C9 Petroleum Resin and Polyethylene-Based High-Viscosity Modified Asphalt Binder Proportioning Optimization and Performance Study

Abstract

This study, based on 90# matrix asphalt binder, investigates the use of SBS, C9 petroleum resin, and polyethylene (PE) as modifiers to prepare high-viscosity modified asphalt binders. Using the uniform design method, the modifier proportions were optimized to meet engineering requirements for high viscosity. The effects of modifier dosages on asphalt binder properties, including penetration, ductility, softening point, and dynamic viscosity, were systematically analyzed, and a multivariate nonlinear regression model was constructed to determine the optimal proportioning. Subsequently, the aging resistance and high-temperature performance of the modified asphalt binders were evaluated through short-term aging tests and rheological property tests. The results show that SBS and PE have a significant positive impact on penetration and softening point, while C9 petroleum resin mainly enhances ductility. The synergistic effect of SBS and PE significantly improves dynamic viscosity. Under the optimal proportioning (SBS 7.5%, C9 petroleum resin 6.0%, PE 5.0%), the high-viscosity modified asphalt binders meet technical standards for key performance indicators. The short-term aging test reveals an elastic recovery ratio exceeding 95%. Rheological performance testing indicates that the modified asphalt binders exhibit excellent rutting resistance and temperature adaptability under high-temperature conditions.

1. Introduction

In recent years, with the rapid development of the transportation industry and the increasing proportion of heavy-load traffic, the performance requirements for road asphalt materials have gradually increased [1,2]. However, traditional asphalt materials are prone to rutting under high temperatures, cracking in low-temperature environments, and performance degradation due to aging over prolonged use [3,4]. This makes them unable to meet the modern highway requirements for high-temperature stability, low-temperature crack resistance, and long-term durability [4,5]. Therefore, developing modified asphalt binders with high viscosity has become an effective solution to this problem.

High-viscosity modified asphalt binder, a research focus in recent years, is widely used in the construction of highways and heavy-load roads due to its excellent high-temperature rutting resistance, low-temperature extensibility, and long-term anti-aging properties [6,7]. Among various modification technologies, the introduction of polymer modifiers is the key method to enhance asphalt binder performance. SBS (Styrene–Butadiene–Styrene) and PE (Polyethylene), two typical polymer modifiers, have been shown to significantly improve their properties [1,8]. SBS forms a three-dimensional network structure through physical cross-linking, significantly enhancing the high-temperature stability and low-temperature flexibility of asphalt binders [9,10]. In contrast, PE, due to its high crystallinity and reinforcing effect, helps to improve the rigidity and shear resistance of asphalt binders [11,12]. Compared to SBS, polyethylene (PE) is a relatively new modifier that has gained increasing popularity in recent years [13]. PE is not only effective in significantly improving the performance of asphalt binders, such as enhancing their resistance to aging, fatigue, and rutting [12,14], but it also offers several environmental benefits. PE can be sourced from recycled plastic waste, which helps mitigate the accumulation of “white pollution” and promotes the development of a circular economy [15]. The recycled polyethylene extracted from discarded plastic not only contributes to environmental protection but also reduces costs while simultaneously improving the performance of the asphalt [16]. Furthermore, recent studies have highlighted the considerable potential of PE-modified asphalt in specialized applications, such as airport runways, where it has shown outstanding performance, especially in high-temperature environments [17,18].

In addition, the incorporation of tackifiers (such as C9 petroleum resins) improves the inter-molecular interactions, effectively enhancing the adhesive properties and low-temperature flexibility of asphalt binders [19,20]. However, the synergistic mechanisms of multiple modifiers are complex, and the design of their dosages needs to strike a balance between performance optimization and economic costs. Currently, determining the appropriate dosages of SBS, PE, and C9 petroleum resins, as well as their synergistic effects on asphalt binder performance, remains one of the key challenges in the study of high-viscosity modified asphalt binders.

Existing research primarily focuses on the mechanisms of single or dual modifiers, with relatively few systematic studies on multiple modifiers [4,21]. When multiple modifiers coexist, significant nonlinear interactions may occur [22], and traditional empirical design methods struggle to reveal their multi-level impacts on asphalt binder performance. Additionally, while some studies attempt to optimize modifier dosages using regression analysis, most focus solely on fitting a single performance indicator, lacking exploration of a comprehensive balance of multiple performance metrics [23,24]. This limitation results in insufficient guidance for modifier formulation design and may lead to overlooking the synergy of overall performance in practical engineering applications due to the optimization of individual properties.

In the performance evaluation of high-viscosity modified asphalt binders, basic indicators such as penetration, ductility, and softening point are commonly used to characterize the viscoelastic properties and temperature sensitivity of asphalt binders [25,26]. Dynamic viscosity and elasticity recovery ratio, among other indicators, are used to reflect its adhesive properties and deformation resistance [27]. These performance indicators can intuitively reflect the degree of improvement in asphalt binder performance with varying modifier dosages. However, existing research often limits performance evaluation to qualitative descriptions of the above indicators, lacking systematic analysis [28]. Particularly under the synergistic effect of multiple modifiers, there may be inherent correlations between different performance indicators. However, there is a lack of in-depth exploration and modeling analysis of this complex relationship, which limits the understanding of the mechanism for asphalt binder performance enhancement.

Based on the aforementioned issues, this study systematically explores the synergistic effects of SBS, C9 petroleum resins, and PE on the performance of high-viscosity modified asphalt binders using a uniform design method. The uniform design method can fully account for the combinatory effects of multiple factors and levels with a limited number of experiments, providing theoretical support for optimizing the modifier dosages. Using multiple nonlinear regression analysis, a relationship model between the dosages of different modifiers and key asphalt binder performance indicators (such as penetration, ductility, softening point, and dynamic viscosity) is constructed and validated, while exploring the interactive effects of different modifiers. Finally, based on the results of film heating tests and dynamic shear rheometer performance tests, the optimal mixture ratio is proposed, and its applicability is verified.

2. Materials and Methods

2.1. Materials

In this study, 90# base asphalt binder was used, with the technical specifications provided in

Table 1. Technical specifications of base asphalt binder.

Test Item		Test Value	Test Method
Penetration (25 °C, 0.1 mm)		82.5	T 0604 2011
Softening point (℃)		46.8	T 0606 2011
Ductility (15 °C, cm)		>100	T 0605 2011
TFOT Residue	Mass Loss (%)	−0.12	T 0609 2011
	Penetration Ratio (25 °C, %)	76.8
	Ductility (5 cm/min,15 °C)	105.9

. Star-shaped SBS (styrene–butadiene–styrene) and YP510-type PE (polyethylene) were selected as modifiers. C9 petroleum resin was used as a tackifier. High-viscosity modified asphalt binder additives are divided into compatibilizers and stabilizers, which effectively improve the stability of asphalt binders [29]. Aromatic oil was selected as a compatibilizer, with a dosage of 3.0% by weight of the asphalt binder. Sulfur was selected as a stabilizer, with a dosage of 0.2% by weight of the asphalt binder. The various raw materials are shown in Figure 1.

2.2. Design Method

In this study, the three modifiers, SBS, C9 petroleum resin, and PE, were selected as influencing factors to investigate their effects on the performance of high-viscosity modified asphalt binders. Each factor was tested at eight levels, resulting in a three-factor, eight-level experiment, as shown in

Table 2. Three-factor eight-level experimental design table.

Factor	SBS (A)	C9 Petroleum Resin (B)	PE (C)
1	5.5%	5.0%	1.5%
2	6.0%	6.0%	2.0%
3	6.5%	7.0%	2.5%
4	7.0%	8.0%	3.0%
5	7.5%	9.0%	3.5%
6	8.0%	10.0%	4.0%
7	8.5%	11.0%	4.5%
8	9.0%	12.0%	5.0%

. The uniform design used in this experiment [30,31] is shown in

Table 3. Experimental design.

Test Number	Level			Combination	Factor
	A	B	C		SBS	C9	PE
1	1	4	7	A1B4C7	5.50%	8.0%	4.5%
2	2	8	5	A2B8C5	6.00%	12.0%	3.5%
3	3	3	3	A3B3C3	6.50%	7.0%	2.5%
4	4	7	1	A4B7C1	7.00%	11.0%	1.5%
5	5	2	8	A5B2C8	7.50%	6.0%	5.0%
6	6	6	6	A6B6C6	8.00%	10.0%	4.0%
7	7	1	4	A17B1C4	8.50%	5.0%	3.0%
8	8	5	2	A8B5C2	9.00%	9.0%	2.0%

2.3. Preparation Method

The preparation process of high-viscosity modified asphalt binders is divided into three stages: the first stage involves stirring and swelling, the second stage involves shear dispersion, and the third stage involves stirring and development. Due to the presence of aromatic components in C9 petroleum resin, it promotes the swelling process of SBS and is added to the asphalt binders first. The specific preparation method for high-viscosity modified asphalt binders is as follows.

• Place the asphalt binders in a 160 °C oven and heat it until fully melted. Add aromatic oil and C9 petroleum resin, and stir thoroughly at 600 rpm for 3–5 min until evenly dispersed;
• Add SBS and PE modifiers, and stir thoroughly at 600 rpm for 30 min at 160 °C;
• Perform high-speed shear at 5000 rpm for 60 min at 180 °C;
• Add stabilizers, and stir at 600 rpm for 60 min at 180 °C. The high-viscosity modified asphalt binder product is obtained and immediately poured into molds for subsequent tests. The specific preparation process is shown in Figure 2.

2.4. Test Method

• Basic Indicators

According to the test requirements outlined in the JTG E20-2011, this study tested the penetration (three parallel specimens), softening point (two parallel specimens), and ductility (three parallel specimens) of high-viscosity modified asphalt binders under standard conditions. Dynamic viscosity (three parallel specimens) at 60 °C and 40 kPa vacuum was tested using the vacuum capillary method.

$$\eta =K\times \mathrm{t}$$

(1)

where is the dynamic viscosity of the asphalt binder specimen at the determination temperature (Pa·s). Viscometer constant (Pa·s/s) for the selected first pair of markers over the first pair of markers asked for over the first pair of markers over the first pair of markers asked for over 60s. The time interval (s) for passing the first pair of markers over 60 s.

2.

Aging Resistance

The high-viscosity modified asphalt binders were subjected to a Thin Film Oven Test (TFOT) at 163 °C, and their performance was tested to evaluate aging resistance.

3.

Rheological Properties

A DSR (dynamic shear rheometer, DHR-2, Waters Technology Co., Ltd.) was used to conduct a temperature sweep test at a frequency of 10 rad/s. The temperature scanning range was from 70 °C to 124 °C, and the strain was always controlled within the linear viscoelastic range. From the rheological test (two parallel specimens), complex modulus and phase angle evaluation indicators were obtained to characterize the rheological properties of the high-viscosity modified asphalt binders.

3. Results and Discussion

3.1. Test Results Analysis

The modified asphalt binders were prepared according to the guidelines in Table 3, and their penetration, ductility, softening point, and 60 °C dynamic viscosity were tested. The results are shown in

Table 4. High-viscosity modified asphalt binder performance test result.

Test Number	Penetration (25 °C, 0.1 mm)	Ductility (5 °C, cm)	Softening Point (°C)	Dynamic Viscosity (Pa·s)
Requirement	40–60	≥30	≥80	≥200,000
1	45.0	35.4	98.2	24,243
2	37.9	26.0	95.8	48,941
3	42.1	32.2	100.4	43,008
4	43.8	42.1	82.6	107,770
5	53.7	39.9	106.1	237,157
6	40.7	32.5	103.5	657,860
7	36.8	35.0	104.4	590,908
8	47.0	31.9	103.8	543,591

. The experimental results indicate that the ratio of SBS, C9 petroleum resin, and PE modifiers significantly affects the performance of the high-viscosity modified asphalt binders. Penetration test results show that the values for all groups range from 36.8 to 53.7 (0.1 mm), which all meet the technical requirements, indicating that different ratios effectively control the hardness of the asphalt binder. The penetration of Group 5 was the highest at 53.7, demonstrating good flexibility. The ductility ranged from 26.0 to 42.1 cm, with Group 2 failing to meet the technical requirements, while the other groups met the standard. The best ductility performance was observed in Group 4 (42.1 cm), which showed higher flexibility, although its softening point was relatively low (82.6 °C). The softening point ranged from 82.6 °C to 106.1 °C, all meeting the technical requirement (≥80 °C). Group 5 had a softening point of 106.1 °C, demonstrating excellent high-temperature deformation resistance. Dynamic viscosity test results show that Groups 5 through 8 met the technical requirements, exhibiting significant high-viscosity performance. However, the dynamic viscosity of the first four groups was lower, which may be related to insufficient PE content. These results highlight that the proper ratio of the three modifiers and their synergistic effects is crucial for optimizing the performance of modified asphalt binders.

3.2. Regression Analysis

3.2.1. Linear Regression

Multivariate linear analysis of the various indicators of high-viscosity modified asphalt binders was performed using SPSS software, with the model structure shown in Equation (2). The detailed analysis results are presented in

Table 5. Multivariate Linear Regression Analysis.

Indicator	Multivariate Linear Regression Model	R2
Penetration	$Y=59.7-72.7433X_1-98.5333X_2-73.6218X_3$	0.36
Ductility	$Y=0+455.0171X_1+4.7211X_2+13.6070X_3$	0.97
Softening Point	$Y=82.32+265.2401X_1-58.4952X_2+93.0309X_3$	0.30
Dynamic Viscosity	$Y=0+489.3477X_1-36.5603X_2-158.589X_3$	0.64

(Note: X₁, X₂, and X₃ correspond to the contents of SBS, C9 petroleum resin, and PE. The formula has a 95% confidence interval).

. According to the correlation coefficient (R²) values in the table, it can be observed that, except for the ductility, which is significantly high, the significance of other parameters does not meet the regression requirements. Moreover, the model obtained for ductility does not align with objective laws. Therefore, none of the four multivariate linear models can be used as mathematical models for the four performance parameters of modified asphalt binders, and further selection of multivariate nonlinear models is needed.

$$Y=a+b{X}_1+c{X}_2+d{X}_3$$

(2)

3.2.2. Nonlinear Regression

Multivariate nonlinear analysis was performed on the asphalt binder indicators. First, single-factor curve fitting was conducted for each individual indicator. The regression model was constructed in the form of a multivariate quadratic function by comparing the correlation coefficient R of each fitting curve, as shown in Equation (3). The detailed analysis results are presented in

Table 6. Multivariate Nonlinear Regression Analysis.

Indicator	Multivariate Nonlinear Regression Model	R2	Standard Error
Penetration	$\begin{array}{l}Y=75.0-1167.4X_1+1145.8X_2-2705.3X_3+9381.7X_1^2-4420.7X_2^2\\ +35755.3X_3^2-4957.0X_1{X}_2+8773.4X_1{X}_3-2080.2X_2{X}_3\end{array}$	0.88	3.17
Ductility	$\begin{array}{l}Y=0+474.9X_1+1212.1X_2-1847.2X_3-2217.4X_1^2-4237.5X_2^2\\ +19890.9X_3^2-5699.9X_1{X}_2+10738.8X_1{X}_3-4490.0X_2{X}_3\end{array}$	0.99	4.29
Softening Point	$\begin{array}{l}Y=45.0+1415.1X_1-557.4X_2+1083.9X_3-6459.1X_1^2-431.2X_2^2\\ -9339.1X_3^2+3129.8X_1{X}_2-13346.8X_1{X}_3+9223.7X_2{X}_3\end{array}$	0.88	3.64
Dynamic Viscosity	$\begin{array}{l}Y=0-760.2X_1-1024.9 X_2-143.3X_3+15643.6X_1^2+3141.0 X_2^2\\ -25763.1 X_3^2+2550.1X_1{X}_2+18493.1X_1{X}_3+13449.4X_2{X}_3\end{array}$	0.95	13.59

(Note: only applicable to C9 petroleum resin and PE-based high-viscosity modified asphalt binders, with modifier content ranges of X₁ 5.5%–9.0%, X₂ 5.0%–12.0%, and X₃ 1.5%–5.0%. The formula has a 95% confidence interval.).

.

$$Y=a+b{X}_1+c{X}_2+d{X}_3+e{X}_1^2+f{X}_2^2+g{X}_3^2+h{X}_1{X}_2+i{X}_1{X}_3+j{X}_2{X}_3$$

(3)

Scatter plots comparing the calculated and experimental values for each model were created to visually assess the correlation between them, as shown in Figure 3. From the analysis of Table 6 and Figure 3, it is evident that the models for ductility, penetration, softening point, and dynamic viscosity all exhibit strong correlations. Among these, the ductility model stands out with R = 0.997, almost fully explaining the variation in ductility. The scatter plot reveals that the experimental values for ductility align closely with the calculated values, with most points falling near the ideal line, confirming the accuracy of the model.

Further analysis indicates that the primary factor driving the improvement in ductility is the positive effect of C9 petroleum resin (X₂), while the main effect of SBS (X₁) and its interaction with PE (X₃) play significant roles in the synergistic regulation of ductility. The models for penetration and softening point also demonstrate strong predictive capabilities, with R values of 0.939 and 0.940, respectively. The scatter plots show minimal fitting errors between the calculated and experimental values, suggesting that the models can reliably predict performance changes under different modifier ratios. The variation in penetration is primarily influenced by the main effect of SBS and the nonlinear effect of PE, while the softening point is mainly driven by the positive contribution of SBS. Additionally, the negative effect of C9 petroleum resin on the softening point requires further optimization to improve prediction accuracy.

The dynamic viscosity model, with R = 0.972, exhibits high fitting accuracy. However, the scatter distribution shows some errors in the high dynamic viscosity range. Model analysis reveals that the variation in dynamic viscosity is predominantly influenced by the quadratic effect of SBS (X₁) and the synergistic effect of PE (X₃), with the interaction between C9 and PE also contributing significantly to improving dynamic viscosity performance. Overall, the models provide a thorough understanding of the relationship between modifier content and performance, offering valuable theoretical and practical guidance for the formulation design and performance optimization of high-viscosity modified asphalt binders.

3.3. Correlation Analysis

3.3.1. Penetration

Three-dimensional response surfaces were plotted based on the model to visually demonstrate the effect of modifier content on performance. Figure 4 shows that the SBS content has the most significant impact on penetration, with penetration increasing significantly as the SBS content rises, especially when the SBS content exceeds 7%, where the rate of increase accelerates. This indicates that SBS effectively enhances the flexibility and adhesive properties of the material in asphalt binders [32]. PE also significantly improves penetration, particularly when the PE content exceeds 4%, where the penetration response curve exhibits a significant nonlinear change and an accelerating upward trend [12]. Additionally, the interaction effect between SBS and PE shows high significance, with their high-level combination (SBS > 8%, PE > 5%) resulting in the most notable increase in penetration. This result emphasizes the synergistic effect of SBS and PE in the formulation of modified asphalt binders. In contrast, the contribution of C9 petroleum resin to penetration is relatively weak. Although its effect on penetration is positive, the increase is limited, and its interaction effects with other factors are minimal. This may be due to C9 petroleum resin primarily serving as a tackifier, with a relatively limited strengthening effect on the asphalt binder system.

3.3.2. Ductility

Ductility, a key indicator of low-temperature cracking resistance in the modified asphalt binders, is critical for asphalt binders’ flexibility and tensile deformation capacity under low temperatures. In this study, a multivariate quadratic regression model was used to plot the ductility response surface for various factors, as shown in Figure 5. The results indicate that C9 petroleum resin positively contributes to ductility within a certain dosage range. However, when the C9 petroleum resin content exceeds approximately 8%, ductility begins to decline. This may be due to the disruption of the asphalt binder matrix’s molecular uniformity at high C9 petroleum resin dosages, where excessive rigidity weakens ductility under low-temperature conditions [33]. In contrast, ductility decreases when PE content is low (<4%) but increases rapidly when PE content exceeds 4%. This can be attributed to PE enhancing the molecular structure stability of asphalt binders at higher dosages, thereby improving its flexibility [34]. Similarly, ductility rises sharply as SBS content increases, validating the mechanism by which SBS forms a network structure through physical crosslinking, significantly improving the low-temperature cracking resistance of asphalt binders [35]. Furthermore, the interaction between SBS and PE positively impacts ductility. Their high-level combination (SBS > 8%, PE > 5%) notably enhances ductility, demonstrating a strong synergistic effect in improving asphalt binder flexibility.

3.3.3. Softening Point

The response surface plot for the softening point was generated using a multivariate quadratic regression model (Figure 6) to investigate the impact mechanisms and interactions of the three modifiers on the softening point. Among the modifiers, SBS has the most significant effect on enhancing the softening point, particularly when its content exceeds 7%, where the positive effect becomes increasingly pronounced. This highlights SBS as the key factor influencing the softening point [32]. By reinforcing the crosslinked structure of the asphalt binder matrix, SBS significantly improves the material’s high-temperature deformation resistance. The effect of PE exhibits a nonlinear characteristic. At lower dosages (<4%), PE has a noticeable positive impact on the softening point [36]. However, as the PE content approaches 6%, the improvement stabilizes. In contrast, C9 petroleum resin exerts a negative effect on the softening point. As the C9 petroleum resin content increases, the softening point declines linearly. This may be attributed to its rigidity, which could counteract the improvement in the softening point [37]. Additionally, the interaction between C9 petroleum resin and SBS has a negative influence, indicating the possibility of competitive effects at higher dosages.

3.3.4. Dynamic Viscosity

Dynamic viscosity is a key indicator of the viscosity of the modified asphalt binders. The response surface plot (Figure 7) visually explores the effects of the three modifiers on dynamic viscosity and their interactions. As the SBS content increases, dynamic viscosity rises rapidly and significantly. This suggests that SBS, through its crosslinked network structure, significantly enhances the intermolecular interactions in asphalt binders, thereby increasing their viscosity. The effect of C9 petroleum resin on dynamic viscosity is relatively mild. As the C9 petroleum resin content increases, its effect on dynamic viscosity becomes limited, and negative effects may even occur at higher dosages. This could be due to the increase in rigidity caused by C9 petroleum resin in the asphalt binder matrix, which reduces the overall viscosity of the material [38]. The effect of PE shows a distinct nonlinear characteristic. At lower dosages (<4%), the impact of PE on dynamic viscosity is weak, with gradual changes in the curve. However, when the PE content increases to 4%–5%, dynamic viscosity rises significantly. At this stage, the reinforcing effect of PE becomes evident, peaking between 5%–6%. As the PE content continues to increase, dynamic viscosity stabilizes, indicating that high PE dosages significantly improve the molecular network structure of the asphalt binder matrix, but the effect becomes saturated at higher dosages [36]. This nonlinear behavior may be due to PE forming a more uniform dispersed structure at higher dosages, which enhances the overall resistance to flow.

3.4. Optimal Ratio of Modifier

3.4.1. Model Validation

To validate the accuracy of the multivariate linear model in Table 6, experiments were conducted, and the test data are presented in

Table 7. Validation group test result.

Type		1	2	3
SBS Content (%)		7.0	6.5	8.0
C9 Petroleum Resin Content (%)		9.0	9.5	10.0
PE Content (%)		4.5	4.5	2.4
Penetration (25 °C, 0.1 mm)	Experimental Value	41.9	44.8	38.3
	Calculated Value	45.2	44.5	39.9
	Error	−3.31	0.27	−1.59
Ductility (5 °C, cm)	Experimental Value	31.7	30.7	41.5
	Calculated Value	34.0	32.6	34.0
	Error	−2.33	−1.88	7.50
Softening Point (°C)	Experimental Value	101.1	102.5	100.7
	Calculated Value	103.6	102.4	99.0
	Error	−2.54	0.07	1.70
Dynamic Viscosity (10,000 Pa·s)	Experimental Value	18.7	8.2	22.9
	Calculated Value	17.8	10.1	25.3
	Error	0.9	−1.9	−2.4

. The data indicate that the multivariate linear model has a small prediction error range across various performance indicators. The prediction errors for all indicators are within a reasonable range, demonstrating the model’s high accuracy in predicting asphalt binder performance. However, for certain indicators, such as ductility and dynamic viscosity, some groups exhibit relatively larger prediction errors, which may be attributed to the complex nonlinear interactions between modifiers. Overall, the experimental validation results indicate that the multivariate linear model has strong predictive capability and can be utilized for the rapid assessment of modified asphalt binder performance and mix ratio optimization.

3.4.2. Modifier Ratio Determination

Based on the calculations from the model in Table 6 and considering practical economic factors, the SBS modifier dosage was reduced. The target proportioning for the high-viscosity modified asphalt binders that meet the design requirements is shown in

Table 8. Modifier ratio.

Type	SBS	C9 Petroleum Resin	PE	Aromatic Oil	Sulfur
Content (%)	7.5	6.0	5.0	3.0	0.20%

, with the experimental results presented in

Table 9. Results of target proportioning tests for high-viscosity modified asphalt binders.

Type	Test Value	Requirement	Test Method
Penetration (25 °C, 0.1 mm)	53.7	40–60	T 0604 2011
Ductility (5 °C, cm)	39.3	≥30	T 0606 2011
Softening Point (°C)	106.1	≥80	T 0605 2011
Dynamic Viscosity (Pa·s)	237,157	≥200,000	T 0620 2011

.

The price of SBS modifier is between 12,200 and 14,000 RMB, while the price of C9 petroleum resin ranges from 3200 to 4200 RMB. The price of PE is between 7600 and 8300 RMB, and the price of 90# matrix asphalt binder is between 3200 and 3500 RMB. As a result, the price of high-viscosity modified asphalt binders is between 3960 and 4410 RMB per ton. In comparison, the commonly used high-viscosity modifier is priced between 19,000 and 26,000 RMB. The modifier content is generally above 10%, and the price of high-viscosity modified asphalt binders is between 4640 and 5272 RMB per ton. Therefore, the high-viscosity modified asphalt binders studied in this paper can save approximately 15% in raw material costs.

3.5. Performance Evaluation

3.5.1. Ageing Resistance

This study assessed the short-term aging performance of the high-viscosity modified asphalt binders using the Thin Film Oven Test (TFOT). TFOT replicates the actual heating conditions experienced during asphalt mixture production, and the test results strongly correlate with the properties of asphalt binders under production conditions. The results (

Table 10. TFOT test results.

Type	Test Value	Requirement	Test Method
Mass Loss (%)	0.30	≤±1.0	T 0609 2011
Penetration Ratio (25 °C, 0.1 mm)	75.3%	≥75	T 0604 2011
Ductility (5 °C,cm)	30.7	≥20	T 0606 2011
G*/sinδ (85 °C)	2.64	≥2.2	T 0628 2011
Elastic Recovery Ratio (25 °C)	97.5%	≥60	T 0662 2000

) show that the mass loss of asphalt binders after TFOT short-term aging is less than 0.3%, which is significantly lower than the 1% technical requirement for high-viscosity modified asphalt binders. This indicates that the asphalt binders contain a low level of volatile components, such as light fractions.

Moreover, its penetration ratio meets technical standards, and critical performance indicators—including 5 °C ductility, rutting factor, and elastic recovery ratio—satisfy the technical requirements. Notably, the elastic recovery ratio exceeds 95%, far surpassing the technical standard threshold of 60%. This demonstrates that the asphalt binders retain their elasticity after short-term aging, exhibiting stable performance and excellent resistance to aging.

3.5.2. Rheological Properties

The test results for the phase angle and rutting factor of the high-viscosity modified asphalt binders are shown in Figure 8. The phase angle exhibits a trend of initially decreasing and then increasing with rising temperature, which is directly influenced by the synergistic effects of the added modifiers. SBS forms a stable three-dimensional elastic network within the asphalt binders, significantly enhancing energy storage capacity at lower temperatures. This increased elasticity leads to a decrease in the phase angle. PE, with its high crystallinity and structural reinforcement, improves the asphalt binders’ resistance to shear deformation, providing enhanced viscoelastic balance below 94 °C. However, as the temperature exceeds 94 °C, the SBS network structure begins to degrade, the viscosity effect of C9 petroleum resin weakens, and the stabilizing influence of PE becomes limited. This results in significantly increased fluidity of the asphalt binders and a subsequent rise in the phase angle. Overall, the three modifiers demonstrate strong synergistic effects at lower temperatures, significantly improving the elastic and viscous properties of asphalt binders. At higher temperatures, however, their effects diminish, as evidenced by the phase angle’s increase due to greater fluidity.

The rutting factor decreases significantly with rising temperature but remains relatively high at 1.01 kPa at 118 °C, indicating excellent rutting resistance even at elevated temperatures. This performance is primarily due to the elastic support of SBS and the high-viscosity contribution of C9 petroleum resin. Even under high-temperature conditions, these modifiers play a critical role in enhancing the high-temperature performance of asphalt binders.

4. Conclusions

This study optimized the dosages of SBS, C9 petroleum resin, and PE modifiers using the uniform design method. The specific conclusions are as follows:

• SBS, PE, and C9 petroleum resin significantly influence asphalt binder performance. Penetration and softening point are primarily driven by the positive effects of SBS and PE, while C9 petroleum resin has a smaller impact. Ductility is mainly dominated by the positive contribution of C9 petroleum resin, but high dosages may lead to negative effects. Dynamic viscosity strongly depends on the synergistic effects of SBS and PE, with C9 petroleum resin playing a relatively limited role.
• Based on multivariate nonlinear regression model analysis, the optimal proportioning ratio is SBS 7.5%, C9 petroleum resin 6.0%, and PE 5.0%. Under this ratio, the high-viscosity modified asphalt binders meet technical standards for key performance indicators, including penetration, ductility, softening point, and dynamic viscosity.
• In aging resistance tests, the high-viscosity modified asphalt binders exhibited excellent anti-aging performance, with an elastic recovery ratio exceeding 95%, significantly surpassing the technical standard requirements. Rheological test results indicate that the asphalt binders maintain a high rutting factor at elevated temperatures, demonstrating superior rutting resistance and temperature adaptability.
• This study primarily focused on optimizing modifier dosages and their effects on the performance of high-viscosity modified asphalt binders. However, further research is required to address aspects such as long-term durability, freeze–thaw cycles, mixture adaptability, and life cycle assessment (costs and environment). Future studies should also incorporate microstructural characterization techniques to comprehensively explore the mechanisms underlying performance optimization of asphalt binders and their mixtures.