Preparation and Performance Test of UV Resistant Composite-Modified Asphalt

Abstract

Ultraviolet radiation is the main cause of degradation in asphalt pavement. To improve the performance of the pavement used in the strong ultraviolet (UV) region of the western plateau, China, this study explores the effects of adding nano-montmorillonite and carbon black to SBS-modified asphalt. Through conventional index detection, dynamic shear rheological tests, low-temperature bending creep tests, and UV aging tests, the high- and low-temperature performance, fatigue performance, UV aging resistance, and other aspects of the asphalt were studied. Various performance and price factors were considered in the optimization of various UV resistant composite-modified asphalt formulas. Increasing the contents of nano-montmorillonite and carbon black increases the high-temperature performance and the UV aging resistance but reduces the low-temperature and fatigue performance of asphalt; hence, their total content should be limited to <4%. Nano-montmorillonite has a better high-temperature performance and UV aging resistance than carbon black and is also less favorable to low-temperature and fatigue performance. Hence, it is recommended that its content not exceed 3%. UV resistant composite-modified asphalt has obvious advantages in high-temperature performance and UV aging resistance compared with conventional SBS-modified asphalt, and its low-temperature performance meets the use requirements of the strong-UV areas in the western plateau.

1. Introduction

The diseases afflicting asphalt pavement in China’s western plateau are mostly related to intense ultraviolet radiation. Hence, improving the anti-ultraviolet aging ability of asphalt pavement is one way to alleviate pavement diseases. At present, the most commonly used types of road asphalt in China are mainly road petroleum asphalt and polymer-modified asphalt. Most of the polymers used are thermoplastic elastomers, which have a low UV resistance.

Research on the aging of polymer-modified asphalt has always been a hot topic. M. Giunta [1] proposed a new viscoelastic plastic constitutive model for asphalt concrete that was verified by experiments and met the general thermodynamic requirements. This model can characterize the nonlinear time-varying characteristics of asphalt materials. J. Zhu [2] described the history of asphalt polymer modifications in chronological order, discussed the advantages and disadvantages of the plastic and thermoplastic elastomers commonly used in asphalt modification, and proposed that functionalization is a promising method for improving the performance of the polymers currently used and developing new polymer modifiers. C. Celauro [3] studied the short-term aging effects when using different types of modifiers (such as polymers recovered from waste). The results showed that polymer modification can reduce the aging effect, that is, the increase of the elastic modulus experienced by the original adhesive. G. Sun [4] has aged styrene butadiene styrene (SBS) modified asphalt, recycled polyethylene (RPE) modified asphalt, and its base asphalt through thermal oxidation aging and all-weather aging tests. The results showed that all-weather aging runs through almost the entire depth of the base asphalt. On the other hand, the SBS’s space network structure can significantly reduce the oxidation depth of SBS asphalt, while the mitigation effect of the RPE asphalt on all-weather aging was weakened. I. Joohari [5] analyzed whether the aging of mixed a PMB of styrene butadiene styrene (SBS) and linear low density polyethylene (RLLDPE) recovered from waste plastics was caused by asphalt aging, polymer degradation, or both. The results showed that asphalt aging caused by thermal oxidation was dominant, and polymer degradation had the least impact on asphalt hardening. N.I.M. Yusoff [6] investigated the effect of mixing different percentages of nano silica (NS) with PMB under the conditions of no aging and aging. The results show that adding NS to PMB could improve its viscoelastic and anti-aging properties. I. Binti Joohari [7] evaluated the effects of styrene butadiene styrene (SBS), rubber crumbs (CR), ethylene vinyl acetate (EVA), and various polyethylene modifiers on the rheological properties of mixed polymer-modified asphalt (PMB) using the multiple stress creep and recovery (MSCR) and linear amplitude scanning (LAS) tests. G. Sun [8] conducted a fatigue healing fatigue (FHF) test to study the effects of temperature and thermal oxidation aging on the self-healing ability of styrene butadiene styrene (SBS) modified asphalt (SBS-MB) and polyethylene (PE) modified concrete (PE-MB). The results showed that the self-healing ability of PMB gradually weakened with the progression of aging. It is worth noting that thermal oxidative aging has a completely different effect on the self-healing ability of SBS-MB and PE-MB at lower temperatures. Y. Tian [9] selected four types of adhesives for aging tests over different periods of time. The results showed that polymer degradation mainly occurred at an early age, and that the oxidation of asphalt phase was the main process of long-term aging. R. Kleizienė [10] extended the regeneration of standard polymer-modified asphalt (PMB) by introducing nano materials such as nano SiO₂ and nano TiO₂ into traditional regeneration agents. The most promising results were obtained after the aging PMB was regenerated with a modified soft asphalt containing 6% nano TiO₂. It can be seen from the above studies that the aging of asphalt is still dominated by thermal oxygen aging, but that the aging effects of ultraviolet light cannot be ignored.

There has been much research on improving the anti-ultraviolet ability of asphalt pavement. The most common method is to modify asphalt by adding materials with anti-ultraviolet properties. The majority of Chinese research has focused on improving the ultraviolet resistance of asphalt by using the strong ultraviolet-absorption properties of carbon black and the thermal resistance of nanomaterial intercalation structures. Some scholars have studied the dry preparation of a carbon black asphalt mixture and successfully paved a surface test road with a UV resistance function [11,12,13]. The research of Li et al. [14] showed that carbon black improves the high-temperature and anti-aging performance of asphalt but reduces its low-temperature performance. The research of Zhang et al. [15] revealed how carbon black can improve the high-temperature and anti-aging performance and storage stability of styrene butadiene styrene block copolymer (SBS) modified asphalt. Fa et al. [16] modified SBS with nanographene oxide, which effectively improved the UV resistance performance of SBS-modified asphalt. Lu et al. [17] proved the feasibility of a technical scheme for a hydrotalcite/waste rubber powder composite-modified asphalt. Their results proved that hydrotalcite improves the UV resistance of the composite-modified asphalt. Sui et al. used different combinations of nanomaterials, such as SiO₂, ZnO, TiO₂, organic vermiculite, and organic montmorillonite, to develop a nanomaterial/SBS composite-modified asphalt, which demonstrated excellent high- and low-temperature performance [18,19,20,21,22].

Following from the above research, this study aimed to improve the performance of the asphalt pavement used in the strong ultraviolet region of the western plateau, China. Nano-montmorillonite and carbon black were used to amend SBS-modified asphalt to prepare a UV resistant composite-modified asphalt. Through conventional index detection, dynamic shear rheological tests, low-temperature bending creep tests, and UV aging tests, the high- and low-temperature performance, fatigue performance, and UV resistance were studied and analyzed. The aim was to develop an asphalt with excellent high- and low-temperature performance and outstanding UV resistance for use in the western plateau area.

2. Materials and Methods

2.1. Materials

2.1.1. SBS-Modified Asphalt

The physical properties of the SBS-modified asphalt are shown in

Table 1. Basic physical properties of the SBS-modified asphalt.

Property	Specification	Measured Value
Penetration (25 °C) (0.1 mm)	40–60	54
Penetration index	≥0	0.6
Softening point (°C)	≥60	75.2
Ductility (5 °C) (cm)	≥20	33
Apparent viscosity (135 °C) (Pa·s)	≤3	1.975
Recovery elastic (RE) (%)	≥75	90
Flash point (°C)	≥230	280
Storage stability (segregation, 48 h softening point difference) (°C)	≤2.5	0.3
Mass loss (%)	−1.0–1.0	−0.070
Penetration ratio (%)	≥65	86
Ductility (5 °C) (cm)	≥15	21
Performance grade	/	PG76-22

; all met the relevant specifications in [23].

2.1.2. Carbon Black

Carbon black was prepared by pyrolysis of waste tires at a production site in Shanghai, China; its technical indicators are shown in

Table 2. Carbon black test results.

Property	Specification	Property
Ash content (%)	≤18.5	13.2
Oil absorption value (mL/100 g)	≥7.0	11.5
Sieve residue (%)	/	0.008
Fineness (μm)	/	10
Moisture (%)	≤3.0	0.5
Specific surface area (m2/g)	/	120
pH	≥6.0	7

. Its price is 4500 yuan (645.3 U.S. dollars) per ton.

2.1.3. Nano-Montmorillonite

The physical and chemical properties of nano-montmorillonite are shown in

Table 3. Physical and chemical properties of nano-montmorillonite.

Property	Measured Value
Appearance (color)	White powder
Particle size (200 mesh pass rate) (%)	97.5
Density (g/cm3)	1.8
Montmorillonite content (%)	≥95
pH	8.0

. Its price is 28,000 yuan (4015.2 U.S. dollars) per ton.

2.2. Sample Preparation

Firstly, the SBS-modified asphalt was heated to a molten state in an oven at 163 °C. Then, carbon black was added slowly and uniformly while stirring at 1000 r/min. After 30 min of stirring, the stirring speed was increased to 2000 r/min, and then nano-montmorillonite was added slowly. After all the carbon black was added, it was uniformly stirred for 1 h, and then the mold was poured for inspection.

2.3. Orthogonal Experimental Design

The formulation of UV resistant composite-modified asphalt with different combinations of raw materials was conducted via an orthogonal test design. The relevant indexes were then tested. The specific test scheme is shown in

Table 4. The specific test schemes.

Recipe	SBS-Modified Asphalt (%)	Carbon Black (%)	Nano-Montmorillonite (%)
A	100	0	0
B	99	0	1
C	98	0	2
D	97	0	3
E	96	1	3
F	97	1	2
G	98	1	1
H	99	1	0
I	95	2	3
J	96	2	2
K	97	2	1
L	98	2	0
M	94	3	3
N	95	3	2
O	96	3	1
P	97	3	0

.

2.4. Test Methods

(1) Routine index detection

According to the relevant provisions and requirements of the specifications in [24], the softening point, apparent viscosity (135 °C), and ductility (5 °C) index of the UV resistant composite-modified asphalt were determined.

(2) Dynamic shear rheological tests

A dynamic shear rheometer was used (TR2000, TA Company, Boston, MA, USA) to carry out temperature scanning, frequency scanning, and time scanning tests.

Temperature sweep tests: During this test, the control strain was 1%, the diameter of the parallel plate was 25 mm, the distance between the upper and lower parallel plates was 1 mm, and the frequency was fixed at 10 rad/s. The test was carried out in a temperature range of 28–82 °C with a step size of 6 °C. The complex shear modulus G *, phase angle δ, and rutting factor G */sin δ were collected.

Frequency sweep tests: The strain was controlled at 5%, the temperature was set to 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C, and the frequency scanning was carried out within the frequency range of 0.01–10 Hz. The complex shear modulus G * and phase angle δ were collected.

Time sweeps tests: The temperature was set at 25 °C, the frequency was 10 rad/s, the strain was controlled at 10%, and the complex shear modulus G * under different loading times was measured.

(3) Low-temperature bending creep tests: A low-temperature bending beam rheometer was used (TE-BBR-T, Cannon, Cranberry Township, PA, USA). The test temperature was −12 °C, and the creep stiffness modulus s and creep rate m were collected.

(4) UV aging tests: A melted asphalt sample was evenly distributed on a flat-bottom disc and then placed in a self-developed ultraviolet aging oven (Figure 1). The power of the ultraviolet lamp was 400 W, and the axis of the lamp was 40 cm away from the sample surface. The manufacturer of ultraviolet lamp is the China Guangzhou Langpu Optoelectronic Technology Co., Ltd., Guangzhou, China. The power supply voltage is 220 V, the maximum working temperature is 45 °C, the maximum service life is 8000 h, the length is 330 mm, and the pipe diameter is 28 mm. The oven was continuously ventilated to prevent thermal aging due to excessive heat. The temperature was kept at about 35 °C for 96 h. The aged samples were used in 60 °C temperature scanning tests, low-temperature bending creep tests, and 135 °C viscosity tests. The relevant test parameter settings were consistent with the other test methods described in this section.

3. Results

3.1. Optimization of UV Resistant Composite-Modified Asphalt Formula

The influences of nano-montmorillonite and carbon black on the performance of SBS-modified asphalt are shown in Figure 2 and Figure 3. Figure 2 shows the sample with only nano- montmorillonite added, corresponding to Schemes A, B, C, and D. Figure 3 shows the sample with only carbon black added, corresponding to Schemes A, H, L, and P.

It can be seen from Figure 2 and Figure 3 that mixing with nano-montmorillonite and carbon black had the same effect on the performance of SBS-modified asphalt. With increases in the mixing amount, the softening point and 135 °C viscosity of the SBS-modified asphalt gradually increased, and the increased apparent viscosity presented a greater resistance to flow deformation. Under a given load, relatively weak deformation occurred, and the elastic part could recover readily, which is conducive to a good high-temperature anti-rutting performance. However, the ductility at 5 °C decreased gradually, the ability to resist deformation at low temperatures decreased, and the low-temperature crack resistance decreased. This shows that both nano-montmorillonite and carbon black can improve the high-temperature performance of SBS-modified asphalt, but not its low-temperature performance. According to the literature [25,26,27], nano-montmorillonite has a lamellar structure with upper and lower spacings that are uniformly dispersed in asphalt by stirring and shearing. The lamellar structure is interlocked with SBS molecules, resulting in a change in its microstructure, which is conducive to its storage stability. The intercalation effects of montmorillonite and the light components in asphalt and the barrier to oxygen diffusion improve the anti-aging performance of UV resistant composite-modified asphalt. Carbon black contains active agent components that can easily promote the cross-linking reaction of the modifier in SBS-modified asphalt and improve the high-temperature and water-loss resistance of SBS-modified asphalt [15].

It can be seen from

Table 5. Physical properties of composite-modified asphalt.

Recipe	Softening Point (°C)	Apparent Viscosity (135 °C) (Pa·s)	Ductility (5 °C) (cm)
E	86.4	3.94	22
F	84.2	3.37	26
G	81.3	2.79	27
I	87.3	4.03	21
J	86.1	3.91	23
K	82.2	3.17	25
M	89.4	4.23	18
N	86.8	3.95	19
O	82.9	3.62	22

that, at the same dosage, the influence of nano-montmorillonite on the performance index of the SBS-modified asphalt is greater than that of carbon black, which is due to the larger specific surface area of nano-montmorillonite and its intercalation effect. The climate of the western plateau is not only exposed to strong ultraviolet radiation but also large temperature differences. This requires the composite-modified asphalt to have an excellent high-temperature performance and a good low-temperature performance and UV aging resistance.

The price of nano-montmorillonite is 28,000 yuan (4015.2 U.S. dollars) per ton, while the price of carbon black is 4500 yuan (645.3 U.S. dollars) per ton. The price of nano-montmorillonite is 6.2 times that of carbon black at the same dosage. Therefore, the formula of the composite-modified asphalt was preliminarily determined as Schemes E, F, G, J, K, and O based on conventional indexes and cost.

3.2. Performance of UV Resistant Composite-Modified Asphalt

3.2.1. High-Temperature Performance

The temperature sweep test results for the samples of the preferred formulas are shown in Figure 4. The rutting factor G */sinδ of the sample of the optimized formula is better than that of Scheme A (SBS-modified asphalt) without nano-montmorillonite and carbon black. The rutting factor G */sinδ increases with the total amount of nano-montmorillonite and carbon black, and the larger the rutting factor, the stronger the resistance to the flow dynamic deformation under load. The rutting factor G */sinδ of Scheme E (3% nano-montmorillonite + 1% carbon black) is greater than that of Scheme O (1% nano-montmorillonite + 3% carbon black). When the total content is 4%, the rutting factor of Scheme E (3% nano-montmorillonite + 1% carbon black) is greater than that of Scheme J (1% nano-montmorillonite + 3% carbon black content). This indicates that, at a given content of nano-montmorillonite and carbon black, the contribution of nano-montmorillonite to the high-temperature performance of the composite-modified asphalt is greater than that of carbon black. The reason is that nano-montmorillonite is an inorganic material that is uniformly dispersed in SBS-modified asphalt after shearing and forms intercalated nano-microstructures with the SBS, which restricts the movement of the SBS molecular chain and prevents the deformation of the SBS-modified asphalt under high-temperature stress. Carbon black adsorbs light components in the asphalt via its strong adsorption function so that the asphalt has a strong deformation resistance. Under high-temperature stress, the light components adsorbed by carbon black will precipitate, altering the high-temperature performance.

Frequency sweep tests were carried out on samples of the preferred formula. The test data at different temperatures and frequencies were converted using the principle of time-temperature equivalence, allowing a complex modulus master curve at 60 °C to be established. The results are shown in Figure 5, which shows that, in general, the complex modulus of the asphalt mixed with nano-montmorillonite and carbon black in the low-frequency region is better than that of the SBS-modified asphalt, indicating that the high-temperature rutting resistance of the preferred samples is higher than that of the SBS-modified asphalt. However, the complex shear modulus of the samples with high nano-montmorillonite contents in the high-frequency region is less than that of the SBS-modified asphalt, which indicates that those samples have excellent high-temperature rutting resistance but insufficient shear deformation resistance at low temperatures, so the content of nano-montmorillonite should be limited.

3.2.2. Low-Temperature Performance

The low-temperature performance results for the samples of the preferred formulas are shown in Figure 6 and Figure 7. They show that, after adding nano-montmorillonite and carbon black, the creep rate m of the SBS-modified asphalt decreases, and the creep stiffness s increases. The carbon black content of the samples in Schemes E, F, and G is 1%, while the contents of nano-montmorillonite are 3%, 2%, and 1%, respectively. Through comparative analysis of the creep rate m and creep stiffness s of Schemes E, F and G, it can be seen that, with increases in the nano-montmorillonite content, the creep rate m gradually decreases and the creep stiffness s gradually increases, indicating that the SBS-modified asphalt becomes brittle after adding nano-montmorillonite. The amount of nano-montmorillonite in Schemes G, K, and O is 1%, and the amounts of carbon black are 1%, 2%, and 3%, respectively. By comparing the creep rate m and creep stiffness s of Schemes G, K, and O, it can be seen that, with increases in the amount of carbon black, the creep rate m gradually decreases and the creep stiffness s gradually increases, indicating that the addition of carbon black also increases the brittleness of the SBS-modified asphalt. Comparing Schemes F and K, it can be seen that the low-temperature flexibility reduction of the SBS-modified asphalt caused by adding nano-montmorillonite is greater than that caused by adding carbon black at the same dosage. According to the conventional indexes and rheological tests, the addition of nano-montmorillonite and carbon black can improve the high-temperature performance of asphalt and reduce its low-temperature flexibility. The reason is that the main components of nano-montmorillonite are kaolinite minerals, while those of carbon black are simple carbon particles. Both exhibit characteristics of good weather resistance and poor plasticity similar to those of inorganic materials, which are favorable to the high-temperature performance and unfavorable to the low-temperature performance of the SBS-modified asphalt. Therefore, the total content of nano-montmorillonite and carbon black should be controlled to be within 4%.

3.2.3. Fatigue Performance

At present, time scanning tests are mainly used to evaluate the fatigue performance of asphalt. There are two data processing methods, using (1) the complex shear modulus and (2) the cumulative dissipation energy. The fatigue life of asphalt is taken as the corresponding load action times when the two decrease to 50% of their initial values [28,29,30]. The first method was used in this test to evaluate the fatigue performance of the UV resistant composite-modified asphalt. The test results are shown in Figure 8 and Figure 9.

It can be seen from Figure 8 that the fatigue performance of Scheme A was greater than those of other schemes. By comparing the fatigue performance of Schemes E, F, G, K, and O, it can be seen that the fatigue life of the composite-modified asphalt gradually decreases with the content of carbon black or nano-montmorillonite. This is related to nano-montmorillonite and carbon black improving the high-temperature performance, and the disadvantage of the low softness of the SBS-modified asphalt. That is, the asphalt becomes hard and brittle, the number of load-bearing actions decreases, and the durability becomes poor. At the same dosage, the specific surface area of nano-montmorillonite is larger, and it has an intercalation structure, which creates a greater binding force with the SBS modifier and reduces the fatigue life.

3.2.4. UV Aging Resistance

Based on the UV aging tests, the complex shear modulus G *, creep stiffness s, creep rate m, and apparent viscosity (135 °C) η before and after aging were measured. The ultraviolet aging resistance of the preferred asphalt was evaluated using four indexes: the complex shear modulus rate of increase (MIR), the creep stiffness increasing ratio (SIR), the creep rate decreasing ratio (MRR), and the viscosity aging index (VAI). The calculation method is shown in Formulas (1)–(4), and the test results are shown in Figure 10.

$$MIR=\left(\frac{G_a^{*}-G_f^{*}}{G_f^{*}}\right)\times 100,$$

(1)

where

• $G_a^{*}$ is the complex shear modulus of the original asphalt;
• $G_f^{*}$ is the complex shear modulus of the aged asphalt.

$$SIR=\left(\frac{s_a-s_f}{s_f}\right)\times 100,$$

(2)

where

• $s_f$ is the creep stiffness of the original asphalt;
• $s_a$ is the creep stiffness of the aged asphalt.

$$MRR=\left(\frac{m_f-m_a}{m_f}\right)\times 100,$$

(3)

where

• $m_f$ is the creep rate of the aged asphalt;
• $m_a$ is the creep rate of the original asphalt.

$$VAI=\left(\frac{{\eta }_a-{\eta }_f}{{\eta }_f}\right)\times 100,$$

(4)

where

• ${\eta }_a$ is the apparent viscosity (135 °C) of the aged asphalt;
• ${\eta }_f$ is the apparent viscosity (135 °C) of the original asphalt.

It can be seen from Figure 10 that, after ultraviolet aging, the complex modulus, creep stiffness, and 135 °C viscosity η of the different asphalt samples are greater than those of fresh asphalt, with decreased creep rates. The MIR, SIR, MRR, and VAI values of the asphalt samples containing nano-montmorillonite and carbon black are lower than those of the SBS-modified asphalt. This indicates that, although the materials are mixed with an anti-ultraviolet material (nano-montmorillonite and carbon black), ultraviolet aging cannot be prevented; however, that of the SBS-modified asphalt can be alleviated. Comparing the UV aging evaluation indexes of Schemes E, F, G, K, and O, it can be seen that, with increases in the nano-montmorillonite or carbon black content, the UV aging resistance of the composite-modified asphalt is enhanced. At the same dosage, the contribution of nano-montmorillonite to the anti-UV aging ability is stronger than that of carbon black. The greater the total amount of nano-montmorillonite and carbon black, the stronger the anti-ultraviolet aging ability. This is because the nano-montmorillonite lamellar structure has the function of preventing oxygen and heat from diffusing into the asphalt. Combined with the ultraviolet-absorption ability of carbon black, the two synergistically improve the anti-ultraviolet aging performance of the composite-modified asphalt.

In summary, the general rule is that nano-montmorillonite and carbon black are favorable to the high-temperature and UV aging performance of UV resistant composite-modified asphalt and unfavorable to its low-temperature and fatigue performance. The greater the content of nano-montmorillonite, the more obvious the decline in the fatigue performance; its price is also higher than that of carbon black. Considering the performance and price factors, Schemes G, J, K, and O were finally selected.

4. Conclusions

(1).

Nano-montmorillonite and carbon black are beneficial to the high-temperature performance and UV aging resistance of the composite-modified asphalt, but unfavorable to its low-temperature performance and fatigue performance. The total amount should be controlled to be within 4%. Nano-montmorillonite has a better ability to improve the high-temperature and anti-ultraviolet aging performance than carbon black and is also less favorable to the low-temperature and fatigue performance. It is recommended that its amount should not exceed 3%.

(2).

Based on factors such as the performance and prices of nano-montmorillonite, carbon black, and SBS composite-modified asphalt, Schemes G, J, K, and O provide the best performance.

(3).

Compared with SBS-modified asphalt, UV resistant composite-modified asphalt has obvious advantages in high-temperature performance and UV aging resistance, and its low-temperature performance meets the use requirements of the western plateau and other strong-UV areas.

This research is only limited to the initial formulation of UV resistant composite-modified asphalt determined in the laboratory, and has not been applied in actual projects. Research on the storage stability of the UV resistant composite-modified asphalt is still lacking, the evaluation methods for the samples are still limited, and the relevant properties have not been characterized by microscopic means such as infrared spectroscopy, scanning electron microscopy, etc. The actual factory production of composite-modified asphalt has not been studied.