Effect of Waste Engine Oil and Waste Cooking Oil on Performance

applied sciences

Article Eﬀect of Waste Engine Oil and Waste Cooking Oil on Performance Improvement of Aged Asphalt

Haibin Li 1,*, Bo Dong 1 , Wenjie Wang 1, Guijuan Zhao 1, Ping Guo 2 and Qingwei Ma 2

1 School of Architecture and Civil Engineering, Xi’an University of Science and Technology, Xi’an 710054, China; [email protected] (B.D.); [email protected] (W.W.); [email protected] (G.Z.) 2 Xi’an Highway Research Institute, Xi’an 710054, China; [email protected] (P.G.); [email protected] (Q.M.) * Correspondence: [email protected]; Tel.: +86-1370-0222-165

Received: 21 March 2019; Accepted: 18 April 2019; Published: 28 April 2019

Abstract: In order to explore the applicability of waste engine oil and waste cooking oil used in aged asphalt, the effect of waste engine oil and waste cooking oil on aged asphalt recycling was studied through the analysis of the improvement of its physical, chemical, and rheological properties. Six aged asphalt binders with different aging times were obtained by indoor test simulation using the Thin Film Oven Test at 163 ◦C. Then, waste engine oil and waste cooking oil with five different dosages were added to investigate improvement performances. The results clearly demonstrated that waste engine oil and waste cooking oil could soften and recover the work ability of aged asphalt effectively. Furthermore, the physical, chemical, and rheological performances of six aged asphalts could be improved to normal level of virgin asphalt if the content of waste engine oil or waste cooking oil was suitable. The rheological properties of aged asphalt with waste cooking oil had better improvement than that with waste engine oil. Overall, the good applicability would provide waste oil a much wider service range in asphalt pavement recycling field. It also provided a method of developing new rejuvenating agent with the two waste oils to achieve complex synergism effect. Moreover, it realized the waste cyclic utilization and environmental protection.

Keywords: asphalt binder; aged asphalt; rejuvenating; properties improvement; waste engine oil; waste cooking oil

1. Introduction Recent societal and economic developments have resulted in an annual increase in the total mileage of highways in China. Less than 10 years after construction or operation, many asphalt pavements required different degrees of maintenance due to the different damages sustained during their service lives. This in turn led to the generation of large quantities of reclaimed asphalt pavement materials [1]. Asphalt pavement maintenance was facing the problems of disposal of waste asphalt concrete. The continued use of nonrenewable sources caused environmental pollution as a result of improper waste disposal [2,3]. Therefore, the recycling technology of waste asphalt pavement is becoming more and more attractive from the perspective of energy and environmental protection in the world [4,5]. On the other hand, with the development of automobile and living conditions, large amounts of waste oils, such as waste cooking oil (WCO) and waste engine oil (WEO), are generated. In previous studies, many scholars have proposed various asphalt rejuvenators and analyzed their effects on the properties of aged asphalt [6–8]. It was also important to develop new rejuvenators using the WEO and waste cooking oil (WCO). Researchers found that WCO and WEO were similar in molecular structure to asphalt, which was a favorable condition for their reuse. It was well known that the reused of

Appl. Sci. 2019, 9, 1767; doi:10.3390/app9091767 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 1767 2 of 20 aged asphalt was the key to recycling asphalt pavement. From the chemical point of view, asphalt regeneration is a reversal of its aging. As such, adding new asphalt binders or regenerators with appropriate chemical compositions and properties that had been reduced in aged asphalt could recover the performances of aged asphalt [9]. Asphalt binders consist of four fractions including saturates aromatics resins and asphaltenes. Based on the compatibility theory of rejuvenation, WCO and WEO can be used as a low viscosity component to recycle aged asphalt. Compared with other low viscosity components, flash points of WCO and WEO were above 200°C, which showed that the use of WCO and WEO in hot mix asphalt mixes had high structural safety. The effective treatment or reuse of these materials not only reduced environmental pollution and conserves energy, but also represented an innovative method of recycling waste. The proposed method could recover or improve the properties of aged asphalt and provide an effective method to regenerate the aged asphalt using waste oils. Therefore, it was practically significant and would provide a broad application prospect for WEO and WCO in the asphalt pavement recycling field. In recent years, many studies were carried out on the use of WEO or WCO as asphalt rejuvenators. Due to similarity in molecular structure of WEO and WCO with asphalt, several attempts had been made to use WEO and WCO in conjunction with asphalt binder. Sara R.M. [10] studied, by thermochemical characterization, the bituminous binders modified with different WEO and recycled engine oil bottoms combined with polymers were studied with penetration, softening point and viscosity tests. The modified bituminous binders had similar penetration values and softening point temperatures higher than those of commercially modified binders. Liu [11] studied the effect of WEO on the rheological properties of asphalt. The results indicated that WEO-modified asphalt had lower elastic portion, heat sensitivity, zero shear viscosity, and antirutting ability, but had higher fatigue resistance and temperature sensitivity. Jia [12] showed the improvement of rheological properties of aged asphalt using dynamic shear rheometer with up to 5% WEO content. However, Hesp and Shurvell [13] found that it could result in poor low temperature performance of rejuvenated asphalt with the WEO content beyond 15%. Hallizza Asili.et.al [14–16] also studied the physical and chemical properties of rejuvenated asphalt to prove its application. Zhang et al. [17] evaluated the effects of WCO viscosity and acid value on the basic, rheological, and chemical properties of typical rejuvenated asphalt. The experimental results indicated that WCO qualities influenced the rejuvenation behaviors of aged asphalt significantly, and that WCO with higher qualities tended to achieve better rejuvenation effects. Recently, Zargar, M [18] conducted a study using natural oils, including WCO and recycled motor oils, as potential natural regenerators. It was found that 3-4% of the WCO could restore the physical properties of the original asphalt binder compared to 20% recycled oil. P. Caputo et al. [19] investigated the efficiency of bitumen rejuvenator investigated through Powder X-ray Diffraction analysis and T2-NMR spectroscopy. The results demonstrated that the HR (an oleic acid-based rejuvenator) additive effectively reconstituted the correct balance between asphaltenes and maltenes, resulting in a reactive colloid network. Yu [20] discussed the rejuvenation effects of WCO on the rheological, microscopic, and chemical characterization of RAP binders. The results demonstrated that adding WCO could restore the rheological properties and reproduce the surface microstructures of aged binders. Zhang [21] studied the physical properties and structure of WCO-rejuvenated asphalt and WEO-rejuvenated asphalt. It was found that both waste oils could significantly reduce sulfoxide groups S=O and carboxyl groups C=O in aged asphalt. These conclusions indicated that WCO or WEO in suitable contents could rejuvenate aged asphalt to achieve the properties of original asphalt and meet all physical requirements. In summary, WEO and WCO could both have positive effects on recovering aged asphalts properties to the original asphalt level with addition of a suitable content. In this paper, the effects of WEO and WCO on the performances of six aged asphalts with different aging times were studied. The physical, chemical, and rheological properties of the six aged asphalts with different WEO and WCO dosages were analyzed. According to the observed improvements on the properties of aged asphalts, optimum dosages of WEO and WCO were proposed. Thin-layer chromatography with flame ionization detection (TLC-FID), Fourier-transform infrared (FTIR) and Appl. Sci. 2019, 9, 1767 3 of 20 dynamic shear rheometer (DSR) tests were conducted to further evaluate the regeneration effects of WCO and WEO. Though some researches indicated that waste oil could rejuvenate aged asphalts, little research has been conducted to investigate different effects of different oils using comparative analysis and to identify shortcomings of some waste oils to rejuvenate aged asphalt. The objective of this paper was to investigate properties improvement of aged asphalt with WEO or WCO and analyze different improvement effects to illustrate which waste oil can lead to better rejuvenated asphalt. This project could lay the foundations for the application of WEO or WCO in the asphalt recycling field and was also an effective attempt to recycle the waste oils and waste asphalt concrete.

2. Materials

2.1. Asphalt The virgin asphalt (VA) used in this research was KLMY Pen70 asphalt (One of the petroleum asphalts types named by the Karamay Oilfield), which was produced in western China. TOFT was used to prepare aged asphalts test samples. The TFOT was set up at 163 ◦C for 300 min in terms of JTG E20 T0609 which was similar with ASTM D1754 [22]. At the same time, in order to improve the accuracy of the test data, the aging time interval was set to 2 h. It simulated different aging times during operation process. The aged asphalt binders were obtained by laboratory test simulations of the TFOT with different aging times of 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h at 163 ◦C. The different aging times could reflect different service times of actual asphalt pavement. The basic properties of VA and six aged asphalts are shown in Table1.

Table 1. The basic properties of virgin asphalt (VA) and six aged asphalts.

Penetration Softening Ductility Viscosity Categories (25 ◦C)/0.1 mm Point/◦C (10 ◦C)/cm (135 ◦C)/mPa.s VA 64.8 51.4 >100 752 Aged 5 h 51.9 52.0 26.0 816 Aged 7 h 48.6 53.2 17.1 886 Aged 9 h 45.1 54.9 15.8 981 Aged 11 h 43.0 55.3 13.7 1140 Aged 13 h 41.2 55.9 13.0 1190 Aged 15 h 39.0 56.2 12.3 1270

It can be seen from Table1 that the basic physical properties of the asphalt change most obviously after 7 to 9 h of aging. The penetration of aged asphalts (5–9 h) was reduced by ~20–30% compared to the VA. This stage belongs to the initial rapid aging stage of asphalt. When the aging time increased, the penetration of aged asphalt (11–15 h) decreased by ~33–40%. This stage belonged to the rate aging stage of asphalt. Comparing different aging time in the laboratory with the aged asphalt with different service life of asphalt pavement recovery, it could be considered that the aging time of 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h were chosen to simulate the service time of 1–4 years, which was a simplified simulation method for test [23]. Therefore, these aging times were selected to evaluate the asphalt aging. All the aged asphalts were produced as aged asphalt samples in this research to analyze the different applicability effects of WCO or WEO.

2.2. Waste Engine Oil and Waste Cooking Oil The WEO utilized in the study was collected from a local auto repair shop. The WCO used in this study was soybean oil, which had been used several times. The basic properties of WEO and WCO were then tested. Based on previous studies, metals such as lead, zinc, calcium, and magnesium, were found in the used engine oil [24,25]. Therefore, WEO and WCO were filtered in order to remove solid impurities to ensure regeneration effectiveness. The basic properties of WEO and WCO were tested and the test results were present in Table2. A medical absorbent cotton (grade SD-I) was selected Appl.Appl. Sci. Sci. 2019 2019, ,9 9, ,x x 44 of of 20 20 Appl. Sci. 2019, 9, 1767 4 of 20 orderorder to to remove remove solid solid impurities impurities to to ensure ensure regene regenerationration effectiveness. effectiveness. The The basic basic properties properties of of WEO WEO andand WCOWCO werewere testedtested andand thethe testtest resultsresults werewere presentpresent inin TableTable 2.2. AA medicalmedical absorbentabsorbent cottoncotton overand WCO of filtration were screenstested asand shown the test in Figure results1. Thewere WEO present was in dark Table in color, 2. A whilemedical the WCOabsorbent was yellow,cotton (grade(grade SD-I)SD-I) waswas selectedselected overover ofof filtrationfiltration scrscreenseens asas shownshown inin FigureFigure 1.1. TheThe WEOWEO waswas darkdark inin as(grade shown SD-I) inFigures was selected2 and3 ,over respectively. of filtration screens as shown in Figure 1. The WEO was dark in color,color, while while the the WCO WCO was was yellow, yellow, as as shown shown in in Figures Figures 2 2 and and 3, 3, respectively. respectively. Table 2. The basic properties of waste engine oil (WEO) and waste cooking oil (WCO). TableTable 2. 2. The The basic basic properties properties of of waste waste engine engine oil oil (WEO) (WEO) and and waste waste cooking cooking oil oil (WCO). (WCO). Acid Categories Flash Point/ C Viscosity/Pa s Torque/% Acid ◦ . AcidAcid CategoriesCategories FlashFlash point/°C point/°C Viscosity/Viscosity/ Pa Pa·.s.s Torque/%Torque/%Value /mgKOH/g Categories Flash point/°C Viscosity/ Pa s Torque/% Value/mgKOH/gValue/mgKOH/g WEO 195 0.093 18.6 0.63Value/mgKOH/g WEO 195 0.093 18.6 0.63 WEOWEO WCO195195 2750.0930.093 0.059 11.718.618.6 0.50 0.63 0.63 WCOWCO 275275 0.0590.059 11.711.7 0.50 0.50

Figure 1. FigureFigure 1. 1. The The filter ﬁlterfilter device. device.

FigureFigure 2. 2. Filtered Filtered waste waste engine engine oil oil (WEO). (WEO).

Figure 3. Filtered waste cooking oil (WCO). FigureFigure 3. 3. Filtered Filtered waste waste cooking cooking oil oil (WCO). (WCO).

3.3. Experimental Experimental Sections Sections

3.1.3.1. Rejuvenated Rejuvenated Asphalts Asphalts Preparation Preparation TheThe rejuvenatedrejuvenated rejuvenated asphalt asphalt asphalt samples samples samples were were were made made made by by mixingby mixing mixing six agedsix six aged aged asphalts asphalts asphalts with with ﬁvewith WEO five five WEO andWEO WCO and and contentsWCOWCO contents contents (1%, 2%, (1%, (1%, 3%, 2%, 2%, 4%, 3%, and3%, 4%, 5%,4%, and byand mass 5%, 5%, by ofby asphalt).mass mass of of asphalt). Aasphalt). propeller A A propeller mixerpropeller at constant mixer mixer at at speed constant constant (2000 speed speed rpm) was(2000(2000 used rpm)rpm) to waswas blend used used the to mixtureto blendblend theforthe 15 mixturemixture min at for for 135 15 15◦ C. minmin During atat 135 135 the °C. °C. mixing, During During the thethe timemixing, mixing, and the temperaturethe timetime andand remainedtemperaturetemperature stable remained remained to ensure stable stable stable to to ensure experimentalensure stable stable expe expe results.rimentalrimental After results. results. blending, After After the blending, blending, homogenous the the homogenous homogenous rejuvenated asphaltrejuvenatedrejuvenated binders asphalt asphalt were binders binders produced were were for produced produced the property for for the tests.the propertyproperty During tests. testing,tests. DuringDuring when testing, testing, the basic when when properties the the basic basic of agedpropertiesproperties asphalt of of wereaged aged asphalt tested,asphalt thewere were waste tested, tested, oils the the were waste waste added oils oils to were were the otheradded added aged to to the the asphalt other other samplesagedaged asphalt asphalt immediately samples samples afterimmediatelyimmediately recovering after after the recovering recovering aged asphalt the the fromaged aged theasphalt asphalt TFOT from from plates the the toTFOT TFOT avoid plates plates reheat to to andavoid avoid extra reheat reheat aging. and and extra extra aging. aging. Appl. Sci. 2019, 9, 1767 5 of 20 Appl. Sci. 2019,, 9,, xx 5 of 20

3.2. Physical Physical Properties Properties Tests In order to evaluateevaluate thethe physicalphysical propertiesproperties of WEO-WEO- and WCO-rejuvenatedWCO-rejuvenated asphalts, the basic tests, suchsuch asas penetration penetration at at 25 25◦C, °C, softening softening point, poin ductilityt, ductility at 10 at◦C, 10 and °C, rotational and rotational viscosity viscosity at 135 ◦atC, were135°C, conducted were conducted in this study,in this in study, accordance in accord withance JTG with E20 JTG T0604-2011, E20 T0604-2011, JTG E20 JTG T0606-2011, E20 T0606-2011, JTG E20 JTGT0605-2011, E20 T0605-2011, and JTG E20and T0625-2011,JTG E20 T0625-2011, respectively. resp Allectively. tests were All similartests were toASTM similar D5, to ASTMASTM D36,D5, ASTM D113,D36, ASTM and ASTM D113, D4402. and ASTM The penetrationD4402. The penetration reflected the reflected viscosity the and viscosity the degree and of the hardness degree of hardnessasphalt. Generally, of asphalt. the Genera smallerlly,lly, penetration thethe smallersmaller asphalt, penetrationpenetration the larger asphalt,asphalt, viscosity thethe largerlarger and harderviscosityviscosity the andand asphalt harderharder would thethe asphaltbe. The softeningwould be. point The ofsoftening the asphalt pointint reflected ofof thethe the asphaltasphalt viscosity reflectedreflected and the thethe temperature viscosityviscosity andand sensitivity thethe temperaturetemperature of asphalt. sensitivityIt would increase of asphalt. with theIt would viscosity increase values increasing.with the viscosity The asphalt values with increasing. a higher softening The asphalt point with would a higherhave greater softening viscosity, point better would temperature have greater and viscos thermality,ity, stability. betterbetter temperaturetemperature The ductility anan couldd thermal be used stability. to measure The ductilityand characterize could be the used ability to ofmeasure asphalt toand undergo characterize tensile the deformation ability of and asphalt flexibility to undergo under external tensile deformationforces without and damage flexibility and fractureunder external [26,27]. Theforces test without processes damage were shown and fracture in Figure [26,27].4. The test processes were shown in Figure 4.

(a) Penetration test (b) Softening point test (c) Rotational viscosity test

Figure 4. BasicBasic physical physical properties properties tests of re rejuvenatedjuvenatedjuvenated asphalt asphalt with with WEO WEO or or WCO. WCO. 3.3. Chemical Properties Tests 3.3. Chemical Properties Tests To analyze the influence of WEO or WCO on component composition and structural change of the To analyze the influence of WEO or WCO on component composition and structural change of different degrees of aged asphalts, the samples were tested and characterized with chemical methods. the different degrees of aged asphalts, the samples were tested and characterized with chemical The four components of asphalts were explored and analyzed using TLC-FID. The different samples methods. The four components of asphalts were explored and analyzed using TLC-FID. The were prepared by solution of 80 mg asphalt in 4 mL toluene; the concentration of solutions was 2% different samples were prepared by solution of 80 mg asphalt in 4 ml toluene; the concentration of (w/v)[28]. It could explain the asphalt components of saturates, aromatics, resins, and asphaltenes solutions was 2% (w/v) [28]. It could explain the asphalt components of saturates, aromatics, resins, by TLC-FID. and asphaltenes by TLC-FID. Afterwards, the FTIR was used to determine the different functional groups of VA, aged asphalts Afterwards, the FTIR was used to determine the different functional groups of VA, aged 1 1 and rejuvenated asphalts in wave numbers ranging from 4000 cm to 500 cm −1. The FTIR spectrometer−1 asphalts and rejuvenated asphalts in wave numbers ranging from− 4000 cm− −1 toto 500500 cmcm−1.. TheThe FTIRFTIR was shown in Figure5. spectrometer was shown in Figure 5.

Figure 5. FTIR spectrometer. Figure 5. FTIR spectrometer.

3.4. Rheological Properties Tests Appl. Sci. 2019, 9, 1767 6 of 20

3.4. Rheological Properties Tests To evaluate the high temperature performance recovery of rejuvenated asphalt, the dynamic shear rheometer (DSR) test was often used and analyzed, and the phase angle and the complex modulus imparted basic rutting resistance [29]. Phase angle (δ) is defined as the ratio of loss modulus to storage modulus, and it reflected the viscous response of asphalt binders. Generally, phase angle was much sensitive to asphalt structure. Asphalt with smaller phase angle had better elastic recovery performance. Complex modulus (G*) was defined as the ratio of maximum shear stress to maximum strain, and it provided a measure of total resistance to deformation during shear loading. Asphalt with large complex modulus had better resistance to flow deformation. Rutting resistance factor (G*/sinδ) reflected unrecoverable deformation of asphalts during loading process. Asphalt with higher G*/sinδ, but smaller flow deformation at high temperature, had a higher rutting resistance, which was demonstrated by its better high temperature performance. The DSR test was in accordance with JTG E20 T0628, which was similar to ASTM D7175-15. The sinusoidal oscillating load with a frequency of 10 rad/s was applied to the samples. The strain value range of aged asphalt was 8–12%. For the regenerated asphalt, it was better for the strain value to achieve 8–12%, which would prove the regeneration effect of WEO or WCO.

4. Results and Discussion

4.1. Penetration

The different penetration values at 25 ◦C for six aged asphalt binders with different aging times are illustrated in Figure6. It can be clearly observed that the penetration values of all aged asphalts had a similar trend whether it was WEO or WCO that was added, as all the aged asphalts were softened with increased WEO or WCO dosages. The penetration values of the aged asphalts were significantly larger than that of VA. As revealed in Figure6, di fferent aged asphalts could reach or exceed the hardness degree of VA with different oil contents. Compared with the VA, the penetration of 5-h- and 7-h-aged asphalts recovered up to 96.8% and 92.0% with 1% WEO content, 9 h- and 11 h-aged asphalts recovered up to 110.3% and 97.7% with 2% WEO content, while 13-h- and 15-h-aged asphalts recovered up to 105.2% and 99.4% with 3% and 4% WEO contents, respectively. This proved that WEO could soften aged asphalt. The effect of WEO content on asphalt penetration was better for specific aged asphalt. Although WCO had similar effects on penetration, it could achieve the same regeneration effects in lesser contents, thereby confirming its better regeneration efficiency than WEO. With 1%, 2%, and 3% WCO content, the recovery extents for asphalts aged 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h were 102.9%, 87.3%, 93.4%, 98.1%, 107.7%, and 102.9%, respectively. Moreover, it could be inferred that there were more light components in the WCO which gave the aged asphalt better fluidity. Although more WEO or WCO could achieve better improvements, excessive oil content affected other properties of aged asphalt. There was a suitable WEO or WCO content range, which depended on the aging degree of asphalt. The asphalt recovered from real reclaimed asphalt pavement (RAP) had a more severe aging state. Therefore, the optimum dosage of regenerating agent in actual road engineering should be determined by considering the actual aging conditions. Appl. Sci. 2019, 9, 1767 7 of 20 Appl. Sci. 2019, 9, x 7 of 20

120 120 5h+WEO 5h+WCO VA 7h+WEO 7h+WCO VA

100 100 (0.1mm) (0.1mm) 80 80 ℃ ℃

60 60

40 40 Penetration 25 Penetration 25 20 20

0 0 01234 01234 Oil Content (%) Oil Content (%)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (7 h aging time of VA)

120 100 9h+WEO 9h+WCO VA 11h+WEO 11h+WCO VA

100 80 (0.1mm)

80 (0.1mm)

℃ 60 ℃ 60 40 40 Penetration 25 20 Penetration 25 20

0 0 01234 01234 Oil Content (%) Oil Content (%)

(c) Rejuvenated asphalt (9 h aging time of VA) (d) Rejuvenated asphalt (11 h aging time of VA) 120 120 13h+WEO 13h+WCO VA 15h+WEO 15h+WCO VA

100 100 (0.1mm) 80 (0.1mm) 80 ℃ ℃ 60 60

40 40 Penetration 25 Penetration 25 20 20

0 0 01234 012345 Oil Content (%) Oil Content (%)

(e) Rejuvenated asphalt (13 h aging time of VA) (f) Rejuvenated asphalt (15 h aging time of VA)

FigureFigure 6.6.E Effectsﬀects ofof WEOWEO oror WCOWCO onon penetrationpenetration of of di differentﬀerent aged aged asphalt. asphalt.

4.2.4.2. SofteningSoftening PointPoint TheThe e effectsﬀects of of WEO WEO and and WCO WCO on on the the softening softening point point of ofaged agedasphalts asphaltswith with didifferentﬀerent aging aging times times areare displayed displayed in in Figure Figure7. It7. could It could also also be observed be obse thatrved the that softening the softening point values point ofvalues the aged of the asphalt aged bindersasphalt werebinders consistent were consistent with the previouswith the conclusionprevious co innclusion 4.1 as they in decreased4.1 as they with decreased increase with in WEOincrease or WCOin WEO contents. or WCO contents. As shown in Figure 7, different aged asphalts could reach or exceed the softening point of VA with different oil content. The softening point of asphalts aged 5 h, 7 h, and 9 h recovered up to 93.8%, 93.0%, and 101.0%, respectively, with 1% WEO content. 11h-aged asphalt recovered up to 104.7% with 2% WEO content. 13-h- and 15-h-aged asphalts recovered up to 101.2% and 103.5% with Appl. Sci. 2019, 9, x 8 of 20

3% WEO content, respectively. This proved that WEO could recover some of the aged asphalt’s properties, but the effect of WEO content on aged asphalt was better for specific aged asphalt. Meanwhile, the WCO also had a similar effect on softening point. With 1% and 2% WCO contents, asphalts aged 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h were able to recover up to 90.7%, 95.1%, 98.1%, 97.5%, 103.1%, and 94.9%, respectively; though more WEO or WCO could result in better improvement performance, an excessive amount of oil content would affect other properties of aged asphalt. Appl. Sci. 2019, 9, 1767 8 of 20 There was a suitable oil content related to the aging degree of asphalt.

60 60 5h+WEO 5h+WCO VA 7h+WEO 7h+WCO VA

50 50 ) ) ℃ 40 ℃ 40

30 30

Softening Point( 20 20 Softening Point(

10 10

0 0 01234 01234 Oil Content (%) Oil Content (%) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (7 h aging time of VA)

60 9h+WEO 9h+WCO VA 60 11h+WEO 11h+WCO VA

50 50 ) ) ℃ ℃ 40 40

30 30

Softening Point( 20

10 10

0 0 01234 01234 Oil Content (%) Oil Content (%) (c) Rejuvenated asphalt (9 h aging time of VA) (d) Rejuvenated asphalt (11 h aging time of VA)

60 13h+WEO 13h+WCO VA 60 15h+WEO 15h+WCO VA

50 50 ) ) ℃ 40 ℃ 40

30 30

20 20 Softening Point( Softening Point(

10 10

0 0 01234 012345 Oil Content (%) Oil Content (%) (e) Rejuvenated asphalt (13 h aging time of VA) (f) Rejuvenated asphalt (15 h aging time of VA)

Figure 7. EffectsEﬀects of WEO and WCO on softening point of didifferentﬀerent agedaged asphalt.asphalt.

4.3. DuctilityAs shown in Figure7, di fferent aged asphalts could reach or exceed the softening point of VA with different oil content. The softening point of asphalts aged 5 h, 7 h, and 9 h recovered up to 93.8%, 93.0%, and 101.0%, respectively, with 1% WEO content. 11 h-aged asphalt recovered up to 104.7% with 2% WEO content. 13-h- and 15-h-aged asphalts recovered up to 101.2% and 103.5% with 3% WEO content, respectively. This proved that WEO could recover some of the aged asphalt’s properties, but the effect of WEO content on aged asphalt was better for specific aged asphalt. Meanwhile, the WCO also had a similar effect on softening point. With 1% and 2% WCO contents, asphalts aged 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h were able to recover up to 90.7%, 95.1%, 98.1%, 97.5%, 103.1%, and 94.9%, respectively; Appl. Sci. 2019, 9, 1767 9 of 20 though more WEO or WCO could result in better improvement performance, an excessive amount of oil content would affect other properties of aged asphalt. There was a suitable oil content related to the aging degree of asphalt.

Appl. Sci. 2019, 9, x 9 of 20 4.3. Ductility

TheThe test test results results of ductility of ductility at 10 at◦ C10 were °C were shown shown in Figure in Figure8. Obvious 8. Obvious di fferences differences could could be observed be observed between the effects of WEO and WCO on ductility at 10°C. Regenerated asphalt with between the effects of WEO and WCO on ductility at 10 ◦C. Regenerated asphalt with WCO had much betterWCO ductility had much than better that with ductility WEO, than indicating that with that WEO, WCO indicating could resultthat WCO in better could low result cracking in better resistance low cracking resistance and temperature flexibility of aged asphalt binders. and temperature flexibility of aged asphalt binders. Compared with the VA, the ductility at 10°C of 5-h- and 7-h- aged asphalts totally recovered up Compared with the VA, the ductility at 10 C of 5-h- and 7-h- aged asphalts totally recovered to the VA’s ductility with 3% WEO content. When◦ the WEO content was 4%, the 9-h-, 11-h-, and up to the VA’s ductility with 3% WEO content. When the WEO content was 4%, the 9-h-, 11-h-, and 13-h-aged asphalts achieved a ductility value also similar to that of the VA at 10°C, while the WCO 13-h-agedalso had asphalts similar achievedeffects on a ductilityductility, valuealthough also the similar influence to that of ofthe the WEO VA aton 10 the◦C, basic while physical the WCO alsoproperties had similar of eagedffects asphalt on ductility, was different. although With the influence1% WCO ofcontent, the WEO the ductility on the basic for 5-h-aged physical asphalt properties of agedrecovered asphalt up was to the di ffVA’serent. ductility With 1% value WCO at 10°C. content, For the7-h-, ductility 9-h-, and for 11-h- 5-h-aged aged asphalts asphalt with recovered WCO up to thecontent VA’s of ductility 3%, the valueductility at 10of ◦theC. VA For at 7-h-, 10°C 9-h-, was and also 11-h- achieved. aged When asphalts the WCO with WCOcontent content was upof to 3%, the4%, ductility the 13-h- of the and VA at15-h-aged 10 ◦C was asphalts also achieved. also showed When similar the WCO ductility content with was VA up at to 10°C. 4%, the It 13-h-could and 15-h-agedtherefore asphalts be concluded also showed that WEO similar or ductilityWCO could with im VAprove at 10 the◦C. different It could property therefore indexes be concluded of aged that WEOasphalt. or WCO After could fully improve considering the dithefferent performance property of indexes other aspects, of aged it asphalt. was concluded After fully that, considering though the performancemore WEO or of WCO other could aspects, improve it was the concluded low temperat that,ure though performance, more WEO an orexcessive WCO could amount improve of oil the lowcontent temperature was not performance, a favorable choice. an excessive There should amount be ofa suitable oil content WEO was or notWCO a favorablecontent to choice.give WEO There shouldand beWCO a suitable better regeneration WEO or WCO function. content to give WEO and WCO better regeneration function.

200 160 5h+WEO 5h+WCO VA 7h+WEO 7h+WCO VA 175 140

150 120 (cm) (cm) ℃ ℃ 125 100

100 80

75 60 Ductility 10 Ductility 10

50 40

25 20

0 0 01234 01234 Oil Content (%) Oil Content (%)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (7 h aging time of VA)

180 180 9h+WEO 9h+WCO VA 11h+WEO 11h+WCO VA 160 160

140 140 (cm)

120 (cm) 120 ℃ ℃ 100 100

80 80

Ductility 10 60 Ductility 10 60

40 40

20 20

0 0 01234 01234 Oil Content (%) Oil Content (%) (c) Rejuvenated asphalt (9 h aging time of VA) (d) Rejuvenated asphalt (11 h aging time of VA)

Figure 8. Cont. Appl. Sci. 2019, 9, 1767 10 of 20 Appl. Sci. 2019, 9, x 10 of 20

160 160 13h+WEO 13h+WCO VA 15h+WEO 15h+WCO VA 140 140

120 120 (cm) (cm) 100 100 ℃ ℃ 80 80

60 60 Ductility 10 Ductility 10 40 40

20 20

0 0 01234 012345 Oil Content (%) Oil Content (%) (e) Rejuvenated asphalt (13 h aging time of VA) (f) Rejuvenated asphalt (15 h aging time of VA)

FigureFigure 8. E8.ﬀ Effectsects of of WEO WEO and and WCO WCO onon ductilityductility of different diﬀerent aged aged asphalts asphalts at at10°C. 10 ◦ C.

4.4.4.4. Viscosity Viscosity ViscosityViscosity reflected reflected the the frictional frictional resistance resistance between between the the internal internal molecules molecule ofs of the the asphalt asphalt during during flow deformation.flow deformation. According According to mixing to andmixing compaction and comp temperatureaction temperature of the asphaltof the asphalt mixture, mixture, the rotational the viscosityrotational of asphalt viscosity at 135 of ◦asphaltC was closeat 135 related °C was to close the frictional related to resistance the frictional between resistance the internal between molecules the of theinternal asphalt. molecules The eff ofects the of asphalt. WEO and TheWCO effects on of theWEO viscosity and WCO of agedon the asphalt viscosity at 135of aged◦C with asphalt diff aterent aging135 are °C shownwith different in Figure aging6. All are viscosity shown in values Figure decreased 6. All viscosity as the WEOvalues or decreased WCO content as the increased.WEO or WCO content increased. As shown in Figure9, di fferent aged asphalts could reach the 135 ◦C viscosity of VA with different As shown in Figure 9, different aged asphalts could reach the 135 °C viscosity of VA with oil contents. The 5-h-aged asphalt recovered up to 98.3% of the VA’s viscosity at 135 ◦C with 1% WEO different oil contents. The 5-h-aged asphalt recovered up to 98.3% of the VA’s viscosity at 135 °C content. With 2% WEO content, it reached 100.3% for the 7-h-aged asphalt. For 9-h-aged asphalt and with 1% WEO content. With 2% WEO content, it reached 100.3% for the 7-h-aged asphalt. For 3%WEO content, the 135 C viscosity reached 105.1%. For 11-h- and 13-h-aged asphalts with WEO 9-h-aged asphalt and 3%WEO◦ content, the 135 °C viscosity reached 105.1%. For 11-h- and 13-h-aged contentasphalts of 3%, with 97.7% WEO and content 91.8% ofof the3%, VA 97.7% were and recovered, 91.8% of respectively. the VA were However, recovered, for therespectively. asphalt aged 15 hHowever, with WEO for content the asphalt of 5%, aged the viscosity15 h with could WEO onlycontent reach of 96.8%.5%, the Theviscosity improvement could only eff reachect on 96.8%. viscosity decreasedThe improvement gradually effect with increasedon viscosity aged decreased asphalt. gradually The WCO with displayed increased aged similar asphalt. effects The on WCO asphalts viscositydisplayed with similar 5-h-, 7-h-,effects 9-h-, on 11-h-,asphalts 13-h-, viscosity and 15-h-aged with 5-h-, asphalts7-h-, 9-h-, containing 11-h-, 13-h-, 2%, and 3%, 15-h-aged 4%, and 5% WCOasphalts contents, containing recovering 2%, 3%, 93.1%, 4%, 97.3%,and 5% 104.1%,WCO contents, 101.7%, recovering 98.3%, and 93.1%, 114.5%, 97.3%, respectively. 104.1%, 101.7%, Though more98.3%, WEO and or 114.5%, WCO couldrespectively. improve Though the frictionalmore WEO resistance or WCO could of aged improve asphalt, the frictional excessive resistance oil content wouldof aged affect asphalt, other excessive properties oil of content aged asphalt.would affect If the other viscosity properties of recycled of aged asphalt. asphalt If becomes the viscosity too of high, therecycled asphalt mixtureasphalt wouldbecomes not too be high, uniformly the asphal dispersed,t mixture segregation would not would be thenuniformly occur, dispersed, which could adverselysegregation affects would mixture then performance. occur, which could If the adversely viscosity ofaffects recycled mixture asphalt performanc becomese. If too the low, viscosity the asphalt of roadsrecycled would asphalt be prone becomes to rutting. too Tolow, satisfy the asphalt the adhesion roads performancewould be prone of recycledto rutting. asphalt, To satisfy the WEO the or WCOadhesion dosage performance should be in of a reasonablerecycled asphalt, range. the WEO or WCO dosage should be in a reasonable range. Appl. Sci. 2019 9 Appl. Sci. 2019,, 9,, 1767 x 11 ofof 2020

1 1 5h+WEO 5h+WCO VA 7h+WEO 7h+WCO VA

0.8 0.8 ）） Pa·s Pa·s

（ 0.6 （ 0.6 ℃ ℃

0.4 0.4

Viscosity 135 Viscosity 0.2 135 Viscosity 0.2

0 0 01234 01234 Oil Content (%) Oil Content (%) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (7 h aging time of VA)

1.2 9h+WEO 9h+WCO VA 11h+WEO 11h+WCO VA 1.2 1 1 ）） 0.8 Pa·s Pa·s 0.8 （（

℃ 0.6 ℃ 0.6

0.4 0.4 Viscosity 135 Viscosity 135 Viscosity 0.2 0.2

0 0 01234 01234 Oil Content (%) Oil Content (%) (c) Rejuvenated asphalt (9 h aging time of VA) (d) Rejuvenated asphalt (11 h aging time of VA)

1.4 13h+WEO 13h+WCO VA 15h+WEO 15h+WCO VA 1.4 1.2 1.2

） 1 ） 1 Pa·s Pa·s

（ 0.8 （

℃ ℃ 0.8 0.6 0.6

0.4 0.4 Viscosity 135 Viscosity 135 Viscosity 0.2 0.2

0 0 01234 012345 Oil Content (%) Oil Content (%) (e) Rejuvenated asphalt (13 h aging time of VA) (f) Rejuvenated asphalt (15 h aging time of VA)

FigureFigure 9.9. EEffectsﬀects ofof WEOWEO andand WCOWCO onon viscosityviscosityof ofdi differentﬀerent aged aged asphalt. asphalt.

BasedBased onon the the physical physical test conclusions,test conclusions, WEO andWEO WCO and showed WCO di showedfferent e ffdifferentects on rejuvenation effects on ofrejuvenation aged asphalts. of aged After asphalts. a comprehensive After a comprehensiv analysis consideringe analysis the considering regeneration the e ffregenerationect of different effect aged of asphalt,different the aged proposed asphalt, optimal the proposed ranges areopti shownmal ranges in Tables are shown3 and4 .in Tables 3 and 4.

Table 3. Effect of different WEO contents on physical properties in different aged asphalts.

Aging Time 5–7 h 7–11 h 11–13 h >13 h Appl. Sci. 2019, 9, 1767 12 of 20

Table 3. Effect of different WEO contents on physical properties in different aged asphalts.

Aging Time 5–7 h 7–11 h 11–13 h >13 h penetration 1–2% 1–2% 2–3% 3–4% softening point 1–2% 2–3% 2–3% 3–4% ductility 1–3% 3–5% 4–5% >5% viscosity 1–3% 3–4% 3–4% >4%

Table 4. Effect of different WCO contents on physical properties in different aged asphalts.

Aging Time 5–7 h 7–11 h 11–13 h >13 h penetration 1–2% 1–2% 2–3% 3–4% softening point 1–2% 1–2% 1–2% >2% ductility 1–3% 1–3% 3–4% >4% viscosity 1–3% 3–4% 3–4% 4–5%

From the above analysis, it could be observed that WEO or WCO could improve the different property index of aged asphalt. Generally, less WCO content could achieve the same regeneration effect when compared with WEO which ascertains that WCO was a better regenerative agent. According to the different aging time, aged asphalt could recover its basic physical performance with 1–5% WEO content and 1–4% WCO content (by mass of asphalt).

4.5. Chemical Properties

4.5.1. Four Components Compared with 7–h-aged asphalt and VA, the components composition results of rejuvenated asphalt with 3% WEO and 2% WCO are shown in Table5. Correspondingly, for the components of aged asphalt, VA had higher saturates and aromatics, but less resins and asphaltenes which was the same with changing rule of aged asphalt. It also illustrated that the percentages of components composition of aged asphalt could be slightly changed by WEO and WCO. Moreover, compared with common aged asphalt, the waste oils could slightly reduce the asphaltenes and increase aroma components in aged asphalt the result was drawn from the 7-h-aged asphalt; similar conclusions could be speculated with longer aging time.

Table 5. Four components of VA, aged asphalts, and rejuvenated asphalts.

Rejuvenated Rejuvenated Asphalt Asphalt VA Aged Asphalt (7 h) Asphalt (3% WEO) (2% WCO) Saturates (%) 5.68 4.25 5.93 6.22 Aromatics (%) 61.59 51.96 48.51 46.57 Resins (%) 20.01 26.33 29.19 31.57 Asphaltenes (%) 12.73 17.46 16.37 15.64

On the macrolevel, penetration, softening point, ductility, and viscosity of aged asphalt showed a decrease in varying aging degrees. Therefore, the different changes of the four components were consistent with asphalt physical properties. From the view of decreasing asphaltenes and aromatics content and increasing resins and saturates content of rejuvenated asphalt, waste oil had an obvious effect on recycled aged asphalt, which made it possible to use it as a regenerator. In addition, WCO could achieve better regeneration effect than that of WEO with less content as proven earlier.

4.5.2. Functional Groups The rejuvenated asphalt with 2% WCO was selected for the FTIR microexperiment. Based on the results of the four components, if the rejuvenated asphalt with WCO could improve the asphalt’s Appl. Sci. 2019, 9, x 13 of 20

As illustrated in Figure 10, the absorption peaks of the aged asphalt (AH-70) and the VA (AH-70) were similar. However, the tensile vibration absorption peak of methane –CH2– of aged asphalt at 2923 cm−1 and 2851 cm−1 was enhanced. Carbonyl (C=O) and sulfoxide (S=O) peak area intensities reflected the aging and rejuvenating degree of asphalt. Compared with the VA, aged asphalt exhibited a notable increase in C=O (1600 cm−1) and S=O (1031 cm−1) peak areas. The absorption peaks indicating aromatics (813 cm−1 and 865 cm−1) were also enhanced. The absorption peaks of the rejuvenated asphalt and the VA were also basically similar, while their aromatic absorption peaks were also significantly higher than that of the aged asphalt. However, the rejuvenated asphalt had two new absorption peaks, which appeared at 1746 cm−1 and Appl.1164 Sci.cm2019−1, belonging, 9, 1767 to C=O stretching of carbonyl. The new absorption peaks are the characteristic13 of 20 peaks of soybean oil. Moreover, the oxygenated function (C=O and S=O) peak area intensity of the rejuvenated asphalt showed a notable decrease in carbonyl peak compared to that of aged asphalt. properties, then so should the rejuvenated asphalt with WEO. The infrared spectroscopy analysis This was due to the proportionality of the decrease in intensity of band from C=O and S=O for curves of VA, aged asphalt (7 h) and rejuvenated asphalt at wavenumbers between 4000 cm 1 and recycled asphalts, and decrease in asphaltene content had an effective impact on rejuvenated asphalt− 500 cm 1 are shown in Figure 10. performance− with WEO or WCO.

Figure 10. FTIRFTIR spectra spectra results of VA, aged asphalt, and rejuvenated asphalt.

4.6. RheologicalAs illustrated Properties in Figure 10, the absorption peaks of the aged asphalt (AH-70) and the VA (AH-70) were similar. However, the tensile vibration absorption peak of methane –CH2– of aged asphalt at 1 1 29234.6.1. cmPhase− and Angle 2851 (δ cm) − was enhanced. Carbonyl (C=O) and sulfoxide (S=O) peak area intensities reflectedThe thetemperature aging and rejuvenatingdependence degree of the of phase asphalt. angle Compared of rejuvenated with the VA, asphalts aged asphalt is illustrated exhibited in a 1 1 notableFigures increase11 and in12. C= OIt (1600revealed cm− that) and viscous S=O (1031 pr cmoperty− ) peak performance areas. The absorptionincreased with peaks increasing indicating 1 1 aromaticstemperature. (813 Also, cm− theand phase 865cm angle− ) wereincreased also enhanced.with increasing waste oil content. Compared with the 5h agingThe absorptiontime, it had peaks much of the better rejuvenated improvement asphalt than and thethat VA of were 15 h also aging basically time similar,at the whilesame theirtemperature aromatic and absorption waste oil peaks content. were also significantly higher than that of the aged asphalt. However, 1 1 the rejuvenatedMeanwhile, asphalt different had elastic two newrecovery absorption performa peaks,nce whichoccurred appeared with WEO at 1746 and cm WCO.− and At 1164 the cmsame− , belongingtemperature to and C=O oil stretching content, rejuvenated of carbonyl. asphalt The new with absorption WCO had peaks a slightly are the larger characteristic phase angle peaks than of soybeanthat of WEO. oil. Moreover, Asphalt thewith oxygenated a smaller phase function angle (C= Ohas and better S=O) elastic peak arearecovery, intensity and of WEO the rejuvenated had better asphaltimpact on showed elastic a notablerecovery decrease performance in carbonyl than WCO. peak comparedWith the temperature to that of aged increasing, asphalt. Thisall the was phase due toangles the proportionalityincreased, but ofthe the rejuvenated decrease in asphalt intensity wi ofth bandWCO from had C a= Omuch and more S=O forstable recycled change. asphalts, Thus andmaintaining decrease stable in asphaltene elastic recovery content hadperformance an effective and impact reducing on rejuvenatedthe occurrence asphalt of damages performance due to with the WEOviscous or response WCO. change. The phase angles increased obviously when the temperature increased from 58 °C to 70 °C. There was no significant difference when the oil content was 2%, 3%, and 4% 4.6. Rheological Properties with the temperature rising. This indicated there would be a suitable dosage for better elastic 4.6.1.recovery Phase performance Angle (δ) of aged asphalt which depended on the aged asphalt types and field construction requirements. The temperature dependence of the phase angle of rejuvenated asphalts is illustrated in Figures 11 and 12. It revealed that viscous property performance increased with increasing temperature. Also, the phase angle increased with increasing waste oil content. Compared with the 5 h aging time, it had much better improvement than that of 15 h aging time at the same temperature and waste oil content. Meanwhile, different elastic recovery performance occurred with WEO and WCO. At the same temperature and oil content, rejuvenated asphalt with WCO had a slightly larger phase angle than that of WEO. Asphalt with a smaller phase angle has better elastic recovery, and WEO had better impact on elastic recovery performance than WCO. With the temperature increasing, all the phase angles increased, but the rejuvenated asphalt with WCO had a much more stable change. Thus maintaining stable elastic recovery performance and reducing the occurrence of damages due to the viscous response Appl. Sci. 2019, 9, 1767 14 of 20

change. The phase angles increased obviously when the temperature increased from 58 ◦C to 70 ◦C. There was no significant difference when the oil content was 2%, 3%, and 4% with the temperature rising. This indicated there would be a suitable dosage for better elastic recovery performance of aged Appl.Appl. Sci. Sci. 2019 2019, 9,, 9x, x 1414 of of 20 20 asphalt which depended on the aged asphalt types and field construction requirements.

90 90 9090 1%1% 2%2% 3%3% 4%4% 1%1% 2%2% 3%3% 4%4%

88 88 8888

86 86 86））

° ° 86 ）） ° ° （（ δ δ （（ δ δ 84 84 84 84

82 82 82 82

80 80 80 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 80 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ ℃ ℃ ℃ ℃ ℃ ℃ Temperature (℃) 58 64 Temperature70 76 (℃) 82 88 Temperature (℃) Temperature (℃) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) Figure 11. Influences of WEO on phase angel of rejuvenated asphalt (different aging time of VA). FigureFigure 11.11. InﬂuencesInfluences of WEO on on phase phase angel angel of of rejuvena rejuvenatedted asphalt asphalt (different (diﬀerent aging aging time time of of VA). VA).

90 90 90 1% 2% 3% 4% 90 1% 2% 3% 4% 1% 2% 3% 4% 1% 2% 3% 4% 88 88 88 88

86 86 ）） ° °

86（ 86 （）） δ ° δ ° （（

δ 84

δ 84 84 84

82 82 82 82

80 80 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 80 80 Temperature (℃) Temperature (℃) 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ (a) Rejuvenated asphaltTemperature (5 h aging (℃) time of VA) (b) Rejuvenated asphaltTemperature (15 h aging (℃) time of VA)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) FigureFigure 12. 12.Influences Influences of of WCO WCO on on phasephase angelangel of rejuvena rejuvenatedted asphalt asphalt (different (different aging aging time time of ofVA). VA). Figure 12. Influences of WCO on phase angel of rejuvenated asphalt (different aging time of VA). 4.6.2.4.6.2. Complex Complex Modulus Modulus (G*) (G*) 4.6.2.Asphalt ComplexAsphalt with withModulus large large complex (G*)complex modulus modulus has has better better resistance resistance to to flow flow deformation. deformation. FiguresFigures 13 13 andand 14 illustrated14 Asphaltillustrated the with eff theects large effects of WEO,complex of WCO,WEO, modulus andWCO, di hasff erentand better different dosages resistance ondosages theto flow complex on deformation. the moduluscomplex Figures ofmodulus rejuvenated 13 andof asphalts14rejuvenated illustrated at diff asphaltserentthe effects temperatures. at different of WEO, temperatures. WCO, and different dosages on the complex modulus of rejuvenatedIt wasIt was well-known asphalts well-known at thatdifferent that the the higher temperatures. higher the the|G* |G*|,|, the the higher higher the the resistance resistance to flowto flow deformation. deformation. As As seen in FiguresseenIt inwas Figure15 well-known and 15 16 and, the 16, complexthat the the complex modulushigher modulus the of |G*|, rejuvenated of therejuvenated higher asphalt the asphalt withresistance WEOwith WEOto and flow WCO and deformation. WCO had the had similar the As similar trend. Complex modulus decreased as the oil content and temperature increased, which trend.seen in Complex Figure 15 modulus and 16, the decreased complex as modulus the oil contentof rejuvenated and temperature asphalt with increased, WEO and which WCO appeared had the appeared much more obvious after the temperature exceeded 76 °C. With the temperature rising, muchsimilar more trend. obvious Complex after themodulus temperature decreased exceeded as the 76 oil◦C. content With the and temperature temperature rising, increased, all the resistance which all the resistance to flow deformation of rejuvenated asphalts kept decreasing; especially when the toappeared flow deformation much more of rejuvenatedobvious after asphalts the temperatur kept decreasing;e exceeded especially 76 °C. whenWith thethe oiltemperature content was rising, larger oil content was larger than 3%. At the same time, the corresponding anti-rutting performance of thanall the 3%. resistance At the same to flow time, deformation the corresponding of rejuvenated anti-rutting asphalts performance kept decreasing; of rejuvenated especially asphalt when the was rejuvenated asphalt was deteriorating. However, when the temperature was above 76 °C, the deteriorating.oil content was However, larger than when 3%. the At temperaturethe same time, was the above corresponding 76 C, the ruttinganti-rutting factor performance of rejuvenated of rutting factor of rejuvenated asphalt was close to that of the aged◦ asphalt. This indicated that the asphaltrejuvenated was closeasphalt to thatwas ofdeteriorating. the aged asphalt. However, This when indicated the thattemperature the effect was of wasteabove oil 76 would °C, the be effect of waste oil would be weakened at high temperature. Therefore, a proper range should be rutting factor of rejuvenated asphalt was close to that of the aged asphalt. This indicated that the weakenedselected to at get high better temperature. high temperature Therefore, performa a propernce for rangerejuvenated should asphalts be selected with WEO to get or betterWCO. high effect of waste oil would be weakened at high temperature. Therefore, a proper range should be temperatureIn addition, performance with the for aging rejuvenated time increasing, asphalts withcomplex WEO modulus or WCO. of both rejuvenated asphalts selecteddecreased to get notably. better Ahigh similar temperature trend with performa ruttingnce resistance for rejuvenated factor was asphalts observed. with Though WEO or the WCO. WEO andIn WCO addition, had awith similar the trend, aging the time WCO-rejuvenate increasing, complexd asphalt modulus kept higher of both complex rejuvenated modulus asphalts at the decreasedsame temperature notably. Aand similar aging trendtime, whichwith rutting would showresistance good factor performance was observed. at high temperatures. Though the WEOThe and WCO had a similar trend, the WCO-rejuvenated asphalt kept higher complex modulus at the same temperature and aging time, which would show good performance at high temperatures. The Appl. Sci. 2019, 9, x 15 of 20 Appl. Sci. 2019, 9, x 15 of 20 conclusions also confirmed the previous analysis of the different regeneration effect on WEO and Appl.WCOconclusions Sci. in2019 different, 9 ,also 1767 confirmedcontents. the previous analysis of the different regeneration effect on WEO15 and of 20 WCO in different contents. 20,000 20,000 20,000 1% 2% 3% 4% 20,000 1% 2% 3% 4% 18,000 1% 2% 3% 4% 18,000 1% 2% 3% 4% 18,000 18,000 16,000 16,000 16,000 16,000 14,000 14,000 ） 14,000 ） 14,000 Pa

） 12,000

Pa 12,000 ）（（ Pa 12,000

Pa 12,000 10,000 G* 10,000 （ G* 10,000 （ G* 10,000 8,000 G* 8,000 8,000 8,000 6,000 6,000 6,000 6,000 4,000 4,000 4,000 4,000 2,000 2,000 2,000 2,000 0 0 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ Temperature70℃ 76 (℃) 82℃ 88℃ 58℃ 64℃ Temperature70℃ 76 (℃℃) 82℃ 88℃

Temperature (℃) Temperature (℃)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) Figure 13. Effects of WEO on complex modulus of rejuvenated asphalt (different aging time of VA). FigureFigure 13.13. EEffectsﬀects of WEO on complex modulus of of rejuvena rejuvenatedted asphalt asphalt (different (diﬀerent aging aging time time of of VA). VA).

20,000 20,000 20,000 1% 2% 3% 4% 20,000 1% 2% 3% 4% 18,000 1% 2% 3% 4% 18,000 1% 2% 3% 4% 18,000 18,000 16,000 16,000 16,000 16,000 14,000 14,000 14,000 14,000 ）） 12,000 12,000 Pa ） Pa ） 12,000 12,000 （（ Pa Pa 10,000 10,000 G* （ G* （ 10,000 10,000 G* G* 8,000 8,000 8,000 8,000 6,000 6,000 6,000 6,000 4,000 4,000 4,000 4,000 2,000 2,000 2,000 2,000 0 0 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ Temperature70℃ 76 (℃) 82℃ 88℃ 58℃ 64℃ Temperature70℃ 76 (℃℃) 82℃ 88℃

Temperature (℃) Temperature (℃)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) FigureFigure 14.14. EffectsEffects of WCO on complex modulus modulus of of rejuvena rejuvenatedted asphalt asphalt (different (different aging aging time time of of VA). VA). Figure 14. Effects of WCO on complex modulus of rejuvenated asphalt (different aging time of VA). 4.6.3.In Rutting addition, Resistance with the Factor aging (G*/sin timeδ increasing,) complex modulus of both rejuvenated asphalts decreased4.6.3. Rutting notably. Resistance A similar Factor trend (G*/sin withδ) rutting resistance factor was observed. Though the WEO The test results of rutting resistance factor of rejuvenated asphalt with WEO and WCO at 5 h and WCO had a similar trend, the WCO-rejuvenated asphalt kept higher complex modulus at the and 15The h test are results presented of rutting in Figures resistance 15 and factor 16, of respectively. rejuvenated WCOasphalt and with WEO WEO affect and WCOthe rutting at 5 h same temperature and aging time, which would show good performance at high temperatures. resistanceand 15 h ofare the presented rejuvenated in Figuresasphalt by15 improvingand 16, respectively. its viscosity. WCOAs shown and inWEO Figures affect 15 andthe rutting16, the The conclusions also confirmed the previous analysis of the different regeneration effect on WEO and ruttingresistance resistance of the rejuvenated factor decreased asphalt with by improving increasing its temperature. viscosity. As With shown the in same Figures temperature, 15 and 16, the WCO in different contents. rejuvenatedrutting resistance asphalt factor of aging decreased 15 h had with smaller increasi ruttingng temperature.resistance than With that the of agingsame 5h,temperature, which proved the rejuvenated asphalt of aging 15 h had smaller rutting resistance than that of aging 5h, which proved 4.6.3.that longer Rutting aging Resistance time had Factor a negative (G*/sin influenceδ) on the high-temperature property. At the same aging time,that longer the rutting aging resistance time had afactor negative decreased influence nota onbly the with high-temperature the content and property. temperature At the increasing. same aging time,TheWhen the test rutting the results temperature resistance of rutting factor was resistance decreasedup to 70 factor °C, nota ofthebly rejuvenated rutting with the resistance content asphalt and withfactor temperature WEO reduced and WCOnotably increasing. at 5and h and it 15decreased h areWhen presented sharply the temperature in with Figures a temperature 15was and up 16 to, higher respectively. 70 °C, than the 76rutting WCO °C. Therefore, and resistance WEO the a fffactorect increase the reduced rutting in waste resistancenotably oil content and of theit rejuvenateddiddecreased not lead sharply asphalt to a largerwith by improving a ruttingtemperature resistance its viscosity. higher fa thanctor. As shown76Though °C. Therefore, in the Figures WCO the 15 and andincrease WEO16, the in were waste rutting much oil resistance content more factorimportantdid not decreased lead for toproperty witha larger increasing recovery rutting of temperature.resistance aged asphalt factor. With and Though thehigh-temperature same the temperature, WCO and performance WEO the rejuvenated were of rejuvenatedmuch asphalt more ofasphalt,important aging 15there for h had shouldproperty smaller be recovery reasonable rutting of resistance agedchoice asphalt according than and that high-temperatureto of the aging asphalt 5 h, whichperformance performance proved requirements that of longerrejuvenated agingand timemaximumasphalt, had there a negativetemperature should influence be in reasonable the onconstruction the choice high-temperature region.according to property. the asphalt At theperformance same aging requirements time, the rutting and resistancemaximumThere factor temperaturewere decreaseddifferent in reductions the notably construction with for therejuvenated region. content andasphalt temperature in rutting increasing. resistance factor. At the same There were different reductions for rejuvenated asphalt in rutting resistance factor. At the same temperature,When the aging temperature time and was waste up oil to 70dosage,◦C, the rejuvenated rutting resistance asphalt with factor WEO reduced had much notably smaller andit temperature, aging time and waste oil dosage, rejuvenated asphalt with WEO had much smaller decreased sharply with a temperature higher than 76 ◦C. Therefore, the increase in waste oil content did not lead to a larger rutting resistance factor. Though the WCO and WEO were much more important for property recovery of aged asphalt and high-temperature performance of rejuvenated asphalt, Appl. Sci. 2019, 9, 1767 16 of 20 there should be reasonable choice according to the asphalt performance requirements and maximum temperatureAppl. Sci. 2019 in, 9, thex construction region. 16 of 20 Appl. Sci. 2019, 9, x 16 of 20 There were different reductions for rejuvenated asphalt in rutting resistance factor. At the same temperature,ruttingrutting resistanceresistance aging factorfactor time thanthan and wastethatthat withwith oil WCO.WCO. dosage, WithWith rejuvenated temperaturetemperature asphalt increasing,increasing, with thethe WEO decreasingdecreasing had much extentextent smaller ofof ruttingrejuvenatedrejuvenated resistance asphaltasphalt factor withwith than WCOWCO that waswas with lowerlower WCO. thanthan With thatthat temperature withwith WEO,WEO, increasing, especiallyespecially whenwhen the decreasing thethe temperaturetemperature extent of rejuvenatedwas higher asphalt than 76 with °C WCO(this was was similar lower than with that the withconclusions WEO, especially of softening when point the and temperature viscosity). was Meanwhile, this illustrated that the WCO and WEO could both recover part of the performance of higherMeanwhile, than 76 this◦C (thisillustrated was similar that the with WCO the and conclusions WEO could of softening both recover point part and of viscosity). the performance Meanwhile, of aged asphalt, but WCO could achieve the same results with less content. The conclusions confirmed thisaged illustrated asphalt, thatbut WCO the WCO could and achieve WEO the could same both resu recoverlts with less part content. of the performance The conclusions of agedconfirmed asphalt, the previous analysis which WCO had better regeneration effect than WEO with different aged butthe WCO previous could analysis achieve which the same WCO results had withbetter less regene content.ration The effect conclusions than WEO confirmed with different the previous aged asphalts. analysisasphalts. which WCO had better regeneration effect than WEO with different aged asphalts. In addition, rutting resistance factor reflected unrecoverable deformation of asphalt during the InIn addition, addition, rutting rutting resistance resistance factorfactor reflectedreflected unrecoverable deformation deformation of of asphalt asphalt during during the the loading process. At high temperature, bitumen with higher G*/sinδ but smaller flow deformation loading process. At high temperature, bitumen with higher G*/sinδ δ but smaller flow deformation loadingwould process. have much At high higher temperature, rutting resistance. bitumen All with these higher facts G* indicated/sin but that smaller the flowrutting deformation resistance wouldhad havewould much have higher much rutting higher resistance. rutting re Allsistance. these All facts these indicated facts indicated that the rutting that the resistance rutting resistance had satisfactory had satisfactory improvement with waste oil content range of 1 to 3%. When the dosage was more than improvement with waste oil content range of 1 to 3%. When the dosage was more than 3% and the 3% and the temperature was higher 76 °C, the WCO could keep better high temperature property. temperature was higher 76 C, the WCO could keep better high temperature property. Therefore, Therefore, the range of 1 to◦ 3% was a more suitable dosage with WEO and WCO for better high the range of 1 to 3% was a more suitable dosage with WEO and WCO for better high temperature temperaturetemperature performance,performance, whichwhich dependeddepended onon thethe agedaged asphaltasphalt conditioncondition andand actualactual constructionconstruction performance, which depended on the aged asphalt condition and actual construction requirements. requirements.requirements.

14,000 16,000 14,000 1% 2% 3% 4% 16,000 1% 2% 3% 4% 1% 2% 3% 4% 1% 2% 3% 4% 12,000 14,000 12,000 14,000 12,000 10,000 12,000 10,000 10,000 10,000

(Pa) 8,000 (Pa)

(Pa) 8,000 (Pa) δ δ δ

δ 8,000 8,000 6,000

G*/sin 6,000 G*/sin 6,000 G*/sin G*/sin 6,000 4,000 4,000 4,000 4,000 2,000 2,000 2,000 2,000 0 0 0 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ Temperature (℃) Temperature (℃)

Temperature (℃) Temperature (℃)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) Figure 15. Influences of WEO on rutting resistance factor of rejuvenated asphalt (different aging Figure 15. Influences of WEO on rutting resistance factor of rejuvenated asphalt (different aging Figuretime 15.of VA).Inﬂuences of WEO on rutting resistance factor of rejuvenated asphalt (diﬀerent aging time time of VA). of VA).

16,000 18,000 16,000 1% 2% 3% 4% 18,000 1% 2% 3% 4% 1% 2% 3% 4% 1% 2% 3% 4% 14,000 16,000 14,000 16,000 14,000 12,000 14,000 12,000 12,000 10,000 12,000 10,000 (Pa) (Pa) 10,000 (Pa) (Pa) δ δ 10,000

δ 8,000 δ 8,000 8,000 8,000 G*/sin 6,000 G*/sin G*/sin 6,000 G*/sin 6,000 6,000 4,000 4,000 4,000 4,000 2,000 2,000 2,000 2,000 0 0 0 0 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ 58℃ 64℃ 70℃ 76℃ 82℃ 88℃ Temperature (℃) Temperature (℃) ℃ Temperature ( ) Temperature (℃)

(a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) (a) Rejuvenated asphalt (5 h aging time of VA) (b) Rejuvenated asphalt (15 h aging time of VA) Figure 16. Influences of WCO on rutting resistance factor of rejuvenated asphalt (different aging FigureFigure 16. 16.Inﬂuences Influences of of WCO WCO on on rutting rutting resistance resistance factor factor of of rejuvenated rejuvenated asphalt asphalt (di (differentﬀerent aging aging time time of VA). oftime VA). of VA).

4.7. Scanning Electron Microscopy (SEM) Test Appl. Sci. 2019, 9, 1767 17 of 20

4.7.Appl. ScanningSci. 2019, 9, Electron x Microscopy (SEM) Test 17 of 20 The SEM device is shown in Figure 17. The images of VA, aged asphalt, and rejuvenated asphalt The SEM device is shown in Figure 17. The images of VA, aged asphalt, and rejuvenated are shown in Figure 18. As seen from Figure 18a, VA had good homogeneity and was close to a asphalt are shown in Figure 18. As seen from Figure 18a, VA had good homogeneity and was close homogeneous structure. After 7 h of aging time, some small folds and little impurities could be found to a homogeneous structure. After 7 h of aging time, some small folds and little impurities could be at some surfaces, which proved the asphalt structure was affected. When the WCO was added into the found at Appl.some Sci. surfaces,2019, 9, x which proved the asphalt structure was affected. When the WCO17 of was 20 added aged asphalt, there was not obvious change in the appearance compared to the aged asphalt. While into the aged asphalt, there was not obvious change in the appearance compared to the aged asphalt. some little tinyThe white SEM pointsdevice is could shown be in seen Figure in some17. The asphalt images surface, of VA, whichaged asphalt, appeared and rejuvenated as extremely small While some little tiny white points could be seen in some asphalt surface, which appeared as particlesasphalt of WCO are shown related in toFigure the 18. filtered As seen sieve from holesFigure during18a, VA had the good lab testhomogeneity preparation. and was What close is more, extremelyto asmall homogeneous particles structure. of WCO After related 7 h of toaging the time filtered, some sieve small holesfolds and during little impurities the lab test could preparation. be it speculated that WEO had the same situation. As seen in Figure 18c, though rejuvenated asphalt was What is foundmore, at someit speculated surfaces, which that proved WEO the had asphalt the structure same situation.was affected. As When seen the inWCO Figure was added 18c, though apparently no longer homogeneous, its properties were improved which was proven by the previous rejuvenatedinto theasphalt aged asphalt, was apparently there was not no obvious longer change homogeneous, in the appearance its propertiescompared to werethe aged improved asphalt. which test results.While It illustratedsome little tiny that white WEO points or WCO could collectedbe seen in from some the asphalt factory surface, could which be regenerativeappeared as agents was proven by the previous test results. It illustrated that WEO or WCO collected from the factory after concentrateextremely small filtering particles system, of WCO and related the existingto the filtered extremely sieve holes small during particles the lab hadtest preparation. little effect on the could be regenerative agents after concentrate filtering system, and the existing extremely small performanceWhat improvement.is more, it speculated that WEO had the same situation. As seen in Figure 18c, though particles rejuvenatedhad little effectasphalt on was the apparently performance no longer improvement. homogeneous, its properties were improved which was proven by the previous test results. It illustrated that WEO or WCO collected from the factory could be regenerative agents after concentrate filtering system, and the existing extremely small particles had little effect on the performance improvement.

Figure 17. Scanning electron microscope test device. FigureFigure 17. 17.Scanning Scanning electron electron microscope microscope test test device. device.

× 500 times × 5000 times (a ) VA × 500 times × 5000 times (a) VA

× 500 times × 5000 times (b) Aged asphalt (7 h)

Figure 18. Cont.

× 500 times × 5000 times (b) Aged asphalt (7 h) Appl. Sci. 2019, 9, 1767 18 of 20

Appl. Sci. 2019, 9, x 18 of 20

× 200 times × 5000 times (c) Rejuvenated asphalt (2% WCO)

FigureFigure 18. 18.The The SEM SEM images images of different diﬀerent asphalt asphalt states. states.

5. Conclusions5. Conclusions In this study, some conventional and specific experiments were conducted to evaluate the In thisregeneration study, someproperties conventional of the aged asphalts. and specific Based on experiments the experiments were results conducted and analysis to evaluatefrom the regenerationdifferent properties aged asphalts, of the the agedfollowing asphalts. conclusions Based can be on drawn. the experiments results and analysis from different aged(1) asphalts, WEO and theWCO following could improve conclusions the basic canphysical be drawn.properties of aged asphalts to the normal (1) WEOlevel. To and satisfy WCO better could performance improve of theregenerated basic physical asphalt, the properties WEO or WCO of aged dosage asphalts should be to in the a normal reasonable range, which was different for different aged asphalts. level. To satisfy better performance of regenerated asphalt, the WEO or WCO dosage should be in a (2) In comparison, WCO had better function than WEO as a regenerative agent. Less WCO reasonablecontent range, could which achieve was better different regeneration for diff propertierent agedes. According asphalts. to the different aging time, aged (2) Inasphalt comparison, could recover WCO its had basic better physical function performance than WEO with as 1–5% a regenerative WEO content agent. and 1–4% Less WCOWCO content could achievecontent better (by mass regeneration of asphalt). properties. According to the different aging time, aged asphalt could recover its basic(3) The physical addition performance of WEO or WCO with could 1–5% increase WEO saturate, content resin, and and 1–4% asphaltene WCO content content and (by mass of decrease aromatics dosage, intensity of carbonyl, and sulfoxide of aged asphalt, but it could not asphalt). change its colloidal structure. Moreover, there was a suitable oil content related to the aged asphalt (3) Thecondition addition and actual of WEO construction or WCO requirements. could increase An excessive saturate, amount resin, of oil and content asphaltene would affect content and decreaseother aromatics properties dosage, of aged intensity asphalt. of carbonyl, and sulfoxide of aged asphalt, but it could not change its colloidal structure.(4) The rheological Moreover, properties there wasof aged a suitable asphalts oilcould content also be related regained to to the normal aged level asphalt of VA condition and actualwith construction different contents requirements. of WEO or WCO. An excessive Overall, WEO amount or WCO of oil were content adaptable would regenerative affect other agents properties to improve aged asphalt performances. It provided a new application method for WEO or WCO in of aged asphalt.asphalt pavement recycling field, which realized the wastes cyclic utilization and environmental (4) Theprotection. rheological properties of aged asphalts could also be regained to normal level of VA with different contents of WEO or WCO. Overall, WEO or WCO were adaptable regenerative agents to improve aged6. Future asphalt Researches performances. It provided a new application method for WEO or WCO in asphalt pavement recyclingThe scope field, of this which study realized proved the the adaptability wastes cyclic of WEO utilization and WCO and for environmentalaged asphalt through protection. basic properties, partial rheological, and chemical characterization. This study helps form the 6. Futurefoundation Researches to develop a new type of regenerative agent with WEO and WCO as the basis materials. Some other performances, such as resistance to fatigue cracking and moisture sensitivity, were not Theevaluated. scope of thisAlso, study it was proveduncertain the whether adaptability waste oil ofwould WEO affect and the WCO bonding for agedability asphalt of asphalt through and basic properties,aggregates. partial rheological,The research andteam chemical is conducting characterization. these above related This studyexperiments helps and form performance the foundation to developdetection a new type of re-aging of regenerative asphalt. After agent obtaining with WEO the test and data, WCO a new as theregenerative basis materials. agent will Some be other developed. Afterwards, it will be used in the hot in-place recycling field and related performance performances, such as resistance to fatigue cracking and moisture sensitivity, were not evaluated. indexes will be evaluated. Based on the testing results, components will be adjusted to obtain better Also, it wasasphalt uncertain property. whether Finally, a wastestable regenerative oil would agent affect product the bonding will be formed ability by of recycling asphalt waste and oil. aggregates. The research team is conducting these above related experiments and performance detection of re-aging Author Contributions: All authors discussed extensively. H.L. and B.D. conceived the experiments. H.L., B.D., asphalt. AfterP.G., and obtaining G.Z. conducted the test the data,experiments. a new H.L., regenerative W.W., G.Z., agentand Q.M. will analyzed be developed. the results. Afterwards, All authors it will be used inreviewed the hot the in-placemanuscript. recycling field and related performance indexes will be evaluated. Based on the testing results, components will be adjusted to obtain better asphalt property. Finally, a stable regenerative agent product will be formed by recycling waste oil.

Author Contributions: All authors discussed extensively. H.L. and B.D. conceived the experiments. H.L., B.D., P.G., and G.Z. conducted the experiments. H.L., W.W., G.Z., and Q.M. analyzed the results. All authors reviewed the manuscript. Funding: This research was funded by the Shaanxi Science and Technology Project (No.2018SF-364), the Qinghai Transportation Science and Technology Project (No.2017-ZJ-763), the Shaanxi Transportation Science and Appl. Sci. 2019, 9, 1767 19 of 20

Technology Project (No.17-12K), and the Fundamental Research Funds for the Central Universities of China (No.310831153409, No.300102218502 and No. 300102318401). Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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