Using Sustainable Oil Shale Waste Powder Treated with Silane Coupling Agent for Enriching the Performance of Asphalt and Asphalt Mixture

sustainability

Article Using Sustainable Oil Shale Waste Powder Treated with Silane Coupling Agent for Enriching the Performance of Asphalt and Asphalt Mixture

Xuedong Guo 1, Xing Chen 1, Yingsong Li 2, Zhun Li 1 and Wei Guo 1,*

1 School of Transportation, Jilin University, Changchun 130022, China 2 School of Transportation, Changchun college of architecture, Changchun 130604, China * Correspondence: [email protected]; Tel.: +86-153-3511-9826

Received: 16 August 2019; Accepted: 4 September 2019; Published: 5 September 2019

Abstract: The increase in cost of bitumen and polymer modifiers and the importance of silicon waste material management have encouraged pavement researchers to use reusable sustainable sources. Oil shale waste powder (OSP) is considered a silicon waste material, and when used in pavement prevents leaching. However, OSP, as an acidic inorganic material, has compatibility issues with asphalt, and its use with ashpalt should be considered carefully. This paper investigates the pavement performance and modification mechanism of OSP and silane coupling agent (SCA) composite modified asphalt and asphalt mixture according to conventional physical property tests: thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and a pavement performance test. The test results showed that the incorporation of OSP and SCA improved the overall properties of asphalt and asphalt mixture and the direct mixing method is more effective than the surface pretreatment method for the modification of composite modification of asphalt. Moreover, the FTIR test and DSC test indicated that the incorporation of OSP and SCA creates new chemical bonds and changes the form and quantity of the crystalline component and the transformation of components in the bitumen.

Keywords: Oil shale waste powder; Silane coupling agent; Composite modiﬁed asphalt; modiﬁcation mechanism; pavement performance

1. Introduction Asphalt has been widely used in airfield and high-grade road pavement due to its numerous advantages such as smoothness, low-vibration, high-automated construction, and easy maintenance [1–4]. Worldwide, annually, over 86 million tons of asphalt binder is combined with gravel or sand to pave roads [5–7]. However, it has been observed that the production of asphalt requires a major expenditure of natural resources, and the associated mining, reﬁning, production, and construction produce considerable greenhouse gas emissions [8–11]. Consequently, the industry has been steadily moving towards adopting more sustainable practices [12–14]. The main objective of sustainable development is to use natural resources in the most optimized way so that, environmental and socioeconomic issues are minimized [15–17]. In the past few years, studies regarding alternative environmental friendly materials in asphalt pavement to improve its mechanical properties have been conducted [18–21]. The use of industrial waste is a promising solution to minimize environmental pollution by sinking the accumulation of waste materials, which results in a reduction of the construction costs [22,23]. Tarbay et al. presents the use of waste materials (marble and granite) and byproduct material (steel slag) as alternative to the mineral conventional ﬁller. The test results show that all materials enhanced rutting resistance compared to the traditional

Sustainability 2019, 11, 4857; doi:10.3390/su11184857 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 4857 2 of 23

Sustainability 2019, 11, x FOR PEER REVIEW 2 of 24 limestone filler [24]. Abo El-Naga et al. investigated the effect of using polyethylene terephthalate wastewaste plasticplastic materials (PTP) (PTP) on on improving improving the the perf performanceormance and and properties properties of asphalt of asphalt pavement. pavement. The Theconclusion conclusion indicatedindicated that that addition addition of 12% of 12% of PTP of PTP increased increased the thepavement pavement service service life life2.81 2.81 times times and andsaved saved ~20% ~20% of the of theasphalt asphalt layer layer thickness thickness [25]. [25 Saberi]. Saberianan et al. et assessed al. assessed the theeffect effect of crushed of crushed glass glass on onthe the behavior behavior of ofthe the crushed crushed recycled recycled materials materials together together with with crumb crumb rubber forfor roadroad pavementpavement applications.applications. TheThe resultsresults indicatedindicated thatthat thethe blendsblends ofof wastewaste materials,materials, asas aa low-carbonlow-carbon concept,concept, couldcould bebe aa viableviable andand satisfactorysatisfactory alternative alternative solution solution for for future future base base/subbase/subbase applications applications [ 26[26].]. OilOil shale,shale, aa sedimentarysedimentary rock containing organic organic matter, matter, belongs belongs to to high-mineral high-mineral sapropelite, sapropelite, a alow-calorific low-calorific solidsolid fossil fossil fuel fuel with with a light-gray a light-gray to todark-brown dark-brown color color [27,28]. [27,28 Oil]. shale Oil shale has more has more than than40% 40%ash, ash,which which is the is themain main difference difference from from coal. coal. The The inorganic inorganic mineral mineral content content of of oil shaleshale isis approximatelyapproximately 50–80%,50–80%, mainlymainly includingincluding quartz,quartz, potassiumpotassium feldspar,feldspar, plagioclase,plagioclase, kaolin,kaolin, clay,clay, mica,mica, carbonate,carbonate, pyrite,pyrite, etc.etc. TheThe oiloil shaleshale resourcesresources inin thethe worldworld areare veryvery rich rich [ 29[29].]. AccordingAccording toto statisticsstatistics releasedreleased by by thethe U.S.U.S. EnergyEnergy InformationInformation Administration,Administration,world world shaleshale oiloil reservesreserves totaltotal approximatelyapproximately 1111 trilliontrillion toto13 13 trillion trillion tons tons,, far far exceeding exceeding oil oil reserves. reserves. Global Global shale shale oil oil is is generated generated from from Cambrian Cambrian toto Tertiary,Tertiary, mainly mainly in in nine nine countries: countries: UnitedUnited States,States, Congo,Congo, Brazil,Brazil, Italy,Italy, Morocco,Morocco, Jordan,Jordan, Australia,Australia, China,China, andand Canada.Canada. TheThe worldwideworldwide distributiondistribution ofof shaleshale oiloil resourcesresources is is shown shown in in Figure Figure1 [130 [30].].

Figure 1. Worldwide distribution of oil shale resources. Figure 1. Worldwide distribution of oil shale resources. At present, more than 90% of oil shale is used to generate electricity by combustion and refine shale oil by distillation. With the large-scale exploitation of oil shale, a large amount of waste is At present, more than 90% of oil shale is used to generate electricity by combustion and refine produced after combustion or distillation [31]. However, the majority of oil shale waste is directly piled shale oil by distillation. With the large-scale exploitation of oil shale, a large amount of waste is up in the nearby waste residue field, which causes many environmental problems. Oil shale waste is a produced after combustion or distillation [31]. However, the majority of oil shale waste is directly polar material that is similar to volcanic rocks and contains traces of organic residual carbon, and has piled up in the nearby waste residue field, which causes many environmental problems. Oil shale a strong activity. After combustion or distillation of oil shale, the organic matter is instantaneously waste is a polar material that is similar to volcanic rocks and contains traces of organic residual carbon, removed during the rapid heating process to form a porous structure. Since oil shale waste has a and has a strong activity. After combustion or distillation of oil shale, the organic matter is porous internal structure, the usage of oil shale waste is very extensive [32,33]. Hadi et al. produced instantaneously removed during the rapid heating process to form a porous structure. Since oil shale low-cost, compressed, strong, lightweight masonry bricks, similarly using the oil shale ash mixed waste has a porous internal structure, the usage of oil shale waste is very extensive [32,33]. Hadi et with marble and granite sludge [34]. Aljbour prepared ceramics specimens from oil shale ash and al. produced low-cost, compressed, strong, lightweight masonry bricks, similarly using the oil shale waste glass by pressing followed by heat treatment [35]. Wei et al. prepared a long-service-life asphalt ash mixed with marble and granite sludge [34]. Aljbour prepared ceramics specimens from oil shale mixture by drying and sieving the oil shale waste after combustion to replace the fine aggregate ash and waste glass by pressing followed by heat treatment [35]. Wei et al. prepared a long-service- below 4.75 mm as required by the Open-Grade Friction Course (OGFC) [36]. Wang et al. assessed life asphalt mixture by drying and sieving the oil shale waste after combustion to replace the fine high- and low-temperature properties of asphalt pavements incorporating dry oil shale waste ash aggregate below 4.75 mm as required by the Open-Grade Friction Course (OGFC) [36]. Wang et al. (particle size less than 0.075 mm) as partial filler. The results illustrated that the sustainable asphalt assessed high- and low-temperature properties of asphalt pavements incorporating dry oil shale materials have better high-temperature stability and rutting resistance, and also fulfill the requirements waste ash (particle size less than 0.075 mm) as partial filler. The results illustrated that the sustainable of low-temperature cracking resistance [37]. asphalt materials have better high-temperature stability and rutting resistance, and also fulfill the OGFC is a high permeable mixture used as a surface coat for good friction, and splash-and-spray requirements of low-temperature cracking resistance [37]. reduction during rain storms [38]. However, limitations of the use of such mixtures are greatly affected OGFC is a high permeable mixture used as a surface coat for good friction, and splash-and-spray by the relatively low strength and low stiffness. More specifically, the pavement fails when the reduction during rain storms [38]. However, limitations of the use of such mixtures are greatly affected by the relatively low strength and low stiffness. More specifically, the pavement fails when the asphalt binder ages and becomes brittle. Draindown—a separation of asphalt mastic from the

Sustainability 2019, 11, 4857 3 of 23 asphalt binder ages and becomes brittle. Draindown—a separation of asphalt mastic from the course skeleton—can occur during storage or transport, resulting in a thin binder coating that cannot prevent particles being dislodged by traffic [39]. The thin binder film can also age more rapidly, aggravating the ravelling problem. Sometimes, this failure occurs when the pavement is only 6–8 years old; such a short life is difficult to accept [40,41]. To effectively reduce and prevent the occurrence of ravelling damages in OGFC pavements, technologies adding the modifier are effective for prolonging the OGFC pavement service life [42,43]. However, such types of modifiers have high cost, restricting their application in modifying paving asphalt. In the past few years, many studies have been conducted on alternative environmentally friendly materials in OGFC to improve its mechanical properties [44]. The use of industrial waste is a promising solution to minimize environmental pollution by sinking the accumulation of waste materials, which results in a reduction of the construction costs. Since oil shale waste is an acidic inorganic material formed by oil shale after distillation or combustion, its compatibility with asphalt is a serious issue in the application of oil shale waste in pavement construction. However, as a new type of coupling agent, silane coupling agents contain two functional groups with different chemical properties: one is a hydrophilic fuctional group, which can be easy to react with inorganic materials, the other is an organophilic functional group, which can be easy to chemically react with an organic polymer material or to form a hydrogen bond, so that the silane coupling agent can effectively improve the compatibility of the organic material and the inorganic material, especially the acidic inorganic material. In this study, the pavement performance and modification mechanism of oil shale waste powder and silane coupling agent composite modified asphalt and asphalt mixture are systematically investigated according to conventional physical property tests: TGA test, FTIR test, DSC test, DSR test, and a pavement performance test. Moreover, the preparation method of the oil shale waste powder and silane coupling agent composite modified asphalt and the surface pretreatment method and direct mixing method are also discussed in this paper.

2. Raw Materials

2.1. Asphalt The asphalt used in this study is Panjin 90# asphalt, which is widely used in highways, permary pavement, urban expressways, and other heavy-traffic asphalt pavement; it can also be used as raw material for emulsified asphalt, diluted asphalt, and modified asphalt. The asphalt produced by Qilu Branch of Sinopec Corp and its technical parameters are shown in Table1.

Table 1. Technical parameters of Panjin 90# asphalt.

Penetration 15 C Technical ◦ Softening Wax Flash Solubility Density Parameters Ductility Point Content Point 15 ◦C 25 ◦C 30 ◦C 3 Units 0.1 mm cm ◦C% ◦C% g cm ≥ · − Test results 31.7 86.9 142.4 >100 44.2 1.7 340 99.9 1.003 ≥ GB/T0605- GB/T0606- GB/T0615- GB/T0611- GB/T0607- GB/T0603- Test procedure GB/T0606-2011 2011 2011 2011 2011 2011 2011

2.2. Oil Shale Waste Powder Oil shale waste is an acidic inorganic material formed by oil shale after dry distillation or combustion and has the characteristics of porosity and high activity. The oil shale waste selected in this paper is the waste residue generated after the combustion of the Huadian Longteng Power Plant in Jilin Province, China, as shown in Figure2. Sustainability 2019, 11, x FOR PEER REVIEW 4 of 24 Sustainability 2019, 11, x 4857 FOR PEER REVIEW 4 of 24 23

Figure 2. OilOil shale shale waste waste in in a a power power plant plant in Jilin province China. Figure 2. Oil shale waste in a power plant in Jilin province China. The color of oil shale wastewaste isis gray-brown,gray-brown, andand thethe oiloilhas has a a layered layered joint joint structure structure of of shale shale and and a The color of oil shale waste is gray-brown, and the oil has a layered joint structure of shale and alarge large amount amount of of ﬂake flake particles. particles. After After magnifying magnifying observation, observation, it was it was found found that thethat surface the surface of oil of shale oil a large amount of flake particles. After magnifying observation, it was found that the surface of oil shalewaste waste is rougher, is rougher, the oil the shale oil shale waste waste has a has large a large number number of micron-sized of micron-sized pores, pores, and and the edgethe edge of the of shale waste is rougher, the oil shale waste has a large number of micron-sized pores, and the edge of thepores pores is surrounded is surrounded by mossyby mossy and and petal-like petal-like protrusions protrusions [36 ].[36]. Figure Figure3 shows 3 shows the the appearance appearance of oil of the pores is surrounded by mossy and petal-like protrusions [36]. Figure 3 shows the appearance of oilshale shale waste. waste. oil shale waste.

Figure 3. The appearance characteristics of oil shale waste. Figure 3. TheThe appearance appearance characterist characteristicsics of oil shale waste.

The chemical composition of oil shale waste is sh shownown in Figure 44.. FigureFigure4 4 shows shows that that the the oil oil The chemical composition of oil shale waste is shown in Figure 4. Figure 4 shows that the oil shale waste still retains some of the characterist characteristicsics of the rock, and its main component is SiO2,, which which shale waste still retains some of the characteristics of the rock, and its main component is SiO2, which accounts for ~53% of of the the total. total. This This means means that that the the oil oil shale shale waste waste can can be be used used as as a a filler filler to reinforce accounts for ~53% of the total. This means that the oil shale waste can be used as a filler to reinforce bitumen. The The other components are Al22O5,, Fe Fe22OO33, ,MgO, MgO, etc., etc., which which indicates indicates that that the the oil oil shale shale waste waste bitumen. The other components are Al2O5, Fe2O3, MgO, etc., which indicates that the oil shale waste has a function. In In conclusion, oil oil shale waste, like other silicon inorganic asphalt modifiers modifiers such as has a function. In conclusion, oil shale waste, like other silicon inorganic asphalt modifiers such as silica, diatomite, asbestos, etc., can can be be used used for for asph asphaltalt modification modification in in terms terms of of chemical chemical composition. composition. silica, diatomite, asbestos, etc., can be used for asphalt modification in terms of chemical composition. Moreover, in terms of the appearance characteristics of oil shale wastes, the porous structure can also Moreover, in terms of the appearance characteristics of oil shale wastes, the porous structure can also increaseincrease the bonding between asphalt and oil shale waste. increase the bonding between asphalt and oil shale waste.

Sustainability 2019, 11, x FOR PEER REVIEW 5 of 24

Sustainability 2019, 11, 4857 5 of 23

Figure 4. The chemical composition of oil shale waste

The physical propertiesFigure of oil 4. The shale chemical waste arecomposition shown in of Tableoil shale2. Table waste2 shows that the apparent densityThe ofphysical the oil properties shale waste of oil (OSW) shale iswaste very are close shown to thatin Table of the 2. Table stone 2 andshows the that OSW the hasapparent some densitycharacteristics of the ofoil the shale rock. waste However, (OSW) the is OSW very generated close to fromthat of the the oil shalestone afterand extractionthe OSW hashas highersome characteristicscrushing value of and the water rock. absorption.However, the The OSW higher generated crushing from value the indicates oil shale that after the extraction residue can has not higher bear crushingloads as avalue skeleton and in water the asphalt absorption. mixture. The Higher higher water crushing absorption value indicates may lead that to poor the waterresidue stability can not of bearOSW loads in the as pavement a skeleton material in the application.asphalt mixture. In a previous Higher study,water theabsorption standard may immersion lead to Marshall poor water test stabilityshowed of that OSW utilization in the pavement of oil shale material waste as application. fine aggregate In a withoutprevious any study, auxiliary the standard modifiers immersion reduced Marshallthe water test stability showed of asphalt that utilization mixtures, of the oil residual shale waste stability as isfine 70.21 aggregate % after 48without h immersion, any auxiliary which modifiersdoes not meetreduced Chinese the water requirement stability of of residual asphalt stabilitymixtures, greater the residual than 75% stability [36]. is Therefore, 70.21 % after auxiliary 48 h immersion,modifiers are which needed does to improvenot meet water Chinese stability requiremen duringtapplication. of residual stability greater than 75% [36]. Therefore, auxiliary modifiers are needed to improve water stability during application. Table 2. Physical parameters of OSW.

Apparent TableWater 2. Physical parameters of OSW. Internal Optimum Physical Crushing Cohesion Density Absorption Friction Water Rate Property Apparent3 Water Value (%) (Kpa) Internal Optimum Physical (g/cm ) (%) Crushing Cohesion Angle (◦) (%) Density Absorption Friction Water Rate PropertyOSW 2.627 18.6Value 42.2 (%) 13.84(Kpa) 33.3 28.3 (g/cm3) (%) Angle (°) (%) OSW 2.627 18.6 42.2 13.84 33.3 28.3 It is recognized that the fineness of the inorganic asphalt modifier will determine the modification effectItof is the recognized asphalt. The that smaller the fineness the particle of sizethe ofinorganic the modifier, asphalt the moremodifier obvious will thedetermine modification the modificationeffect. Therefore, effect oil of shale the asphalt. waste powder The smaller with athe particle particle size size below of the 0.075 modifier, mm was the prepared more obvious as asphalt the modificationmodifier in this effect. paper. Therefore, The oil oil shale shale waste waste used powder in this paperwith a isparticle accumulated size below outdoors 0.075mm for a longwas preparedtime. Since as theasphalt oil shale modifier waste in hasthis a paper. high moisture The oil shale absorption waste rate,used thein this oil shalepaper waste is accumulated should be outdoorspretreated for before a long utilization. time. Since The the pretreatmentoil shale waste procedure has a high of moisture oil shale absorption waste includes rate, twothe oil steps shale of wastedrying should and smashing. be pretreated before utilization. The pretreatment procedure of oil shale waste includes two stepsStep 1:of Thedrying oil shaleand smashing. waste was palced in 60 ◦C oven for 6 h to ensure removal of moisture from the oilStep shale 1: The waste. oil shale waste was palced in 60°C oven for 6h to ensure removal of moisture from the oilStep shale 2: Thewaste. dried oil shale waste was immediately crushed and sieved, and oil shale waste powder withStep a particle 2: The size dried below oil 0.075shale mm waste was was selected immedi as asphaltately crushed modifier. and sieved, and oil shale waste powderAfter with the a oilparticle shale size waste below powder 0.075mm was prepared,was selected it wasas asphalt placed modifier. in dry box to prevent moisture intrusion.After Thethe oil oil shale waste powderpowder iswas donoted prepared, as OSP it was in this placed paper. in dry box to prevent moisture intrusion. The oil shale waste powder is donoted as OSP in this paper. 2.3. Silane Coupling Agent 2.3. SilaneSilane Coupling coupling Agent agent was first developed by Union Carbide Corp, United States. The molecular structureSilane of coupling the silane agent coupling was first agent developed includes by both Un organicion Carbide functional Corp, United groups States. reactive The with molecular organic structurecompounds of the and silane silane coupling oxygen agent functional includes groups both reactive organic with functional inorganic groups materials. reactive Therefore, with organic the compoundssilane coupling and agent silane can oxygen form a functional stable bonding groups layer reactive between with the inorganic inorganic substancematerials. andTherefore, the organic the substance, which can effectively solve the problem of compatibility between the organic material and

Sustainability 2019, 11, 4857 6 of 23 the inorganic material [45]. At present, silane coupling agents have been widely used in various fields. Typical silane coupling agents are KH550, KH570, etc. Among different varieties of silane coupling agent, KH550 is mainly used in mineral-filled thermoplastic and thermosetting resins, such as polyester, epoxy, PBT, carbonate, etc., which can significantly improve and enhance the physical and mechanical properties of the material such as compressive strength, dry and wet flexural strength, shear strength, and electrical properties in the wet state. It can also be applied to the surface treatment of inorganic fillers such as silica, clay, mica, pottery clay, kaolin, etc., to enhance the wettability and dispersibility of the filler in the polymer. According to the previous research of our project team, it was found that the silane coupling agent KH550 has an obvious modification effect on acid stone. Since the oil shale waste powder is an acid stone, the silane coupling agent is finally selected as an auxiliary modifier. The auxiliary modifier silane coupling agent KH550 used in this paper is produced by Shanghai Yiyan Co., Ltd. The technical parameters of silane coupling agent KH550 are shown in Table3.

Table 3. Technical parameters of silane coupling agent KH550.

Technical 25 C 25 C Flash Ignition Boiling Molecular Chromaticity Purity ◦ ◦ Parameters Viscosity Density Point Point Point Weight 3 Units - % cp g/cm ◦C ◦C ◦C 1 Test results <25 98.5 16 0.946 96 297 217 221.37 ≥

2.4. Aggregate Since the surface of the alkaline aggregate is extremely active, it can obtain a stronger adhesion eﬀect with the asphalt. In engineering, alkaline stone is generally used as the aggregate for pavement construction. The aggregate used in the paper is the limestone produced from Jiutai Stone Factory, and the technical parameters of the coarse aggregate, ﬁne aggregate, and mineral powder are shown in Tables4–6 according to the Chinese Test Methods of Aggregate For Highway Engineering (JTG E42-2005).

Table 4. Technical parameters of coarse aggregate

Technical Parameters Unit Values Requirements Test Procedure Crushing value % 21.2 26 T 0316-2005 ≤ Los Angeles abrasion value % 25 28 T 0317-2005 ≤ Elongated particles content % 9.3 15 T 0312-2005 ≤ Water absorption % 0.61 2.0 T 0307-2005 ≤ 16 mm g cm 3 2.788 · − 13.2 mm g cm 3 2.787 Apparent speciﬁc gravity · − 2.6 T 0304-2005 9.5 mm g cm 3 2.787 ≥ · − 4.75 mm g cm 3 2.749 · −

Table 5. Technical parameters of ﬁne aggregate

Technical Parameters Unit Values Requirements Test Procedure Apparent specific gravity g cm 3 2.71 2.5 T 0330-2005 · − ≥ Specific gravity of gross volum g cm 3 2.64 N/A T 0328-2005 · − Surface dry specific gravity g cm 3 2.60 N/A T 0331-1994 · − Mud content % 1.02 3.0 T 0333-2000 ≤ Sustainability 2019, 11, 4857 7 of 23

Table 6. Technical parameters of mineral powder.

Technical Parameters Unit Values Requirements Test Procedure Apparent speciﬁc gravity g cm 3 2.83 2.5 T 0352-2000 · − ≥ Water absorption % 0.2 1 T 0353-2005 ≤ No No Appearance characteristic N/A N/A agglomeration agglomeration <0.6 mm % 100 100 Granular composition <0.15 mm % 98 90–100 T 0351-2000 <0.075 mm % 92 75–100

3. Sample Preparation

3.1. Preparation of OSP/SCA Composite Modified Asphalt There are two application methods of silane coupling agent for auxiliary modification: direct mixing method and surface pretreatment method. The direct mixing method is a method in which silane coupling agent stock solution is added during the mixing of inorganic material and organic filler. Generally, the silane coupling agent stock solution is first added to the organic polymer material and uniformly mixed, and then the inorganic filler is added. The surface pretreatment method involves dipping, spraying, or brushing the silane coupling agent solution on the surface of inorganic filler for surface modification.

3.1.1. Surface Pretreatment Method Surface pretreatment method mainly consists of two steps: hydrolysis and solidification. Step 1: Hydrolysis. Before surface modification, the silane coupling agent should be mixed with a proportion of water and ethanol solution for a period of time to achieve hydrolysis. Then, the surface of OSP is dipped with the hydrolyzed silane coupling agent solution. The silanol hydroxyl group formed by the hydrolysis reaction first forms a hydrogen bond on the surface of OSP, and then forms a coating film on the surface of OSP by dehydration reaction. During the hydrolysis reaction, the degree of hydrolysis of the silane coupling agent affects surface modification of OSP. The ratio of silane coupling agent, water, and ethanol is 5: 45: 50, and the hydrolysis time is 20 min. Step 2: Solidfication. After the surface of OSP is treated with the silane coupling agent solution, it should also be subjected to solidfication reaction, that is, heat drying. After the solidfication reaction, part of the hydrogen bond forms a covalent bond due to dehydration, and the silane coupling agent will be in a firm or fixed state on the surface of OSP. Both the solidfication temperature and the solidfication time have an effect on the strength of the silane film. According to the previous research conclusions and actual preheating requirements of the aggregate in laboratory, the solidfication temperature is selected as 160 ◦ C and the solidification time is 2 h. In addition to the above two factors, the amount of silane coupling agent also needs to be considered in the procedure of surface modification of OSP. According to the experimental research, the surface modification effect is best when the amount of silane coupling agent solution is 2 wt% of OSP. Since there is no currently existing literature on asphalt binders with OSP modified by SCA, at the beginning of this study, conventional tests, including penetration (ASTM D5), softening point (ASTM D36), and ductility (ASTM D113), were conducted to optimize the preparation procedure of OSP/SCA composite modified asphalt by surface pretreatment method. The test results showed that 5% OSP modified by SCA by weight of the base asphalt binder could be appropriate. Figure5 schematically shows the preparation procedure of OSP/SCA composite modified asphalt by surface pretreatment method. Sustainability 2019, 11, 4857 8 of 23 Sustainability 2019, 11, x FOR PEER REVIEW 8 of 24

FigureFigure 5. Preparation 5. Preparation procedure procedure of OSP of /SCAOSP/SCA composite composite modified modified asphalt asphalt by surface by surface pretreatment pretreatment method. method. 3.1.2. Direct Mixing Method The3.1.2. whole Direct preparationMixing Method procedure of OSP/SCA composite modified asphalt by direct mixing method can,The generally, whole preparation be divided procedure into four of stages:OSP/SCA composite modified asphalt by direct mixing Stepmethod 1: Thecan, basegenerally, asphalt be divided was heated into four to ~135 stages:◦ C to ensure that the asphalt is completely melted and in a flowingStep 1: The state. base asphalt was heated to ~135 ° C to ensure that the asphalt is completely melted Stepand in 2: a Theflowing SCA state. stock solution was directly mixed into the base asphalt, and then manually Step 2: The SCA stock solution was directly mixed into the base asphalt, and then manually stirred for 3 min. stirred for 3 minutes. Step 3: The OSP was mixed into the asphalt containing SCA in batches, and then manually stirred Step 3: The OSP was mixed into the asphalt containing SCA in batches, and then manually for 5 min.stirred for 5 minutes. Step 4:Step The 4: asphaltThe asphalt containing containing SCA SCA and and OSP OSP was was immediately immediately stirred stirred at 5000at 5000 rpm rpm for for 1 h1 toh evenlyto disperseevenly SCA disperse and OSP. SCA and OSP. The amountThe amount of SCA of andSCA OSPand andOSP theand shear the shear temperature temperature are the are main the main factors factors affecting affecting the property the of OSPproperty/SCA composite of OSP/SCA modified composite asphalt. modified The asphalt. OSP/SCA The composite OSP/SCA modifiedcomposite asphalt modified with asphalt direct with mixing methoddirect were mixing prepared method via similarwere prepared optimization via similar procedure. optimizati The optimizationon procedure. procedure The optimization is based on a orthogonalprocedure experimental is based on design a orthogonal method, experimental in which the design amount method, of SCA in iswhich 0 wt%, the1 amount wt%, 2 wt%,of SCA and is 30 wt% wt%, 1 wt%, 2 wt%, and 3 wt% of asphalt; the amount of OSP is 0 wt%, 3 wt%, 6 wt%, and 9 wt% of of asphalt; the amount of OSP is 0 wt%, 3 wt%, 6 wt%, and 9 wt% of asphalt; and the shear temperature is asphalt; and the shear temperature is 135 °C, 145 °C, 155 °C, and 165 °C. Moreover, the evaluation 135 C, 145 C, 155 C, and 165 C. Moreover, the evaluation indicators are penetration index, softening ◦ indicators◦ are penetration◦ index,◦ softening point, and ductility, which characterize the temperature point,susceptibility, and ductility, high-temperature which characterize properties, the temperature and low-temperature susceptibility, properties high-temperature of composite properties, modified and low-temperatureasphalt, respectively. properties The of optimization composite modified results sh asphalt,ow 6 wt% respectively. OSP of the Thebase optimizationasphalt binder, results 2 wt% show 6 wt%SCA OSP of ofthe the base base asphalt, asphalt and binder, 145 °C shear 2 wt% temperature SCA of the could base be asphalt, appropriate. and 145In addition,◦C shear in temperature another couldset be of appropriate. samples, SBS In modified addition, asphalt in another was also set pr ofepared samples, for SBScomparison. modified The asphalt SBS modified was also asphalt prepared for comparison.was obtained The from SBS the modified Jilin Traf asphaltfic Planning was obtainedand Design from Institute, the Jilin China. Traffi Forc Planning convenience, and the Design Institute,OSP/SCA China. composite For convenience, modified asphalt the OSPprepared/SCA by composite surface pretreatment modified asphaltmethod and prepared direct mixing by surface pretreatmentmethod methodare denoted and as direct OSMA-SP mixing and method OSMA-DM, are denoted respectively. as OSMA-SP Meanwhile, and OSMA-DM,base asphalt and respectively. SBS modified asphalt are denoted as BA and SMA, respectively. Meanwhile, base asphalt and SBS modified asphalt are denoted as BA and SMA, respectively. 3.2. Preparation of Composite Modified Asphalt Mixture 3.2. Preparation of Composite Modified Asphalt Mixture The asphalt mixture specimens modified by OSP and SCA in this paper consisted of OGFC with Thea nominal asphalt maximum mixture specimenssize of 16mm, modified which byhas OSPbeen and extensively SCA in thisapplied paper for consistedsustainable of pavement OGFC with a nominal maximum size of 16 mm, which has been extensively applied for sustainable pavement around the world because of high skid resistance, low noise and splash-and-spray reduction. The gradation of OGFC-16 is illustrated in Figure6. Sustainability 2019, 11, x FOR PEER REVIEW 9 of 24

Sustainability 2019, 11, 4857 9 of 23 around the world because of high skid resistance, low noise and splash-and-spray reduction. The gradation of OGFC-16 is illustrated in Figure 6.

Figure 6. Gradation of OGFC-16 in the test. Figure 6. Gradation of OGFC-16 in the test. Moreover, unmodified asphalt mixture and SBS modified asphalt mixture were prepared for comparison.Moreover, The unmodified optimized bitumen–aggregateasphalt mixture and ratioSBS modified of the asphalt asphalt mixture mixture used were in prepared the study for was determinedcomparison. by The Schellenberg optimized binder bitumen–aggregate drainage test andratio Cantabro of the asphalt test. Themixture optimized used in bitumen–aggregate the study was determined by Schellenberg binder drainage test and Cantabro test. The optimized bitumen– ratio of unmodified OGFC, SBS modified OGFC, and OSP/SCA composite modified OGFC is 4.8%, aggregate ratio of unmodified OGFC, SBS modified OGFC, and OSP/SCA composite modified OGFC 4.2%, and 4.6%, respectively. In order to simplify the sample appellation, unmodified OGFC, SBS is 4.8%, 4.2%, and 4.6%, respectively. In order to simplify the sample appellation, unmodified OGFC, modified OGFC, and OSP/SCA composite modified OGFC are donated as OGFC, SBS-OGFC, and SBS modified OGFC, and OSP/SCA composite modified OGFC are donated as OGFC, SBS-OGFC, OSP/SCA-OGFC, respectively, in this study. and OSP/SCA-OGFC, respectively, in this study. 4. Experimental Procedures 4. Experimental Procedures The detailed experimental procedures of this paper are listed in Table7. In order to assess the The detailed experimental procedures of this paper are listed in Table 7. In order to assess the propertyproperty of of asphalt asphalt and and asphalt asphalt mixturemixture systematical systematically,ly, the the experimental experimental procedures procedures are are divided divided into into twotwo aspects: aspects: experimentalexperimental procedure proceduress of of asphalt asphalt and and asphalt asphalt mixture. mixture. The Themechanical mechanical properties properties of ofORF/SCA ORF/SCA composite composite modified modified asphalt, asphalt, in in terms terms of of low-temperature low-temperature properties, properties, high-temperature high-temperature properties,properties, temperature temperature susceptibility,susceptibility, and anti-aging properties, properties, were were determined determined by bythree three major major indexindex tests tests (penetration, (penetration, softeningsoftening point, and and ductilit ductility)y) and and the the rolling rolling thin thin film film oven oven test test (RTFOT). (RTFOT). TheThe eff effectect of of ORF ORF andand SCASCA on the the behavior behavior and and stability stability properties properties of asphalt of asphalt were weredetermined determined by byTGA TGA test test (Netzsch (Netzsch Co., Co., Berlin, Berlin, Germany). Germany). The The temperature temperature range range of the of thetest test was was from from room room temperaturetemperature to to900 900 ◦°C,C, and and the the heating heating rate rate was was controlled controlled at 20 at °C/min. 20 ◦C/ Themin. FTIR The and FTIR DSC and tests DSC were tests wereconducted conducted to explore to explore the modification the modification mechanism mechanism of OSP/SCA of OSPcomposite/SCA compositemodified asphalt. modified A Vertex asphalt. A70 Vertex Fourier 70 Transform Fourier Transform Infrared Spectroscope Infrared Spectroscope (Bruker Optics (Bruker Co., OpticsChangchun, Co., Changchun,China) was employed China) was −1 1 −1 1 employedwith wavelength with wavelength ranging from ranging 40 cm from to 404000 cm cm− to. DSC 4000 tests cm− were. DSC conducted tests were using conducted a DSC-500B using a DSC-500B(Shanghai (Shanghai yinuo precision yinuo precision instrument instrument co. Ltd, co.Chin Ltd.,a) to China) get the to thermographs get the thermographs of both ofneat both and neat andmodified modified asphalt asphalt binders. binders. InIn this this section, section, highhigh- andand low-temperaturelow-temperature mechan mechanicalical properties, properties, moisture-sensitive moisture-sensitive properties, properties, ravelingraveling resistance resistance properties, properties, andand permeabilitypermeability of of OSP/SCA OSP/SCA composite composite modified modified asphalt asphalt mixture mixture were studied respectively. Specifically, the high-temperature mechanical properties of OSP/SCA were studied respectively. Specifically, the high-temperature mechanical properties of OSP/SCA composite modified asphalt mixture was evaluated by Marshall stability test and wheel tracking test. composite modified asphalt mixture was evaluated by Marshall stability test and wheel tracking test. The low-temperature mechanical properties of OSP/SCA composite modified asphalt mixture was The low-temperature mechanical properties of OSP/SCA composite modified asphalt mixture was analyzed through the −15°C splitting test and −10 °C beam-bending test. The moisture-sensitive analyzed through the 15 C splitting test and 10 C beam-bending test. The moisture-sensitive properties of the asphalt− ◦mixture were evaluated− by◦ immersion Marshall test and self-designed propertiesspring-thawing of the stability asphalt test. mixture To better were evaluate evaluated the bywater immersion stability of Marshall OGFC in test the andspring-thawing self-designed spring-thawingseason, we use stability the spring-thawing test. To better stability evaluate index the to water evaluate stability the water of OGFC stability in the of spring-thawingOGFC in the season, we use the spring-thawing stability index to evaluate the water stability of OGFC in the spring-thawing season. The specimens were treated by vacuum saturation at 97.3 kPa for 15 min and submerged in a container containing water, then the container with specimens were placed in Sustainability 2019, 11, x FOR PEER REVIEW 10 of 24 spring-thawingSustainability 2019, 11season., 4857 The specimens were treated by vacuum saturation at 97.3 kPa for 15 min10 and of 23 submerged in a container containing water, then the container with specimens were placed in the precision temp-enclosure at −15 °C and frozen 12 h. Then, the specimens were soaked in water at the precision temp-enclosure at 15 ◦C and frozen 12 h. Then, the specimens were soaked in water 15 °C for 12 h through controlling− the precision temp-enclosure. As described above, a complete at 15 ◦C for 12 h through controlling the precision temp-enclosure. As described above, a complete freeze–thawfreeze–thaw cycle cycle is is completed. completed. After After 5 5 freeze–t freeze–thawhaw cycles, cycles, damaged damaged specimens specimens were were collected collected for for MarshallMarshall test test according according to to Chinese Chinese standards standards GB/T GB/T0709-20110709-2011 [36]. [36]. The The raveling raveling resistance resistance properties properties ofof asphalt asphalt mixture mixture was was analyzed analyzed through through standard standard Cantabro Cantabro test, test, and and permeability permeability was was evaluated evaluated by constantby constant head head permeability permeability test. test. In order In order to toensure ensure the the validity validity and and repeatability repeatability of of the the data, data, the the numbernumber of of parallel parallel tests tests in in each each group group of of experiments experiments was 4–6.

7 TableTable 7.. ExperimentalExperimental procedure procedure of of OSP/SCA OSP/SCA mo modifieddified asphalt asphalt and and asphalt mixture. ASTM TypeType PerformancePerformance Tests Tests Specification Specification ASTM Standards Standards PenetrationPenetration T0604T0604 DD 5 5 Softening point T0606 D 36-00 Physical properties Softening point T0606 D 36-00 Physical properties Ductility T0605 D 113-99 Ductility T0605 D 113-99 RTFOT T0609 D 2872 AsphaltAsphalt RTFOT T0609 D 2872 TGA N/AN/A Thermal property TGA N/A N/A Thermal property DSC N/AN/A DSC N/A N/A Modification Modification mechanism FTIR FTIR N/AN N/A N/A/A mechanism High-temperature Marshall stability test T0709 D 5581-01 High-temperatureproperty MarshallWheel stability tracking test test T0709 T0919 D 5581-01 propertyLow-temperature Wheel− tracking15°C splitting test test T0919 T0716 D 4123 Low-temperatureproperty 15−10C °C splitting beam-bending test test T0716 T0715 D 4123N/A − ◦ property 10 ◦CImmersion beam-bending Marshall test test T0715 T0709 DN /1075A AsphaltAsphalt Moisture-sensitive − Moisture-sensitive ImmersionSpring-thawing Marshall test stability T0709 D 1075 mixturemixture property N/A N/A property Spring-thawing stabilitytest test N/AN/A RavelingRaveling resistance resistance StandardStandard Cantabro Cantabro test test T0733 T0733 T T 305-97 305-97 propertyproperty Constant head PermeabilityPermeability Constant head permeability test T0730T0730 PSPS 129 129 permeability test

5.5. Experimental Experimental Results Results and and Discussion Discussion 5.1. Conventional Physical Property Test Results 5.1. Conventional Physical Property Test Results The penetration test results of asphalt sample are shown in Figure7. The penetration test results of asphalt sample are shown in Figure 7.

(a) (b)

Figure 7. Penetration test results of four asphalt samples: (a) 25°C penetration of four asphalt samples Figure 7. Penetration test results of four asphalt samples: (a) 25 ◦C penetration of four asphalt samples andand (b) (b) temperature temperature sensitivity sensitivity coefficient coeﬃcient of of four four asphalt asphalt samples. samples.

ItIt can can be be seen seen from from Figure Figure 7a7a that that the the incorpor incorporationation of of modifier modifier reduces reduces the the penetration penetration value value of asphaltof asphalt sample. sample. This This may may due due to tothe the swelling swelling and and absorption absorption reaction reaction between between the the asphalt asphalt and and modifiermodifier after the incorporationincorporation ofof modifier modifier and and mechanical mechanical stirring, stirring, which which changes changes the the structure structure of theof asphalt colloid and enhances the gelation of the asphalt. The intercept (K) and slope (A) were obtained

SustainabilitySustainability 20192019,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 1111 ofof 2424 Sustainability 2019, 11, 4857 11 of 23 thethe asphaltasphalt colloidcolloid andand enhancesenhances thethe gelationgelation ofof thethe asphalt.asphalt. TheThe interceptintercept (K)(K) andand slopeslope (A)(A) werewere obtainedtoobtained calculate toto calculate penetrationcalculate penetrationpenetration index (PI) indexindex through (PI)(PI) linearly throughthrough regressing linearlylinearly regressingregressing the logarithm thethe oflogarithmlogarithm penetration ofof penetrationpenetration (P) against (P)temperature(P) againstagainst temperaturetemperature (T). Slope A (T). is(T). defined SlopeSlope asAA aisis temperature defineddefined asas a sensitivitya temperaturetemperature coeffi sensitivitysensitivitycient of asphalt. coefficientcoefficient Figure ofof7 basphalt.asphalt. shows FigurethatFigure the 7b7b temperature showsshows thatthat sensitivity thethe temperaturetemperature coefficient sensitivitysensitivity of asphalt cocoefficient is,efficient generally, ofof asphaltasphalt reduced is,is, after generally,generally, modification reducedreduced and afterafter the modificationtemperaturemodification sensitivityandand thethe temperaturetemperature coefficient sensitivitysensitivity of SBS modified coefficicoeffici asphaltentent ofof SBSSBS is the modifiedmodified smallest. asphaltasphalt This is isis due thethe to smallest.smallest. the fact ThisThis that isSBS,is duedue as toto a polymer,thethe factfact thatthat has SBS,SBS, a large asas molecularaa polymer,polymer, weight hashas aa largelarge and viscoelastic molecularmolecular weightweight range. Theandand temperatureviscoelasticviscoelastic range.range. sensitivity TheThe temperaturecoetemperaturefficient of sensitivity OSPsensitivity/SCAcomposite coefficientcoefficient modified ofof OSP/SCAOSP/SCA asphalt compositecomposite with direct modifiedmodified mixing method asphalasphaltt is withwith almost directdirect the samemixingmixing as methodSBSmethod modified isis almostalmost asphalt, thethe and samesame it also asas has SBSSBS excellent modifiedmodified temperature asasphalt,phalt, susceptibility.andand itit alsoalso Thishashas mayexcellentexcellent be because temperaturetemperature OSP as susceptibility.asusceptibility. filler absorb lightThisThis may componentsmay bebe becausebecause with OSPOSP smaller asas aa molecularfillerfiller absorbabsorb weight lightlight components incomponents the OSP/SCA withwith composite smallersmaller molecularmolecular modified weightasphalt,weight inin so thethe that OSP/SCAOSP/SCA the distance compositecomposite between modifiedmodified the asphalt asphalt,asphalt, colloid soso and thatthat colloid thethe distancedistance formed betweenbetween by OSP the isthe reduced, asphaltasphalt andcolloidcolloid the andinteractionand colloidcolloid forceformedformed is increased.byby OSPOSP isis reduced,reduced, Moreover, andand the thethe bonding inteinteractionraction interaction forceforce isis of increased.increased. SCA can Moreover, eMoreover,ffectively the improvethe bondingbonding the interactioncompatibilityinteraction ofof SCASCA of the cancan two effectivelyeffectively components, improveimprove ensuring thethe compatibilitycompatibility OSP and asphalt ofof thethe are twotwo mixed components,components, to form a ensuringensuring stable system. OSPOSP andTheand reasonasphaltasphalt why areare mixed themixed temperature toto formform aa susceptibility stablestable system.system. of ThTh OSPee reasonreason/SCA composite whywhy thethe temperaturetemperature modified asphalt susceptibilitysusceptibility with direct ofof OSP/SCAmixingOSP/SCA method compositecomposite is better modifiedmodified than surface asphaltasphalt pretreatment withwith directdirect methodmixingmixing methodmethod may due isis to betterbetter the large thanthan specific surfacesurface surface pretreatmentpretreatment area of methodOSP,method which maymay is due easierdue toto to thethe agglomerate largelarge specificspecific under surfacesurface surface areaarea pretreatment ofof OSP,OSP, whichwhich method, isis easiereasier resulting toto agglomerate aagglomerate negative influence underunder surfaceonsurface the dispersion pretreatmentpretreatment and method,method, uniformity resultingresulting of modified aa negativenegative asphalt. influenceinfluence onon thethe dispersiondispersion andand uniformityuniformity ofof modifiedmodifiedThe softeningasphalt.asphalt. point test results of asphalt sample are shown in Figure8. TheThe softeningsoftening pointpoint testtest resultsresults ofof asphaltasphalt samplesample areare shownshown inin FigureFigure 8.8.

Figure 8. Softening point test results of four asphalt samples FigureFigure 8.8. SofteningSoftening pointpoint testtest resultsresults ofof fourfour asphaltasphalt samplessamples It can be seen from Figure8 that the softening point of modified asphalt samples is improved ItIt cancan bebe seenseen fromfrom FigureFigure 88 thatthat thethe softeningsoftening pointpoint ofof modifiedmodified asphaltasphalt samplessamples isis improvedimproved toto to different degrees compared with that of base asphalt. SBS modified asphalt, OSP/SCA composite differentdifferent degreesdegrees comparedcompared withwith thatthat ofof basebase asphalt.asphalt. SBSSBS modifiedmodified asphalt,asphalt, OSP/SCAOSP/SCA compositecomposite modified asphalt with direct mixing method, and OSP/SCA composite modified asphalt with surface modifiedmodified asphaltasphalt withwith directdirect mimixingxing method,method, andand OSP/SCAOSP/SCA compositcompositee modifiedmodified asphaltasphalt withwith surfacesurface pretreatment method are 17.9%, 12.4%, and 9% higher than base asphalt, respectively. This indicates pretreatmentpretreatment methodmethod areare 17.9%,17.9%, 12.4%,12.4%, andand 9%9% higherhigher thanthan basebase asphalt,asphalt, respectively.respectively. ThisThis indicatesindicates that both the polymer modifier and inorganic modifier can effectively improve the high temperature of thatthat bothboth thethe polymerpolymer modifiermodifier andand inorganicinorganic modifiermodifier cancan effectivelyeffectively improveimprove thethe highhigh temperaturetemperature asphalt. The main reason is due to the increase in the proportion of high-molecular-weight compounds ofof asphalt.asphalt. TheThe mainmain reasonreason isis duedue toto thethe incrincreaseease inin thethe proportionproportion ofof high-molecular-weighthigh-molecular-weight and the increase of the interaction between the structures. The softening point of the composite compoundscompounds andand thethe increaseincrease ofof thethe interactioninteraction bebetweentween thethe structures.structures. TheThe softeningsoftening pointpoint ofof thethe modified asphalt is higher than that of the base asphalt partly due to the aging of the asphalt caused by compositecomposite modifiedmodified asphaltasphalt isis higherhigher thanthan thatthat ofof thethe basebase asphaltasphalt partlypartly duedue toto thethe agingaging ofof thethe long-term shearing during the preparation process. asphaltasphalt causedcaused byby long-termlong-term shearingshearing duringduring thethe preparationpreparation process.process. The 10 C ductility test results of asphalt sample are shown in Figure9. TheThe 10°C10°C◦ ductilityductility testtest resultsresults ofof asphaltasphalt samplesample areare shownshown inin FigureFigure 9.9.

Figure 9. 10 ◦C ductility test results of four asphalt samples. FigureFigure 9.9. 10°C10°C ductilityductility testtest resultsresults ofof fourfour asphaltasphalt samples.samples.

Sustainability 2019, 11, 4857 12 of 23

It can be seen from Figure9 that the SBS modified asphalt has the largest ductility, which is beacuse SBS, as a polymer component, absorbs or adsorbs more asphalt, forming a relatively developed three-dimensional network structure in the asphalt. This three-dimensional network structure restrict the flow and sliding deformation of the asphalt molecules and improves the low temperature performance of the asphalt. Whether using the direct mixing method or surface pretreatment method, the ductility of the OSP/SCA composite modified asphalt is less than the base asphalt. This is because the temperature stress is easily concentrated at the interface of two-component at low temperature, thus the low-temperature of OSP/SCA composite modified asphalt is affected. The 10 ◦C ductility of OSP/SCA composite modified asphalt with surface pretreatment method is lower than direct mixing method, which is related to the a agglomerate phenomenon of OSP under surface pretreatment method. The RTFOT aging test results of asphalt sample are shown in Table8.

Table 8. RTFOT aging test results of four asphalt samples.

Unaged Binder RTFO Aged Binder 25 C 10 C 25 C 10 C Materials Weight ◦ ◦ Weight ◦ ◦ Penetration Ductility Penetration Ductility (g) (g) (d-mm) (cm) (d-mm) (cm) BA 34.18 86.9 411 33.91 52.2 234 SMA 34.04 67 554 34.01 46.1 353 OSMA-DM 34.17 72.3 311 34.16 49.0 239 OSMA-SP 34.03 68.4 266 33.86 43.0 189

Table8 shows that the penetration, ductility, and mass of four asphalt samples decreased after the RTFOT aging test. This loss of mass is due to the volatilization of light components after the thermo-oxidative aging of asphalt. The decrease in penetration and ductility indicates that the hardening of asphalt after RTFOT aging test, which is due to the increase of colloid and asphaltene in asphalt. The mass loss rate, 25 ◦C residual penetration ratio, and 10 ◦C residual ductility can reflect the anti-aging ability of asphalt; the smaller the mass loss rate, the greater 25 ◦C residual penetration ratio and 10 ◦C residual ductility, the better the anti-aging performance. After calculation, it is found that all the asphalt modifiers used in this paper can effectively improve the anti-aging ability of asphalt. Among them, OSMA-DM has the lowest mass loss rate and largest residual penetration ratio and residual ductility compared with the other asphalt samples, which indicates that OSMA-DM has the best anti-aging ability among the four kinds of asphalt. This is because the OSP can absorb more asphalt components to form a poly group, and the formed poly group has a thick colloidal interface layer; the long-range interaction between molecules is wide, thereby the formed structure is relatively stable. Meanwhile, the bonding interaction of SCA ensures that the adsorbed asphalt component does not precipitate from the poly group, thereby effectively enhancing the stability of the asphalt and improving the anti-aging property of the asphalt. The reason why the anti-aging property of SMA is worse than that of OSMA-DM is that SBS is a high molecular polymer. The substructure of the polymer is prone to change after thermal oxidation process, while OSP is an inorganic material that is not susceptible to thermal oxidation process.

5.2. Thermogravimetric Analysis Test Results TGA was employed to evaluate the thermal properties of the OSP/SCA composite modified asphalt. Figure 10 presents the thermogravimetric curves of the four asphalt samples. As observed, TGA thermographs relate to particular phases of degradation with distinct initial and final degradation temperatures, and the addition of modifiers changes the distinct initial and final degradation temperatures, which is the result of pyrolysis of the specimen. The TGA of SMA is significantly different from other three kinds of asphalt, especially in the range of 400 to 500 ◦C, the weight loss of Sustainability 2019, 11, 4857 13 of 23 Sustainability 2019, 11, x FOR PEER REVIEW 13 of 24

SMA is faster. This may be due to the rapid cracking and volatilization of the high molecular polymer weight loss of SMA is faster. This may be due to the rapid cracking and volatilization of the high modiﬁer between the temperature range. molecular polymer modifier between the temperature range.

Figure 10. Thermogravimetric curves of the four asphalt samples. Figure 10. Thermogravimetric curves of the four asphalt samples. From TGA curves of all the asphalt samples, the following parameters were calculated for further From TGA curves of all the asphalt samples, the following parameters were calculated for comprehension of the thermal properties of OSP/SCA composite modiﬁed asphalt. (1) Start of thermal further comprehension of the thermal properties of OSP/SCA composite modified asphalt. (1) Start degradation (temperature at 90% weight loss) (Ts, ◦C), (2) peak temperature (temperature at 50% of thermal degradation (temperature at 90% weight loss) (Ts, °C), (2) peak temperature (temperature weight loss) (Tp, ◦C), and (3) residual mass (Me, %). Table9 present a summary of the TGA test at 50% weight loss) (Tp, °C), and (3) residual mass (Me, %). Table 9 present a summary of the TGA parameters of asphalt samples. test parameters of asphalt samples. Table 9. TGA test parameters of of four asphalt samples. Table 9. TGA test parameters of of four asphalt samples. Types Ts/◦C Tp/◦C Me/% Types Ts / °C Tp / °C Me / % BA 329.2 453.0 16.1 BA 329.2 453.0 16.1 SMA 324.0 446.5 15.9 OSMA-DMSMA 324.0 326.4 446.5 457.7 15.9 20 OSMA-DMOSMA-SM 326.4 309.1 457.7 453.8 14.2 20 OSMA-SM 309.1 453.8 14.2

AsAs shown shown in in Table Table 99,, thethe TsTs valuesvalues ofof BA,BA, SMA,SMA, andand OSMA-DMOSMA-DM areare approximate,approximate, butbut thethe Ts valuevalue of of OSMA-SP OSMA-SP is is lower lower than than that that of of the the other other th threeree kinds kinds of of asphalt, asphalt, which which indicates indicates that that the the OSP OSP with surface surface pretreatment pretreatment of of SCA SCA is ispoorly poorly dispersed dispersed in inthe the asphal asphalt.t. The TheTp value Tp value of OSMA-DM of OSMA-DM was increasedwas increased by 4.7 by °C 4.7 compared◦C compared with with BA, BA, and and the the Me Me value value of of OSMA-DM OSMA-DM was was increased increased by by 24% 24% comparedcompared with with BA, BA, indicating indicating that that the the high high temper temperatureature stability stability of of the the as asphaltphalt is is improved improved under under thethe composite composite modification modification of of OSP OSP and and SCA SCA and and the the high high temperature cracking cracking of of the the asphalt asphalt is is effectivelyeffectively suppressed. suppressed. OSMA-DM OSMA-DM has has obvious obvious impr improvementovement in Ts, in Tp, Ts, and Tp, Me and compared Me compared with SMA with andSMA OSMA-SP, and OSMA-SP, thus thusindicating indicating OSMA-DM OSMA-DM with with better better thermal thermal property, property, and and OSP OSP has has higher higher dispersibilitydispersibility and and thermal thermal stability in OSP/SCA OSP/SCA composite modified modified asphalt.

5.3.5.3. Fourier Fourier Transform Transform Infrared Spectroscopy Test ResultsResults BitumenBitumen is is a a mixture of substanc substanceses with different different molecular size sizes,s, chemical compositions, and and structures.structures. The The properties properties of of modified modified asphalt asphalt are are determined determined by by the the nature nature of of asphalt asphalt and and modifier modifier andand the the interaction interaction between between the the two. two. At At present, present, the the modification modification mechanis mechanismm between between modifier modifier and and asphaltasphalt is is generally generally divided divided into into physical physical blending blending modification modification and and chemical chemical blending blending modification. modification. TheThe physical blending blending modification modification means means that that th thee modifier modifier is is swelled swelled and and dissolved dissolved by by the the action ofof aromatic aromatic hydrocarbons hydrocarbons and and saturated saturated hydrocarbon, hydrocarbon, and and uniformly uniformly dispersed dispersed in the in asphalt the asphalt to form to aform blend a blendsystem system during during the preparation the preparation process. process. Furthermore, Furthermore, there is thereno chemical is no chemical reaction reactionand the formationand the formation of related of relatedchemical chemical bonds bonds during during the thepreparation preparation process. process. The The chemical chemical blending blending modification refers to a chemical reaction between modifier and bitumen, which produces chemical cross-linking, chemical addition, or chemical bonds. The Fourier transform infrared spectroscopy test

Sustainability 2019, 11, 4857 14 of 23 Sustainability 2019, 11, x FOR PEER REVIEW 14 of 24 modificationwas employed refers to explore to a chemical the modification reaction between mechan modifierism of OSP/SCA and bitumen, composit whiche modified produces asphalt. chemical For cross-linking,the comprehension chemical of FTIR addition, spectra, or chemicalthe whole bonds. range is The generally Fourier divided transform into infrared two regions spectroscopy of 4000– test1300cm was− employed1 and 1300–600cm to explore−1. The the peak modification emerged mechanism at 4000–1300cm of OSP−1 is/SCA an absorption composite band modified generated asphalt. by Forstretching the comprehension vibration. Since of FTIRthe characteristic spectra, the wholeabsorption range peak is generally of the group divided is usually into two located regions in this of 1 1 1 4000–1300high frequency cm− region,and 1300–600 and the cmabsorption− . The peakpeak emergedis parsley atdistributed 4000–1300 in cm this− region,is an absorption this region bandis the generatedmost valuable by stretching region for vibration.identifying Since the functional the characteristic group, which absorption is called peak the functional of the group group is usually region. locatedIn the region in this highof 1300 frequency to 600cm region,−1, in and addition the absorption to the stretching peak is parsley vibration distributed of single in bond, this region, there this are regioncomplex is thespectra most valuablegenerated region by deformation for identifying vibration. the functional When group,the molecular which is calledstructure the functionalis slightly 1 groupdifferent, region. there In is the a slight region difference of 1300 to in 600 the cm absorp− , intion addition peaks to in the this stretching region. This vibration phenomenon of single bond,is like therethat each are complex person spectrahas a different generated fingerprint, by deformation so this vibration. region is Whennamed the the molecular fingerprint structure region. is Analysis slightly diofff erent,FTIR therespectra is agenerally slight diff erencerequires in searching the absorption for the peaks characteristic in this region. stretching This phenomenon vibration isof likethe thatfunctional each person group has in a ditheff erentfunction fingerprint,al group so region, this region and is further named theconfirming fingerprint the region. existence Analysis of the of FTIRfunctional spectra group generally and the requires combination searching with for other the characteristicfunctional group stretching according vibration to the ofabsorption the functional peaks groupin the fingerprint in the functional region. group The correspondence region, and further betwee confirmingn representative the existence chemical of thebonds functional of asphalt group and andFTIR the spectra combination peak position with other is shown functional in Table group 10 [46] according. to the absorption peaks in the fingerprint region. The correspondence between representative chemical bonds of asphalt and FTIR spectra peak position is shown in Table 10Table[46]. 10. Featured chemical bonds of asphalt binder. Wave Number Table 10. Featured chemical bondsChemical of asphalt Bonds binder. (cm−1) 1 The antisymmetric stretchingChemical vibration Bonds absorption band of the alkyl (C– Wave2924 Number (cm− ) 2924 The antisymmetric stretching vibrationH) absorption band of the alkyl (C–H) 28522852 The The symmetric symmetric stretching stretching vibration vibration absorptionabsorption band band of of the the alkyl alkyl (C–H) (C–H) 27292729 Extensible Extensible vibration vibration ofof aldehyde aldehyde groups groups 16711671 The The C=O C= Ostretching stretching vibration vibration ofof primaryprimary amide amide carbonyl carbonyl 16001600 Conjugated Conjugated double double bonds bonds (C=C) (C=C) stretchingstretching vibration vibration in aromaticsin aromatics 1456 The C–H asymmetric deformations in CH2 and CH3 vibrations 1456 The C–H asymmetric deformations in CH2 and CH3 vibrations 1377 The C–H symmetric deformation in CH3 vibrations 13771250 The The C–H C–O symmetric stretching vibrationdeformation in saturated in CH3 alcoholsvibrations 12501031 The TheC–O sulfoxide stretching group vibratio (S=O)n stretching in saturated vibration alcohols 1031966 The C–HThe out-plane sulfoxide bending group vibrations (S=O) stretching in unsaturated vibration hydrocarbons 966868 The C–H out-plane Benzene bending ring vibratio stretchingns in vibration unsaturated hydrocarbons 747 Bending vibration of aromatic branches 868 Benzene ring stretching vibration 747 Bending vibration of aromatic branches The FTIR spectra of the BA, SMA, OSMA-SP, and OSMA-DM are given in Figures 11–14. The FTIR spectra of the BA, SMA, OSMA-SP, and OSMA-DM are given in Figures 11–14.

Figure 11. FTIR spectra of BA. Figure 11. FTIR spectra of BA.

Sustainability 2019, 11, x FOR PEER REVIEW 15 of 24 SustainabilitySustainability2019 2019, ,11 11,, 4857 x FOR PEER REVIEW 1515 ofof 2324 Sustainability 2019, 11, x FOR PEER REVIEW 15 of 24

Figure 12. FTIR spectra of SMA. FigureFigure 12.12.FTIR FTIR spectraspectra ofof SMA.SMA. Figure 12. FTIR spectra of SMA.

FigureFigure 13.13. FTIRFTIR spectraspectra ofof OSMA-SP.OSMA-SP. Figure 13. FTIR spectra of OSMA-SP. Figure 13. FTIR spectra of OSMA-SP.

Figure 14. FTIR spectra of OSMA-DM. Figure 14. FTIR spectra of OSMA-DM. 1 From the FTIR spectrum ofFigure BA, it 14. can FTIR be seenspectra that of OSMA-DM. the strong absorption peaks at 2918 cm− From the1 FTIR spectrum of BA, it can be seen that the strong absorption peaks at 2918 cm−1 and and 2851 cm− are the asymmetricFigure and 14. symmetric FTIR spectra stretching of OSMA-DM. vibration absorption bands of C–H From−1 the FTIR spectrum of BA, it can be seen that the strong absorption peaks at 2918 cm−1 and in2851 aliphatics cm are (mainly the asymmetric alkanes and and naphthenes), symmetric respectively,stretching vibration and the peakabsorption at 1600 bands cm 1 isof the C–H C–C in −1 − −1 aliphatics2851 Fromcm (mainlytheare FTIRthe alkanesasymmetric spectrum and of andnaphthenes),BA, itsymmetric can be seenrespectively, stretching that the1 strong vibrationand the absorption peakabsorption1 at peaks1600 bands cmat 2918−1 isof cmtheC–H C–C and in stretching vibration in aromatics. The peaks at 1458 cm− and 1375 cm− are the in-plane bending aliphatics2851 cm−1 (mainlyare the alkanesasymmetric and andnaphthenes), symmetric respectively, stretching−1 vibrationand the peakabsorption−1 at 1600 bands cm−1 isof theC–H C–C in vibrationstretching absorption vibration peaksin aromatics. of C–H The in aliphatics, peaks at the1458 peak cm at and 1032 1375 cm 1cmis the are sulfoxide the in-plane group bending (S=O) −1 − −1 −1 stretchingvibrationaliphatics absorption(mainlyvibration alkanes inpeaks aromatics. ofand C–H naphthenes), The in aliphatics, peaks atrespectively, 1458the peak cm atand and 1032 1375 the cm −cmpeak1 is the areat sulfoxide 1600the in-plane cm group is1 thebending (S=O) C–C stretching vibration, and the four small absorption peaks in the range of 863 to 724 cm− are the vibrationstretching absorption vibration inpeaks aromatics. of C–H The in aliphatics, peaks at 1458the peak cm− 1at and 1032 1375 cm −cm1 is− 1the are sulfoxide the in-plane− 1group bending (S=O) out-of-planestretching vibration, bending vibrationsand the four of C–Hsmall on absorption aromatic benzenepeaks in rings.the range Thus, of asphalt 863 to 724 is mainly cm are composed the out- stretchingvibration absorptionvibration, andpeaks the of four C–H small in aliphatics, absorption the peaks peak in at the 1032 range cm− 1of is 863 the to sulfoxide 724 cm− 1group are the (S=O) out- ofof-plane saturated bending hydrocarbons, vibrations aromatics, of C–H on aliphatics aromatic and benzene heteroatom rings. Thus, derivatives. asphalt is mainly composed of of-planestretching bending vibration, vibrations and the of four C–H small on aromatic absorption benzene peaks rings.in the Thus, range asphalt of 863 tois mainly724 cm −composed1 are the out- of saturatedThe FTIR hydrocarbons, spectra of aromatics, SMA is similar aliphatics to thatand heteroatom of BA, it has derivatives. a strong absorption peak around saturatedof-planeThe bendingFTIR hydrocarbons,1 spectra vibrations of aromatics,SMA of isC–H similar aliphaticson aromatic to that and of benzene heteroatomBA, it has rings. a derivatives.strong Thus, absorptionasphalt is mainly peak around composed 2800– of 2800–3000 cm− and the peak position is also basically the same as that of BA. In the functional 3000saturated Thecm−1 FTIR andhydrocarbons, the spectra peak ofposition aromatics,SMA is is similaralso aliphatics basically to that and the of BA,heteroatomsame it ashas that a strongderivatives. of BA. absorptionIn the functional peak aroundgroup region, 2800–1 group region, It can be seen from FTIR spectra of SMA that a absorption peak emerged at 2360.67 cm− , 3000 cmThe−1 FTIRand the spectra peak ofposition SMA isis similaralso basically to that the of BA,same it as has that a strongof BA. Inabsorption the functional peak −grouparound1 region, 2800– whichIt can maybe seen bedue from to FTIR the inﬁltration spectra of of SMA carbon that dioxide a absorption during peak the preparation emerged at of 2360.67 SMA. Incm the, ﬁngerprintwhich may It3000 can cm be− 1seen and fromthe peak FTIR position spectra is of also SMA basically that a absorptionthe same as peak that ofemerged BA. In the at 2360.67 functional cm −group1, which region, may It can be seen from FTIR spectra of SMA that a absorption peak emerged at 2360.67 cm−1, which may

Sustainability 2019, 11, 4857 16 of 23

1 1 1 region, two peaks emerged at 744.47 cm− and 1029.91 cm− . The peak at 1029.91 cm− is the blending vibration of C–H in RCH=CH2, indicating the RCH=CH2 structure in both styrene and butadiene of SBS. 1 Peak at 744.47 cm− is the blending vibration of aromatic branches. It can be seen that the incorporation of SBS does not change the chemical structure unit of itself and the asphalt, the modification mechanism of SMA is mainly physical blending modification. The FTIR spectra of OSMA-SP and OSMA-DM are approximately the same. Strong absorption 1 peaks emerged around 2800–3000 cm− are the C–H vibration of cycloalkane and alkane. Among 1 1 them, the absorption peak of -CH2- is the strongest, and the peaks at 2921 cm− and 2851 cm− are stretching vibration of -CH2-. Different from the base asphalt, OSMA-SP and OSMA-DM have a 1 strong absorption peak at 3675.41 cm− in the functional group region, and the peak represents an O–H vibration of the carboxyl group. This indicates that there is a new chemical bond formation in the OSMA-SP and OSMA-DM due to the graft reaction of SCA with OSP. In the fingerprint region, 1 it was found that a new absorption peak was emerged at 1056.35 cm− in the FTIR spectra of OSMA-SP and OSMA-DM. The peak is vibration of sulfoxide group (S=O), and sulfoxide group is generally considered to be an important indicator to evaluate the aging of asphalt, which indicates that there is some thermo-oxidative aging caused by long-term shearing has occurred during the modification process of OSMA-SP and OSMA-DM.. The chemical reaction of the modifier with asphalt causes the appearance of new functional groups and the change of peak height and peak area of absorption peak. In order to quantitatively analyze the modification mechanism of three modified asphalt samples, the peak height and peak area of main functional groups of the four asphalts were statistically analyzed through ORIGIN software, as shown in Tables 11 and 12.

Table 11. The main peak area of four asphalt samples (cm).

Functional Group Region Fingerprint Region Types 1 1 1 1 1 1 3675.4 cm− 2852 cm− 2360.7 cm− 1456.2 cm− 1056.3 cm− 1029.91 cm− BA N/A 17.729 0.114 5.960 N/AN/A SMA N/A 20.129 1.749 6.328 N/A 0.228 OSMA-SP 0.895 17.670 3.742 5.248 2.301 N/A OSMA-DM 1.150 22.694 3.032 7.019 3.320 N/A

Table 12. The main peak height of four asphalt samples (cm).

Functional Group Region Fingerprint Region Types 1 1 1 1 1 1 3675.4 cm− 2852 cm− 2360.7 cm− 1456.2 cm− 1056.3 cm− 1029.91 cm− BA N/A 0.3941 0.0072 0.1603 N/AN/A SMA N/A 0.4617 0.0372 0.1707 N/A 0.0082 OSMA-SP 0.0225 0.4 0.0799 0.1461 0.0311 N/A OSMA-DM 0.0291 0.4924 0.0672 0.1991 0.0392 N/A

It can be seen from Tables 11 and 12 that the peak area and peak height of OSMA-DM are much 1 larger than OSMA-SP at 3675.4 cm− , which indicates that more chemical bonds are generated in the OSMA-DM and SCA reacts more adequately with OSP. This conclusion is also consistent with the results of conventional physical property test. The peak height and peak area of SMA, OSMA-SP and 1 OSMA-DM at 2360.7 cm− are much higher than that of BA. Due to the consistency of the experimental environment, only the infiltration of carbon dioxide during the preparation of modified asphalt can explain this phenomenon. The peak area and peak height of SMA and BA are slightly different at 1 1 2852 cm− and 1456.2 cm− , but the difference is not large, which indicates that the modification mechanism of SMA is mainly based on physical blending modification, but there is also certain chemical blending modification. Sustainability 2019, 11, 4857 17 of 23 Sustainability 2019, 11, x FOR PEER REVIEW 17 of 24

5.4. Differential Differential Scanning Calorimetry Test ResultsResults The thermalthermal e ffeffectect of asphaltof asphalt during during temperature temper changeature change can be measuredcan be measured by DSC. The by microscopic DSC. The changesmicroscopic of the changes regate of structure the regate in asphalt structure can in be as characterizedphalt can be characterized through the endothermic through the peakendothermic position andpeak heat position absorption and heat of theabsorption DSC spectrum; of the DSC thus, spectrum; the temperature thus, the stabilitytemperature of asphalt stability can of be asphalt evaluated can andbe evaluated the modification and the modification mechanism can mechanism be speculated. can be The speculated. DSC spectrum The DSC of fourspectrum asphalt of four samples asphalt are shownsamples in are Figure shown 15. in Figure 15.

Figure 15. DSC spectrum of four asphalt samples. Figure 15. DSC spectrum of four asphalt samples. As can be seen from Figure 15, the DSC spectra of the four asphalt samples are equivalent, but thereAs canare be di seenfferences from in Figure some 15, endothermic the DSC spectra peak positionsof the four and asphalt heat absorption.samples are Theequivalent, DSC curve but ofthere OSMA-DM are differences is flatter in thansome the endothermic other three peak types positions of asphalt, and and heat the absorption. endothermic The peak DSC is relativelycurve of small.OSMA-DM This indicatesis flatter thatthan the the thermal other three stability types of OSMA-DM of asphalt, isand better the thanendothermic that of the peak other is three relatively types ofsmall. asphalt, This indicates which is that consistent the thermal with stability the conclusions of OSMA-DM of TGA is test.better As than the that temperature of the other changes, three types the asphaltof asphalt, has which three states—glassyis consistent with state, the viscoelastic conclusions state, of TGA and viscoustest. As flowthe temperature state—and the changes, change the of stateasphalt is causedhas three by states—glassy the change of regatestate, viscoelastic structure with state, temperature. and viscous When flow thestate—and temperature the change is above of state is caused by the change of regate structure with temperature. When the temperature is above 80 ◦C, The DSC curve of modified and unmodified asphalt has almost no endothermic peak, which indicates80°C, The that DSC most curve components of modified of asphaltand unmodified have completed asphalt the has transition almost no from endothermic the viscoelastic peak, state which to indicates that most components of asphalt have completed the transition from the viscoelastic state the viscous state at 80 ◦C. The DSC spectrum also indicates that the asphalt is in an endothermic or to the viscous state at 80°C. The DSC spectrum also indicates that the asphalt is in an endothermic or exothermic instability stage at 15 ◦C, 25 ◦C, and 30 ◦C, which is also the evolution process of regate structure,exothermic thus instability the penetration stage at test15°C, is greatly25°C, and affected 30°C, with which temperature is also the under evolution this temperature process of regate range. structure,The phase thus the of asphaltpenetration changes test is with greatly increasing affected temperature with temperature and it appearsunder this as temperature a peak on the range. DSC curve.The Two phase main of parametersasphalt changes can bewith obtained increasing on the temperature DSC curve, and one it appears is the heat as absorptiona peak on the during DSC regatecurve. Two structure main transformation, parameters can andbe obtained the other on is th thee DSC temperature curve, one range is the at heat which absorption regate structure during transformationregate structure occurs. transformation, The endothermic and the peak other data is of the modified temperature and unmodified range at asphaltwhich regate are summarized structure intransformation Table 13. occurs. The endothermic peak data of modified and unmodified asphalt are summarized in Table 13. Table 13. Endothermic peak data of four asphalt samples. Table 13. Endothermic peak data of four asphalt samples. Interval Heat Absorption Total Heat Types Number of Peaks Interval Heat Absorption Absorption (J/g) Number of Temperature Range (◦C) Heat Absorption (J/g) Total Heat Types Temperature4.10 C–41.98 Range CHeat Absorption 3.9782 BAPeaks 2 ◦ ◦ Absorption5.9325 (J/g) 41.98(°C) ◦C–46.92 ◦C(J/g) 1.9543 4.10°C–41.98°C 3.9782 BASMA 2 1 40.34 ◦C–46.29 ◦C 1.85365.9325 1.8536 41.98°C–46.92°C 1.9543 OSMA-SM 1 41.53 ◦C–48.83 ◦C 0.9805 0.9805 SMA 1 40.34°C–46.29°C 1.8536 1.8536 3.19 C–42.00 C 1.9718 OSMA-DMOSMA- 2 ◦ ◦ 3.8063 1 41.53°C–48.83°C42.00 ◦C–49.66 ◦C0.9805 1.8345 0.9805 SM OSMA- 3.19°C–42.00°C 1.9718 2 3.8063 DMThe heat absorption reflects42.00°C–49.66°C the amount of transformed 1.8345 regate structure and the ratio of solid and liquid composition in the asphalt. The smaller the heat absorption, the smaller the amount of solid–liquidThe heat conversion absorption in reflects the asphalt the amount and more of tran stablesformed the properties. regate structure Table 13 and shows the ratio that theof solid total and liquid composition in the asphalt. The smaller the heat absorption, the smaller the amount of solid–liquid conversion in the asphalt and more stable the properties. Table 13 shows that the total

Sustainability 2019, 11, 4857 18 of 23 heat absorption of modified asphalt is reduced compared with base asphalt, which indicates that the modification process is not only a process of physical blending of two materials, but also an improvement and reinforcement of the properties of the asphalt. SCA and OSP change the large endothermic peak of base asphalt to a small endothermic peak; the DSC curve becomes relatively flat and the peak width becomes relatively narrow. This illustrates that the form and quantity of crystalline component and the transformation of components in the bitumen are changed through the incorporation of OSP and SCA. Meanwhile, the melting temperature of some components is changed, and the temperature stability and temperature susceptibility of asphalt is improved.

5.5. Pavement Performance Test Results The pavement performance test results are shown in Table 14.

Table 14. Pavement performance test results of asphalt mixtures.

Test Item Evolution Index OGFC SMA-OGFC ORF/SCA-OGFC Marshall stability test Marshall stability/KN 6.47 9.12 7.26 Wheel tracking test Dynamic stability/n/min 3340 5250 3897 15 C splitting test Splitting strength/(MPa) 2.74 3.87 3.24 − ◦ Bending tensile strength/(MPa) 5.202 7.465 5.920 10 C beam-bending test Maximum bending Strain/(µε) 2886 4155 3122 − ◦ Bending Stiﬀness Modulus/(MPa) 1802 1796 1896 Immersion Marshall test Immersion Marshall stability/(KN) 5.73 8.21 6.4 Spring-thawing stability test Spring-thawing stability/(KN) 5.84 8.16 6.73 Standard Cantabro test Cantabro losses/(%) 17.4 14.2 16.8 Constant head permeability test Permeability coeﬃcient/(cm/s) 0.19 0.28 0.22

Table 14 shows that the high-temperature properties of the asphalt mixture are improved after the incorporation of modifier. The specification requires that the Marshall stability of OGFC should be greater than 5 KN and dynamic stability be greater than 3000 n/mm; all three asphalt mixtures meet the specifications. The Marshall stability and dynamic stability of ORF/SCA-OGFC increased by 12.2% and 16.6%, respectively, compared to OGFC, demonstrating that OSP/SCA composite modified asphalt can effectively improve the high-temperature performance of OGFC. OGFC is a skeleton structure with a large porosity. In high temperature environments, once the asphalt mortar does not provide sufficient constraints and restrictions on the skeletal structure, it will cause permanent deformation of pavement. As a kind of high viscosity modified asphalt, SBS modified asphalt can effectively increase the adhesion between asphalt and aggregate, effectively limit the relative movement between aggregates, thus, SMA-OGFC has obvious improvement in high temperature mechanical properties, especially rutting resistance. The enhancement mechanism of of high-temperature mechanical properties of SMA-OGFC and ORF/SCA-OGFC is different. The main difference is that there is a certain chemical adsorption between OSP/SCA composite modified asphalt and aggregate. The SCA in OSP/SCA composite modified asphalt has a silicon functional group and an organic group, and the silicon functional group can react with the hydroxyl group on the surface of aggregate to form a chemical bond; the organic group can react with asphalt to achieve chemical bonding, thereby the two materials of very different properties of asphalt and aggregate are “coupled” by chemical bonds, and the chemical bonding reaction is confirmed by FTIR test in the Section 5.3. It can be seen from the 15 C splitting test and 10 C beam-bending test that the splitting − ◦ − ◦ strength and bending tensile strength of ORF/SCA-OGFC increased by 18.2% and 13.8%, respectively, compared with OGFC. This illustrates that ORF/SCA composite modified asphalt can effectively improve the low-temperature mechanical properties of OGFC. The improvement of low-temperature mechanical properties of SMA-OGFC is greater than that of ORF/SCA-OGFC. This is because OSP is an inorganic material, which is very different from the low temperature modulus of asphalt. At low Sustainability 2019, 11, 4857 19 of 23 temperature, the stress is prone to generate at the interface of two-phase (OSP-asphalt) to form a shear band, which results in a relatively small improvement in low-temperature mechanical properties of ORF/SCA-OGFC. The immersion Marshall test, spring-thawing stability test, and Cantabro Test results reveal that ORF/SCA composite modified asphalt can effectively improve the moisture damage and raveling resistance of OGFC. The immersion Marshall stability and spring-thawing stability of ORF/SCA-OGFC was 4.7% and 12.2% higher than OGFC, respectively; Cantabro losses of ORE/SCA-OGFC is 5.3% smaller than OGFC. The greater Cantabro losses indicates that the worse raveling resistance. The main reason for this is that the OSP has a special microscopic structure such as porous and large specific surface. The OSP can absorb the light weight component with less molecular weight in the asphalt, and form a series of complex interactions with asphalt, such as dispersion, superfolding, embedding, and cross-linking, which enhances the aggregate–bitumen interface bond strength and improve the mechanical structure of OGFC. Moreover, the bonding reaction of SCA at aggregate–bitumen interface is also a reason for reinforcement of mechanical properties. The permeability coefficients of OGFC, SMA-OGFC, and ORF/SCA-OGFC are 0.19 cm/s, 0.28 cm/s, and 0.22 cm/s, according to the constant head permeability test. It is well known that asphalt–aggregate ratio plays a key role in permeability performance of OGFC when the gradation is consistent. The lower the asphalt–aggregate ratio, the better the permeability performance. The permeability test results of three asphalt mixtures also confirmed this regular pattern. In conclusion, the ORF/SCA composite modified asphalt can effectively improve the overall performance of the OGFC, although the improvement is not as good as the SBS modified asphalt, but the ORF/SCA composite modified asphalt has a strong advantage in reducing the construction cost, protecting the environment, and recycling solid waste.

5.6. Economic and Environmental Analysis In this section, the economic and environmental analysis of SMA-OGFC and ORF/SCA-OGFC mixture in improving properties is conducted compared normal OGFC mixture. The price ratio PR and performance improvement ration PIR can be calculated by the following equation. The results are listed in Table 15. PR = Pm/POGFC

PIR = PIm/PIOGFC where Pm and PIm are the price and properties of SBS-OGFC and SM-OGFC, respecitvely, and POGFC and PIOGFC are the price and properties of the normal OGFC mixture [47]. It should be noted that when referring to the marked price in China, the prices of unmodified asphalt binder, SBS and silane coupling agent are 4 CNY/kg, 15 CNY/kg and 6 CNY/kg, respectively. The average price of OGFC-16 unmodified asphalt mixture is 0.380 CNY/kg. It can be calculated that the price of graded broken stone of OGFC-16 is 0.1975 CNY/kg. At present, oil shale waste is generally deposited on open space due to no post-procedure of oil shale waste in China, so the environmental protection costs by waste accumulation cannot be accurately calculated. Therefore, the resettlement fee for construction waste is defined as the environmental protection costs of oil shale waste, and the price is ~10 CNY/kg. Since in the three asphalt mixtures only ORF/SCA-OGFC can consume oil shale waste, the environmental protection costs should be deducted for the mixture price of ORF/SCA-OGFC, and the environmental protection costs for 100 kg ORF/SCA-OGFC asphalt mixture is 2.76 CNY. Sustainability 2019, 11, 4857 20 of 23

Table 15. Economic and environmental beneﬁt analysis.

Marshall Dynamic Bending Cantabro Immersion Permeability Asphalt Mixture –15 C Splitting Spring-Thawing Mixture Type Stability STABILITY ◦ Tensile Losses Marshall Coeﬃcient Price Price Strength (Mpa) Stability (kn) (kn) (n/min) Strength (Mpa) (%) Stability (kn) (cm/s) (CNH/kg) (CNH/kg) SMA-OGFC 9.12 5250 3.87 7.465 14.2 8.21 8.16 0.28 4.64 0.384 ORF/SCA-OGFC 7.26 3897 3.24 5.920 16.8 6.4 6.73 0.22 4.04 0.347 OGFC 6.47 3340 2.74 5.202 17.4 5.73 5.84 0.19 4.00 0.380 PIR and SMA-OGFC 1.41 1.57 1.41 1.44 0.81 1.43 1.40 1.47 1.16 1.01 PRSMA-OGFC PIRORF/SCA-OGFC and 1.12 1.17 1.18 1.14 0.96 1.12 1.15 1.16 1.01 0.91 PRORF/SCA-OGFC Sustainability 2019, 11, 4857 21 of 23

As shown in Table 15, the ORF/SCA composite modiﬁed asphalt improved the overall performance of the OGFC by ~10% compared with normal OGFC. Although there is a certain gap between the increase of OFR/SCA-OGFC and SBS-OGFC, the price of ORF-OGFC is lower than that of SMA-OGFC, and OFR/SCA-OGFC played an important role in reducing the cost compared with high-priced modiﬁed asphalt, especially in protecting the environment and enriching the utilization ways of oil shale waste

6. Conclusions In this paper, the pavement performance and modiﬁcation mechanism of oil shale waste powder, silane coupling agent composite modiﬁed asphalt, and asphalt mixture was systematically investigated according to conventional physical property tests: TGA test, FTIR test, DSC test, DSR test, and pavement performance test. The main conclusions are as follows.

1. The conventional physical properties test results illustrated that OSP/SCA composite modified asphalt prepared by surface pretreatment method or direct mixing method has good low-temperature properties, high-temperature properties, temperature susceptibility, and anti-aging properties. The direct mixing method is more effective than surface pretreatment method for the modification of composite modification of asphalt. 2. The TGA test results manifests that OSP/SCA composite modified asphalt has better thermal properties. Moreover, OSP/SCA composite modified asphalt with direct mixing method has better high temperature stability than surface pretreatment method, and OSP has higher dispersibility and thermal stability in composite modified asphalt. 3. The FTIR test, DSC test were carried to explore the modification mechanism of OSP/SCA composite modified asphalt. The test results indicated that the modification mechanism of OSP/SCA composite modified asphalt is not only physical blending modification but also a certain chemical blending modification. The incorporation of OSP and SCA creates new chemical bonds, and changes the form and quantity of the crystalline component and the transformation of components in the bitumen. 4. Through the pavement performance test, it was found that the OSP/SCA composite modified asphalt can effectively improve the overall performance of the OGFC. The main reason for this is that the OSP has a special microscopic structure such as porous and large specific surface. The OSP can absorb the lightweight component with less molecular weight in the asphalt, which enhances the aggregate–bitumen interface bond strength and improve the mechanical structure of OGFC. Moreover, the bonding reaction of SCA at aggregate–bitumen interface is also a reason for reinforcement of mechanical properties.

Author Contributions: Conceptualization, W.G.; Data curation, Y.S.L. and Z.L.; Formal analysis, X.C. and Z.L.; Funding acquisition, X.D.G.; Investigation, X.C.; Methodology, X.C.; Project administration, X.D.G. and W.G.; Writing—original draft, X.D.G., X.C., and Y.S.L.; Writing—review & editing, W.G. Funding: This research was funded by the National Nature Science Foundation of China (NSFC) (Grant No. 51178204). Conﬂicts of Interest: The authors declare no conﬂicts of interest.

References

1. Yuan, J.; Wang, J.Y.; Xiao, F.P.; Amirkhanian, S.; Wang, J.; Xu, Z.Z. Impacts of multiple-polymer components on high temperature performance characteristics of airfield modified binders. Constr. Build. Mater. 2017, 134, 694–702. [CrossRef] 2. Özen, H.; Aksoy, A.; Tayfur, S.; Çelik, F. Laboratory performance comparison of the elastomer-modified asphalt mixtures. Build. Environ. 2008, 43, 1270–1277. [CrossRef] 3. Pasetto, M.; Baldo, N. Unified approach to fatigue study of high performance recycled asphalt concretes. Mater. Struct. 2017, 50, 113. [CrossRef] Sustainability 2019, 11, 4857 22 of 23

4. Guo, W.; Guo, X.D.; Chang, M.Y.; Dai, W.T. Evaluating the effect of hydrophobic nanosilica on the viscoelasticity property of asphalt and asphalt mixture. Materials 2018, 11, 2328. [CrossRef] 5. Rath, P.; Love, J.E.; Buttlar, W.G.; Reis, H. Performance analysis of asphalt mixtures modified with ground tire rubber modifiers and recycled materials. Sustainability 2019, 11, 1792. [CrossRef] 6. Arafat, S.; Kumar, N.; Wasiuddin, N.M.; Owhe, E.O.; Lynam, J.G. Sustainable lignin to enhance asphalt binder oxidative aging properties and mix properties. J. Clean. Prod. 2019, 217, 456–468. [CrossRef] 7. Vahidi, S.; Mogawer, W.S.; Booshehrian, A. Effects of GTR and treated GTR on asphalt binder and high-RAP mixtures materials. J. Mater. Civ. Eng. 2014, 26, 721–727. [CrossRef] 8. Swamy, A.K.; Mitchell, L.F.; Hall, S.J.; Daniel, J.S. Impact of RAP on volumetrics, stiffness, strength, and low-temperature properties of HMA. J. Mater. Civ. Eng. 2011, 23, 1490–1497. [CrossRef] 9. Fang, C.; Wu, C.; Hu, J.; Yu, R.; Zhang, Z.; Nie, L. Pavement properties of asphalt modified with packaging-waste polyethylene. J. Vinyl Addit. Technol. 2014, 20, 31–35. [CrossRef] 10. Hassana, N.A.; Airey, G.D.; Jaya, R.P.; Mashros, N.; Aziz, M.M.A. A review of crumb rubber modification in dry mixed rubberised asphalt mixtures. J. Teknologi 2014, 4, 127–134. 11. Brasileiro, L.; Moreno-Navarro, F.; Tauste-Martinez, R.; Matos, J.; Rubio-Gámez, M.D.C. Reclaimed polymers as asphalt binder modifiers for more sustainable roads: A review. Sustainability 2019, 11, 646. [CrossRef] 12. Rashad, A.M. A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials. Int. J. Sustain. Built Environ. 2016, 5, 46–82. [CrossRef] 13. Appiah, J.K.; Berko-Boateng, V.N.; Tagbor, T.A. Use of Waste Plastic Materials for Road Construction in Ghana. Case Stud. Constr. Mater. 2017, 6, 1–7. [CrossRef] 14. Chen, M.-Z.; Lin, J.-T.; Wu, S.-P.; Liu, C.-H. Utilization of recycled brick powder as alternative filler in asphalt mixture. Constr. Build. Mater. 2011, 25, 1532–1536. [CrossRef] 15. Lastra-González, P.; Calzada-Pérez, M.A.; Castro-Fresno, D.; Vega-Zamanillo, Á.; Indacoechea-Vega, I. Comparative analysis of the performance of asphalt concretes modified by dry way with polymeric waste. Constr. Build. Mater. 2016, 112, 1133–1140. [CrossRef] 16. Cao, W. Study on properties of recycled tire rubber modified asphalt mixtures using dry process. Constr. Build. Mater. 2016, 21, 1011–1015. [CrossRef] 17. Modarres, A.; Hamedi, H. Effect of waste plastic bottles on the stiffness and fatigue properties of modified asphalt mixes. Mater. Des. 2014, 61, 8–15. [CrossRef] 18. Hu, J.; Fang, C.; Zhou, S.; Jiao, L.; Zhang, M.; Wu, D. Rheological properties of packaging-waste- polyethylene-modified asphalt. J. Vinyl Addit. Technol. 2014, 21, 215–219. [CrossRef] 19. Cai, J.; Song, C.; Zhou, B.C.; Tian, Y.; Li, R.; Zhang, J.; Pei, J. Investigation on high-viscosity asphalt binder for permeable asphalt concrete with waste materials. J. Clean. Prod. 2019, 228, 40–51. [CrossRef] 20. Bowers, B.F.; Huang, B.S.; Shu, X.; Miller, B.C. Investigation of reclaimed asphalt pavement blending efficiency through GPC and FTIR. Constr. Build. Mater. 2014, 50, 517–523. [CrossRef] 21. Hosseinnezhad, S.; Kabir, S.F.; Oldham, D.; Mousavi, M.; Fini, E.H. Surface functionalization of rubber particles to reduce phase separation in rubberized asphalt for sustainable construction. J. Clean. Prod. 2019, 225, 82–89. [CrossRef] 22. Dong, Z.J.; Zhou, T.; Luan, H.; Williams, R.C.; Wang, P.; Leng, Z. Composite modification mechanism of blended bio-asphalt combining styrene-butadiene-styrene with crumb rubber: A sustainable and environmental-friendly solution for wastes. J. Clean. Prod. 2019, 214, 593–605. [CrossRef] 23. Galan, J.J.; Silva, L.M.; Perez, I.; Pasandin, A.R. Mechanical behavior of hot-mix asphalt made with recycled concrete aggregates from construction and demolition waste: A design of experiments approach. Sustainability 2019, 11, 3730. [CrossRef] 24. Tarbay, E.W.; Azam, A.M.; El-Badawy, S.M. Waste materials and by-products as mineral fillers in asphalt mixtures. Innov. Infrastruct. Solut. 2019, 4, 13. [CrossRef] 25. Abo El-Naga, I.; Ragab, M. Benefits of utilization the recycle polyethylene terephthalate waste plastic materials as a modifier to asphalt mixtures. Constr. Build. Mater. 2019, 219, 81–90. [CrossRef] 26. Saberian, M.; Li, J.; Cameron, D. Effect of crushed glass on behavior of crushed recycled pavement materials together with crumb rubber for making a clean green base and subbase. J. Mater. Civ. Eng. 2019, 31, 04019108. [CrossRef] 27. Wang, Q.; Chen, X.; Jha, A.N.; Rogers, H. Natural gas from shale formation—The evolution, evidences and challenges of shale gas revolution in United States. Renew. Sustain. Energy Rev. 2014, 30, 1–28. [CrossRef] Sustainability 2019, 11, 4857 23 of 23

28. Gale, J.F.W.; Laubach, S.E.; Olson, J.E.; Eichhubl, P.; Fall, A. Natural fractures in shale: A review and new observations. AAPG Bull. 2014, 98, 2165–2216. [CrossRef] 29. Jarvie, D.M.; Hill, R.J.; Ruble, T.E.; Pollastro, R.M. Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment. AAPG Bull. 2007, 91, 457–499. [CrossRef] 30. Montgomery, S.L.; Jarvie, D.M.; Bowker, K.A.; Pollastro, R.M. Mississippian Barnett Shale, Fort Worth basin, north-central texas: Gas-shale play with multi-trillion cubic foot potential. AAPG Bull. 2005, 89, 155–175. [CrossRef] 31. Bowker, K.A. Barnett Shale gas production, Fort Worth Basin: Issues and discussion. AAPG Bull. 2007, 91, 523–533. [CrossRef] 32. Vohla, C.; Koiv, M.; Bavor, H.J.; Chazarenc, F.; Mander, Ü. Filter materials for phosphorus removal from wastewater in treatment wetlands—A review. Ecol. Eng. 2011, 37, 70–89. [CrossRef] 33. Al-Qodah, Z. Adsorption of dyes using shale oil ash. Water Res. 2000, 34, 4295–4303. [CrossRef] 34. Hadi, N.A.R.A.; Abdelhadi, M. Characterization and utilization of oil shale ash mixed with granitic and marble wastes to produce lightweight bricks. Oil Shale 2018, 35, 56–69. [CrossRef] 35. Aljbour, S.H. Production of ceramics from waste glass and jordanian oil shale ash. Oil Shale 2016, 33, 260–271. [CrossRef] 36. Guo, W.; Guo, X.D.; Chen, X.; Dai, W.T. Properties analysis of oil shale waste as partial aggregate replacement in open grade friction course. Appl. Sci. 2018, 8, 1626. [CrossRef] 37. Cheng, Y.C.; Wang, W.S.; Tan, G.J.; Shi, C.L. Assessing high- and low-temperature properties of asphalt pavements incorporating waste oil shale as an alternative material in Jilin Province, China. Sustainability 2018, 10, 2179. [CrossRef] 38. Punith, V.S.; Suresha, S.N.; Raju, S.; Bose, S.; Veeraragavan, A. Laboratory investigation of open-graded friction-course mixtures containing polymers and cellulose fibers. J. Trans. Eng. 2012, 138, 67–74. [CrossRef] 39. Alvarez, A.E.; Martin, A.E.; Estakhri, C. A review of mix design and evaluation research for permeable friction course mixtures. Constr. Build. Mater. 2011, 25, 1159–1166. [CrossRef] 40. Hassan, H.F.; Al-Oraimi, S.; Taha, R. Evaluation of open-graded friction course mixtures containing cellulose fibers and styrene butadiene rubber polymer. J. Mater. Civ. Eng. 2015, 17, 416–422. [CrossRef] 41. Onyango, M.; Woods, M. Analysis of the Utilization of Open-Graded Friction Course (OGFC) in the United States. In Proceedings of the International Conference on Highway Pavements and Airfield Technology, Philadelphia, PA, USA, 27–30 August 2017. 42. Luo, S.; Qian, Z.D.; Xue, Y.C. Performance evaluation of open-graded epoxy asphalt concrete with two nominal maximum aggregate sizes. J. Cent. South Univ. (Engl. Ed.) 2015, 22, 4483–4489. [CrossRef] 43. Yang, B.; Xiong, B.; Ji, Y.; Ban, G. Experimental study of the fatigue performance of open-graded asphalt mixture friction course. Mater. Res. Innov. 2015, 19, 464–468. [CrossRef] 44. Fang, F.T.; Chong, Y.C.; Nyunt, T.T.; Loi, S.S. Development of environmentally sustainable pavement mix. Int. J. Pavement Res. Technol. 2013, 6, 440–446. 45. Xie, Y.J.; Hill, C.A.S.; Xiao, Z.F. Silane coupling agents used for natural fiber/polymer composites: A review. Compos. Part A 2010, 41, 806–819. [CrossRef] 46. Zhang, P.; Guo, Q.L.; Tao, J.; Ma, D.; Wang, Y. Aging mechanism of a diatomite-modified asphalt binder using fourier-transform infrared (FTIR) spectroscopy analysis. Materials 2019, 12, 988. [CrossRef] 47. Cai, L.C.; Shi, X.G.; Xue, J. Laboratory evaluation of composed modified asphalt binder and mixture containing nano-silica/rock asphalt/SBS. Constr. Build. Mater. 2018, 172, 204–211. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).