C 1252-06

Test

19–12.5 mm (basalt)

12.5–5 mm (basalt)

Mixture ratio (%) Gradation  (3/4)″  (1/2)″  (3/8)″  No. 4  No. 10  No 40  No. 80  No. 200

15

45

40

100 35.7 2.5 0.4 0.3 0.2 0.15 0.10

100 100 89 16 1.2 0.7 0.4 0.2

100 100 100 100 81 33 22 13

Limits Basalt

2.686 2.701 2.727

2.666 2.810 2.706

2.687 2.703 2.732 2.725 24.4 7.5 1.47 47.85

2.652 2.770 2.688 2.731 14.2 5.5 2.6 58.1

5–0 mm (limestone)

– – – – – – – Max. 45 Max. 10 Max. 10–20 min. 40

Combined gradation (%)

Specification limits

100 90.5 80.5 47.3 33 13.5 9 5.3

100 83–100 70–90 40–55 25–38 10–20 6–15 4–10

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hydrocarbon produced from the Fischer–Tropsch (FT) chemical process with a melting temperature of 120 °C. The longer chains help keep the organic additive in solution, and it is known as an “asphalt flow improver” which reduces bitumen viscosity at typical asphalt production and compaction temperatures [20]. Based on the available literature, dosage rates for organic additive ranged from 1.0 to 4.0% by weight of the bitumen [21–23]. The organic WMA additive concentration in the base bitumen was chosen as 3.0%. The utilization of this content is based on a past research made by O’Sullivan and Wall [10]. They concluded that organic additive should be added at a rate of 3.0% by mass of bitumen for maximum effectiveness [10]. Rediset® WMX is a chemical additive that uses a combination of cationic surfactants and organic additive-based rheology modifier. Chemical additive chemically modifies the bitumen and obtains active adhesion force which improves coating of aggregates with bitumen [14]. Hence, there is no need for additional anti-striping agent in the mixture [24]. Chemical additive can also encourage both processing of asphalt mixture at lower temperatures. Recent researches conducted between 2008 and 2012 suggest that the chemical additive should be used at dosage rates of 1.5, 2 or 3% by weight of the bitumen for better performance of mixture [14–17]. Chemical additive content in the base bitumen was chosen as 2.0% taking the recommendation of Jones et al. [17]. Foaming processes is based on the reality when a given volume of water turns to steam at atmospheric pressure [25]. At present, one type of water-containing additive WMA technologies is Advera®. It is powdered synthetic zeolite that has been hydrothermally crystallized. It contains about 18–21% water of crystallization which is released by increasing temperature above 85 °C. The expansion of water causes foaming of asphalt bitumen. Austerman et  al. [22] and Estakhri et  al. [26] reported that the maximum rate of synthetic zeolite in base bitumen varies between 4 and 6% by weight of bitumen. Synthetic zeolite concentration in the base bitumen was chosen as 5% based on a past research made by Estakhri et al. [26]. The term zeolite originally was derived from Greek words (zeo) meaning “to boil” and (lithos) meaning “stone” as it releases adsorbed water in form of steam when heated rapidly. There are plenty of mineral zeolites in nature. Most are made up of aluminosilicate minerals. Zeolites are commonly used in industry due to their microporous structure. Depending on the size of the pores in their structure, zeolites can be used in different industrial fields. The most abundant zeolite in Turkey is clinoptilolite. It can be found plentifully around Manisa—Gördes area. Reports claim about the existence of 18 million tons of visible clinoptilolite and 20 million tons of its volcanic tuff deposits [27].

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Natural zeolite can be considered as an alternative to water-containing WMA additive. The complex formula is ­(Na3K3)(Al6Si30O72).27H2O. It forms as white to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness (indicating the ability of the mineral to scratch another mineral visibly) of 3.5–4.0 and a specific gravity of 2.1–2.2. Based on a past research made by Sengoz et al., the content of natural zeolite for this study has been chosen as 5% by weight of bitumen [18]. 2.2 Testing Program 2.2.1 Conventional Bitumen Tests The base samples and the bitumen samples containing organic, chemical, synthetic zeolite and natural zeolite additives were subjected to the following conventional bitumen tests: penetration (ASTM D5-97), ring and ball softening point (ASTM D36-95 (2000)), thin-film oven test (TFOT) (ASTM D 1754-97), penetration and softening point after TFOT and storage stability test (EN 13399). In addition, the temperature susceptibility of the bitumen samples has been calculated in terms of penetration index (PI) using the results obtained from penetration and softening point tests [28]. The viscosity is one of the most important rheological properties of fluid that is defined as resistance to flow [29]. The effect of viscosity on asphalt bitumen’s workability is very important in selecting proper mixing and compacting temperatures. Brookfield viscometer was employed to inspect the mixing and compaction temperatures in according to ASTM D4402-06. Approximately 30 g of bitumen was heated in an oven so that it was sufficiently fluid to pour into the sample chamber. Based on the procedure of the test, #27 spindle size was utilized. The sample chamber containing the bitumen sample was then placed in the thermocontainer. After the desired temperature was stabilized for about 30 min, the spindle was lowered into the chamber to test the viscosity [30]. The test was performed at 135 and 160 °C. The temperatures corresponding to bitumen viscosities 170 ± 20 and 280 ± 30  mPa  s were chosen as mixing and compaction temperatures, respectively. 2.2.2 Marshall Stability and Flow Analysis There are many methods that evaluate the properties of asphalt concrete such as stability, permanent deformation, creep test and fatigue test [31]. The mechanical properties of HMA and WMA have been determined by the Marshall method (ASTM D1559) in terms of stability, flow and air void content. In order to achieve the optimum bitumen content for control and WMA mixtures, specimens were prepared with

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various bitumen contents according to Marshall mix design method. The optimum bitumen contents for each WMA technology were measured by obtaining the optimum additive content for each technology. Asphalt concrete specimens were prepared with a compaction effort of 75 blows simulating the heavy traffic loading conditions. After preparing Marshall specimens with various bitumen amounts, required measurements such as height, weight, weight in water and saturated surface dry (SSD) weight were obtained, and then, specimens were tested for stability and flow by Marshall stability and flow test device. 2.2.3 Rutting Test High traffic volume and tire pressure cause serious premature failures in pavements in different environmental conditions [32]. The loss of pavement serviceability is a common result from rutting which is defined as the formation of the longitudinal depressions under the wheel paths caused by the progressive movement of materials under traffic loading in the asphalt pavement layers [33]. The Hamburg wheel-tracking device is designed to evaluate the rutting characteristics of bituminous mixtures by dint of aggregate structure, bitumen properties, moisture susceptibility and adhesion between bitumen and aggregates. The test is carefully contemplated to simulate bearing capacity of pavement under actual wheel tracks. The working principle is to roll a steel wheel with a specified diameter over a bituminous mixture specimen with a standard thickness for a specified number of wheel passes. The test measures the depth of rut after the specified number of passes is reached. Various organizations may define their own specifications with different testing conditions such as specimen dimensions, wheel diameter, rolling length, applied load and temperature. Within this context, there are many devices to test rutting susceptibility under various conditions. The test device used within the scope of this study was an electronically powered device which rolls a steel wheel (capable of using rubber wheel) with a diameter of 203 mm and width of 50 mm over a well-compacted specimen with dimensions of 430 × 280 × 50 mm. The device is capable of making about 50 passes in a minute over the specimen’s surface by rolling a length of 230  mm. The applied load was chosen as 710 N by default as per EN 12697-22 standard test method at 60 °C. Prior to compaction of the specimens, HMA and WMA mixtures were carefully mixed at their pre-defined mixing temperatures using a mixer capable of mixing adequate amount of materials at desired temperature. The Hamburg wheel-tracking device comes with a roller compactor in order to compact mixtures within standard molds to fit in wheel-tracking device frames. The roller compactor also makes it convenient to prepare

specimens with desired thickness (50  mm) with specified air voids (4%). The amount of loose mix to reach the desired compacted bulk specific gravity corresponding to 4% air voids considering mold dimensions was calculated and poured into compaction molds. After cooling the specimens at room temperature, the specimens were subjected to 30.000 passes of wheel tracks. For each mixture assessed in this study, two specimens of same mixture were prepared and tested for right and left wheels. The rut depth was measured and recorded for right and left wheels simultaneously by an electronic system at every 5.000 passes while the test was running.

3 Results and Discussions 3.1 Conventional Test Results The conventional properties of the bitumen prepared with organic, chemical, synthetic zeolite and natural zeolite additives are presented in Table 4. As depicted in the table, the addition of the additives resulted in a decrease in penetration and increase in softening point values. The increase in softening point is favorable since bitumen with higher softening point may be less susceptible to permanent deformation (rutting) [34]. Organic, chemical and synthetic zeolite and natural zeolite WMA additives reduce temperature susceptibility (as determined by the penetration index—PI) of the bitumen. Lower values of PI indicate higher-temperature susceptibility. As shown in Table  4, all WMA samples exhibit less temperature susceptibility compared to base bitumen. Natural zeolitebitumen sample exhibits satisfactory temperature susceptibility characteristics in terms of PI values as presented in Table 4. Besides among all the additives, organic additivebitumen sample exhibits the lowest temperature susceptibility. Asphalt mixtures containing bitumen with higher PI are more resistant to low-temperature cracking as well as permanent deformation [34]. Softening point test results on bitumen samples prepared with WMA additives taken from the top and bottom of the tube in the storage stability test indicate that both natural and synthetic zeolite-bitumen samples exhibit similar storage stability characteristics as presented in Table 4. Besides, chemical additive-bitumen samples are much more storage stable compared to other warm mix additives added bitumen samples. The additives also reduce the viscosity of bitumen. This indicates that all warm mix asphalt additives increase the workability and make relative reductions for mixing and compaction temperatures. The viscosity of results related to each WMA additive 135 °C and 160 °C is drawn at semilogarithmic figure, and

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0.5

1.6

1.6

Additives

Contents (%)

Mixing temp. (°C)

Compaction temp. (°C)

Base bitumen Natural zeolite Synthetic zeolite Organic Chemical

0 5 5 3 2

156–163 150–157 149–152 144–149 148–153

143–149 137–142 135–142 134–138 133–142

then, the temperature corresponding to compaction and mixing ranges is summarized in Table 5. It is evident that addition of natural zeolite, synthetic zeolite, organic and chemical WMA additives reduced the mixing temperature by 6, 9, 13 and 9 °C, respectively. Besides, the addition of the previously mentioned additives reduces the compaction temperatures by 6, 7, 10 and 8 °C, respectively. 3.2 Marshall Stability and Flow Analysis Results After making sure that all parameters are satisfying values based on standards, the optimum bitumen contents for each WMA mixture were retrieved directly as the bitumen content corresponding to 4% air voids. In this study, the optimum bitumen contents related to HMA, WMA including organic additive, chemical additive, synthetic zeolite additive and natural zeolite were determined as 4.76, 4.25, 4.46, 4.32 and 4.56%, respectively. The mechanical properties of HMA and WMA specimens including organic, chemical, synthetic zeolite and natural zeolite additives in terms of stability and flow are presented in Figs. 1 and 2, respectively. As illustrated in Fig.  1, HMA mixtures and all WMA mixtures provide adequate stability. The stability values increases with utilization of organic, chemical, synthetic zeolite and natural zeolite in comparison with HMA. As presented in Fig.  2, WMA mixtures containing organic, chemical, synthetic zeolite and natural zeolite satisfy the specification limits of flow values. As the flow values are indicator of deformation characteristic, the flow values less than the specification limits (2  mm.) are not favorable since it implies that the mix is very stiff and brittle.

Chemical

3.3 Rutting Test Results Organic

Synthetic zeolite

0 5 0 5 0 3 0 2

55 51 55 52 55 37 55 44

49.1 55.0 49.1 56.0 49.1 69.3 49.1 56.7

412.5 325.0 412.5 312.5 412.5 287.5 412.5 337.5

137.5 113.0 137.5 112.5 137.5 75.0 137.5 87.5

0.04 0.16 0.04 0.16 0.04 0.07 0.04 0.04

75 85 75 84 75 87 75 84

5.0 3.7 5.0 4.1 5.0 4.0 5.0 2.5

−0.04 −0.17 −0.04 −0.18 −0.04 −0.07 −0.04 −0.07

74 83 74 79 74 85 74 83

5.3 3.7 5.3 4.5 5.3 4.3 5.3 2.5

−1.20 0.02 −1.20 0.27 −1.20 1.95 −1.20 0.04

2.0

Table 5  Mixing and compaction temperatures

Natural Zeolite

Soft. Point Pen. Index (PI) diff. (°C) Soft. Point Loss of mass (%) Retained diff. (°C) Pen. (%) Retained Pen. (%) 135 °C 160 °C Loss of mass (%)

Thin-film oven test (TFOT) Viscosity (mPa s) WMA additive types Contents (%) Pen. (0.1 mm) Softening point (°C)

Table 4  Conventional properties of bitumen prepared with warm mix asphalt additives

Rolling thin-film oven test (RTFOT)

Storage stability (°C)



The Hamburg wheel-tracking test was performed in accordance with EN 12697-22 standard. The rut depths presented in Figs. 3, 4, 5, 6 and 7 are given as percent values

Int J Civ Eng Fig. 1  Marshall stability values for control samples and WMA samples

Fig. 2  Flow values for control samples and WMA samples

Fig. 3  The rut depth percent values corresponding number of passes for HMA mixture

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Fig. 4  The rut depth percent values corresponding number of passes for specimens containing organic WMA additive

Fig. 5  The rut depth percent values corresponding number of passes for specimens containing chemical WMA additive

indicating the ratio of actual rut depth over the total thickness of tested specimen (50 mm). As expected in all figures regarding HMA and WMA specimens, the rut depth increases with increase in the number of wheel passes. As depicted in Figs. 3, 4, 5, 6 and 7, the mixtures prepared with all WMA additives exhibit higher rutting performance compared to HMA mixtures. This indicates that despite lower mixing and placement temperature, WMA mixtures resist permanent deformation. A clear distinction can also be made within the mixtures prepared with WMA additives. It is evident that at a specified number of passes (15,000 passes) organic additive mixtures exhibit the lowest rut depth percentage. This result is attributable to crystallized structure arising from

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the modification effect of organic WMA additive [35]. Among all WMA additives, synthetic zeolite mixture sample depicts the lowest rutting performance. In light of the findings from that presented in Figs. 6 and 7, mixtures prepared with natural zeolite exhibited better rutting performance compared to synthetic zeolite.

4 Conclusions and Recommendations Reduction in mixing and compaction temperatures and low emissions during placement of the mixture are the most important benefits of utilizing WMA. The properties of bitumen are improved by means of WMA organic, chemical, synthetic zeolite and natural zeolite additives.

Int J Civ Eng Fig. 6  The rut depth percent values corresponding number of passes for specimens containing synthetic zeolite WMA additive

Fig. 7  The rut depth percent values corresponding number of passes for specimens containing natural zeolite additive

These results have been reached by the conventional test methods such as penetration, softening point, rotational viscosity and TFOT test results. Besides, the utilization of organic, chemical, synthetic zeolite and natural zeolite additives helps in the reduction in viscosity values leading to the reduction in energy costs as well as emissions. The results obtained from Marshall test, the optimum bitumen content decreases by use of WMA additives compared to HMA mixtures. This reduction may be described as an advantage of using WMA additives in terms of initial cost. Marshall stability values related to WMA mixtures have been found higher than the control mixtures (HMA). The other properties of WMA samples including organic,

chemical, synthetic zeolite and natural zeolite such as flow and air void level are also within specification limits. The Hamburg wheel-tracking device is designed to simulate bearing capacity of pavement under actual wheel tracks. The test results indicated that all WMA mixtures performed better than HMA mixture in terms of rut depth. Lower application temperature significantly reduces the short-term aging effects for bituminous mixtures. Rather than the influence of modification by WMA additives on binder properties, aging is the main attributable reason for rutting performance of WMA mixtures. Acknowledgements  This research was sponsored by the Scientific and Technological Research Council of Turkey (TUBITAK) under the

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project number 110M567 for which the authors are greatly indebted. The findings and evaluations of the results of this study are not the official view of TUBITAK. The authors would also like to thank Republic of Turkey General Directorate of Highways and General Directorate of Research and Development that helped with the rutting tests.

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