applied sciences

Article Properties Analysis of Waste as Partial Aggregate Replacement in Open Grade Friction Course

Wei Guo 1, Xuedong Guo 1, Xing Chen 2 and Wenting Dai 1,* 1 School of Transportation, Jilin University, Changchun 130022, China; [email protected] (W.G.); [email protected] (X.G.) 2 Jilin Traffic Planning and Design Institute, Changchun 130000, China; [email protected] * Correspondence: [email protected]; Tel.: +86-130-8681-4298

 Received: 2 August 2018; Accepted: 10 September 2018; Published: 12 September 2018 

Featured Application: This paper developed a new modified open grade friction course. The modified OGFC was prepared by replacing the fine aggregate below 4.75 mm in OGFC with the oil shale waste, and the silane coupling agent modifier was used to assist modification. The technology of the modified OGFC preparation is an effective technique for improving the strength and stiffness of the OGFC and reducing environmental degradation.

Abstract: Open graded friction course (OGFC) is a high permeable mixture used to reduce noise, improve friction. However, limitations with the use of OGFC are due to the relatively low strength and stiffness. Therefore, investigating environmental and economic benefits, as well as service life of OGFC technology is the future of the pavement. In this study, a new modified OGFC (SM-OGFC) was prepared by replacing the fine aggregate below 4.75 mm in OGFC with the oil shale waste (OSW), and the silane coupling agent modifier was used to assist modification. The preparation process of SM-OGFC was optimized by central composite design, to obtain an SM-OGFC with the best mechanical properties. The Marshall test, rutting test, −15 ◦C splitting test, −10 ◦C beam bending test, immersion Marshall test, spring-thawing stability test, Cantabro test and permeability test were conducted to evaluate the properties of SM-OGFC. The results prove that SM-OGFC has excellent overall performance in comparison with OGFC and styrene-butadiene-styrene (SBS) modified OGFC. Furthermore, Scanning Electron Microscopy (SEM) observation illustrates that the unique laminar columnar connected structure and cell-like structure antennae of OSW could be the main reasons why SM-OGFC obtained excellent performance. Furthermore, economic analysis indicated that the SM-OGFC mixture had higher cost effectiveness.

Keywords: oil shale waste; silane coupling agent; replace fine aggregate; response surface methodology; central composite design

1. Introduction The pavement community is actively using sustainable pavement options, such as extending pavement life to reduce life-cycle cost and work zones, increasing usage of recycled material, and industrial by-product, improving pavement surface characteristics for high skid resistance and low noise [1]. Open-graded friction course (OGFC) is a high permeable mixture used as a surface coat for good friction, and splash- and-spray reduction during rain storms. It also decreases the potential for hydroplaning and improve visibility by reducing glare from standing water on pavement [2–5]. However, limitations with the use of such mixtures are much more affected by the relatively low strength and low stiffness. OGFC pavements typically fail by raveling. More specifically, the pavement

Appl. Sci. 2018, 8, 1626; doi:10.3390/app8091626 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 1626 2 of 22 fails when the asphalt binder ages and becomes brittle. Draindown, a separation of asphalt mastic from the course skeleton, can occur during storage or transport, which would result in a thin binder coating that is inadequate to prevent particles from being dislodged by traffic. The thin binder film can also age more rapidly, aggravating the raveling problem. Sometimes, the failure occurs when the pavement is only six to eight years old. Such a short life is difficult to accept [6–8]. In order to effectively reduce and prevent the occurrence of raveling damages in OGFC pavements, many researchers all over the world have conducted a large number of fruitful studies. Lyons et al. used different stabilizing additives (cellulose fibers, and styrene-butadiene-styrene (SBS)), and crumb rubber modifier (CRM) in a porous asphalt mixture. The results emphasized the importance of stabilizing additives in porous. Further, the results indicated that CRM or the combination of fibers and SBS were the most effective at increasing the abrasion resistance [9]; Luo et al. investigated a new open-graded asphalt mixture that used epoxy asphalt as binder to improve mix durability. Results showed superior overall performance of the open-graded epoxy asphalt mix compared to conventional open-graded asphalt mix [10]. Yang et al., conducted a material testing system fatigue test to investigate the fatigue performance of open graded friction courses modified with rock asphalt and rubber powder under different stress ratios. The results showed that modifiers, including natural rock asphalt and rubber powder, were added into OGFC could improve its fatigue performance [11]. Shen used rubber aggregate to prepare pavement friction course material. The results indicated that the polymer-rubber aggregate modified porous with the optimum replacing ratio of rubber aggregate to mineral aggregate had higher flexural strength and compressive strength than the ordinary polymer modified porous concrete with mineral aggregate [12]. The technologies of adding the modifier is an effective technique for prolonging the OGFC pavement service life. However, such type of modifier presents high cost that restricts its application in modifying paving asphalt. In the past few years, many studies have been conducted on alternative environmental friendly materials in OGFC to improve its mechanical properties. 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 [13–15]. Hainin et al. investigated utilization of steel slag as an aggregate replacement in porous asphalt mixtures. It was observed that the use of steel slag could perform admirably during high traffic loading [16]. Cheng et al. used oil shale ash instead of partial mineral powder in the mixture to improve the high- and low-temperature properties of asphalt pavement [17]. In conclusion, investigating environmental and economic benefits, as well as mechanical performance of OGFC technology is the future of the pavement. However, to the best of our knowledge, no work has been conducted on mechanical performance evaluation of oil shale waste (OSW) as partial aggregate replacement in OGFC. Therefore, this research aimed to evaluate the comprehensive performance of the replacement of 100% of the virgin aggregates with particle sizes below 4.75 mm in OGFC with OSW and explore the optimized conditions for the preparation of the high-strength OGFC.

2. Materials and Methods

2.1. Materials ‘Pan Jin’ base asphalt (90#, F40-2004, Table1) acquired from China Petrochemical was used in this paper. OSW, acquired from oil shale, was produced by a power plant in Jilin province China, as is shown in Figure1. Properties of OSW are shown in Table2. Appl. Sci. 2018, 8, 1626 3 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 23

Figure 1. Oil shale waste (OSW) in a power plant in Jilin province China.

Table 1. Table 1. Technical parameters of ‘Pan Jin’ asphalt.

TechnicalTechnical PenetrationPenetration 25 °C 25 ◦C SofteningSoftening WaxWax FlashFlash SolubilitySolubilityDensity Density ParametersParameters 15 °C15 ◦C 25 °C 25 ◦C 30 °C 30 ◦DuctilityC Ductility PointPoint ContentContent PointPoint Units 0.1 mm cm °C %≤ °C %≥ g·cm−3 Units 0.1 mm cm ◦C%≤ ◦C%≥ g·cm−3 Test results 27.5 81.3 132.6 >130 44.2 18 340 99.9 1.003 Test results 27.5 81.3 132.6 >130 44.2 18 340 99.9 1.003

Table 2. Physical parameters of OSW. Table 2. Physical parameters of OSW. Physical Apparent Water Crushing Cohesion Internal Friction Optimum Water PropertyPhysical DensityApparent (g/cm3) AbsorptionWater (%) CrushingValue (%) Cohesion(Kpa) InternalAngle Friction (°) OptimumRate (%) 3 ◦ PropertyOSW Density2.627 (g/cm ) Absorption 18.6 (%) Value 42.2 (%) (Kpa)13.84 Angle33.3 ( ) Water 28.3 Rate (%) OSW 2.627 18.6 42.2 13.84 33.3 28.3 According to Table 2, it can be seen that the apparent density of the OSW is very close to that of the stone,According and the to OSW Table 2has, it some can be characteristics seen that the of apparent the rock. density However, of the the OSW OSW is generated very close from to that the oilof theshale stone, after and extraction the OSW has has higher some crushing characteristics value and of thewater rock. absorption. However, The the higher OSW generated crushing value from indicatesthe oil shale that after the extractionresidue cannot has higher bear crushingloads as valuea skeleton and waterin the absorption. asphalt mixture. The higher Higher crushing water valueabsorption indicates may that lead the to residue poor water cannot stability bear loads of asOSW a skeleton in the inpavement the asphalt material mixture. application. Higher water So, auxiliaryabsorption modifiers may lead are to poorneeded water to improve stability ofwater OSW stability in the pavement during application. material application. Silane coupling So, auxiliary agent, producedmodifiers areby neededShuanglong to improve Chemical water Co., stability Ltd. during (Changchun, application. China), Silane was coupling selected agent, as producedauxiliary modifiers,by Shuanglong since Chemicalit had been Co., reported Ltd. (Changchun, to be amon China),g the most was effective selected asadditives auxiliary for modifiers, water stability since currentlyit had been available. reported Silane to be among coupling the mostagent effectivehas a special additives molecular for water feature, stability in currentlywhich it available.has two differentSilane coupling types of agent functional has a special groups, molecular including feature, organofunctional in which it has groups two different and hydrolysable types of functional groups. Silanegroups, coupling including agent organofunctional can easily bond groups silicate and ma hydrolysableterial and organic groups. material, Silane coupling due to agent this molecular can easily featurebond silicate [18,19]. material and organic material, due to this molecular feature [18,19].

2.2. Oil Shale Waste Preparation OSW isis obtainedobtained from from combustion combustion of of oil oil shale. shale. Due Due to theto the high high water water absorption absorption of OSW, of OSW, the OSW the OSWstored stored in open in open air should air should be dried be dried in an in ovenan oven at 120at 120◦C °C for for 4 h.4 h. Afterwards, Afterwards, the the drieddried OSWOSW was smashed in the pulverizer, for 3 min, and the used OSW was obtained by sieving the crushed OSW through the 4.75 mm aperture-sized sieve.sieve.

2.3. SM-OGFC Sample Preparation SM-OGFC samples are prepared to determine the optimization of SM-OGFC with different asphalt-aggregate ratio,ratio, different different compaction compaction times, times, different different mixing mixing temperature temperature and differentand different silane silanecoupling coupling agent agent content. content. Due toDue the to high the high specific specif surfaceic surface of OSW, of OSW, the silanethe silane coupling coupling agent agent is not is notsuitable suitable for for surface surface treatment treatment of of the the OSW OSW directly, directly, so so pre-mixing pre-mixing of of silane silane coupling coupling agentagent andand the heated base asphalt is necessary for better mixing. Firstly, the silane coupling agent was mixed into the base asphalt at 160 °C to stir for 5 min. After pre-mixing, the asphalt with silane coupling agent, granites with grain size greater than 4.75 mm in gradation, OSW with grain size less than 4.75 mm in Appl. Sci. 2018, 8, 1626 4 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 4 of 23

◦ gradationthe base and asphalt mineral at 160 powderC to stir with for particle 5 min. Aftersize less pre-mixing, than 0.075 the mm asphalt were with mixed silane in couplingthe vacuum agent, mixinggranites pot. with Finally, grain the size SM-OGF greater thanC samples 4.75 mm are in formed gradation, through OSW withthe compaction grain size less of thanmixture. 4.75 mmThe in gradationgradation of and OGFC mineral used powder in this with paper particle is sizethe lessmost than commonly 0.075 mm used were mixedone in in China, the vacuum which mixing is demonstratedpot. Finally, in the Table SM-OGFC 3. The samples flowchart are of formed preparation through of the the compaction SM-OGFC of is mixture. shown in The Figure gradation 2. Moreover,of OGFC two used types in this of OGFC paper iswere the used most for commonly the performance used one comparison, in China, which a conventional is demonstrated OGFC in mixtureTable3 with. The ’Pan flowchart Jin’ base of preparationasphalt (OGFC), of the and SM-OGFC a modified is shown OGFC in with Figure SBS2 .modified Moreover, asphalt two types (SBS- of OGFC).OGFC All were asphalt used formixtures the performance were specified comparison, based on a conventionalTechnical Specifications OGFC mixture for withConstruction ’Pan Jin’ of base Highwayasphalt Asphalt (OGFC), Pavement and a modified in China OGFC (JTG with F40-2004 SBS modified), and the asphalt optimum (SBS-OGFC). asphalt content All asphalt was mixturesfound to werebe 4.8% specified and 4.1% based for the on control Technical mixture. Specifications for Construction of Highway Asphalt Pavement in China (JTG F40-2004), and the optimum asphalt content was found to be 4.8% and 4.1% for the control mixture. Table 3. Properties of aggregate and gradation of OGFC-16.

Sieve (mm) Table 16 3. Properties 13.2 9.5 of aggregate 4.75 2. and36 gradation1.18 0.6 of OGFC-16. 0.3 0.15 0.075 Apparent density 2.78 2.78 2.78 2.74 2.74 2.75 2.70 2.70 2.69 2.67 Sieve (mm) 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 Bulk density 2.77 2.76 2.75 2.68 2.64 2.59 2.60 2.59 2.57 2.55 Apparent density 2.78 2.78 2.78 2.74 2.74 2.75 2.70 2.70 2.69 2.67 Bulk densityGradation (%) 2.77 97.5 2.76 65 2.75 47.5 23.2.685 11.5 2.64 11.5 2.59 9 2.60 7.5 6.0 2.59 4.5 2.57 2.55 Gradation (%) 97.5 65 47.5 23.5 11.5 11.5 9 7.5 6.0 4.5

Figure 2. The flowchart of preparation of the SM-OGFC.

Figure 2. The flowchart of preparation of the SM-OGFC. Appl. Sci. 2018, 8, 1626 5 of 22

2.4. Performance Evaluation of SM-OGFC

2.4.1. High-Temperature Mechanical Performance Test Marshall test and rutting test are conducted to evaluate the high-temperature performance of SM-OGFC according to Chinese standards GB/T0709-2011 and GB/T0719-2011 in this study. By assessing Marshall stability (MS) and dynamic stability (DS), the resistance of SM-OGFC to , horizontal and shear stress induced from the loading in the high-temperature environment can be predicted.

2.4.2. Low-Temperature Mechanical Performance Test The low-temperature properties of SM-OGFC is observed via Low-temperature splitting test and Low-temperature beam bending test. The splitting strength (RT) of mixtures is obtained by −15 ◦C splitting test according to Chinese standards GB/T0716-2011. The −15 ◦C splitting strength is an important factor for assessing the capacity of SM-OGFC to bear dynamic loads at low temperature. The bending-tensile strength (RB), maximum bending strain (εB) and the bending ◦ stiffness modulus (SB) of mixture is acquired through −10 C beam bending test according to Chinese standards GB/T0715-2011.

2.4.3. Water Stability Test Immersion Marshall test was carried out, to evaluate the water stability of SM-OGFC according to Chinese standards GB/T0709-2011 in this study. Due to the interconnected pores and large porosity of OGFC, most of the water can freely discharge in the interconnected pores. However, there is always a part of the moisture remaining in the mixture, due to the surface tension and capillary action of the water, and the presence of the semi-intersecting void semi-connected pore. The volume of free water has expanded after freezing, which generates the internal temperature stress in the OGFC, and this effect can enlarge the micropore and the original crack in the OGFC. The ice crystalloid is transformed into free water, which caused moisture damage with the increase of temperature. In order to better evaluate the water stability of OGFC in spring-thawing season, this paper use the spring-thawing stability index to evaluate the water stability of OGFC in spring-thawing season. The specimens were treated by vacuum saturation in 97.3 kPa for 15 min and 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 15 ◦C for 12 h through controlling the precision temp-enclosure. As described above, a complete freeze-thaw cycle is completed. After 5 freeze-thaw cycles, damaged specimens were collected for Marshall test according to Chinese standards GB/T0709-2011.

2.4.4. Cantabro Test Standard Cantabro Test was conducted to check the raveling resistance of SM-OGFC mixtures. The SM-OGFC mixtures were mixed and compacted in the laboratory using the Marshall compactor for the Cantabro Test (Chinese standards GB/T0733-2011). The specimens were conditioned to 20 ◦C for several hours before testing, and the Los Angeles abrasion drum was conditioned to 20 ◦C ± 0.5 ◦C. Specimens were weighed, individually subjected to 300 revolutions (30–33 rpm) in the Los Angeles abrasion drum without steel charge, brushed with a soft-bristled brush, and weighed again. The Cantabro losses for each specimen are the mass lost during testing, divided by the specimen initial mass.

2.4.5. Permeability Test and Scanning Electronic Microscopy Test OGFC mixture is a special type of hot mix asphalt characterized by high interconnected air voids and a coarse, granular skeleton, with proper stone-on-stone contact. The presence of a larger Appl. Sci. 2018, 8, 1626 6 of 22 percentage of internal air voids leads to a relatively highly porous structure of OGFC mixes, which helps in quick and effective removal of surface water from the pavement. Thus, the permeability capacity of SM-OGFC determines the performance of permeable pavements. The permeability capacity of SM-OGFC is evaluated via permeability test. The laboratory permeability test is divided into constant head permeability test and falling head permeability test based on Darcy’s law. The constant head permeability test is generally applied to measure the permeability coefficient of high permeability material and the falling head permeability test is applicable to low permeability material [20,21]. Therefore, the constant head permeability test was conducted to evaluate the permeability coefficient of SM-OGFC, in accordance with the Specifications for Design of Highway Asphalt Pavement (JTG D50-2006), and the permeability coefficient (K) is obtained by the Equation (1):

QL K ◦ = . (1) 20 C At∆t

Q: The quality of the water permeating through the specimen during t time (cm3) L: Infiltration length (cm) A: Cross-sectional area of the specimen (cm2) t: Infiltration time (s) ∆t: Water head difference (cm) Scanning Electron Microscopy test (SEM) was used to magnify the sample and observe its microscopic structure. In this research study, Hitachi SU8000 (Tianmei.co, Tokyo, Japan) scanning electronic microscopy was utilized to observe the micro-structure of OSW particles.

3. Optimization of SM-OGFC by Response Surface Methodology (RSM)

3.1. Central Composite Design In regards to the optimization of SM-OGFC, several factors, such as the asphalt-aggregate ratio, silane coupling agent content, compaction times and mixing temperature, could remarkably influence the compressive strength SM-OGFC. However, if just a single variable of the aforementioned factors is analyzed, cross-impact of the variables would usually be neglected. On the other hand, a complete experimental design to explore the relationships of the exploratory variables is often time-consuming. In this context, response surface methodology (RSM) has been suggested to find the most valuable point, or called optimization to simplify the experimental design and simultaneously, maximize the production, or minimize the cost, side reactions, etc. RSM has been applied in many fields, such as chemical reactions, industry manufacture and many other product optimization. In regards to the RSM, central composite design (CCD) is often used to support the optimization of a two-level factorial or fraction factorial design, which is usually coded as −1 and 1 so as to simplify the experimental expression and calculation [22–24]. Nassar et al. applied a central composite design (CCD) with response surface methodology (RSM) to optimize the mix design parameters of cold bitumen emulsion mixture, namely bitumen emulsion content (BEC), pre-wetting water content (PWC) and curing temperature (CT) [25]. Wang et al. designed an experimental scheme to optimize three preparation parameters of styrene-butadiene-styrene (SBS)-modified asphalt mixture reinforced with eco-friendly basalt fiber based on response surface methodology (RSM) [26]. In this study, asphalt-aggregate ratio and silane coupling agent content are considered as key factors in the preparation of SM-OGFC samples; compaction times and mixing temperature are also considered as vital factor in the preparation study. Experiments are designed with six central points. Table4 shows the range of asphalt-aggregate ratio, silane coupling agent content, compaction times and mixing temperature respectively. The Marshall stability, −15 ◦C splitting strength, and spring-thawing stability are considered as the response of the software. In this study, CCD approach suggests 30 experiments; six of them are replicated as the central point. Table5 reveals the proffered experiments and results. Appl. Sci. 2018, 8, 1626 7 of 22

Table 4. The coded level of affected variable.

Name Units Lower Limit (−1) Upper Limit (+1) Asphalt-aggregate ratio % 4.3 5.7 Silane coupling agent content % 1 3 Mixing temperature ◦C 140 160 Compaction times n 50 70

Table 5. Central composite design.

Asphalt- Silane Coupling Mixing Marshall −15 ◦C Compaction Spring-Thawing Run Aggregate Agent Content Tem-Perature Stability Splitting Times (D) Stability (KN) Ratio (A) (B) (C) (KN) Strength (Mpa) 1 1 −1 1 −1 9.01 3.06 7.62 2 −1 1 −1 1 8.49 2.04 7.32 3 1 1 1 −1 9.33 3.4 7.99 4 0 0 2 0 8.98 3.55 7.80 5 1 −1 −1 1 8.98 3.93 7.63 6 −1 −1 1 −1 8.50 2.67 7.30 7 1 1 −1 −1 9.02 3.55 7.73 8 0 −2 0 0 8.78 3.38 7.82 9 1 1 −1 1 8.97 3.42 7.80 10 1 1 1 1 8.67 3.5 7.52 11 1 −1 −1 −1 8.67 3.15 7.63 12 0 0 0 0 9.57 3.89 8.24 13 0 0 0 0 9.64 4.05 8.17 14 −1 1 1 1 8.14 2.41 7.17 15 −1 1 1 −1 8.56 2.45 7.62 16 0 0 −2 0 9.06 3.18 7.93 17 2 0 0 0 7.10 2.54 6.07 18 −1 −1 1 1 8.17 2.93 7.14 19 0 0 0 2 9.30 3.91 8.07 20 0 0 0 0 9.87 3.82 8.66 21 −1 1 −1 −1 8.28 2.48 7.19 22 0 0 0 0 9.22 3.68 8.27 23 0 0 0 −2 9.81 3.48 8.42 24 −1 −1 −1 1 8.06 2.7 7.27 25 −1.429 0 0 0 7.57 1.8 6.52 26 0 2 0 0 9.13 3.09 8.24 27 1 −1 1 1 8.67 3.73 7.28 28 0 0 0 0 9.63 3.57 8.41 29 −1 −1 −1 −1 8.09 2.43 6.91 30 0 0 0 0 9.67 3.82 8.36

3.2. Build RSM Model Model Fit Summary tab is a statistical appraisement used to suggest the most appropriate model. Take −15 ◦C splitting strength response model as an example, the details of Model Fit Summary tab are summarized in Table6. The proposed quadratic model is suggested, due to the p-value of the model is less than 0.0001 and the F-value is equal to 44.51.

Table 6. Different statistical values form Model Fit Summary tab.

Sequential Lack of Fit Adjusted Predicted Source p-Value p-Value R-Squared R-Squared Linear 0.0345 0.0050 0.2225 0.0708 2Fl 0.9022 0.0030 0.0783 −0.1258 Quadratic <0.0001 0.8855 0.9546 0.9240 Cubic 0.7924 0.9204 0.9382 Appl. Sci. 2018, 8, 1626 8 of 22

Based on the experimental data of Table5, the regression equation of −15 ◦C splitting strength is calculated by the Equation (2):

RT = 3.79 + 0.49 × A − 0.08 × B + 0.05 × C + 0.097 × D + 0.084 × AB −0.073 × AC + 0.086 × AD + 0.006 × BC − 0.16 × BD + 0.032 × CD − 0.56 × A2 (2) −0.13 × B2 − 0.1 × C2 − 0.018 × D2.

Moreover, it is found that A, B, D, AB, AC, AD, BD, A2,B2, and C2 terms are significant factors with p-values less than 0.0500 through ANOVA Analysis. The details of ANOVA Analysis are summarized in Table7. Based on the analysis above, the original regression is revised. Equation (3) presents the modified regression equation, which deletes the non-significant model terms:

R = 3.79 + 0.49 × A − 0.08 × B + 0.097 × D + 0.084 × AB T (3) −0.073 × AC + 0.086 × AD − 0.16 × BD − 0.56 × A2 − 0.13 × B2 − 0.1 × C2.

Credibility analysis of modified regression equation is summarized in Table8. According to Table8, the value of R 2 is almost one, and therefore the experimental results are in good agreement 2 2 with the predicted values. In addition, the difference between R and RAdj is 0.02, and there is a good 2 2 accordance between RPred and RAdj indicating the accuracy of the proposed model.

Table 7. ANOVA Analysis of −15 ◦C splitting strength response model.

Source Sum of Squares df Mean Square F-Value p-Value Model 10.6 14 0.76 44.51 <0.0001 A-Asphalt-aggregate ratio 5.06 1 5.06 297.6 <0.0001 B-Silane coupling agent content 0.16 1 0.16 9.12 0.0086 C-Mixing temperature 0.059 1 0.059 3.47 0.0823 D-Compaction times 0.23 1 0.23 13.29 0.0024 AB 0.11 1 0.11 6.69 0.0206 AC 0.086 1 0.086 5.03 0.0405 AD 0.12 1 0.12 6.89 0.0191 BC 5.06 × 10−4 1 5.06 × 10−4 0.03 0.8654 BD 0.39 1 0.39 22.77 0.0002 CD 0.016 1 0.016 0.96 0.3439 A2 5.94 1 5.94 349.09 <0.0001 B2 0.49 1 0.49 28.95 <0.0001 C2 0.28 1 0.28 16.54 0.001 D2 9.14 × 10−3 1 9.14 × 10−3 0.54 0.475 Residual 0.26 15 0.017

Table 8. Credibility analysis of modified regression equation.

Std.Dev. 0.13 R2 0.9765 2 Mean 3.19 RAdj 0.9546 2 C.V.% 4.09 RPred 0.9240 PRESS 0.82 Adeq Precisior 21.416

3.3. RSM Model Validation The validation of the model can be examined with the diagnostic tab in the design-expert software. The normal plot of the residuals of −15 ◦C splitting strength is shown in Figure3. A straight line almost covers all the points, and therefore, there is a normal distribution of errors in the experiments. In addition, there is no abnormal pattern or structure in the residuals plot (Figure4). The difference between predicted and actual values of the response is shown in Figure5. A straight line almost cover all the points, and therefore there are negligible errors between the predicted and actual responses. Thereupon, the proposed mathematical regression is authentic. Appl. Sci. 2018, 8, 1626 9 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 23 Appl. Sci. 2018,, 8,, xx FORFOR PEERPEER REVIEWREVIEW 9 of 23

Figure 3. Normal probability plot of residuals of −15 °C splitting strength. FigureFigure 3. 3.Normal Normal probability probability plot plot ofof residualsresiduals ofof −1515 °C◦C splitting splitting strength. strength.

Figure 4. Residual versus predicted values of −15 °C◦ splitting strength. FigureFigure 4. 4.Residual Residual versus versus predicted predicted valuesvalues ofof −1515 °CC splitting splitting strength. strength.

FigureFigure 5. 5.Predicted Predicted against against actualactual responses of −−1515 °C◦C spli splittingtting strength. strength. Figure 5. Predicted against actual responses of −15 °C splittinging strength.strength. Appl. Sci. 2018, 8, 1626 10 of 22

Appl. Sci. 2018, 8, x FOR PEER REVIEW 10 of 23 3.4. Response Surface Interaction Analysis 3.4. Response Surface Interaction Analysis Response surface and Contour plot of regression model is shown in Figure6A –D . Response surface and Contour plot of regression model is shown in Figure 6A1–D22

A1

A2

B1

Figure 6. Cont. Appl. Sci. 2018, 8, 1626 11 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 11 of 23

B2

C1

C2

Figure 6. Cont. Appl. Sci. 2018, 8, 1626 12 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 12 of 23

D1

D2

◦ FigureFigure 6. 6( A(A1)1) 3D 3D surface surface graphgraph ofof −−15 °CC splitting splitting strength strength against against A A and and B; B; (A (A2)2 contour) contour plot plot of of −15 ◦ ◦ −15°C splittingC splitting strength strength against against A Aand and B; B;(B (1B) 13D) 3D surface surface graph graph of of−15− 15°C splittingC splitting strength strength against against A Aand ◦ andC; C;(B (2B) 2contour) contour plot plot of of −15−15 °C Csplitting splitting strength strength against against A Aand and C; C; (C (C1)1 )3D 3D surface surface graph graph of of −−1515 °C ◦ ◦ Csplitting splitting strength strength against against B Band and C; C;(C (2C) contour2) contour plot plot of − of15− °C15 splittingC splitting strength strength against against B and B C; and (D1) ◦ ◦ C;3D (D 1surface) 3D surface graph graph of −15 of °C− 15splittingC splitting strength strength against against C and CD; and (D2 D;) contour (D2) contour plot of plot −15 of°C− splitting15 C splittingstrength strength against against C and CD. and D.

AsAs shown shown in thein comparisonthe comparison between between the four the group four diagrams,group diagrams, the influence the ofinfluence asphalt-aggregate of asphalt- ◦ ratioaggregate on −15 ratioC splitting on −15 strength °C splitting is the strength most significant, is the most which significant, is characterized which byis thecharacterized steepness of by the the surfacesteepness in Figure of the6A surface1,B1. in Figure 6A1,B1. ◦ FigureFigure6B 6B1 shows1 shows a three-dimensionala three-dimensional plot plot of of− 15−15 C°C splitting splitting strength strength against against asphalt-aggregate asphalt-aggregate ratioratio and and mixing mixing temperature temperature when when silane silane coupling coupling agent agent content content isis 2%2% andand thethe compactioncompaction times is ◦ is60. 60. As As can bebe seenseen fromfrom FigureFigure6 B6B1,1, with with the the increase increase of of the the asphalt-aggregate, asphalt-aggregate,− 15−15C °C splitting splitting ◦ ◦ strengthstrength continues continues to growto grow until until it reaches it reaches a stable a stab value.le value. At the At mixing the mixing temperature temperature of 140 ofC, 140− 15°C, C−15 splitting°C splitting strength strength rises from rises 2.52 from Mpa 2.52 to Mpa 3.64 Mpato 3.64 with Mpa the with increase the ofincrease asphalt-aggregate of asphalt-aggregate ratio from 4.3ratio ◦ tofrom 5%. In 4.3 addition, to 5%. In with addition, the increasing with the increasing of asphalt-aggregate of asphalt-aggregate ratio within ratio the within reasonable the reasonable range, −15 range,C splitting−15 °C strengthsplitting isstrength maintained is maintained at about 3.64 at about Mpa. 3.64 This Mpa. is because This is the because OSW hasthe OSW higher has specific higher surface specific areasurface compared area compared with stone, with thus stone, it can thus absorb it can more absorb free asphalt. more free With asphalt. the increase With the of asphalt-aggregateincrease of asphalt- aggregate ratio, the structural asphalt adsorbed on the aggregate surface gradually increased. Therefore, the mechanical properties of SM-OGFC to resist low temperature load are improved. Appl. Sci. 2018, 8, 1626 13 of 22 ratio, the structural asphalt adsorbed on the aggregate surface gradually increased. Therefore, the mechanical properties of SM-OGFC to resist low temperature load are improved. TheAppl. Sci. shape 2018, of8, x contourFOR PEER REVIEW can reflect the strength of interaction. Oval indicates that the13 interaction of 23 of two factors is significant while circle is the opposite. It can be seen the contour line is oval The shape of contour can reflect the strength of interaction. Oval indicates that the interaction of from Figure6A ,B and D ), so the interaction of asphalt-aggregate ratio and silane coupling agent two factors is2 significant2 2 while circle is the opposite. It can be seen the contour line is oval from Figure content,6A2,B asphalt-aggregate2 and D2), so the interaction ratio and mixingof asphalt-aggregate temperature, ratio compaction and silane times coupling and mixing agent content, temperature are significant.asphalt-aggregate In comparison, ratio and mixing the interaction temperature, between compaction silane times coupling and mixing agent contenttemperature and are mixing temperaturesignificant. is slightlyIn comparison, weaker. the interaction between silane coupling agent content and mixing temperature is slightly weaker. 3.5. Numerical Optimization 3.5. Numerical Optimization Through the discussion of the RSM model, it is found that the process parameters, including asphalt-aggregateThrough the ratio, discussion silane couplingof the RSM agent model, content, it is found compaction that the process times, parameters, and mixing including temperature haveasphalt-aggregate to confirm in their ratio, ranges silane socoupling that the agent response content, factor compaction would times, be able and to mixing reach temperature to its maximum have to confirm in their ranges so that the response factor would be able to reach to its maximum value. The optimal solution to maximin the response factor is shown in Table9. value. The optimal solution to maximin the response factor is shown in Table 9.

Table 9. Optimal conditions obtained by Numerical optimization. Table 9. Optimal conditions obtained by Numerical optimization.

Asphalt-aggregateAsphalt-aggregate ratio ratio 5.18% 5.18% Silane coupling agent content 2.50% SilaneMixing coupling temperature agent content 2.50% 153 ◦ C MixingCompaction temperature times 153 50°C CompactionDesirability times 50 0.056 Desirability 0.056 4. Results and Discussion 4. Results and Discussion 4.1. Marshall Test and Rutting Test Results 4.1. Marshall Test and Rutting Test Results The Marshall stability of all OGFC mixtures is shown in Figure7. As shown in Figure7, the OSW The Marshall stability of all OGFC mixtures is shown in Figure 7. As shown in Figure 7, the OSW as partial aggregate replacement in OGFC could be effective in enhancing the MS of OGFC mixtures. as partial aggregate replacement in OGFC could be effective in enhancing the MS of OGFC mixtures. The higher MS value indicates that the OGFC mixture is stiffer and has better resistance against The higher MS value indicates that the OGFC mixture is stiffer and has better resistance against permanentpermanent deformation. deformation. The The MS MS value value ofof OGFC,OGFC, SBS-OGFC, SBS-OGFC, and and SM-OGFC SM-OGFC were were found found to be to6.47, be 6.47, 9.12,9.12, and and 9.63, 9.63, respectively. respectively. ItIt should be be noted noted that that the theMS value MS value of SM-OGFC of SM-OGFC was 48.8% was higher 48.8% than higher thanOGFC, OGFC, even even 5.6% 5.6% higher higher than than SBS-OGFC. SBS-OGFC. It is show It isn shown that OSW that helps OSW to increase helps to the increase adhesion the ability adhesion abilityamong among aggregates aggregates of OGFC. of OGFC. The main The mainreason reason for the for increase the increase in adhesion in adhesion among aggregates among aggregates in SM- in SM-OGFCOGFC is that OSW OSW with with porous porous structure structure has hasa stro ang strong tendency tendency to absorb to absorbasphalt asphaltbinder, which binder, can which can makemake thethe contentcontent of the the structural structural asphalt asphalt binder binder increase, increase, and and the thecontent content of free of freeasphalt asphalt binder binder is is decreaseddecreased as a as result. a result. This This structural structural change change improvesimproves the the overall overall ability ability of the of theOGFC OGFC to bear to bearloads. loads. Moreover, The RSM predicated the MS value of the optimal SM-OGFC to 9.78, the measured MS Moreover, The RSM predicated the MS value of the optimal SM-OGFC to 9.78, the measured MS value value of SM-OGFC was 9.63, and the difference between the two was 1.5%, indicating that the RSM of SM-OGFC was 9.63, and the difference between the two was 1.5%, indicating that the RSM has high has high prediction accuracy. Figure 8 shows the dynamic stability of all OGFC mixtures. As seen, predictionthe DS accuracy. value ofFigure SM-OGFC8 shows was the 48.9% dynamic higher stability than OGFC, of all OGFCreached mixtures. 94.7% of As SBS-OGFC. seen, the DSThis value of SM-OGFCobservation was indicated 48.9% higher that SM-OGFC than OGFC, had reached better resistance 94.7% of SBS-OGFC.to permanent This deformation observation at indicatedhigh that SM-OGFCtemperature. had better resistance to permanent deformation at high temperature.

FigureFigure 7. Marshall 7. Marshall stability stability for for allall OpenOpen graded friction friction course course (OGFC) (OGFC) mixtures. mixtures. Appl.Appl. Sci. Sci. 20182018,, 88,, x 1626 FOR PEER REVIEW 1414 of of 23 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 14 of 23

Figure 8. Dynamic stability for all OGFC mixtures. FigureFigure 8. 8. DynamicDynamic stability stability for for all all OGFC OGFC mixtures. mixtures. 4.2.4.2. Low-Temperature Low-Temperature Splitting Test and Low-Temperature BeamBeam BendingBending TestTest Results Results 4.2. Low-Temperature Splitting Test and Low-Temperature Beam Bending Test Results TheThe low-temperature splittingsplitting test test results results are are shown shown in Figurein Figure9. The 9. STheT value ST value of OGFC, of OGFC, SBS-OGFC SBS- The low-temperature splitting test results are shown in Figure 9. The ST value of OGFC, SBS- OGFCand SM-OGFC and SM-OGFC were foundwere found to be 2.74,to be 3.872.74, and 3.87 3.71. and Furthermore,3.71. Furthermore, the S theT value ST value of SM-OGFC of SM-OGFC was OGFC and SM-OGFC were found to be 2.74, 3.87 and 3.71. Furthermore, the ST value of SM-OGFC was35.4% 35.4% higher higher than than OGFC, OGFC, and and almost almost equaled equaled to SBS-OGFC. to SBS-OGFC. The The higher higher ST value ST value indicates indicates that that the was 35.4% higher than OGFC, and almost equaled to SBS-OGFC. The higher ST value indicates that themixture mixture has betterhas better resistance resistance against against pressure, pressure horizontal, horizontal and shear and stressshear inducedstress induced from the from loading the the mixture has better resistance against pressure, horizontal and shear stress induced from the loadingin the low-temperature in the low-temperature environment. environment. It can be seenIt can that be SM-OGFCseen that showedSM-OGFC better showed low-temperature better low- loading in the low-temperature environment. It can be seen that SM-OGFC showed better low- temperaturemechanical performancemechanical performance in comparison in comparis with OGFC.on with Moreover, OGFC. TheMoreover, RSM predicated The RSM thepredicated ST value the of temperature mechanical performance in comparison with OGFC. Moreover, The RSM predicated the StheT value optimal of SM-OGFCthe optimal to SM-OGFC 3.75, the measured to 3.75, StheT value measured of SM-OGFC ST value is 3.71,of SM-OGFC and the difference is 3.71, and between the ST value of the optimal SM-OGFC to 3.75, the measured ST value of SM-OGFC is 3.71, and the differencethe two is 0.8%,between indicating the two that is 0.8%, the RSM indicating has high th predictionat the RSM in predictinghas high prediction the mechanical in predicting properties the of difference between the two is 0.8%, indicating that the RSM has high prediction in predicting the mechanicalSM-OGFC atproperties low temperature. of SM-OGFC at low temperature. mechanical properties of SM-OGFC at low temperature.

◦ Figure 9. −1515 °CC Splitting Splitting strength strength for for all all OGFC OGFC mixtures. mixtures. Figure 9. −15 °C Splitting strength for all OGFC mixtures. ◦ Table 10 shows the −10 C beam bending test results of three OGFC samples. As seen, the RB Table 10 shows the −10 °C beam bending test results of three OGFC samples. As seen, the RB valueTable of SBS-OGFC 10 shows the and − SM-OGFC10 °C beam was bending notably test higher results than of three OGFC. OGFC However, samples. there As areseen, different the RB value of SBS-OGFC and SM-OGFC was notably higher than OGFC. However, there are different valuereasons of forSBS-OGFC the improvement. and SM-OGFC The mainwas notably reason forhigh theer increasethan OGFC. of R BHowever,value of SBS-OGFCthere are different relative reasons for the improvement. The main reason for the increase of RB value of SBS-OGFC relative to reasonsto OGFC for is, the due improvement. to the effective The modification main reason effect for the of SBS.increase The of SBS RB modifier value of enhancesSBS-OGFC the relative adhesion to OGFC is, due to the effective modification effect of SBS. The SBS modifier enhances the adhesion and OGFCand cohesion is, due to of the asphalt effective binder, modification which consequently effect of SBS.contribute The SBS modifier to the capacityenhances of the mixture adhesion to bearand cohesion of asphalt binder, which consequently contribute to the capacity of mixture to bear dynamic cohesiondynamic of loads asphalt at lowbinder, temperature. which consequently The main contribute reason for to the the increase capacity of of RmixtureB value to of bear SM-OGFC dynamic is loads at low temperature. The main reason for the increase of RB value of SM-OGFC is that the OSW loadsthat the at low OSW temperature. with porous The structure main reason absorbs for the the light increase weight of componentRB value of SM-OGFC with less molecular is that the weight OSW with porous structure absorbs the light weight component with less molecular weight of the asphalt, withof the porous asphalt, structure enhances absorbs the bond the light between weight the comp asphaltonent with andless themolecular aggregate, weight and of improves the asphalt, the enhances the bond between the asphalt mortar and the aggregate, and improves the mechanical enhancesmechanical the structure bond between of OGFC. the In asphalt winter, themortar greater and the the stiffness aggregate, modulus and ofimproves the material, the mechanical the weaker structure of OGFC. In winter, the greater the stiffness modulus of the material, the weaker the stress structurethe stress of relaxation OGFC. In performance, winter, the greater the more the brittle stiffn theess material modulus will of be,the andmaterial, the more the likelyweaker the the material stress relaxation performance, the more brittle the material will be, and the more likely the material to relaxationto produce performance, shrinkage cracks. the more Therefore, brittle in the order material to make will the be, OGFC and havethe more good low-temperaturelikely the material crack to produce shrinkage cracks. Therefore, in order to make the OGFC have good low-temperature crack produceresistance, shrinkage a smaller cracks. bending Therefore, stiffness in modulus order to is make expected. the OGFC SM-OGFC have has good the low-temperature smallest SB of the crack three resistance, a smaller bending stiffness modulus is expected. SM-OGFC has the smallest SB of the three resistance,mixes. The a mostsmaller probable bending reason stiffness for modulu this phenomenons is expected. is thatSM-OGFC the low-temperature has the smallest bending SB of the failure three mixes. The most probable reason for this phenomenon is that the low-temperature bending failure mixes.process The of themost specimen probable is reason caused for by thethis tensilephenom failureenon causedis that bythe thelow-temperature internal stress, bending so the adhesion failure process of the specimen is caused by the tensile failure caused by the internal stress, so the adhesion processbetween of the the OGFC specimen skeletons is caused mainly by the play tensile a key fail roleure to caused prevent by the the damage, internal while,stress, theso the added adhesion OSW between the OGFC skeletons mainly play a key role to prevent the damage, while, the added OSW betweenadsorbed the asphalt OGFC binder skeletons to form mainly the OSW-asphalt play a key ro cementle to prevent with greater the damage, stiffness, while, and the the firm added structural OSW adsorbed asphalt binder to form the OSW-asphalt with greater stiffness, and the firm adsorbedasphalt coating asphalt on binder the coarse to form aggregate the OSW-asphal enhances thet adhesioncement with between greater the skeletons.stiffness, and the firm structural asphalt coating on the coarse aggregate enhances the adhesion between the skeletons. structural asphalt coating on the coarse aggregate enhances the adhesion between the skeletons. Appl. Sci. 2018, 8, 1626 15 of 22

Appl. Sci. 2018, 8, x FORTable PEER 10. REVIEWLow-temperature beam bending test results of all OGFC mixtures. 15 of 23

Table 10. Low-temperatureBending-Tensile beam bendingMaximum test results Bending of all OGFC Bendingmixtures. Stiffness Types Strength/RB Strain/εB Modulus/SB Types Bending-Tensile Strength/RB Maximum Bending Strain/εB Bending Stiffness Modulus/SB OGFCOGFC 5.202 5.202 2886 2886 1802 1802 SBS-OGFCSBS-OGFC 7.465 7.465 4155 4155 1796 1796 SM-OGFCSM-OGFC 6.842 6.842 4077 4077 1678 1678

4.3. Cantabro Cantabro Test Test Results Figure 10 shows the the Cantabro Cantabro losses of different different mixtures after Cantabro test. The The Cantabro Cantabro test was conducted onon threethree replicatesreplicates of of each each mixture, mixture, so so the the standard standard deviation deviation values values were were shown shown asthe as theerror error bar frombar from theaverages the averages in the in figure. the figure. The greater The greater Cantabro Cantabro losses indicateslosses indicates that the that worse the raveling worse ravelingresistance. resistance. The SBS-OGFC The SBS-OGFC shows the shows greatest the greate ravelingst raveling resistance resistance among among all OGFC all OGFC mixtures, mixtures, which whichmeans means that the that SBS the modified SBS modified asphalt provides asphalt aprov betterides adhesion a better and adhesion improved and raveling improved resistance raveling of resistanceOGFC. SM-OGFC of OGFC. has SM-OGFC better raveling has better resistance raveling than resi OGFCstance inthan this OGFC paper. in The this conclusionpaper. The drawnconclusion here drawncan be confirmedhere can be by confirmed the result by of the splitting result testof splitting and beam test bending and beam test. bending test.

FigureFigure 10. 10. CantabroCantabro losses losses of of all all OGFC mixtures. 4.4. Immersion Marshall Test and Spring-Thawing Stability Test Results 4.4. Immersion Marshall Test and Spring-Thawing Stability Test Results Figures 11 and 12 present the spring-thawing stability (SS), immersion Marshall stability (MS1) Figures 11 and 12 present the spring-thawing stability (SS), immersion Marshall stability (MS1) and immersion residual stability (MS0) for three mixtures. The MS1 value is obtained by performing and immersion residual stability (MS0) for three mixtures. The MS1 ◦value is obtained by performing Marshall test after the specimen has been immersed in water at 60 C for 48 h, and the MS0 value is Marshall test after the specimen has been immersed in water at 60 °C for 48 h, and the MS0 value is obtained by the Equation (4): obtained by the Equation (4): MS1 MS0 = × 100. (4) 𝑀𝑆MS 𝑀𝑆 = × 100. (4) As shown in Figure 11, the SS value of SM-OGFC 𝑀𝑆 was the largest of the three mixtures, and the SS valueAs of shown SM-OGFC in Figure was 42% 11, higherthe SS thanvalue OGFC, of SM-OGFC even 1.6% was higher the largest than SBS-OGFC. of the three The mixtures, results indicated and the SSthat value SM-OGFC of SM-OGFC had excellent was 42% performance higher than in resisting OGFC, ev moistureen 1.6% damage higher duringthan SBS-OGFC. spring-thawing The results season. indicatedOne reason that for SM-OGFC the increase had of the excellent SS value performance of SM-OGFC in is thatresisting silane moisture coupling damage agent with during two differentspring- thawingtypes of functionalseason. One groups reason has for a the strong increase tendency of the to SS bond value asphalt of SM-OGFC and aggregate, is that silane which coupling can make agent the withcontent two of different moisture types that penetrates of functional into groups the interface has a betweenstrong tendency asphalt and to bond aggregate asphalt decrease and aggregate, as a result. whichThis improves can make the the performance content of of moisture SM-OGFC that against penetrates moisture into damage the interface during spring-thawingbetween asphalt season. and aggregateAs shown decrease in Figure as 12 a, result. the MS Th1 valueis improves of SM-OGFC the performance was 41.4% of higher SM-OGFC than against OGFC, moisture reached 98.7%damage of ◦ duringSBS-OGFC. spring-thawing The results season. showed As that shown SM-OGFC in Figure had 12, a high the MarshallMS1 value stability of SM-OGFC after immersion was 41.4% athigher 60 C thanfor 48h. OGFC, However, reached the 98.7% MS0 value of SBS-OGFC. of SM-OGFC The was results the smallestshowed ofthat the SM-OGFC three mixtures, had a which high indicatedMarshall stabilitythat Marshall after stabilityimmersion attenuation at 60°C for of SM-OGFC48h. However, was thethe largestMS0 value among of SM-OGFC three mixtures wasafter the smallest immersion of ◦ theat 60 threeC for mixtures, 48 h. The which main indicated reason for that this Marshall is the high stability water absorption attenuation of of OSW. SM-OGFC Nevertheless, was the the largest higer amongMS1 value three proved mixtures that after SM-OGFC immersion had a at higher 60 °C bearing for 48 h. capacity The main relative reason to OGFCfor this after is the immersion high water at ◦ absorption60 C for 48 of h. OSW. Nevertheless, the higer MS1 value proved that SM-OGFC had a higher bearing capacity relative to OGFC after immersion at 60 °C for 48 h. Appl. Sci. 2018, 8, x FOR PEER REVIEW 16 of 23

Appl.Appl. Sci. Sci. 20182018,, 88,, x 1626 FOR PEER REVIEW 1616 of of 2223 Appl. Sci. 2018, 8, x FOR PEER REVIEW 16 of 23

Figure 11. Spring-thawing stability for all OGFC mixtures.

FigureFigure 11. 11. Spring-thawingSpring-thawing stability stability for for all all OGFC OGFC mixtures. mixtures. Figure 11. Spring-thawing stability for all OGFC mixtures.

Figure 12. Immersion Marshall stability and Immersion residual stability for all OGFC stability.

FigureFigure 12. 12. ImmersionImmersion Marshall Marshall stability stability and and Immersion Immersion residual residual stability stability for for all all OGFC OGFC stability. stability. 4.5. PermeabilityFigure 12. Test Immersion Results Marshall stability and Immersion residual stability for all OGFC stability. 4.5. Permeability Test Results 4.5. PermeabilityFigure 13 shows Test Results the permeability coefficient of three mixtures at temperature of 20 °C. The K20°C 4.5. Permeability Test Results ◦ valueFigure of OGFC, 13 shows SBS-OGFC the permeability and SM-OGFC coefficient were of threefound mixtures to 0.19, at0.28 temperature and 0.24. ofAccording 20 C. The toK 20the◦C Figure 13 shows the permeability coefficient of three mixtures at temperature of 20 °C. The K20°C technicalvalue of OGFC, requirements SBS-OGFC of the and open SM-OGFC grade asphalt were found mixture to 0.19, in the 0.28 Specifications and 0.24. According for design to theof Highway technical valueFigure of OGFC, 13 shows SBS-OGFC the permeability and SM-OGFC coefficient were of found three mixturesto 0.19, 0.28at temperature and 0.24. Accordingof 20 °C. The to K the20°C Asphaltrequirements Pavement of the in open China grade (JTG asphalt D50-2006), mixture It inis therecommended Specifications that for the design permeability of Highway coefficient Asphalt technicalvalue of requirementsOGFC, SBS-OGFC of the openand SM-OGFC grade asphalt were mi xturefound in to the 0.19, Specifications 0.28 and 0.24. for design According of Highway to the (KPavement20°C) should in China be greater (JTG than D50-2006), 0.01 cm/s, It is and recommended the K20°C value that of the three permeability mixtures coefficientmeets the specifications. (K ◦ ) should Asphalttechnical Pavement requirements in China of the open(JTG gradeD50-2006), asphalt It miis recommendedxture in the Specifications that the permeability for design of20 coefficient HighwayC ItAsphaltbe is greater well Pavementknown than 0.01that in cm/s,asphalt-aggregate China and (JTG the D50-2006),K20◦ ratioC value plays It of is three arecommended key mixturesrole in permeability meets that the the permeability specifications. performance coefficient of It OGFC. is well (K20°C) should be greater than 0.01 cm/s, and the K20°C value of three mixtures meets the specifications. Theknown lower that the asphalt-aggregate asphalt-aggregate ratio ratio, plays the a better key role the in permeability permeability performance performance of of OGFC. OGFC. Thus, The lower SBS- It(K is20°C well) should known be thatgreater asphalt-aggregate than 0.01 cm/s, ratioand the plays K20°C a keyvalue role of threein permeability mixtures meets performance the specifications. of OGFC. OGFCthe asphalt-aggregate shows better permeability ratio, the betterperformance the permeability than OGFC. performance What is interesting of OGFC. is that Thus, SM-OGFC SBS-OGFC has TheIt is lowerwell known the asphalt-aggregate that asphalt-aggregate ratio, the ratio better plays the a permeabilitykey role in permeability performance performance of OGFC. Thus, of OGFC. SBS- ashows higher better asphalt-aggregate permeability performance ratio than OGFC, than OGFC. but has What better is interesting permeability is that performance. SM-OGFC has The a highermain OGFCThe lower shows the better asphalt-aggregate permeability ratio,performance the better than the OGFC. permeability What is performance interesting isof that OGFC. SM-OGFC Thus, SBS- has reasonasphalt-aggregate for this phenomenon ratio than OGFC,is that SM-OGFC but has better has permeability relatively less performance. free asphalt, The which main leads reason to a for lower this aOGFC higher shows asphalt-aggregate better permeability ratio performancethan OGFC, butthan has OGFC. better What permeability is interesting performance. is that SM-OGFC The main has probabilityphenomenon of isfree that asphalt SM-OGFC blocking has relatively the interc lessonnected free asphalt, pores, which thus leadsshowing to a lowerbetter probabilitypermeability of reasona higher for asphalt-aggregate this phenomenon ratiois that than SM-OGFC OGFC, hasbut relatively has better less permeability free asphalt, performance. which leads toThe a lowermain performance.free asphalt blocking the interconnected pores, thus showing better permeability performance. probabilityreason for this of phenomenonfree asphalt blocking is that SM-OGFC the interc hasonnected relatively pores, less freethus asphalt, showing which better leads permeability to a lower performance.probability of free asphalt blocking the interconnected pores, thus showing better permeability performance.

Figure 13. Permeability coefficient for all OGFC mixtures. Figure 13. Permeability coefficient for all OGFC mixtures.

Figure 13. Permeability coefficient for all OGFC mixtures. Figure 13. Permeability coefficient for all OGFC mixtures. Appl. Sci. 2018, 8, 1626 17 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 17 of 23

4.6. Scanning Scanning Electronic Microscopy Test ResultsResults Scanning electron micrographsmicrographs ofof granitegranite and and OSW OSW with with a a grain grain size size of of 0.6 0.6 mm mm were were observed observed at atmagnifying magnifying power power of of× 1000,×1000,× ×10,00010,000 and and× ×60,000,60,000, asas areare shownshown inin FigureFigure 1414a–f.a–f.

(a)

(b)

(c)

(d)

Figure 14. Cont. Appl. Sci. 2018, 8, 1626 18 of 22 Appl. Sci. 2018, 8, x FOR PEER REVIEW 18 of 23

(e)

(f)

Figure 14. (a) ScanningScanning electronelectron microscopemicroscope imageimage ofof granitegranite particlesparticles ((×1000);×1000); ( b) Scanning electron image of OSW particlesparticles ((×1000);×1000); ( (cc)) Scanning Scanning electron electron microscope microscope (SEM) image of granite particles ((×10,000);×10,000); ( (dd)) Scanning Scanning electron electron microscope imageimage ofof OSWOSW particlesparticles ((×10,000);×10,000); ( e) Scanning electron microscope image ofof granitegranite particlesparticles ((×60,000);×60,000); ( (ff)) Scanning electron microscope image of OSW particles ((×60,000).×60,000).

It can be be seen seen from from Figure Figure 14 14 that that the the surface surface of ofOSW OSW is rougher is rougher than than the thegranite granite particles, particles, the themicropores micropores of OSW of OSW are relatively are relatively developed, developed, and andthe void the voidcontent content of OSW of OSW is higher. is higher. On the On low- the low-magnificationmagnification scanned scanned image, image, it was it was found found that that the the OSW OSW has has a large a large number number of of micron-sized micron-sized pores, pores, and thethe edgeedge of of the the pores pores is is surrounded surrounded by by mossy mossy and an petal-liked petal-like protrusions. protrusions. The microporesThe micropores with sizeswith rangingsizes ranging from severalfrom several microns microns to about to 30 aboutµm can 30 be µm seen can in be the seen Figure in 14theb,d. Figure The special 14b,d. structure The special can providestructure high can specific provide surface high areaspecific and adsorptionsurface area capacity and adsorption for OSW. Oncapacity the high-magnification for OSW. On the scanned high- image,magnification the multi-layered scanned image, cave-like the poresmulti-layered are embedded cave-like in the pores micropore, are embedded the cavity in the is embedded micropore, with the acavity plurality is embedded of cave-like with pores, a plurality which of are cave-like connected pores, toeach which other are inconnected the deep to micropore, each othershowing in the deep an irregularmicropore, laminar showing columnar an irregular connected laminar structure. columnar On connected the locally structure. enlarged nano-scaleOn the locally image, enlarged many smallnano-scale cell-like image, structure many small tentacles cell-like appear structure inside tentacles the micropore, appear inside this structure the micropore, has internal this structure surface areahas internal provided surface by the area interlayer provided structure by the interlayer compared structure with the compared granite. with Due tothe the granite. unique Due laminar to the columnarunique laminar connected columnar structure connected and cell-like structure structure and cell antennae-like structure of OSW, antennae it can achieve of OSW, better it can bite achieve with asphalt.better bite Compared with asphalt. with granite-asphaltCompared with mortar, granite-asphalt OSW-asphalt mortar, mortar OSW-as has betterphalt structuralmortar has stability better andstructural mechanical stability properties. and mechanical properties.

5. Economic Analysis In this section,section, the economic analysis of SM-OGFC and SBS-OGFC mixture in improving properties is conductedconducted compared normal OGFCOGFC mixture.mixture. The The price ratio PR andand performanceperformance improvement ration ration PIR PIR can can be be calculated calculated by by the the fo followingllowing equation. equation. The The results results are are listed listed in Table in Table 10 10

PR𝑃𝑅= Pm =𝑃 /⁄P𝑃OGFC (5)(5)

𝑃𝐼𝑅 =𝑃𝐼 ⁄𝑃𝐼 (6) Appl. Sci. 2018, 8, 1626 19 of 22

PIR = PIm/PIOGFC (6) where Pm and PIm are the price and properties of SBS-OGFC and SM-OGFC, POGFC and PIOGFC are the price and properties of the normal OGFC mixture [27]. 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 0.197 (value as 0.20) CNY/kg. As shown in Table 11, when the 2.5% silane coupling agent is added to the base asphalt and the oil shale waste is used to replace the fine aggregate of the mixtures (SM-OGFC mixture), the pavement performance, including high and low temperature stability, water stability, raveling resistance performance and permeability performance, has an improvement compared to OGFC mixture, while its price is also relatively lower. It is also can be seen that SBS-OGFC mixture has better properties than OGFC mixture, while its price is not rising obviously. Moreover, analyzing the data in Table 11, SM-OGFC has almost the same pavement performance as SBS-OGFC, but has a cheaper price. Appl. Sci. 2018, 8, 1626 20 of 22

Table 11. Economic benefit analysis.

−15 ◦C Immersion Marshall Dynamic Permeability Asphalt Mixture Splitting Bending-Tensile Cantabro Marshall Spring-Thawing Mixture Type Stability Stability Coefficient Price Price Strength Strength (Mpa) Losses (%) Stability Stability (kn) (kn) (n/min) (cm/s) (CNH/kg) (CNH/kg) (Mpa) (kn) SBS-OGFC 9.12 5250 3.71 7.465 12.8 8.21 8.16 0.28 4.52 0.382 SM-OGFC 9.63 4972 3.87 6.842 14.2 8.1 8.29 0.24 4.05 0.363 OGFC 6.47 3340 2.74 5.202 17.4 5.73 5.84 0.19 4.00 0.380 PIRSBS-OGFC and PRSBS-OGFC 1.41 1.57 1.35 1.44 0.74 1.43 1.40 1.47 1.13 1.01 PIRSM-OGFC and PRSM-OGFC 1.49 1.49 1.41 1.32 0.82 1.41 1.42 1.26 1.01 0.96 Appl. Sci. 2018, 8, 1626 21 of 22

6. Conclusions From test results the following conclusions were drawn: A new modified OGFC (SM-OGFC) was prepared by replacing the fine aggregate below 4.75 mm in OGFC with the oil shale waste, and the silane coupling agent modifier was used to assist modification. The preparation process of SM-OGFC was optimized by CCD to obtain a SM-OGFC with the best mechanical properties. High-temperature mechanical test, low-temperature mechanical test, water stability test, raveling test and permeability test are adopted to evaluate the comprehensive ability of SM-OGFC. The results prove that SM-OGFC has better high temperature mechanical performance, lower temperature mechanical performance, water stability, raveling resistance and permeability performance than OGFC mixture—and even superior to SBS modified OGFC mixture in some aspects. Therefore, it is likely that the development of SM-OGFC could be helpful to make conventional OGFC qualified for complex service ambient, as well as improve the recycling rate of industrial waste to reduce environmental pollution and reduce the cost of asphalt pavement. SEM analysis are adopted to explore the modification mechanism of oil shale waste. These results indicate that the unique laminar columnar connected structure, and cell-like structure antennae of oil shale waste, could be the main reasons why SM-OGFC obtained excellent comprehensive performance.

Author Contributions: Conceptualization, X.G.; Data curation, W.G., X.C. and W.D.; Formal analysis, W.G.; Funding acquisition, X.G.; Investigation, X.G. and W.D.; Project administration, W.D.; Software, W.G. and X.C.; Supervision, X.G.; Writing—original draft, W.G. and X.C.; Writing—review & editing, X.G. and W.D. Funding: This research was funded by the National Nature Science Foundation of China (NSFC) (Grant No. 51178204). Acknowledgments: This research was funded by the National Nature Science Foundation of China (NSFC) (Grant No. 51178204). This financial support is gratefully acknowledged. Conflicts of Interest: The authors declare that there is no conflict of interests regarding the publication of this paper.

References

1. Chen, J.; Yin, X.J.; Wang, H.; Ding, Y.M. Evaluation of durability and functional performance of porous polyurethane mixture in porous pavement. J. Clean. Prod. 2018, 188, 12–19. [CrossRef] 2. 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] 3. 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] 4. Pattanaik, M.L.; Choudhary, R.; Kumar, B. Evaluation of frictional pavement resistance as a function of aggregate physical properties. J. Trans. Eng. Part B Pavement 2017, 143, 1–8. [CrossRef] 5. Song, W.; Shu, X.; Huang, B.; Woods, M. Laboratory investigation of interlayer shear fatigue performance between open-graded friction course and underlying layer. Constr. Build. Mater. 2016, 115, 381–389. [CrossRef] 6. 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] 7. 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; AlQadi, I.L., Ozer, H., VelezVega, E.M., Murrell, S., Eds.; American Society Civil Engineers: , NY, USA, 2017. 8. Ouyang, X.Y. Research on moisture damage research in Hunan province expressway pavement. In Proceedings of the International Conference on Automation, Communication, Architectonics and Materials, Wuhan, China, 18–19 June 2011; Zhang, H., Shen, G., Jin, D., Eds.; Trans Tech Publications Inc.: Durnten-Zurich, Switzerland, 2011. 9. Lyons, K.R.; Putman, B.J. Laboratory evaluation of stabilizing methods for porous asphalt mixtures. Constr. Build. Mater. 2013, 49, 772–780. [CrossRef] Appl. Sci. 2018, 8, 1626 22 of 22

10. Luo, S.; Qian, Z.D.; Xue, Y.C. Performance evaluation of open-graded epoxy with two nominal maximum aggregate sizes. J. Cent. South Univ. (Engl. Ed.) 2015, 22, 4483–4489. [CrossRef] 11. 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] 12. Shen, W.G.; Shan, L.; Zhang, T.; Ma, H.K.; Cai, Z.; Shi, H. Investigation on polymer-rubber aggregate modified porous concrete. Constr. Build. Mater. 2013, 38, 667–674. [CrossRef] 13. 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. 14. Li, C.H.; Xiang, X.D.; Zhou, X.Y.; Tu, X.Q. Utilization of Steel Slag as Aggregates for Porous Asphalt Mixture. In Proceedings of the Annual Meetings of Chinese-Society’s-Building-Materials, Professional Committees of Stone and Aggregate and Utilization of Solid Waste, Wuhan, China, 28 November–1 December 2013; Wu, S., Chen, M.H., Eds.; Trans Tech Publications Inc.: Durnten-Zurich, Switzerland, 2014. 15. Wang, Y.H.; Wang, G.; Ahn, Y.H. Effects of Using Recycled Asphalt Shingles in Open-Graded Friction Course on Flexible Pavement Performance. J. Test. Eval. 2014, 42, 1173–1182. [CrossRef] 16. Hainin, M.R.; Rusbintardjo, G.; Hameed, M.A.S.; Hassan, N.A.; Yusoff, N.I.M. Utilisation of steel slag as an aggregate replacement in porous asphalt mixtures. J. Teknol. 2014, 69, 67–73. [CrossRef] 17. 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] 18. Peng, C.; Chen, P.X.; You, Z.P.; Lv, S.T.; Zhang, R.; Xu, F.; Zhang, H.; Chen, H.L. Effect of silane coupling agent on improving the properties between asphalt binder and aggregates. Constr. Build. Mater. 2018, 169, 591–600. [CrossRef] 19. Min, Y.; Fang, Y.; Huang, X.; Zhu, Y.; Li, W.; Yuan, J.; Tan, L.; Wang, S.; Wu, Z. Surface modification of basalt with silane coupling agent on asphalt mixture moisture damage. Appl. Surf. Sci. 2015, 346, 497–502. [CrossRef] 20. Chen, J.; Sun, P.T.; Li, F.J. Study on permeability coefficient of asphalt mixture. J. Highw. Transp. Res. Dev. 2006, 23, 5–8. [CrossRef] 21. Woelfl, G.A.; Wei, I.W.; Faulstich, C.N.; Litwack, H.S. Laboratory testing of asphalt concrete for porous pavements. J. Test. Eval. 1981, 9, 175–181. [CrossRef] 22. Bezerra, M.A.; Santelli, R.E.; Oliveira, E.P.; Villar, L.S.; Escaleira, L.A. Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta 2008, 76, 965–977. [CrossRef][PubMed] 23. Zhao, W.Z.; Yu, Z.P.; Liu, J.B.; Yu, Y.D.; Yin, Y.G.; Lin, S.Y.; Chen, F. Optimized extraction of polysaccharides from corn silk by pulsed electric field and response surface quadratic design. J. Sci. Food Agric. 2011, 91, 2201–2209. [CrossRef][PubMed] 24. Borzoei, M.; Zanjanchi, M.A.; Sadeghi-Aliabadi, H.; Saghaie, L. Optimization of a methodology for determination of iron concentration in aqueous samples using a newly synthesized chelating agent in dispersive liquid-liquid microextraction. Food Chem. 2018, 264, 9–15. [CrossRef][PubMed] 25. Nassar, A.I.; Thom, N.; Parry, T. Optimizing the mix design of cold bitumen emulsion mixtures using response surface methodology. Constr. Build. Mater. 2016, 104, 216–229. [CrossRef] 26. Wang, W.S.; Cheng, Y.C.; Tan, G.J. Design Optimization of SBS-Modified Asphalt Mixture Reinforced with Eco-Friendly Basalt Fiber Based on Response Surface Methodology. Materials 2018, 11.[CrossRef][PubMed] 27. 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]

© 2018 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/).