Laboratory Investigation of the Composite Influence of Rock Asphalt and Montmorillonite on the Performance of Bio-Asphalt

Abstract

To improve the rutting resistance and anti-aging performance of bio-asphalt, the composite modifier of rock asphalt and montmorillonite is used to modify the bio-asphalt. The optimum content of each component was determined by orthogonal tests based on the results from penetration, softening point, ductility and viscosity tests. The rheological properties and anti-aging performance of rock asphalt and montmorillonite composite-modified bio-asphalt (RAMB) with the optimum content were evaluated as compared to those of matrix asphalt (MA), untreated/treated bio-asphalt (UBA/TBA) and rock asphalt-/montmorillonite-modified bio-asphalt (RMB/MMB). The test results illustrated that the optimum content of each component in the rock asphalt/montmorillonite composite-modified bio-asphalt—as determined by orthogonal experimental design and penetration, softening point, ductility and viscosity tests—was 7% bio-oil treated by thermostatic water bath, 5% rock asphalt and 30% montmorillonite. The high-temperature performance, low-temperature performance and anti-aging performance of RAMB were studied by comparison to those of matrix asphalt, UBA, TBA, RMB and MMB. Additionally, the composite modification mechanism was studied by Fourier transform infrared spectroscopy (FTIR). The results suggested that the high-temperature of TBA was obviously improved compared with UBA. The reason, as seen from infrared spectrum tests, was that the amount of ester compounds decreased after water bath treatment. The light components and soluble substances in bio-oil decreased. Compared to UBA, the unrecoverable creep compliance (J_nr) of RAMB decreased by 66.6% and the recovery rate (R) increased by 75.9% at 0.1 KPa. The stiffness modulus (S) of RAMB was 0.87 times that of matrix asphalt and the creep rate (m) was 1.03 times that of base asphalt. Compared to single-modified asphalt, the high- and low-temperature performance of RAMB was good. Meanwhile, the complex modulus aging index (CMAI) and stiffness modulus aging index (SAI) of RAMB were lower than all other asphalt studied, while the phase angle aging index (PAAI) and creep rate aging index (mAI) of RAMB were the largest. The results of infrared spectroscopy also suggest that the mixing of rock asphalt, montmorillonite, bio-oil and matrix asphalt is a physical blending process. During the process, no functional groups are formed. Pretreatment and addition of rock asphalt and montmorillonite can improve high-temperature performance, low-temperature performance and anti-aging performance of the bio-asphalt.

1. Introduction

The development of road networks plays an important role in the national economy. Petroleum asphalt is rapidly consumed with the quick development of road networks. There is a desperate shortage of petroleum asphalt. To ensure good road performance, the development of economically- and environmentally-friendly alternative materials is highly significant. Bio-asphalt is considered the alternative material with the most potential. However, the high-temperature performance and anti-aging performance of existing bio-asphalt are seriously insufficient.

According to research findings, bio-oil can replace a portion of petroleum asphalt [1]. The production cost of bio-asphalt is about 3/10~2/5 of that of petroleum asphalt. Bio-asphalt shows reasonable economic and environmental performance [2]. Road workers have performed plenty of tests on the preparation technology, chemical composition, modification mechanism, physicochemical properties and road performance of waste cooking oil bio-asphalt [3,4,5,6]. Waste cooking oil contains high amounts of water and volatile substances. This limits the incorporation of waste cooking oil into bio-asphalt. Compared to petroleum asphalt, bio-oil contains hundreds of oxygenated compounds. Its moisture content and oxygen content are higher. Therefore, bio-oil is unstable and the aging rate of bio-oil accelerates with increasing temperature [7,8]. Wang et al. found that the presence of moisture and volatile substances may lead to delamination of bio-oil. Thus, the bio-oil was distilled at 110 °C before being added to asphalt [9]. Zhang et al. treated bio-oil with distilled water at 50 °C, which can remove polar light components in bio-oil [10]. Yang et al. removed water from bio-oil before addition to petroleum asphalt [11]. The mixture’s physical properties were tested, such as pH value and water content. Ruikun et al. removed the water in the waste cooking oil [12]. Waste cooking oil- and pre-desulfurization rubber powder-modified asphalt were obtained. The results of Maharaj et al. showed that the anti-fatigue of the mixture was improved with the introduction of waste cooking oil [13]. The bio-asphalt mixture has good low-temperature performance and water stability. Conversely, high-temperature performance and anti-aging performance are poor [4,14,15].

To improve the high-temperature performance of bio-asphalt, Yang et al. added 4% polyethylene and found that the rutting resistance was improved [16]. Sun et al. added SBS to bio-asphalt to improve the high-temperature performance. They found that the activation energy of SBS-modified asphalt was reduced by adding bio-oil. SBS-modified asphalt containing bio-oil had a low viscosity value. Bio-oil can lower the high-temperature rutting resistance [17]. The nitrogen and asphaltene content were much higher in rock asphalt compared to matrix asphalt. As such, rock asphalt-modified asphalt showed good high-temperature performance. Lv et al. found that the high-temperature performance of matrix asphalt was improved by rock asphalt because asphaltenes and gums were increased [18,19,20]. Menglan et al. prepared composite-modified asphalt by adding European rock asphalt and castor oil bio-asphalt. The addition of composite modifier was in the range of 20–30%. The high-temperature and anti-aging properties of asphalt were upgraded by adding composite modifier. The low-temperature properties and temperature sensitivity of asphalt were also improved. Different performance requirements can be met by adjusting the upper and lower limits of the content. Rock asphalt played a significant role as a high temperature modifier [21]. Yu et al. carried out X-ray diffraction and found that montmorillonite-modified asphalt could form an intercalated structure, while organic montmorillonite-modified asphalt could form an exfoliated structure. This improved the thermal oxidation aging resistance and ultraviolet aging resistance of asphalt [22]. Fen Ye and Vargas performed dynamic shear rheological tests (DSR). Organic montmorillonite-modified asphalt showed better anti-aging performance and high-temperature performance [23,24]. The temperature sensitivity was reduced. Lu compared the effects of nano-montmorillonite and naphthenic oil on SBS-modified asphalt. They found that nano-montmorillonite reduced the low-temperature performance and high-temperature viscosity [25]. To improve the viscosity and high-temperature stability of bio-asphalt, Siqing Liu [26] added hard asphalt particles, C5 petroleum resin, organic montmorillonite and styrene–butadiene rubber to bio-asphalt. According to research findings, the modified bio-asphalt with the best modifier ratio was still soft (penetration was 123 (0.1 mm)). The high-temperature performance was not ideal. The addition of crosslinking agent, anti-aging agent and dispersant improved the high-temperature stability, anti-aging performance and storage stability of the asphalt. Nevertheless, this is difficult to use in engineering applications due to the complex preparation process and many kinds of modified substances and additives. Therefore, further work is needed to improve the high-temperature performance and anti-aging performance of bio-asphalt.

Therefore, this paper employed pretreatment measures. Organic montmorillonite and rock asphalt were selected to modify bio-asphalt. Organic montmorillonite can form stripping structure and improve the anti-aging performance of asphalt. Asphaltene and colloid content in asphalt were increased and the high-temperature performance of asphalt was improved because of the addition of rock asphalt. The rheological properties and anti-aging of modified asphalt were analyzed. The mechanism of composite modification was revealed by FTIR. This provided a basis for improving the performance of waste cooking oil bio-asphalt. A technology roadmap was established, as shown in Figure 1.

2. Materials and Methods

2.1. Materials

2.1.1. Asphalt

No.70 matrix asphalt was used in this paper. The basic performance was measured by “Standard Test Methods of Asphalt and Bituminous Mixtures for Highway Engineering, JTG E20-2011” [27]. The experimental results are listed in

Table 1. Basic properties of asphalt.

Project		Unit	Demand	Result	Test Method
Penetration (25 °C, 100 g, 5 s)		0.1 mm	60~80	67.6	T 0604-2011
Ductility (10 °C, 5 cm/min)		cm	≥10	13.5	T 0605-2011
Softening point (ring and ball method)		°C	≥46	48.5	T 0606-2011
Penetration index		―	−1.5~+1.0	−0.78	T 0604-2011
Density		g/cm3	Measured	1.027	T 0603-2011
60 °C Dynamic viscosity		Pa·s	≥180	272	T 0620-2000
Flash point		°C	≥260	294	T 0611-2011
After RTFOT	Mass change rate	%	±0.8	−0.083	T 0610-2011
	Residual penetration ratio	%	≥61	81	T 0604-2011
	Residual ductility (10 °C)	cm	≥6	7	T 0605-2011

. According to the “Technical Specifications for Construction of Highway Asphalt Pavement, JTG F40-2004” [28], all indicators of No.70 asphalt are within the range of specification requirements.

2.1.2. Bio-Oil

The bio-oil came from waste cooking oil. It was a by-product obtained in the production of biodiesel. The basic properties are shown in

Table 2. Basic properties of bio-oil.

Project	Unit	Index	Test Method
Density	g/mL	0.92~0.95	GB/T 2540
Water content	%	≤0.3	SH/T 0264
60 °C Dynamic viscosity	Pa·s	0.126	GB/T 265
Acid value	mg KOH/g	30~60	SH/T 264

. Compared to the values in Table 1, the density and viscosity are less than the matrix asphalt and the acid value is larger.

2.1.3. Buton Rock Asphalt

Buton rock asphalt was used, which contains 24.8% asphalt, 74.9% ash and some impurities. After being ground and passed through a 0.15 mm standard sieve, the rock asphalt particles could be used as modifiers.

Table 3. Technical indexes of rock asphalt.

Project	Unit	Demand	Result	Test Method
Trichloroethylene Solubility	%	≥18	26.65	T0607
Density	g/cm3	≤1.9	1.71	T0603
Heating loss	%	≤2.0	0.27	T0608
Flash point	°C	≥230	318	T0611

lists some indexes of rock asphalt.

2.1.4. Montmorillonite

Montmorillonite is a good asphalt modifier to improve aging resistance. The montmorillonite in this paper was purchased from China Zhejiang Feng Hong clay chemical plant. The montmorillonite was modified with organic quaternary ammonium salt. As a cationic surfactant, organic quaternary ammonium salt reduced the surface energy of montmorillonite by exchanging interlayer cations of montmorillonite. Thus, the dispersion of organic nano-montmorillonite in asphalt was significantly improved compared to montmorillonite without organic treatment. In addition, organic nano-montmorillonite also has the advantages of large layer spacing, good dispersion and large cation exchange capacity. Some performance indexes of montmorillonite are summarized in

Table 4. Basic performance of OMMT.

Project	Unit	Result	Test Method
Density	g·cm−3	1.02	ASTM D854-14
Granularity	Mesh	5000	GB/T 2922
Coefficient of expansion	/	0.05	GB/T 50123-2019
Hardness	/	1.02	-
Montmorillonite content	%	>99	GB/T 17188-2016
Specific surface area	m2·g−1	750	-
Diameter thickness ratio	/	200	-

.

2.1.5. Preparation of Rock Asphalt and Montmorillonite Composite-Modified Bio-Asphalt (RAMB)

The distilled water and bio-oil were mixed in a mass ratio of 1:1 and placed in a bath at 50 °C for 10 min. The upper bio-oil was then taken out. Figure 2 shows the bio-oil before and after treatment. The matrix asphalt was heated at 135 °C for 1 h in an oven. When it reached the molten state, the asphalt was taken out and then quickly heated and insulated on the electric furnace. The high-speed shear instrument was turned on and set to a speed of 1000 r/min. Next, 7% bio-oil (mass ratio of bio-oil to matrix asphalt) was added and the rotation speed was adjusted to 3000 r/min; the asphalt was sheared at 150~160 °C for 30 min. At this point, bio-asphalt preparation was complete. Next, 30% montmorillonite (mass ratio of montmorillonite to the matrix asphalt and bio-oil) was added and the mixture was sheared for 60 min. A small amount of 5% of the rock asphalt (mass ratio of rock asphalt to the matrix asphalt and bio-oil) was added after passing through a 0.15 mm standard sieve. This was poured into the asphalt several times and mixed manually while adding. After all rock asphalt was added, this was sheared for 30 min. Rock asphalt swelled and developed with volume expansion. When the rock asphalt particles were dissolved and the surface of the modified asphalt presented a mirror effect, the preparation of RAMB was finished.

2.1.6. Proportion Optimization of RAMB

The orthogonal design method of four factors at three different levels was used to determine the mass ratio of water and bio-oil in RAMB and the optimal content of each material. The influence of bio-oil content, the mass ratio of water and bio-oil and the content of rock asphalt and montmorillonite on penetration, ductility, softening point and rotational viscosity of asphalt was considered. Three levels were set for each factor, as shown in

Table 5. Factors and levels.

Level	Factor
	Mass Ratio of Water and Bio-Oil	Content of Bio-Oil (%)	Content of Rock Asphalt (%)	Content of Montmorillonite (%)
1	1:1	5	20	3
2	2:1	7	30	5
3	3:1	9	40	7

. According to the orthogonal design table of L9(34) (as shown in

Table 6. Combinations of orthogonal test L9(34).

Number	Mass Ratio of Water and Bio-Oil	Content of Bio-Oil (%)	Content of Rock Asphalt (%)	Content of Montmorillonite (%)	Orthogonal Combinations
1	1:1	5	20	3	A1B1C1 D1
2	1:1	7	30	5	A1B2C2 D2
3	1:1	9	40	7	A1B3C3 D3
4	2:1	5	30	7	A2B1C2 D3
5	2:1	7	40	3	A2B2C3 D1
6	2:1	9	20	5	A2B3C1 D2
7	3:1	5	40	5	A3B1C3 D2
8	3:1	7	20	7	A3B2C1 D3
9	3:1	9	30	3	A3B3C2 D1

), nine asphalts with different content combinations were prepared and tested.

Table 7. Basic properties of orthogonal test.

Combinations	Penetration (0.1 mm)	Softening Point (°C)	Ductility at 10 °C (mm)	Rotational Viscosity at 135 °C (Pa·s)
1	59.47	52.2	116.5	0.690
2	63.77	50.6	152.8	0.805
3	62.4	51.3	101.3	0.965
4	52.63	52.7	95.5	0.955
5	62.83	53.3	99.5	0.940
6	95.9	47.6	304.2	0.640
7	57.23	51.4	132.1	0.935
8	81.1	48.3	183.2	0.755
9	83.67	47.8	288.8	0.715

lists the orthogonal test results. The penetration of the matrix asphalt was 67.6 (0.1 mm) and the softening point was 48.5 °C in this paper. The penetration values of No.6, No.8 and No.9 were far larger than matrix asphalt. Additionally, the softening point was slightly lower than that of matrix asphalt. This indicates that the high-temperature performance of these three combinations was poor. Improving the high-temperature performance of bio-asphalt was the main purpose of this paper but these three combinations could not meet the requirements. After these three combinations were eliminated, the remaining six combinations were selected by Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) in multi-objective decision-making. The decision matrix was a 6 × 4 matrix [29,30].

Table 8. Results of TOPSIS.

Combination	Di+	Di−	CI	Sort
1	0.105575933	0.044310354	0.29562647	4
2	0.08704551	0.047591609	0.353480599	1
3	0.114158233	0.03963836	0.257732365	5
4	0.115642707	0.058291842	0.335136648	3
5	0.115200269	0.039523716	0.255446599	6
7	0.058596286	0.115635936	0.352389578	2

lists the ranking results of TOPSIS. According to the table, the second combination was a suitable preparation method for RAMB. In this method, the mass ratio of water and bio-oil was 1:1, the content of bio-oil was 7%, the content of rock asphalt was 30% and the content of montmorillonite was 5%. Note: Di⁺ presents the distance between each combination and positive ideal solution; Di⁻ presents the distance between each combination and negative ideal solution; CI presents approaching index.

2.2. Methods

To prove the performance of RAMB, six asphalts were prepared, including matrix asphalt, untreated bio-asphalt, treated bio-asphalt, rock asphalt-modified bio-asphalt, montmorillonite-modified bio-asphalt and RAMB. When carrying out different tests, parallel samples of each asphalt were prepared. The repeatability error value according to the specification requirements were determined, to ensure the reliability of the experiment. By comparing a series of experimental indicators, the road performance of RAMB was analyzed. Specific tests and indicators are described as follows.

2.2.1. Dynamic Shear Rheological Test (DSR)

Frequency Scanning Test (FS)

The dynamic shear rheological test is one of the most important tests in the American Strategic Highway Research Program (SHRP). This test shears asphalt using the reciprocating motion of oscillating plates parallel to fixed plates. Wheel movement on a road surface is simulated at 55 miles per hour. Due to the viscoelastic properties of asphalt, strain (stress) delayed response occurs under the action of shear stress (strain). The basic principle of the dynamic shear rheometer is shown in Figure 3.

The frequency scanning test of unaged asphalt was carried out. The changes in high-temperature rheological parameters of asphalt at different frequencies were revealed. The test temperature was 58 °C. The frequency range was 0~100 Hz. The measurement was carried out from high frequency to low frequency and 31 data points were recorded. The temperature scanning test of unaged, short-term aging and long-term aging asphalt were used to evaluate the anti-aging properties of asphalt. The test angular frequency was 10 rad/s (that is, a constant frequency of 1.59 Hz). There were four temperatures which ranged from 46 °C to 60 °C, with every 6 °C as a temperature interval. A 25 mm oscillating plate was used for the unaged and short-term aging asphalt. The gap between the two parallel plates was 1 mm. The parallel plate was replaced with an 8 mm oscillating plate for the long-term aging asphalt. The gap between the two parallel plates was 2 mm. The differences were used because the long-term aging asphalt was harder than the unaged and short-term aging asphalt. The angle phase (δ) and complex modulus (G*) of asphalt were obtained and the rutting factor was calculated.

Multiple Stress Creep Recovery Test (MSCR)

MSCR test of the short-term aging asphalt was carried out at 58 °C. The asphalt was subjected to 30 creep recovery cycles at two constant stress levels of 0.1 KPa and 3.2 KPa. The creep occurred for 1 s and the recovery process lasted for 9 s. According to Equations (1)–(3), the R and J_nr values of asphalt at 0.1 KPa and 3.2 KPa were calculated. The elastic recovery ability and high-temperature rutting resistance of asphalt were evaluated.

$${\mathrm{J}}_{\mathrm{nr}}\left(0.1\right)=\frac{{\epsilon }_r-{\epsilon }_0}{0.1}$$

(1)

$${\mathrm{J}}_{\mathrm{nr}}\left(3.2\right)=\frac{{\epsilon }_r-{\epsilon }_0}{3.2}$$

(2)

$$\mathrm{R}=\frac{\left({\epsilon }_1-{\epsilon }_{10}\right)\times 100}{{\epsilon }_1}$$

(3)

2.2.2. Bending Beam Rheological Test (BBR)

The S and m values of asphalt were measured by BBR test, as shown in Figure 4. These two low-temperature rheological indexes are closely related to the low-temperature performance of asphalt. SHRP states that the S value of asphalt should not exceed 300 MPa and the m value of asphalt should not be less than 0.3. BBR tests of the unaged asphalt, short-term aging asphalt and long-term aging asphalt were carried out. The low-temperature performance of asphalt and the effect of aging on the low-temperature performance of asphalt were revealed. An asphalt specimen with a size of 127 mm × 12 mm × 6.35 mm was formed in a cuboid mold without cover. Then, the constant load of 980 mN ± 50 mN was continuously applied to the simply supported beam at −18 °C for 240 s. The deformation and load of specimens were recorded at 8.0 s, 15.0 s, 30.0 s, 60.0 s, 120.0 s and 240.0 s. The S and m values at 60.0 s were acquired as evaluation indexes of the bending beam rheometer test.

2.2.3. Aging of Asphalt

Asphalt ages under high-temperature and it oxidizes during preparation and mixing with aggregate. Laboratories usually use film oven or rotating thin film oven test under standard conditions to simulate the process of aging. In this study, asphalt underwent short-term aging by the rotating thin film oven test. The asphalt after short-term aging was used for further long-term aging and conducted mechanism tests. Each aging bottle was filled with 35 ± 0.5 g asphalt. A group of 8 aging bottles was placed on the annular supports of the rotating thin film oven. The asphalt was aged for 85 min at 163 °C.

Pressure Aging Vessel-accelerated asphalt aging test (PAV) is a method to simulate the long-term aging of asphalt during service. In this method, asphalt aged by rotating thin film oven was separately divided into PAV sample plates. The quantity of short-term aging asphalt in each sample plate was 50 ± 0.5 g, to form about 3.2 mm-thick asphalt film. Then, the plate was kept at 100 °C and 2.1 MPa for 20 h to accelerate the aging process in a constant-temperature and constant-pressure vessel.

2.2.4. Fourier Transform Infrared Spectroscopy Test (FTIR)

To obtain information about functional groups, FTIR was carried out. The effects of the pretreatment of distilled water and the addition of rock asphalt and montmorillonite on the chemical composition of bio-oil were studied. The infrared spectroscope was Thermo Scientific Nicolet iS50 FT-IR. Solid asphalt and solid powder modifiers (rock asphalt and montmorillonite) were directly measured at room temperature without sample preparation. For solid asphalt, such as the liquid bio-oil at room temperature in this study, the method of sample preparation was with potassium bromide pellets. The infrared spectral curve was collected for liquid asphalt. Because potassium bromide had no absorption peak in the infrared band, it showed a blank spectrum. The spectral curve of the sample shows that the band range is 4000–500 cm⁻¹ and the number of scans is 32 [27].

3. Results

3.1. Rheological Properties

3.1.1. High-Temperature Rheological Properties

FS

FS tests were carried out at different frequencies by oscillatory shear strain. They revealed the effect of loading frequency on the viscoelastic properties of RAMB. Figure 5 lists the G* and δ values of six asphalts at different frequencies.

The composite shear modulus, G*, characterizes the resistance value of the asphalt material during repeated deformation in shear. δ represents the hysteresis of the stress relative to the stress. G* and δ together represent the viscoelastic properties of the asphalt: the larger the δ value, the closer the asphalt is to a viscous body, while the smaller the δ value, the closer the asphalt is to an elastomer, meaning the asphalt is more resistant to deformation at high temperatures. The G* value of the six asphalts gradually increased and the δ value decreased with the increase in frequency. Compared to matrix asphalt, the G* value of bio-asphalt was significantly reduced and the δ value improved. The lack of high-temperature performance can be attributed to bio-oil containing lots of free fatty acids. Free fatty acids are introduced when bio-oil replaces part of the matrix asphalt. This is one of the reasons for the poor rutting resistance of bio-asphalt [31]. Compared to the G* value and δ values of untreated bio-asphalt, treated bio-asphalt, rock asphalt-modified bio-asphalt and montmorillonite-modified bio-asphalt, pretreatment, rock asphalt and montmorillonite improved the G* value of bio-asphalt. The δ value of bio-asphalt was also reduced. The modification effect of rock asphalt was most obvious. The G* value of RAMB was greater than the matrix asphalt. The δ value was lower than the matrix asphalt. Thus, pretreatment, rock asphalt and montmorillonite comprehensively increase the elastic component, the G* value and the high-temperature rutting of bio-asphalt. G* values are sorted as follows: RAMB > matrix asphalt > rock asphalt-modified bio-asphalt > montmorillonite-modified bio-asphalt > treated bio-asphalt > untreated bio-asphalt.

MSCR

The shear strain of the six asphalts is shown in Figure 6. The strain of asphalt under 0.1 KPa was small and the difference between different asphalts was also small. However, the strain of asphalt sharply increased under 3.2 KPa. The growth rate showed a significant difference. The untreated bio-asphalt exhibited a large deformation under the action of load. The shear strain increased rapidly with the repeated loading. The pretreatment and single modifier reduced the shear strain of bio-asphalt, but the effect was not as good as that of rock asphalt–montmorillonite materials composite-modified bio-asphalt.

J_nr can reflect the permanent deformation resistance of asphalt: the smaller the value, the higher the deformation resistance of the asphalt at high temperatures. R can represent the elastic component of the asphalt: the larger the value, the more elastic the asphalt. J_nr and R values of six asphalts at 0.1 KPa and 3.2 KPa are shown in Figure 7 and Figure 8. Shown here, bio-asphalt had the lowest R value and the highest J_nr value among the six asphalts. Bio-asphalt had a large shear deformation under the action of stress. The plastic deformation was the main part, with only a small portion of elastic deformation. The R value of montmorillonite-modified bio-asphalt, treated bio-asphalt and untreated bio-asphalt became negative under 3.2 KPa because the high-temperature performance of the three kinds of asphalt at 58 °C was insufficient in the nonlinear viscoelastic range. The order of R values of the 6 groups of asphalt samples was RAMB > MA >RMB > MMB > TBA > UBA. The RAMB had the minimum J_nr value and the maximum R value. Compared to the untreated bio-asphalt, the J_nr value decreased by 66.6% and the R value increased by 75.9% under 0.1 KPa. The improvement effect of the three measures on the high-temperature rutting resistance is significant. This is consistent with the above frequency scanning results.

3.1.2. Low-Temperature Rheological Test

S value reflects the resistance of asphalt binder to load, while m value reflects the rate of change in asphalt stiffness with time. Specifications require S < 300 MPa and m > 0.3; additionally, a smaller S value and a larger m value lead to better low-temperature rheological properties. The S and m values of the six unaged asphalts at −18 °C are shown in Figure 9. As shown in Figure 9, untreated bio-asphalt had the lowest S value and the largest m value among the six asphalts. The low-temperature performance was good. The bio-asphalt had satisfactory performance in terms of low-temperature deformation resistance because of the significant softening effect of bio-oil. The low-temperature performance of RAMB was lower than that of bio-asphalt, but the S value was less than 300 MPa at −18 °C and them value was greater than 0.3. The requirements of SHRP for low-temperature performance of asphalt binder were met. The S value was 0.87 times that of matrix asphalt and the m value was 1.03 times that of matrix asphalt. Its low-temperature rheology energy was better than matrix asphalt.

3.2. Anti-Aging Performance

3.2.1. Anti-Aging Performance of RAMB Based on High-Temperature Rheological Performance

The dynamic shear rheological test was performed on the short-term and long-term aging of asphalt and the δ and G* values were obtained to calculate the aging index. The rutting indexes for the six asphalts were measured at different temperatures and three aging states (no aging, short-term aging and long-term aging), as shown in Figure 10. The G* value of three of the aging asphalts decreased and the δ value increased as the temperature increased. The high temperature increases the mobility of the asphalt and reduces the anti-deforming capability. The G* value of all asphalts increased and the δ value gradually decreased with aging at constant temperature. The physical hardening effect caused by aging favors the anti-deforming capability of asphalt. The rutting indexes of matrix asphalt, rock asphalt-modified bio-asphalt and RAMB met the requirements. RAMB had the highest G^* value and the lowest δ value. The rutting index of the original asphalt was 2.60 times that of the untreated bio-asphalt and 1.12 times that of the matrix asphalt at 64 °C. The rutting index of the short-term aging asphalt at 64 °C was 2.36 times that of the untreated bio-asphalt and 1.11 times that of the matrix asphalt.

The aging resistance of asphalt was evaluated by calculating CMAI and PAAI using Equations (4) and (5). With smaller CMAI, larger PAAI indicates better aging resistance.

$$\mathrm{CMAI}=\frac{\mathrm{Complex} \mathrm{modulus} \mathrm{of} \mathrm{short} \mathrm{or} \mathrm{long} \mathrm{term} \mathrm{aging} \mathrm{asphalt}}{\mathrm{Complex} \mathrm{modulus} \mathrm{of} \mathrm{original} \mathrm{asphalt}}$$

(4)

$$\mathrm{PAAI}=\frac{\mathrm{Phase} \mathrm{angle} \mathrm{of} \mathrm{short} \mathrm{or} \mathrm{long} \mathrm{term} \mathrm{aging} \mathrm{asphalt}}{\mathrm{Phase} \mathrm{angle} \mathrm{of} \mathrm{original} \mathrm{asphalt}}$$

(5)

The changes in CMAI and PAAI after short- and long-term aging of the six asphalts are shown in Figure 11 and Figure 12. As seen from Figure 11 and Figure 12, untreated bio-asphalt had the largest CMAI and the smallest PAAI in the range of 46 °C to 64 °C. This indicates that untreated bio-asphalt has poor aging resistance and the high-temperature rheological properties are greatly affected by aging because there are many light components in bio-asphalt. The volatilization of light components leads to the change in high-temperature performance of asphalt. The CMAI and PAAI of treated bio-asphalt were improved, compared to untreated bio-asphalt. The pretreatment of distilled water reduced the introduction of light components in matrix asphalt by removing the light components in bio-oil. Thus, the volatilization of light components in bio-asphalt was reduced during the aging. The addition of rock asphalt and montmorillonite reduced the CMAI and increased the PAAI of bio-asphalt. The performance of rock asphalt demonstrated little change under the influence of aging, meaning it can bear rutting deformation under high temperature by serving as the hard particles in bio-asphalt. Montmorillonite within the layered structure reduces the volatilization of light components. Stability of asphalt components is maintained. This prevents oxygen incorporation and reduces the oxidation of asphalt components. The changes in bio-asphalt in terms of chemical composition are reduced. Therefore, the high-temperature rheological properties of treated bio-asphalt, rock asphalt-modified bio-asphalt and montmorillonite-modified bio-asphalt change little under the influence of aging. The CMAI of RAMB is less than that of other asphalts. The PAAI is greater than other asphalts. Its anti-aging properties are better. Bio-asphalt has good anti-aging performance with pretreatment, rock asphalt and montmorillonite.

3.2.2. Anti-Aging Performance of RAMB Based on Low-Temperature Rheological Performance

The low-temperature bending beam tests of unaged and aged asphalt were carried out to compare the changes in S and m values. The S value of each asphalt increased after the aging treatment of the original asphalt, as shown in Figure 13. The polymerization reaction occurred inside the asphalt under the influence of aging and the low-molecular weight aromatic phenol was polymerized into high-molecular weight asphaltene. The aging of the asphalt made it physically brittle. Therefore, the aging was more damaging than it was for the original asphalt at low temperature. The m of long-term aging asphalt was greater than that of short-term aging asphalt, while the m of short-term aging asphalt was greater than that of original asphalt. The decrease in the rate of m was accelerated with the increase in aging. On the other hand, the S value of matrix asphalt after short-term aging exceeded 300 MPa and the m value was less than 0.3. The S and m value of rock asphalt-modified bio-asphalt and RAMB after short-term aging met the requirements. This shows that the low-temperature performance of the two asphalts after mixing and paving is better than that of matrix asphalt. Conversely, the S and m values after long-term aging exceeded the standard value. The two asphalts were damaged at low temperature after a period of service, but the time to show damage for these two asphalts was longer than that of matrix asphalt at low temperature under the same service conditions. The low-temperature rheological indexes of the other three asphalts under three aging conditions all met the specification requirements. The stress relaxation ability was good after aging and the deterioration via cracking was slow.

According to Equations (6) and (7), the SAI and mAI were calculated. When SAI is small and mAI is large, that asphalt has strong low-temperature aging resistance. The calculation results of the SAI and mAI are illustrated in Figure 14 and Figure 15. According to Figure 14 and Figure 15, the SAI value of untreated bio-asphalt was the largest among the six asphalts and the mAI value was the smallest. This shows that the deterioration of low-temperature properties was the most serious under the influence of aging. The SAI value was reduced and the mAI value was increased after distilled water treatment. The SAI value of rock asphalt-modified bio-asphalt, montmorillonite-modified bio-asphalt and matrix asphalt showed less differentiation. The anti-aging performance of bio-asphalt was only slightly improved by the addition of rock asphalt. The improvement effect of montmorillonite was obvious, but was not as pronounced as the matrix asphalt. Compared to the matrix asphalt, the SAI value of RAMB was smaller and the mAI value was larger. The SAI value of RAMB after short-term aging was 0.98 times that of matrix asphalt and the SAI value after long-term aging was 0.96 times that of matrix asphalt, while the mAI value after short-term aging was 1.03 times that of matrix asphalt and the mAI value after long-term aging was 1.01 times that of matrix asphalt. RAMB has good anti-aging performance.

$$\mathrm{SAI}=\frac{\mathrm{Stiffness} \mathrm{modulus} \mathrm{of} \mathrm{short} \mathrm{or} \mathrm{long} \mathrm{term} \mathrm{aging} \mathrm{asphalt}}{\mathrm{Stiffness} \mathrm{modulus} \mathrm{of} \mathrm{original} \mathrm{asphalt}}$$

(6)

$$\mathrm{mAI}=\frac{\mathrm{Creep} \mathrm{rate} \mathrm{of} \mathrm{short} \mathrm{or} \mathrm{long} \mathrm{term} \mathrm{aging} \mathrm{asphalt}}{\mathrm{Creep} \mathrm{rate} \mathrm{of} \mathrm{original} \mathrm{asphalt}}$$

(7)

3.3. FTIR

The infrared spectroscopy of untreated bio-oil was coincident with that of treated bio-oil, shown in Figure 16, but the intensity values of some characteristic peaks were different. The intensity of characteristic peaks represents the content of functional groups in asphalt. The peak intensity of two bio-oils were observed at 2923.88 cm⁻¹, 2853.37 cm⁻¹, 1743.18 cm⁻¹, 1463.41 cm⁻¹, 1377.09 cm⁻¹, 1162.01 cm⁻¹ and 967.08 cm⁻¹. The peak intensity of treated bio-oils was smaller than that of untreated bio-oils [32]. The peak corresponding to 967.08 cm⁻¹ is out-of-plane deformation of C-H bond. The peak corresponding to 1162.01 cm⁻¹ is stretching vibration of ester group O=C-O. The peak corresponding to 1377.09 cm⁻¹ is in-plane bending vibration of methyl C-H bond. The peak corresponding to 1463.41 cm⁻¹ is the in-plane bending vibration of methyl and methylene C-H. The peak corresponding to 1743.18 cm⁻¹ is the stretching vibration of ester O-C=O. The peak corresponding to 2923.88 cm⁻¹ is the stretching vibration of methylene CH₂. The peak corresponding to 2853.37 cm⁻¹ is stretching vibration of methyl CH₃ [33]. The peaks corresponding to 1162 cm⁻¹ and 1743 cm⁻¹ indicate that the bio-oil contained ester compounds [16,34]. Ester compounds are volatile substances with low boiling points and strong volatility when heated. The peak intensity of the treated bio-oil was weakened at 1162 cm⁻¹ and 1743 cm⁻¹. The volatile substance content of bio-oil was decreased after treatment with distilled water.

As shown in Figure 17, there were three differences in light absorption in the mid-infrared region between bio-asphalt and matrix asphalt, namely, 1744.54 cm⁻¹, 1159 cm⁻¹ and 966.2 cm⁻¹. The stretching vibration of ester group O-C=O corresponds to 1744.54 cm⁻¹. The peak at 1159.83 cm⁻¹ corresponds to the stretching vibration of ester group O=C-O. The peak at 966.20 cm⁻¹ corresponds to the out-of-plane deformation of trans-carbon–carbon double C-H bond. The three peaks existed in the spectroscopy of bio-oil. Therefore, the three peaks of bio-asphalt were all from bio-oil. The mixing of bio-oil and matrix asphalt is a physical blend system.

As shown in Figure 18, Figure 19 and Figure 20, the infrared spectroscopy of treated bio-asphalt was consistent with the rock asphalt-modified asphalt, but the absorption peak of bio-asphalt was very weak at 873.41 cm⁻¹, while rock asphalt-modified bio-asphalt showed obvious an absorption peak—the carboxyl C-H in CO₃²⁻ of rock asphalt [35]. When montmorillonite was added to bio-asphalt, there was a strong and wide absorption peak at 1085.08 cm⁻¹—the Si-O-Si antisymmetric stretching vibration bond [36,37]. Other absorption peaks did not change. The new peak of bio-asphalt came from montmorillonite. The incorporation of montmorillonite did not react with bio-asphalt to generate new functional groups. When the rock asphalt and montmorillonite were added into the bio-asphalt, the infrared spectroscopy of the bio-asphalt had two changes. From the above analysis, the emergence of these two peaks is due to the strong vibration of the two peaks in the rock asphalt and montmorillonite. Thus, the preparation process of rock asphalt, montmorillonite and bio-asphalt is also a physical blending process.

4. Conclusions

To improve the high-temperature performance and anti-aging performance of bio-asphalt, this paper proposed a preparation method for RAMB. The DSR test, BBR test, anti-aging performance test and FTIR test were carried out. From the research, the primary conclusions are as follows:

(1)

Through the method in the paper, the high-temperature performance of bio-asphalt is significantly improved. The low-temperature cracking resistance can meet the requirements of SHRP for low-temperature performance of asphalt binder.

(2)

The anti-aging performance of RAMB is much better than that of bio-asphalt. The distilled water treatment removes some light components in bio-oil and the addition of rock asphalt and montmorillonite increases the absorption peaks of two functional groups, C-H and Si-O-Si, respectively.

(3)

Based on the results of FTIR, the mixing of rock asphalt, montmorillonite and bio-asphalt is a physical blending system. The modification effect and road performance of this mixture still need further experimental research.