Construction and Building Materials

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1 Construction and Building Materials 36 (2012) Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: Investigating effects of ethylene vinyl acetate and gilsonite modifiers upon performance of base bitumen using Superpave tests methodology Mahmoud Ameri a,b,,1, Ahmad Mansourian b, Amir Hossein Sheikhmotevali a a School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran b Transportation Research Institute, Iran University of Science and Technology, Tehran, Iran highlights " Addition of EVA or Gilsonite to base bitumen improve base bitumen rutting resistance. " Fatigue resistance of EVA-modified bitumens is higher than base bitumen. " Fatigue resistance of gilsonite-modified bitumens is less than base bitumen. " Addition of gilsonite decreases low temperature performance of base bitumen. " Addition of EVA of up to 4% improves low temperature performance of base bitumen. article info abstract Article history: Received 15 January 2012 Received in revised form 19 March 2012 Accepted 25 April 2012 Available online 31 July 2012 Keywords: EVA Gilsonite Superpave BBR DSR RV In this research study, relative performance of a series of ethylene vinyl acetate (EVA) and gilsonite modified bitumens were evaluated in terms of three main distress modes of flexible pavement namely rutting, fatigue damage and low temperature cracking. Seven modified and unmodified bitumens were tested and characterized in accordance with the Superpave performance criteria. The experimental tests performed were dynamic shear rheometer (DSR), bending beam rheometer (BBR) and rotational viscosity (RV). DSR test results for rutting showed that addition of EVA and gilsonite increase the rutting parameter (G / Sin(d)) of the modified bitumens relative to the base bitumen. DSR fatigue test results showed that addition of EVA decreases the fatigue parameter (G Sin(d)) of modified bitumens while addition of gilsonite increases the fatigue parameter of modified bitumens. BBR test results showed that addition of EVA decreases the creep stiffness (S-value) of modified bitumens while addition of gilsonite increases the creep stiffness of modified bitumens. Moreover, the addition of 2% and 4% EVA increase the m-value of modified bitumens while addition of gilsonite decreases the m-value of modified bitumens. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction A careful balance of binder properties is generally required to alleviate one mode of asphalt mixture distress without aggravating other modes, such as the use of a harder bitumen to alleviate rutting without aggravating fatigue cracking [1]. To this end, novel binders with improved rheological characteristics are continuously being developed [1]. The best known form of this binder improvement is by means of polymer modification, traditionally used to improve the temperature susceptibility of bitumen by increasing Corresponding author at: School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran. Tel.: ; fax: address: ameri@iust.ac.ir (M. Ameri). 1 President of Transportation Research Institute and Head of Center of Excellence of PMS, Transportation and Safety. binder stiffness at high service temperatures and reducing stiffness at low service temperatures [2]. The benefits of using modified bitumens in asphalt mixture production are thoroughly investigated by Al-Hadidy and Yi-qiu [3]. Their comprehensive laboratory tests investigation of rutting and fatigue resistance of asphalt mixtures produced with modified and unmodified bitumens indicate the superior rutting and fatigue performance of asphalt mixtures prepared with modified bitumens. In general, polymer modified bitumens (PMBs) improve resistance to permanent deformation and fatigue cracking [1]. The polymers that are used for bitumen modification can be divided into two broad categories known as plastomers and elastomers [1,4]. Plastomers tend to modify bitumen by forming a tough, rigid, three-dimensional network within the binder to resist deformation, while elastomers have a characteristically high elastic response and, therefore, resist permanent deformation by stretching and recovering their initial shape [1,4] /$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.

2 1002 M. Ameri et al. / Construction and Building Materials 36 (2012) The semi-crystalline copolymer, ethylene vinyl acetate (EVA) is one of the principal plastomers used in road construction in order to improve both the workability of the asphalt during construction and its deformation resistance in service [5]. Airey showed that EVA provides the modification of bitumen throughout the crystallization of rigid three-dimensional networks within the bitumen resulting in considerable changes of the physical, chemical and morphological properties of the bitumen. The effect of the base bitumen type on the polymer compatibility and on the degree of modification is, also, outlined [5]. Rheology and stability of bitumen/eva blends was investigated by Gonzalez et al. [6]. Rheological measurements revealed that the viscoelastic properties of a 60/70 penetration grade bitumen were improved when either a virgin EVA or a recycled EVA copolymer of similar vinyl acetate content were mixed with it [6]. Risk of cracking at low temperatures and rutting at high temperatures, were both reduced [6].Stability tests performed combining oscillatory flow and microscopy results disclosed that blends with the higher polymer proportion (3%) were susceptible of phase separation after 24 h of storage at 165 C, but 1% blends were stable for at least 4 days. A general evaluation of the results indicated that the performance of this bitumen as a binder for road pavement, was particularly improved when 1% of recycled EVA or virgin EVA was added [6]. The rheological properties of various polymer modified bitumens were studied by Lu et al. Three bitumens from two different sources were mixed with styrene ethylenebutylene styrene (SEBS), ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) copolymers at different polymer contents. The rheological properties of the modified binders were investigated by means of dynamic mechanical analysis and creep test (bending beam rheometer). The results indicated that polymer modification increased binder elastic responses and dynamic moduli at intermediate and high temperatures, and reduced binder complex and stiffness moduli at low temperatures. Polymer modification also reduced temperature susceptibility, glass transition temperature as well as limiting stiffness temperature. The degree of the improvement generally increased with polymer content, but varied with bitumen source/grade and polymer type [7]. Sengoz and Isikyakar studied properties and morphology of SBS and EVA polymer modified bitumens using conventional and empirical test methods and fluorescence microscopy. The mechanical properties of the hot-mix asphalt (HMA) containing SBS and EVA PMBs have also been analyzed and compared with HMA incorporating base bitumen. The results indicated that, the morphology and properties of the modified bitumens, as well as the mechanical properties of polymer modified HMA are dependent on the type of polymer and polymer content. At low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed. Polymer modification improved the conventional properties of the base bitumen such as; penetration, softening point, temperature susceptibility. It was also concluded that, the mechanical properties of HMA prepared with the SBS PMB samples such as Marshall stability were enhanced with the increasing polymer contents [8]. Properties and microstructure of plastomeric polymer modified bitumens were evaluated by Topal [9]. The results indicated that polymer modification improved the conventional properties of the base bitumen such as; penetration, softening point, temperature susceptibility. The microstructure and properties of the polymer modified bitumens were dependent on the type of polymer, the solubility of polymer in bitumens and polymer content. At low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed for the Evatane Ò 2805 and Elvaloy Ò 3427 polymers. Among the plastomeric polymers no significant polymer phase has been observed for the reactive terpolymer Elvaloy Ò 4170 although its conventional properties have been improved. It is also found out that a relationship exists between the polymer content and percent area distribution of polymers except for reactive terpolymer [9]. Morphology of styrene butadiene styrene (SBS); ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) based polymer modified bitumen samples (PMBs) was investigated by Sengoz et al. The morphology of the samples as well as the percent area distribution of polymers throughout the base bitumen have been characterized and determined by means of fluorescent light optic microscopy and Qwin-Plus image analysis software, respectively. The results indicate that the fundamental properties and morphology of the modified bitumens were dependent on the type of polymer and polymer content. Polymer modification improved the conventional properties of the base bitumen such as penetration, softening point, temperature susceptibility. At low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase was observed. Moreover it is found out that a relationship exists between the polymer content and percent area distribution of polymers [10]. Although various additives such as polymers and rubber powder may improve the performance of bitumen, suitable performance of a special additive should not be the criterion for choosing it, but there are also some other factors such as economical issues, production of modifier and environmental compatibility that should be considered when selecting an additive [11]. Gilsonite which belongs to the hydro carbonates within classification of asphalt binder modifiers is a resinous hydrocarbon that has been evaluated and used in various industrial issues [11]. Addition of gilsonite (as an additive) to asphalt binder increases its viscosity and reduces its penetration. The result of such addition is a modified asphalt binder with higher hardness. Generally, gilsonite can be used in pavement construction in two ways: preliminary addition of gilsonite to the asphalt binder, or addition of gilsonite to aggregates during premixing cycle at batch plant. Research in the field of gilsonite application shows that the American gilsonite causes the performance improvement of asphalt binder in high temperatures, while in low temperatures it causes brittleness of the asphalt binder, and provides a suitable condition for low temperature cracking in pavement [11]. The Strategic Highway Research Program (SHRP) was a highly focused, ambitious research effort, which targeted four specific areas for intense study over the time frame from 1987 to 1993 [1]. Bitumen was one of the four study areas which culminated in the production of Superpave (Superior Performing Asphalt Pavements) by the SHRP asphalt research team [1]. One of the major products of the SHRP asphalt research program was a performance-based asphalt binder specification which was designed to be applicable to both modified and unmodified bituminous binders, including binders with modifiers dispersed, dissolved or reacted with the base bitumen [1]. A major objective of the asphalt research program was to identify and validate engineering properties that could be directly linked to the performance (the response to traffic and environmental loading) of bituminous binders [1]. The SHRP binder specifications, and the measurements upon which they are based, are designed to provide performance-related properties that can be related in a rational manner to pavement performance [1]. The pavement distress modes that are considered in this paper are rutting, caused by inadequate shearing resistance in the asphalt mixture, load associated fatigue cracking and low temperature cracking. This paper presents a laboratory evaluation of the relative performance of modified

3 M. Ameri et al. / Construction and Building Materials 36 (2012) bitumens by EVA and gilsonite in terms of Superpave performance tests. 2. Materials Unmodified bitumen properties are presented in Table 1. The polymer investigated is ethylene vinyl acetate (EVA) copolymer, in which its Melt Index (MI) and its vinyl acetate (VA) were 158 and 18% by mass respectively. Review of past literatures [2,5,7,12]; indicate the lower and upper limits of EVA content for proper mixing of this polymer with base bitumen range between 1% to 7% by weight of base bitumen. Thus in this research study three levels were used, namely 2%, 4% and 6% by weight of base bitumen. The polymer modified bitumens were prepared using a low shear mixer at 180 C and a speed of 125 rpm [7]. The mixing time was 2 h [7]. Gilsonite was prepared from one mine in Kermanshah Province of Iran. Results of tests for specifying the physical properties and elemental analysis of gilsonite have been shown in Table 2. According to the recommendations of the World Road Association (PIARC), the gilsonite powder used for modification of the bitumen should completely pass through sieve no. 50 (0.2 mm) [11]. On this basis the gilsonite powder passed through sieve no. 50 (0.2 mm), in amount of 4%, 8%, and 12% of the weight of the asphalt binder, was added to the base bitumen which was heated up to 140 C and blended for 150 min at the speed of 150 rounds per minute in the mixer. Then the blending temperature was raised to 180 C and the process was repeated for another 30 min at the speed of 4500 round per minute to make sure that a homogenous blend of gilsonite and the base bitumen is produced [11]. Table 3 shows various bitumens used in this research study. 3. Experimental test methods In this research study, for studying the properties of bitumens (unmodified and modified with EVA and gilsonite), rotational viscosity (RV) test, dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test were conducted according to Superpave performance grading specification [11]. Rotational viscosity test was conducted in order to be certain of bitumen pumping and bitumen mixing with hot aggregates. According to ASTM D4402 recommendations, bitumen viscosity should be less than 3000 MPa at 135 C [11]. The dynamic shear rheometer test at the frequency of 10 rad/s (1.6 Hz) was conducted at required high temperatures (46 82 C) and required intermediate temperatures (13 31 C) for control of permanent deformation at high temperatures and fatigue cracking at intermediate temperatures respectively. As a result of dynamic shear rheometer test, the G and d parameters were obtained. According to ASTMD2872 recommendations for control of permanent deformation (rutting), the G / Sin(d) at high performance temperature (HT) for unaged bitumen and residue aged bitumen after rolling thin film oven (RTFO) test should be more than 1 kpa and 2.2 kpa, respectively [11]; moreover, for control of fatigue cracking the G Sin(d) should be less than 5000 kpa for aged bitumen obtained from rolling thin film oven Table 2 Physical properties and elemental analysis of gilsonite. Parameters measured Test method Results Specific 25 C (g/cm 3 ) ASTM D Solubility in CS2 (%) ASTM D Solubility in TCE (%) ASTM D C (0.1 mm) ASTM D5 0 Ash content (%) ASTM D Moisture content (%) ASTM D Carbon content (%) ASTM D Hydrogen content (%) ASTM D Nitrogen content (%) ASTM D Oxygen content (%) ASTM D Sulfur content (%) UOP Table 3 Bitumen codes and composition. Binder code Polymer type Control EVA2 EVA 2 EVA4 EVA 4 EVA6 EVA 6 Gil4 Gilsonite 4 Gil8 Gilsonite 8 Gil12 Gilsonite 12 Polymer content by weight of base bitumen (%) and pressure age vessel (PAV) tests [11]. Generally, in addition to existing requirements for the high performance temperature and the low performance temperature (LT), there is a limiting maximum stiffness at the intermediate temperature (IT) to prevent fatigue cracking; accordingly, at the intermediate service temperature, which equals ðht þ LTÞ=2 þ 4 C should be less than 5000 kpa for aged bitumen from RTFO and PAV tests [11]. For studying the characteristics of bitumen in low temperatures (<0 C), which leads to low temperature cracking, the BBR test was conducted at required low temperatures ( 6 to 24 C). Two parameters were obtained through this test; stiffness and the rate of change of stiffness with time (m-value) at 60 s loading. According to ASTM-D6648 recommendations to control the low temperature cracking at low performance temperature, which is 10 C less than test temperature, stiffness of bitumen should be less than 300 MPa, and m-value should be greater than 0.3 at 60 s loading [11]. Table 1 Properties of unmodified bitumen. Parameters Unit Test method Results ASTM AASHTO Specific gravity gr/cm 3 D70 T Softening point C D36 T53 51 Ductility cm D113 T51 >100 cm Solubility (%) D2042 T Flash point (Cleveland) C D92 T Kinematic 120 C Centistokes D2170 T Kinematic 135 C Centistokes D2170 T Kinematic 160 C Centistokes D2170 T Heating loss D1754 T Penetration after heating loss 0.1 mm 47 Penetration after heating loss to original penetration 85.4 Ductility after heating loss cm >50 cm Penetration index 0.73 PVN (25 135) 0.39

4 1004 M. Ameri et al. / Construction and Building Materials 36 (2012) Summary and results 4.1. Effect of EVA and Gilsonite on high temperature performance grade As observed in Figs. 1 and 2, addition of 2% EVA to the unmodified bitumen, before and after short term aging process, causes slight increase in G /Sin(d) for modified bitumen compared to unmodified one. As seen in Table 4, the high performance temperature (HT) of modified bitumen increases from to 66.7 C. This trend has continued with increase in percentage of EVA from 4% to 6%, and high performance temperature of modified bitumen increases from C to C with 4% of EVA and to C with 6% of EVA (Table 4). As observed in Figs. 3 and 4, addition of 4% gilsonite to the unmodified bitumens, before and after short term aging process, causes increase in G /Sin(d) for modified bitumens compared to unmodified ones. As seen in Table 4, the high performance temperature of modified bitumen increases from to 70.5 C. In fact, the results presented in Figs. 3 and 4, indicate gilsonite has positive effect on high performance temperature of bitumens and increases shear strength of modified bitumens. This trend has continued with increase in percentage of gilsonite from 4% to 12%, and the performance of modified bitumen at high temperatures is improved considerably. Moreover, high performance temperature of modified bitumen increases from C to 74.9 C with 8% of gilsonite and to 84.5 C with 12% of gilsonite (Table 4). Generally, the major reason for the increase in high performance temperature of modified bitumens compared to unmodified bitumen can be the increase in G and simultaneously the decrease in phase angle (d). In other words, the behavior of bitumen is dependent on its viscoelastic characteristics, by which, increased G and decreased phase angle (d) extend the temperature at which bitumen can maintain its elasticity [11]. As seen in Table 4 and Fig. 5, the rutting ranking of the unmodified and modified bitumens are as follows: Gil12 > EVA6 > Gil8 > EVA4 > Gil4 > EVA2 > control Effect of EVA and Gilsonite on low temperature performance grade For assessment of the effect of EVA on the low performance temperature (LT) of bitumen, the BBR test at required low temperatures ( 12 to 24 C) was conducted on unmodified and modified bitumens. As it is observed in Figs. 6 and 7, addition of 2% and 4% EVA to unmodified bitumen causes decrease in the stiffness and increase in the m-value of modified bitumen; that is, the low performance temperature of modified bitumen decrease but addition of 6% EVA to unmodified bitumen causes decrease in the stiffness at all temperatures and increase in the m-value of modified bitumen only at 24 C. EVA2 and EVA4 fulfil the requirements (stiffness Fig. 1. Effect of EVA content on rutting parameter before short term aging process. Fig. 2. Effect of EVA content on rutting parameter after short term aging process. <300 MPa and m-value > 0.3) set at 12 and 18 C. However, addition of 6% EVA to unmodified bitumen is different from that of 2%, 4% to some extent. The results shown in Figs. 6 and 7, confirm that EVA6 only fulfils the requirements (stiffness <300 MPa and m-value >0.3) at 12 C. For assessment of the effect of gilsonite on the low performance temperature of bitumen, the BBR test at low temperatures ( 6 to 24 C) was conducted on unmodified and modified bitumens. As it is observed in Figs. 8 and 9, addition of gilsonite to unmodified bitumen causes increase in the stiffness and decrease in the m-value of modified bitumens; that is, the low performance temperature of modified bitumen increases. These changes fulfil the requirements (stiffness <300 MPa and m-value >0.3) set for unmodified bitumen before and after addition of gilsonite only at 6 C. It must be noted that the more the gilsonite percentage, the more increase in low performance service temperature of the bitumen will occur. One reason for undesirable increase in low performance temperature of modified bitumens with gilsonite may be the increase in their stiffness, which will lead to a decrease in their elasticity. As seen in Table 5 and Fig. 10, the low temperature ranking of the unmodified and modified bitumens is as follows: EVA4 > E- VA2 > EVA6 > control mix > Gil4 > Gil8 > Gil Effect of EVA and Gilsonite on intermediate temperature performance grade It was not possible to perform DSR fatigue test for EVA4 and EVA6 at temperatures lower than 20 C because stiffening effect of EVA at intermediate temperatures. The G Sin(d) trend in Fig. 11 indicates that the EVA4, EVA6 should have far superior fatigue performance compared to unmodified bitumen. As seen in Fig. 11 addition of 6% EVA to unmodified bitumen increases the G Sin(d) compared to EVA4 but the value is still less than unmodified bitumen. The major reason for decrease in intermediate performance temperature (IT) of bitumens after addition of EVA may be the increase in G and the decrease in phase angle (d). As seen in Fig. 12, addition of 4% gilsonite to unmodified bitumen increases the G Sin(d), and this trend will continue with increasing of the amount of gilsonite to 8% and 12%. As shown in Table 7, although the addition of gilsonite affects the performance grade of the original bitumen, the modified bitumens fulfil the necessary requirement (G Sin(d) < 5000 kpa) at intermediate service temperature only when the new performance grade products are considered. The major reason for increase in intermediate service temperature of bitumens after addition of gilsonite may be the increase in G and the decrease in phase angle (d). This phenomenon may have caused the elastic behavior of modified bitumens to prevail at these temperatures.

5 M. Ameri et al. / Construction and Building Materials 36 (2012) Table 4 High temperature performance of modified bitumens. Binder type G 1 (kpa) G 2.2 (kpa) HT ( C) HT improvement ( C) Control EVA EVA EVA Gil Gil Gil Fig. 3. Effect of gilsonite content on rutting parameter before short term aging process. Fig. 6. Effect of EVA content on S-value. Fig. 7. Effect of EVA content on m-value. Fig. 4. Effect of gilsonite content on rutting parameter after short term aging process. Fig. 8. Effect of gilsonite content on S-value. Fig. 5. Effect of EVA and gilsonite content on high temperature. Using the hypothesis that a reduction in G Sin(d) will correspond to improved fatigue resistance, the fatigue ranking of the unmodified and modified bitumens are as follows: EVA4 > EVA6 > EVA2 > control mix > Gil4 > Gil8 > Gil12 (Table 6 and Fig. 13) Effect of EVA and Gilsonite on viscosity The rotational viscosity test on unmodified and modified (with 2%, 4% and 6% EVA and with 4%, 8% and 12% gilsonite) bitumens showed that both EVA and gilsonite cause increase in viscosity of unmodified bitumen in that the more the percentage of modifier, the more the viscosity of modified bitumen. According to viscosity test results shown in Fig. 14 it is clear that the viscosity of all

6 1006 M. Ameri et al. / Construction and Building Materials 36 (2012) Fig. 9. Effect of gilsonite content on m-value. Fig. 12. Effect of gilsonite content on fatigue parameter. Table 6 Effect of EVA and gilsonite content on intermediate temperature performance. Binder type G 5000 (kpa) IT improvement ( C) Control EVA EVA4 EVA6 Gil Gil Gil Fig. 10. Effect of EVA and gilsonite content on low temperature temperature performance. Table 7 Effect of EVA and gilsonite content on performance grade. Binder type Control EVA2 EVA4 EVA6 Gil4 Gil8 Gil12 Performance grade PG64 22 PG64 22 PG70 28 PG76 22 PG70 22 PG70 16 PG Effect of EVA and Gilsonite on performance grade Fig. 11. Effect of EVA content on fatigue parameter. modified bitumen samples are less than optimum limit of 3000 MPa s. Therefore, it may be concluded that addition of EVA and gilsonite to the bitumen has not had any negative effect on the viscosity of modified bitumen. The effect of EVA as an additive on high, low and intermediate performance grade of modified bitumens was presented in Table 7. According to results of performance grades of modified bitumens, which are based on Superpave performance grading system (Table 7), it can be concluded that addition of EVA to unmodified bitumen cause an increase in high performance temperature of the unmodified bitumen. Although addition of EVA has a positive effect on high performance temperature of unmodified bitumen, this additive has no positive impact on unmodified bitumen to improve its low performance temperature except at 4%. Addition of gilsonite to unmodified bitumen cause an increase in high performance Table 5 Effect of EVA and gilsonite content on low temperature performance. Binder type 300 (MPa) 0.3 LT ( C) LT improvement ( C) Control EVA EVA EVA Gil Gil Gil

7 M. Ameri et al. / Construction and Building Materials 36 (2012) these types of additives. The findings of this research study are as follows: Fig. 13. Effect of EVA and gilsonite content on intermediate temperature performance. Both EVA and gilsonite improve rutting resistance of unmodified bitumen. Addition of EVA increases fatigue cracking resistance of modified bitumens while addition of gilsonite decreases fatigue resistance of modified bitumens. Effect of EVA on low temperature cracking resistance of bitumens depends upon EVA content. At low and intermediate EVA contents (2% and 4%), addition of EVA increases low temperature cracking resistance of modified bitumens but at higher EVA contents (6%), addition of EVA decreases low temperature cracking resistance of modified bitumens. In general, the findings of this research study indicate addition of gilsonite decreases low temperature cracking resistance of modified bitumens and also increases low temperature at which low temperature cracking occurs. References temperature of the unmodified bitumen but it does not have positive effect on low temperatures. 5. Conclusions Fig. 14. Effect of EVA content on viscosity. In this research paper performance of ethylene vinyl acetate (EVA) and gilsonite modified bitumens were evaluated using DSR, BBR and RV tests in accordance with the Superpave tests procedures. The major objective of selecting SHRP specifications for this research study was to identify engineering properties of bitumens modified with EVA and gilsonite that could be linked to performance of asphalt concrete mixtures that are produced with [1] Airey GD. Fundamental binder and practical mixture evaluation of polymer modified bituminous materials. Int J Pavement Eng 2004;5(3): [2] Airey GD. Rheological evaluation of ethylene vinyl acetate polymer modified bitumens. Constr Build Mater 2002;16(8): [3] Al-Hadidy AI, Yi-qiu T. Mechanistic approach for polypropylene-modified flexible pavements. Mater Des 2009;30(4): [4] Ahmadinia E et al. Using waste plastic bottles as additive for stone mastic asphalt. Mater Des 2011;32(10): [5] Haddadi S, Ghorbel E, Laradi N. Effects of the manufacturing process on the performances of the bituminous binders modified with EVA. Constr Build Mater 2008;22(6): [6] Gonzalez O et al. Rheology and stability of bitumen/eva blends. Eur Polymer J 2004;40(10): [7] Lu X, Isacsson U, Ekblad J. Rheological properties of SEBS, EVA and EBA polymer modified bitumens. Mater Struct 1999;32(2): [8] Sengoz B, Isikyakar G. Evaluation of the properties and microstructure of SBS and EVA polymer modified bitumen. Constr Build Mater 2008;22(9): [9] Topal A. Evaluation of the properties and microstructure of plastomeric polymer modified bitumens. Fuel Process Technol 2010;91(1): [10] Sengoz B, Topal A, Isikyakar G. Morphology and image analysis of polymer modified bitumens. Constr Build Mater 2009;23(5): [11] Ameri M et al., Technical study on the Iranian gilsonite as an additive for modification of asphalt binders used in pavement construction. Constr Build Mater; [12] Panda M, Mazumdar M. Engineering properties of EVA-modified bitumen binder for paving mixes. J Mater Civil Eng 1999;11:131.