Investigating the Effect of anti Stripping Agents (ASAs) on Fatigue and Rutting Properties of Stone Matrix Asphalt (SMA) Mixtures Modified by Ground Tire Rubber (GTR) and Waste Polyethylene Terephthalate (PET)

The current study assessed the influence of Anti Stripping Agents (ASA), Ground Tire Rubber (GTR) and waste polyethylene terephthalate (PET) on performance behavior of binder and Stone Matrix Asphalt (SMA) mixtures. Through this paper the 85/100 penetration grade bitumen was utilized as original bitumen. Also, three liquid ASA’s (ASA (A), ASA (B), ASA (C)) were used as mixture modifier. For this purpose, softening point, penetration, rotational viscosity, Dynamic Shear Rheometer, Multi Stress Creep Recovery (MSCR) and Linear Amplitude Sweep (LAS) tests were implemented to investigate the rheological properties of modified bitumen. For evaluating the behavior of modified mixtures several tests such as; Resilient Modulus, Tensile Strength, dynamic creep, wheel track and four point beam fatigue tests were implemented. Based on MSCR test results, utilization of mentioned polymers enhanced the elasticity of bitumens and therefore the permanent deformation resistance of binders increases. Also by addition of PET percentage, the rutting resistance improves. Results indicated that utilization of ASAs, PET and Crumb Rubber (CR) enhance the Resilient Modulus (Mr), Indirect Tensile Strength (ITS), rutting resistance, fatigue life and Fracture Energy (FE) of asphalt mixtures. Also based on results, modification of binder by PET/CR with ratio of 50%/50% and ASA (B) have the highest fatigue life which indicates that this mixture have highest resistance against fatigue cracking.


Introduction
All around the world several waste industrial materials are produced. These vast volume of materials have negative influence on environment such as: soil, air and water pollution, that influence the economic issues, human life, energy preservation. For this reason lots of attention was attracted to reuse of mentioned materials as alternatives and reduce consumption of new sources. occupation of vast area by these materials is another drawbacks of waste materials. So further investigations was needed on reusing of waste materials in pavement industry [1][2][3][4][5].
One of the main kinds of plastics is Polyethylene Terephthalate (PET) [6]. This kind of plastics compound of high ratio of thermoplastic polymers. This waste material is a semi-crystalline thermoplastic polymer and is kind of polyester solid [7]. Large amount of waste PET is being produced in the form of different products, for instance, bottles, fibers, molding and sheets are the products mostly manufactured in Europe by application of PET [8]. Utilization of PET is wellknown in food industry because of superlative characteristics offered by PET as a packaging material, mainly as bottles [9,10].
One of the most important asphalt modifiers which is used for many years in pavement industry and reclaimed from vehicle and also truck tires is Ground Tire Rubber (GTR). The GTR is normally added to the bitumen at a range of 15-20%, according to the source and PG of original binder. The utilization of GTR with polymer modified binder cause an enhancement of performance of binder [11]. For many years utilization of GTR in asphalt mixture was evaluated as an convenient material to enhance original mixture properties and removal of crumb tires [12].
Several researches in the past indicated that addition of crumb rubber as a thermoplastic elastomer to original bitumen led to enhance its properties against fatigue and rutting, decrease the rehabilitation and maintenance prices of mixture, improved pavement life, reduced traffic noise [13][14][15].
A good modifier should enhance the performance of bitumen against series of failures. Based on a literature one modifier is incapable of improving all performances of pavements. Therefore, modification of bitumen with more than one modifier is essential, which may obtain multiple performance improvements due to multiple interaction [16 ].
In a study performed by Wang, Wang, Wu, and Zhang [17], the influence of Polyethylene Terephthalate which is composition of polyethylene and crumb rubber on rheological binder.
Results revealed that utilization of mentioned materials could enhance storage modulus of modified binder.
Nazirizad [19] evaluated the influence of ASA and hydrated lime on water sensitivity of samples.
The results showed that mixtures modified by ASA have better resistance against moisture than mixture modified by hydrated lime. Park et al. [20] evaluated that aliphatic amine ASA could enhance the rutting behavior and moisture damage resistance of pavement. Zheng et al. [21] revealed that it is necessary to investigate the adaptability between ASA and bitumen before selection of ASA. Xiao et al. [22] investigated the impact of ASA additive on stripping and permanent deformation properties of pvements. Results indicated that ASA cause a little improvement on rutting performance of mixtures, but used ASAs are incapable of changing the PG of original binder. Also Selvaratnam et al. [23] indicated that ASA with different contents led to better change PG of PG 70-28 and PG 76-28 polymer modified bitumens in comparison with PG 64-22.
Several studies were implemented on using discarded PET in mixtures by replacing with coarse and fine aggregate of asphalt mixture and also for modification of different types of mixtures. By replacing PET materials by coarse aggregates it led to improve the properties of mixture such as Marshall Stability and Marshall Quotient [23]. Also by replacing PET by fine aggregate in mixtures it cause an increase in rutting resistance of mixture and decrease the stiffness of mixture [24]. Ahmadinia investigated the usage of waste PET in dry method in SMA mixtures. The results showed that addition of PET led to enhance the Stability and behavior of SMA specimens [25].
Based on a literature one modifier is incapable of improving all performances of pavements.
Therefore, modification of bitumen with more than one modifier is essential, which may obtain multiple performance improvements due to multiple interaction [16 ].
Far too little research studied on the enhancement in rheological properties of binder and performance of CR/PET modified mixtures. As usual ASAs have indicated an enhancement on water susceptibility and performance of unmodified samples, the feasibility of application of ASAs on PET/CR modified mixtures should be investigated [24]. therefore, it is essential to investigate the performance of PET/CR SMA mixtures. In current work, PET/ground tire rubber (GTR) composites with different composition were utilized for modification of bitumen and enhance its performance. The influence of three ASA on PET/CR modified binders were evaluated through series of physical and rheological tests including; MSCR, LAS, rotational viscosity, softening point, penetration grade, dynamic shear rheometer (DSR) tests. The four point beam fatigue, wheel track, dynamic creep, Resilient Modulus, Indirect Tensile Strength (ITS) test were implemented to investigate the performance of mixtures.

Aggregates
The required aggregates were supplied from Telo Quarry. The aggregate's physical and chemical properties were shown on Table 1 and 2, respectively. In this study the nominal maximum aggregate size of 12.5 mm was utilized and it's gradation was depicted on Figure 1.

bitumen
One type of virgin binder AC-85/100 was utilized and the bitumen's properties were tabulated on Table 3.

fiber
As the National Cooperative Highway Research Pavement (NCHRP) Report No. 425 [30] suggested, by utilizing 0.3% cellulose fiber in dry process to the mixture, the drain down of binder will not be occur. Table 4 tabulated the properties of fiber.

Polymers (PET, Crumb rubber)
The size of GTR is -40 mesh fabricated by an ambient process. Table 5 shows the properties of crumb rubber. The waste plastic bottles were collected to utilize as an additive. At first, the mentioned waste materials were cleaned, dried, cut into smaller parts and added in different percentage (25%, 50% and 75% by weight of aggregates) to the mixture. The properties of PET was shown on Table 6. Based on Table 8, three different blends of PET and CR with constant content of water were combined. Based on previous literature by considering water At high pressure and temperature, the PET depolymerized into its monomers (terephthalic acid) because of acting water as hydrolysis agent [31]. Each blend was separately passed through a twin-screw extruder with the speed of 65 rpm at the temperature of 280°C. Ultimately, in order to better mix the combination in high shear mixer the products were granulated.

ASAs
Three usual liquid ASAs, namely liquid A, liquid B and liquid C were selected.
The liquid ASAs are typically used in percentages between 0.2 and 0.6% by weight of the bitumen based on manufacture's recommendations. In this research the fix percentage of 0.5% was used for all mixtures. Table 7 tabulates the Physical and chemical properties of used ASAs.
that the additives was added gradually at 15% (three blends of PET and CR (25%, 50% and 75%) by weight of original bitumen) to the high shear mixer and mixed at 500 rpm. After that the temperature rose up to 190°C, and also the speed of high shear mixer increased up to 4000 rpm for 2 h. At last, in order to eliminate air bubbles which were produced in high shear mixer in producing procedure, the specimens were located in a vacuum oven for 30 min at 120°C. It is suggested by previous papers to blend ASAs with bitumen instead of adding them to mixture [31]. So three ASAs with constant percentage of 0.5% by weight of binder were utilized into CR/PET modified bitumen and mixed by high shear mixer at 1000 rpm for 45 min. Several samples with different ASA were fabricated and sample identification of modified binders were shown on table 8.
The NCHRP Report No. 425 was used to design and fabricate the SMA mixtures [30]. According to volumetric properties of mixtures the optimum bitumen percentage was calculated as 7.5%. For each mixture type, three specimens were prepare.

Conventional and Rheological binder tests
In present research the penetration grade, softening point, ductility tests were implemented in order to measure the physical properties of binders.

MSCR test
In current work, to evaluate the rutting resistance of binders the MSCR test was performed through AASHTO TP 70 standard [31].

LAS test
In current work to investigate the fatigue resistance of binders, the LAS test was performed according to AASHTO TP 101-14 standard [32]. The fatigue life of bitumens were obtained based on equation (1): where A and B are coefficients of equation measured based viscoelastic continuum damage theory (VECD).

ITS test
The main properties of mixture is tensile strength which is measured by ITS test. In most cases, the ITS test was implemented to investigate the water damage of pavements. According to ASTM D6931-12 standard, the ITS test was performed at 20℃. The following equation was utilized to determine and compare the ITS of specimens.
where, ITS refers to the indirect tensile strength of mixture (kPa), Pmax indicates the maximum load (kN); D shows diameter of the samples (mm); t refers to thickness of the specimens (mm).

test
The of mixtures was calculated based on ASTM D 4123. All mixtures were divided in to two set. One set was remained dry at 25°C, and second set of samples was emerged in water based on AASTHO T283 and referred to as conditioned samples. Then the Mr test was run at 25°C by applying haversine load pulse at 1Hz with 0.1-s loading and unloading time, respectively. At last RMR parameter which was referred to the ratio of of wet samples to the of dry specimens, were measured. The minimum adequate value of 80% was considered for RMR results [33]: Where, P refers to maximum load applied (N); ν = Poisson's ratio; t= length of sample (mm); δ = horizontal recoverable deformation (mm).

Dynamic creep test
In current work the US.

Wheel tracking test
To measure the permanent deformation potential of SMAs the wheel track test was implemented according to AASHTO Standard T-324 [34] at 60°C temperature.

FPB test
for investigating the intermediate temperature behavior of specimens the FPB test was implemented based on AASHTO T321-07. Following equations were used to measure the flexural stiffness [35]: Where, refer to maximum micro-strain; refer to maximum displacement at the middle of the beam (mm); h shows length of beam (mm); indicates outer (355.5 mm); indicates the inner length of the gauge (118.5 mm); shows maximum tensile stress (kPa); P refer to maximum load (kN); B refer to beam width (mm) S refer to flexural stiffness (MPa). Equation (7) was used to evaluate the fatigue life of the samples: Where, is fatigue life of specimens;  is applied levels of micro strains; a and b are coefficients.

Fracture energy
The fracture energy to failure of samples for both dry and unconditioned type were determined from ITS test to investigate the water sensitivity of samples. The fracture energy to failure is defined as the area under the load-deflection curve at failure load. (Figure 2) and can be determined by equation (8)   to unaged samples. This is due to the fact that the light components of binder vaporize and the aromatics and resins change to the asphaltenes in bitumen [37][38].

Rheological and conventional bitumen test result
Results indicated that all ASAs improve the rutting performance of PET/CR modified binders after RTFO aging. Moreover, for ASA (B) the PET/CR with 0.75% PET and 0.25 CR indicates the highest rutting parameter.

MSCR test
In this research to evaluate the rutting behavior of bitumen at two stress levels of 100 Pa and 3200 Pa the MSCR test was performed. The Jnr parameter of bitumens at temperatures of 52 °C to 82°C at mentioned stress levels were depicted on figure 7. Results indicated that as the temperature increases, the jnr parameter and percent recovery increase and decrease, respectively. Table 9 shows the non-recoverable creep compliance and recovery percentage of binders at 64 °C.
Generally, based on the results regardless of the stress levels, the addition of PET/CR to base bitumen decreased the non-recoverable creep compliance value of bitumen which led to enhance the rutting performance of original binder. As results show on As results show, the ASA (C) additive had lowest effect on enhancing percent recovery of modified binders for stress levels of 100 and 3200 pa. This could be due to lower elasticity and of ASA modified binders.

LAS results
The results of LAS test was depicted on tables 10, 11. Results from Table 10  The VECD coefficients of different modified binders was shown in Table 10. utilization of modifiers cause an increase and decrease in coefficient C1 and coefficient C2, respectively. Based on the results, PET/CR modified bitumen containing 50% PET and 50% CR has the highest C1 and the lowest C2 values. it can be concluded that at low damage levels the |G*| parameter decreases significantly adversely at high damage levels the |G*| parameter reduces lower.

Grading of binders based on PG and MSCR system
In current work, the PG and MSCR method are used in order to grade of modified. Results are depicted on Table 12. The G*/Sin δ parameter is limited to 1 kPa to grade of non-aged binder, while for RTFO aged binder the MSCR method in standard traffic (J nr−3.2kPa = 4.5 kPa−1). To evaluate and grade of bitumens at low temperatures, the same criteria like PG system was used.
As results indicated in Table 12 As results show, almost all modified bitumens are graded the same high-temperature and also one grade improvement at a standard traffic level through PG and MSCR system.

Mr test results
The Mr test results of specimens modified by different additives were shown on Figure 8. The Mr of PC2B sample was 15% higher than original mixture, however PC3C specimen had a Mr value approximately 1% higher than original sample.

ITS test
In order to investigate the effect of different modifiers on tensile behavior of mixtures, the ITS test was performed. Figure 9 shows the ITS results of samples. Outcomes of ITS test revealed that specimens modified by PET and CR additive had greater ITS values than control mixture. By addition of ratio of PET in composition, the ITS results first increases up to 50%, and then decreases up to 75% PET. By addition of ASA to PET/CR modified mixtures, the ITS values increased. Among modified mixtures, PC2B mixture has the highest ITS value. Also ITS of specimens modified by ASA (B) are higher than ITS values of mixtures modified by ASA (A) and (C).
As the cohesion of bitumen to aggregate improves, the ITS values becomes higher [39][40][41][42]. It is recognized from the ITS values that utilization of PET/CR and ASA cause to increase and decreases the cohesion and adhesion of binder to aggregate, respectively.

FE test results
The Fracture energy density of different specimens were shown on figure 13. The required energy to initiate the first crack in asphalt called Fracture Energy (FE). Based on Figure 13, utilization of PET/CR result in enhance the fracture energy. This can be due to increase in elasticity of specimens by using PET/CR and consequently the strain energy and strength of specimen to cracking is increased. Addition of PET up to 50% led to increase in fracture energy of specimens and by

Discussions and Conclusion
The • Based on dynamic creep test, using PET/CR enhance the permanent deformation properties of samples. utilization of ASA's cause an enhance the FN of specimens. According to the results, by addition of PET/CR ratio, the rutting resistance improves. It is recognized that utilization of ASA cause an enhance the stiffness and viscosity of mixtures and as a result the rutting behavior enhanced.
• Based on wheel track test results, addition of PET/CR enhanced the permanent deformation behavior of mixtures and by increase of PET/CR ratio, the rutting resistance improves. As results show, addition of ASAs to base bitumen cause an enhance the rutting resistance of specimens.
• According to the four point beam fatigue test utilization of PET/CR enhance the fatigue resistance of specimens. results revealed that utilization of ASA's cause an increase in fatigue performance of specimens. addition of PET/CR enhances the elasticity behavior of mixture and as a result, the fatigue life improves.