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Article

Study on the Performance of Modified Qingchuan Rock/Rubber Asphalt

by
Wuan Li
1,
Yukun Chen
2,
Tengteng Guo
3,4,5,6,
Zhenxia Li
3,4,5,6,* and
Xiaoxiao Jiang
3
1
Zhengzhou Yellow River Engineering Co., Ltd., Zhengzhou 450008, China
2
North China Branch, China Construction Second Engineering Bureau Limited, Beijing 100160, China
3
School of Civil Engineering and Transportation, North China University of Water Resources and Electric Power, Zhengzhou 450045, China
4
Henan Province Engineering Technology Research Center of Environment Friendly and High-Performance Pavement Materials, Zhengzhou 450045, China
5
Technology Innovation Center of Henan Transport Industry of Utilization of Solid Waste Resources in Traffic Engineering (North China University of Water Resources and Electric Power), Zhengzhou 450045, China
6
North China University of Water Resources and Electric Power-Henan Provincial Institute of Transportation Planning and Design Co., Ltd., Green, Low Carbon, and High Performance Road Materials Research and Development Center, Zhengzhou 450045, China
*
Author to whom correspondence should be addressed.
Coatings 2024, 14(10), 1246; https://doi.org/10.3390/coatings14101246
Submission received: 21 August 2024 / Revised: 17 September 2024 / Accepted: 23 September 2024 / Published: 30 September 2024
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Abstract

:
This paper developed a new environmentally friendly composite modified asphalt material and studied the composite modification of Qingchuan rock asphalt (QRA) and waste tire rubber powder (RP) was studied in this paper. QRA/RP composite modified asphalt was prepared by adding these two materials as modifiers into matrix asphalt and compared with matrix asphalt and QRA modified asphalt. The basic properties of asphalt before and after aging were evaluated by the rotating thin film oven test. The high-temperature performance and permanent deformation resistance at different temperatures and frequencies were analyzed by the dynamic shear rheological test. The bending creep stiffness test was used to evaluate the low-temperature performance. In addition, the microstructure and modification mechanism of composite-modified asphalt were analyzed by scanning electron microscopy and infrared spectroscopy. The results show that QRA-modified asphalt is superior to matrix asphalt in terms of mass loss, viscosity ratio, and residual penetration, while QRA/RP composite-modified asphalt is further improved on this basis, QRA/RP composite modified asphalt can effectively improve the high and low temperature performance of asphalt.. Although the addition of RP is mainly based on physical modification, it also causes weak chemical reactions and enhances the adhesion of asphalt. The interaction between Qingchuan Rock asphalt and rubber powder significantly improves the overall stability of asphalt structure.

1. Introduction

Natural asphalt attracted the attention of the road industry with its unique advantages. Rock asphalt is a petroleum derivative with the matrix asphalt and coexists with nature for a long time. Therefore, its performance is stable and can effectively alleviate the segregation of polymer-modifying asphalt. At the same time, natural rock asphalt has outstanding high-temperature performances, aging resistance, and water damage resistance, but low-temperature performance is insufficient [1,2,3,4]. Yadykova et al. [5] studied natural asphalt based on microscopic analysis. The study found that the natural asphalt contains a large number of hydrocarbons and has good compatibility with asphalt. Natural asphalt has high nitrogen content, strong oxidation resistance, can be closely combined with aggregate, and has high viscosity. According to the proportion of infrared absorption band, it is suggested that asphalt can be divided into paraffin type, aromatic type, and resin type. Fan et al. [6] used chemical composition, X-ray, infrared spectroscopy, and other microscopic means to observe and analyze the constituents of QRA and its asphaltene crystals. The results show that Qingchuan rock asphalt contains more minerals and asphaltene components, which belongs to brittle asphalt. Zamhari et al. [7] found that the modified asphalt has superior rigidity, the pavement is not easy to deform in high temperature, and the anti-permanent competency is augmented. Lu [8] studied the impacts of rock asphalt content on the rheological characteristics of asphalt and the interaction mechanism between them by using an asphaltum four component analyzer, infrared spectrometer, and fluorescence microscope. It is found that rock asphalt can upgrade the high-temperature sensitivity and thermo-responsive characteristics in asphalt. After modification, the proportion of saturated and aromatic components of asphaltum decreases, the proportion of resin and asphaltene increases correspondingly, and the equilibrium state of free asphalt colloid is broken. Shi et al. [9] believe that rock asphalt exists in nature for a long time. After hundreds of millions of years of sedimentary fusion and evolution, a unique ‘asphalt-mineral’ stable system is formed, which makes the modified asphalt have good oxidation resistance and anti-aging ability. Xi [10] studied the basic properties and rheology characteristics of domestic rock asphalt modifying asphalt with different contents. The test results show that after adding domestic rock asphalt, the thermal sensitivity and high temperature of asphalt tend to be stable gradually, and the properties related were better. In terms of low temperature, when the dosage of rock asphalt is less than 10%, the cryogenic properties of asphalt remain basically unchanged, and when the dosage is more than 10%, the low-temperature ductility decreases. Based on the comprehensive performance indicators, it is suggested that the dosage of domestic rock asphalt should not exceed 10%. Lin et al. [11] chose to investigate the modifying capabilities of two kinds of additives, Buton rock asphalt and Qingchuan rock asphalt. The results show that the high-temperature rheological behavior and anti-aging properties of matrix asphalt are improved after adding two kinds of modified materials, and there is a positive correlation with the content. Nonetheless, a noticeable tendency was detected for the low-temperature ductility of the asphalt to reduce. Furthermore, at equivalent dosage, Qingchuan rock asphalt demonstrated a superior modification efficacy.
With the high-speed development of China’s automobile industry and rubber industry, car ownership gradually increased. In the meantime, a large amount of waste rubber products were accumulated, and the pollution of waste tires became more and more serious [12]. Therefore, the rational use of waste tires can not only solve the existing problems of environmental pollution and waste of resources, but also hoist the quality characteristics of raw materials through the development of new materials [13]. Relevant studies show that rubber powder, as an asphalt modifier, has obvious promotional effects on asphalt’s resistance to high-temperature rutting and enhances its low-temperature cracking resilience [14,15,16,17].
Dharamveer et al. [18] believed that large particle-size rubber powder is beneficial to the improvement of the elastic recovery competency of matrix bitumen, and shows a good improvement efficacy on fatigue resistance, and comprehensively improves the mechanical properties. Simultaneously, it was observed that fine-grained RP particles facilitate better high-temperature stability of asphalt, as they more readily disperse and swell within the asphalt matrix. Drawing from the results of the freeze–thaw testing, Sun et al. [19] set three test variables of hydrogen peroxide, RP mesh, and mixing amounts to study its influence on rubber powder-modified asphalt mixture. The results show that when the RP dosage is 21% and the mesh number is 60, the RP-modified asphalt mixture has better mechanical properties. Qian [20] prepared modifying asphalt with 5%, 10%, and 15% rubber powder, and compared it with 90% matrix asphalt. The rheological parameters G*, δ, and rutting factor were analyzed by a DSR test. The test shows that RP-modifying asphalt has superior anti-permanent deformation in a high-temperature environment. In the MSCR test, the parameters Jnr value and R value also proved that the RP-modified asphalt had excellent high-temperature performances, and the amount of rubber powder was positively correlated with its high-temperature rheological properties. In addition, Yang [21] found that the RP absorbs the light components during the swelling development process, which makes the modified asphalt have better mechanical properties and viscoelastic properties; the more the amount of rubber powder is added, the better the high and low-temperature anti-deformation are. However, too much rubber powder will lead to excessive viscosity of asphalt and segregation stratification, resulting in insufficient fusion of the two. This limits the promotion of waste RP-modified asphalt, so it is imperative to find a material that can ameliorate the compatibility of RP and matrix asphalt [22].
In summary, rock asphalt can not only improve the thermal sensitivity, aging resistance, permanent deformation resistance, and anti-water damage of matrix bitumen, but also improve the road properties of the mixture, and can also be used in combination with other materials. Nevertheless, the impacts of rock asphalt on ameliorating low-temperature cracking resistance of asphalt are less conspicuous, and even have a certain degree of negative impact, which restrict its efficient usage in the roads field. Therefore, it is very important to introduce a material that can hoist the low-temperature performance of bitumen and mix it with rock asphalt. Rubber powder can play an advantage in improving the high temperature and water stability of asphalt, especially the low-temperature cracking resistance of asphalt. However, the RP-modifying asphalt system has poor compatibility and dispersion, and segregation is easy to occur in the preparation, but it can still be used in combination with other modifiers in order to achieve a holistic enhancement of asphalt pavements. Therefore, based on relevant research, this paper analyzes the aging of QRA/RP compound-modified asphalt and the high and low-temperature performances before and after aging, and studies its modification mechanisms, so that QRA and RP make up for the shortcomings of single modification, takes into account the performance advantages of the two, and provides scientific foundation and technical uphold for the applied innovation of QRA/RP composite-modified asphalt in the road field.

2. Raw Materials

2.1. Matrix Asphalt

In this paper, the 70 a petroleum asphalt provided by Zhengzhou Municipal Engineering Corporation (Zhengzhou, China) (asphalt paving company) is selected. According to the test procedure [23], the basic properties of matrix asphalt are listed in Table 1.

2.2. Qingchuan Rock Asphalt

Qingchuan rock asphalt is mainly distributed in the Sichuan Province in China, with abundant resources. The Qingchuan rock asphalt selected is provided by Sichuan Shuntian Mining Co., Ltd. (Chengdu, China), and the detailed technical specifications are outlined in Table 2.

2.3. Rubber Powder

Waste rubber powder is a material obtained by collecting waste rubber products and crushing and grinding them by physical or chemical methods. The rubber powder appears to be black powder. In this experiment, 40 mesh waste tire RP was selected, which was provided by Hebei Kexu Building Materials Co., Ltd. (Hebei, China). The basic technical indicators are displayed in Table 3.

3. Test Scheme

3.1. The Best Preparation Scheme of Composite-Modified Asphalt

Based on the previous experimental data and research results, this paper determines the four factors that affect the performance of QRA/RP composite-modified asphalt, which are Qingchuan rock asphalt content, rubber powder content, shear time, and shear temperature, and selects the orthogonal test. According to the four-factor three-level test scheme, the range variance analysis method is used to analyze the three indicators, elastic recovery, and Brinell rotational viscosity test data of QRA/RP composite-modified asphalt under nine groups of schemes. Under each factor, the three levels are selected to optimize the best proportion selection standard of QRA/RP composite-modified asphalt. Based on the influence degree of different factors, five preparation schemes were preliminarily selected. Finally, the optimum preparation process of QRA/RP composite-modified asphalt was determined by comparing and analyzing the preparation schemes under different indexes.

3.2. Preparation of Composite-Modified Asphalt

Firstly, the base bitumen is positioned within an electric blast drying oven, heated and dehydrated to a molten state at 180 °C, and 500 g of base bitumen is taken and transferred on an invariant temperature heating electric furnace. The temperature is controlled at about 155 °C to keep it flowing. At the same time, Qingchuan rock asphalt and rubber powder were put into a 100 °C electric blast drying oven for 1 h, and 7% Qingchuan rock asphalt and 17% rubber powder were weighed after drying. Secondly, Qingchuan rock asphalt was mixed with matrix asphalt, sheared by high-speed shear for 10 min, and then RP was slowly added, and then it was sheared at 180 °C for 45 min. Finally, the prepared composite-modified asphalt was placed in an electrothermal blast drying oven to swell and develop for 30 min. During this period, glass rods were used for stirring every 15 min to assist the discharge of air in the asphalt. Finally, QRA/RP composite-modified asphalt with a smooth surface and no bubbles was obtained.

3.3. Rotating Film Oven Test

The short time aging of asphalt was simulated by the rotating thin film oven test (RTFOT). According to the requirements of T0610 in the regulation [23], the rotary film oven is started in advance, and it is preheated for more than 16 h. During the test, the asphalt is heated and flowed first, and then 35 g of asphalt is injected into the sample bottle. It was placed on the ring frame, the rotary switch of the ring frame was opened, and the rotation speed was set to 15 r/min. In the meantime, the hot air was injected into the rotating bottle at a flow rate of 4000 mL/min so that it was heated at 163 °C for 85 min.

3.4. Dynamic Shear Rheological Test

The DHP-1 dynamic shear rheometer was employed to investigate the base bitumen, QRA-modified asphalt, and QRA/RP composite-modified asphalt before and after aging. The 25 mm in diameter metal plate was selected, and the asphalt sample was kept at 1 mm thickness. Among them, the temperature scanning selected temperature range is 46 °C~82 °C, the strain level is 10%, and the shear frequency is 10 rad/s. The variation tendency of G* and δ with different test temperatures is mainly analyzed, and the G*/sinδ is calculated. The temperature range selected by frequency scanning is 40 °C~88 °C, the strain level selected by frequency scanning is 1%, and the frequency is controlled between 0.1 and 100 rad/s. Based on the time–temperature equivalent principle, the main curve of lgG*-lgω is constructed to further evaluate the high-temperature rheology of asphalt. Through MSCR test, the parameters R and Jnr of bitumen were calculated at 0.1 kPa and 3.2 kPa, and the anti-permanent deformation of three kinds of bitumen was comprehensively evaluated.

3.5. Bending Creep Stiffness Test

The ATS low-temperature bending rheometer was used to study the low-temperature behavior. Referring to the ‘Bending Creep Stiffness Test (BBR) Method’ SH/T 0775-2005 specification, the three asphalt samples before and after short-term aging were prepared into trabecular bending specimens, and the specimen size was controlled to 127 mm × 12.7 mm × 6.35 mm. At −6 °C, −12 °C, and −18 °C, 240S stress loading was carried out on the specimens, and the S and m of the specimens were collected to comprehensively analyze the low-temperature creep properties of three asphalts.

3.6. Scanning Electron Microscope Test

The SEM test can act on the surface of the asphalt with a lower energy electron beam so that the electron beam interacts with the atoms and forms a clear three-dimensional image in the form of vacuum scanning and excitation of electronic signals. Compared with ordinary microscopes, it has the unique advantages of high resolution and can detect the morphology and distribution characteristics of materials at the nano level [24]. In this paper, the materials were studied by field emission scanning electron microscopy. QRA, RP-modified materials, and three types of asphalts were quantitatively and qualitatively analyzed by enlarging different multiples.

3.7. Fourier Transform Infrared Spectroscopy Test

The use of continuous wavelength infrared light to continuously irradiate the measured substance will cause some groups inside the substance to oscillate and rotate. At the same time, the infrared beam with the same frequency as the functional group will be selectively absorbed. The absorption state can be recorded by a specific device to obtain the spectra of each substance. Through the change in the characteristic absorption peak, the category of adjacent functional groups is revealed, and the structure of the molecule is determined. The changes in molecular structure and functional groups in the measured substances were analyzed by the abscissa of the absorption peak and the differences in shape, peak position, and intensity, so as to judge the modified form [25]. In this paper, a Nicolet iS10 Fourier transform infrared spectrometer was used to analyze the microstructures and modification mechanisms of three different types asphalt with a scanning range of 4000 cm−1~400 cm−1 and 64 scanning times.

4. Test Results and Analysis

4.1. Aging Performance Analysis

The aging parameters of matrix asphalt, QRA-modified asphalt, and QRA/RP composite-modified asphalt were determined by experiments, that is, mass loss, residual penetration ratio, and viscosity ratio before and after aging. The anti-aging ability of three types of asphalt was compared, and the improvement degree of QRA and RP modifier on asphalt aging performance was analyzed. The results of three asphalts before and after RTFOT are shown in Table 4.
From Table 4, it can be seen that QRA increased the penetration ratio of bitumen residue by 10.4% and decreased the mass loss and viscosity ratio by 12.6% and 0.426, respectively. This indicates that Qingchuan rock asphalt has an anti-aging effect on asphalt. This is because QRA can accelerate the adsorption of asphalt, reduce the probability of contact between asphalt and oxygen, and delay the aging speed. The rubber powder makes the mass loss and viscosity ratio of asphalt further decrease by 3.8% and 0.118 on the basis of QRA-modified asphalt, and the residual penetration ratio further increase by 11.6%. Compared with base asphalt, the mass loss and viscosity ratio decreased by 16.4% and 0.544, and the residual penetration ratio increased by 22.0%, indicating that rubber powder can continue to inhibit the mass change rate of QRA-modified asphalt. Further analysis shows that the improvement of the thermal oxidative aging resistance of QRA/RP composite-modified asphalt is determined by the interaction of the two modifiers, not just the simple superposition of the two modification effects.

4.2. High-Temperature Rheological Properties Analysis

4.2.1. Temperature Scanning

Under the temperature condition of 46 °C~82 °C, the temperature scanning test results of three asphalts before and after aging are shown in Figure 1 and Figure 2.
The improvement of QRA and RP modifiers on the aging performance of asphalt was analyzed, and the complex modulus, phase angle, and rutting factor were selected to evaluate the high-temperature performance of composite-modified asphalt.
On the whole, when the external temperature is low, the G* of the three asphalts is larger and the δ values are smaller, indicating that the bitumen is more elastic at low temperature and can withstand more deformation. With the increase in temperature, the G* of matrix asphalt, QRA-modified asphalt, and QRA/RP compound-modified asphalt decrease continuously, and the δ increases gradually, which reflects that the increase in temperature will cause the decrease in anti-deformation capacity of bitumen. At this time, the interaction force between asphalt molecules is weakened, and the asphalt gradually develops from high elastic state to viscous flow state. Correspondingly, its viscous characteristics are more obvious; that is, the maximum shear stress that asphalt can withstand in the test becomes smaller, which is also consistent with the characteristics of asphalt binder as a temperature-sensitive viscoelastic material.
Under the same temperature conditions, compared with the matrix asphalt, the G* value of QRA-modified asphalt is significantly higher, and the δ is smaller, indicating that the shear resistance of QRA-modified asphalt is improved. This is because the QRA material contains a higher proportion of asphaltene and resin components. After mixed with matrix asphalt, the proportion of saturates and aromatics in the modified asphalt is reduced, the asphalt colloid structure is changed, and the polarity is enhanced. This is beneficial to the enhancement of thermal stability of bitumen.
QRA/RP composite-modified asphalt has the highest G* value and the smallest δ. For example, at 46 °C, the G* of QRA/RP composite-modified asphalt is 45.37 kPa, which is 23.57 kPa larger than base asphalt, indicating that the two kinds of asphalt admixtures can significantly contribute to ameliorating the elasticity and high-temperature characteristics of bitumen. It can be explained that Qingchuan rock asphalt is a petroleum-based solid material with similar properties to petroleum asphalt. The incorporation of rock asphalt can greatly alleviate the compatibility between polymer RP and asphalt. The modulus of the asphalt material is improved, which in turn enhances its overall strength.
The improvement of high-temperature performance of QRA/RP composite-modified asphalt is mainly due to the existence of rubber powder in asphalt in the form of particles, which will increase the elastic component of asphalt. In addition, the volume of rubber powder increases after swelling and development, showing a loose flocculent structure. The asphalt system changes from a pure continuous phase to a semi-continuous phase blended with rubber powder particles, making the modified asphalt more dense; on the other hand, the increase in the consistency of modified asphalt strengthens the ‘frame’ structure of Qingchuan rock asphalt in the asphalt system effectively inhibits the tendency of asphalt flow and makes the asphalt less prone to displacement in the high-temperature environment.
From Figure 2, it can be found that the G* of the three asphalt films increase and the δ decrease after aging, showing better high-temperature rheological properties than before aging. This is because aging makes the hardening trend and elastic characteristics of asphalt more obvious. In the face of high temperature, asphalt has a stronger ability to maintain its own state.
At the same temperature, the G* of matrix asphalt is the smallest, and the high-temperature rheological properties of matrix asphalt are weak, so it is particularly necessary to modify it. The G* of QRA/RP composite-modified asphalt is the largest, and the size relationship of δ is opposite. Observations reveal that after aging, the high-temperature characteristics of QRA/RP composite-modified asphalt is still optimal. The aging effect does not change the fundamental improvement law of QRA and RP on asphalt properties. The G*/sinδ-temperature curves before and after aging are shown in Figure 3 and Figure 4.
In the range of 46 °C~82 °C, the G*/sinδ values of the three asphalts before and after aging show a negative correlation with temperatures, indicating that the rising temperatures make the high-temperature characteristics of asphalt decrease. In the proceeding of temperature tending to 82 °C, the G*/sinδ difference of the three asphalts is becoming smaller and smaller, and the trend change is gradually slowing down and gradually approaching.
According to Figure 3, when the temperature gradually increased from 46 °C to 82 °C, the G*/sinδ of the modifying asphalt was improved after the incorporation of QRA. When the temperature condition is 46 °C, the curve shows the overall trend of the sudden decrease in the rutting factor, and the gap between the G*/sinδ of three different types of bitumen is also the largest. At this time, the G*/sinδ of QRA/RP composite-modified asphalt is 52.81 kPa, which is 30.75 kPa larger than that of base asphalt and 14.67 kPa larger than that of QRA-modified asphalt. At each temperature, the G*/sinδ of QRA/RP composite-modified asphalt is greater than that of QRA-modified asphalt and matrix asphalt, indicating that the matrix asphalt with poor high-temperature performance obtained more excellent high-temperature resistance under the combined action of QRA and RP, which can decelerate the generation of wheel ruts in actual service.
From Figure 4, it can be found that the curve tendency between the G*/sinδ and temperature of three species of asphalt after aging is roughly the same as that before aging; that is, the aging effect will not change the action regulation of modifying materials on the high-temperature characteristics of bitumen. The reason is that the effective combination of QRA and RP makes the material properties of the two, that is, high adhesion and high elasticity, also effectively combined, and thus forms a unified system. This system brought the overall improvement in the mechanical strength of the compound-modified asphalt, and the probability of rutting deformation disease is reduced.

4.2.2. Frequency Scanning

(1)
G* analysis of different asphalt complex modulus
Through the frequency scanning test, the dynamic characteristics of asphalt at higher temperatures can be studied more comprehensively. In this paper, the test temperature is 40 °C~88 °C, and the test results are shown in Figure 5, Figure 6 and Figure 7.
Analysis of Figure 5, Figure 6 and Figure 7 shows that:
Under the condition of constant temperature, the G* and angular frequency of the three kinds of asphalt show an approximate linear positive correlation. With the increase in angular frequency, the complex modulus G* shows an upward trend to varying degrees, indicating that the higher the angular frequency, the more the asphalt material tends to be elastomer, and the ability to resist deformation is improved. The reason is that the continuous increase in angular frequency leads to the shortening of the action time of load on asphalt, so that the interaction force between asphalt molecules can resist the load during this period of time. Therefore, the complex modulus G* of asphalt increases, the permanent deformation decreases, the elastic recovery ability increases, and the anti-deformation ability is improved.
At different temperatures, the change tendency of the G* curves of three asphalts is basically equal, and the curves at five temperatures are roughly parallel. When the same frequency is applied, the G* of three asphalts shows a significant negative correlation with the temperature; that is, the higher the temperature, the smaller the value. The reason is that with the increase in temperature, the structure of asphalt colloid changes, and it is mostly viscous flow. When subjected to heavy-duty vehicles, the competency of bitumen pavement to control distortion is weakened.
At the equal temperature and shear frequency, the G* of the three species of asphalt after short-time aging is higher than the asphalt without aging process, and the asphalt with two admixtures has the largest G*. This shows that QRA/RP composite-modified asphalt has more excellent high-temperature function, and the aging effect plays a vital role in lifting the high-temperature rutting resistance of bitumen. This result is consistent with the conclusion obtained by the temperature scanning test. The significant improvement effect of QRA and RP composite modifier on the high-temperature rutting resistance of asphalt was reaffirmed. The main reason for the analysis is that after the addition of rubber powder, a three-dimensional structure is formed with the matrix asphalt. This staggered structure runs through the rich pores of QRA. The three show a complex, stable, and cohesive state, which weakens the fluidity of asphalt and enhances the anti-rutting plasticity.
With the change in shear frequency, the G* curve of the three asphalts after aging also shows an upward trend, and the effect of angular frequency on the aging asphalt is roughly the same as that before aging. The main reasons are as follows: after the aging test, QRA and RP increase the contents of heavy component asphaltene, the overall structure of asphalt changes to gel type, and the relative increase in heavy component will reduce the viscosity of asphalt and make asphalt binder become hard, which is manifested as the reduction in deformation of QRA/RP compound-modified asphalt under high-temperature and external force conditions.
(2)
Main curve analysis of frequency scanning results
In order to expand the range of frequency analysis, this section is based on the principle of time–temperature equivalence. The G* and angular frequency of the three kinds of asphalt are fitted by double logarithm, and the displacement factor is calculated. Then, the three asphalts move horizontally on the shift factor to form a lgG*-lgω curve with a wide frequency range. The schematic diagram is shown in Figure 8.
①
Determination of three kinds of asphalt displacement factors
Firstly, the displacement factor of matrix asphalt is calculated, and G* and ω are fitted by a double logarithmic curve equation. The results are shown in Table 5.
In order to facilitate the analysis, G* = 1000 Pa is assigned, and lgG* = 3 is obtained. Substituting into the equation, lgω at five temperatures is obtained. Then, based on 40 °C, the corresponding shift factors of lgω at four temperatures are calculated, as shown in Table 6.
On this basis, the corresponding displacement factor values of the two modified asphalts are calculated, as shown in Table 7 and Table 8.
②
Analysis of modulus master curve
Based on the temperature of 40 °C, the lgG*-lgω curve at other temperatures is horizontally translated according to the specific value of the shift factor. Finally, the modulus master curve of three original asphalts is drawn, as shown in Figure 9.
It can be seen from Figure 9 that the G* value of matrix asphalt is small under high-temperature and low frequency conditions, which reflects that it does not have enough abilities to resist permanent deformation when it is in high-temperature surroundings. When the loading angular frequency is constant, the G* of two modifying asphalts is larger than that of matrix asphalt, indicating that QRA and RP can ameliorate the high-temperature performance of asphalt and play a greater role in synergy. At low temperature and high frequency, the G* of the three types of bitumen shows a good positive correlation with the angular frequency and shows a unified tendency of approaching gradually. Among them, the G* value of matrix asphalt is still at the lowest position among the three, indicating that its high-temperature function is still inferior to the two modified asphalts. The G* of QRA/RP composite-modified asphalt is at the highest position among the three, and shows a continuous upward trend, which indicates that QRA/RP composite-modified asphalt has better high-temperature resistance.

4.3. Permanent Deformation Resistance

In this section, the MSCR test temperature is set to 64 °C, the 25 mm rotor is selected, the sample size was controlled to be 25 mm in diameter and 2 mm in thickness, the shape is round cake, and the parallel plate gap is set to 2 mm. The test results are shown in Figure 10.
From Figure 10a,b, it can be seen that at a constant temperature of 64 °C, under 0.1 kPa and 0.3 kPa, the strain–time curve of the matrix asphalt is approximately rectangular in each creep cycle. This shows that under the action of stress, the matrix asphalt has a large shear deformation, and there is almost no unloading recovery strain, and the cumulative unrecoverable strain is extremely large, basically without strain recovery ability.
By comparing Figure 10c,d, it can be found that under 0.1 kPa and 3.2 kPa, at the parallel temperature, the cumulative strain value of QRA/RP composite modifying asphalt shows a decreasing tendency on the basis of QRA-modified asphalt; that is, additives QRA and RP can enhance the creep recovery ability of bitumen.
In order to analyze the difference of permanent deformation resistance of three types of asphalt more clearly and intuitively, R and Jnr at 0.1 kPa and 3.2 kPa are calculated. The results are shown in Figure 11 and Figure 12.
From Figure 11 and Figure 12, it can be seen that under two shear stress conditions, the R (3.2) of three species of asphalt is less than R (0.1), implying a strong correlation between the extent of bitumen’s damage deformation and the magnitude of stress loads applied to it. Therefore, in practical applications, pavements under heavy traffic are more prone to rutting and other diseases. The values of R (0.1) and R (3.2) of matrix asphalt are very small, almost 0, indicating that the proportion of elastic components is very low. This phenomenon shows that the deformation irrecoverable strain of matrix asphalt is very large, and it basically does not have creep recovery ability.
After adding the admixture QRA, the R of QRA-modified asphalt increased by 58.612 and 54.459 percentage points. The reason is that the strength of QRA material itself is high and the stiffness is large. This advantage can help the modified asphalt to effectively control its own displacement and deformation when it is in a high-temperature circumstance. After adding RP, the proportion of elastic composition in bitumen continues to increase, the viscous deformation is relatively reduced, and the R value data of compound-modified asphalt reach the maximum; that is, the strain recovery rate of QRA/RP composite-modified asphalt reaches the optimum, and the permanent deformation resistance is significantly enhanced.
At 0.1 kPa and 3.2 kPa, the Jnr value of QRA-modified asphalt is notably reduced compared to that of the unmodified base asphalt, and the reduction values are 4.711 kPa−1 and 5.773 kPa−1, respectively. The Jnr value of QRA/RP composite-modified asphalt is 15.4% and 16.8% shows a further reduction compared to QRA-modified asphalt. The variation in the two indexes of R and Jnr shows that the QRA/RP compound-modified asphalt has excellent high-temperature creep recovery capacity and can be well applied, which is consistent with the results of the above frequency scanning.

4.4. Analysis of Low-Temperature Creep Performance

4.4.1. Analysis of Low-Temperature Creep Performance of Original Asphalt

The rheological parameters S and m were obtained by bending creep stiffness test to evaluate the rheological properties of asphalt under low temperature and load. The three original asphalts S and m obtained from the BBR test are shown in Figure 13.
The analysis of Figure 13a shows that when the temperature decreases, the S of the three bitumen shows an upward tendency, which is reflected in the fact that when the external environment is colder, the asphalt pavement shows stronger brittleness and hardness, and the probability of cracks increases greatly. The S value of QRA-modified asphalt is larger, which is due to the fact that QRA asphalt has more asphaltenes, less light components, and contains a certain amount of minerals such as ash. The phenomenon of stress concentration and stiffness increase is easy to occur inside the asphalt, which makes the modified asphalt more brittle, and easy to crack. At −6 °C, −12 °C, and−18 °C, the S of QRA/RP composite-modified asphalt is significantly lower than that of QRA-modified asphalt, which is 30.5%, 57.5%, and 40.9%, respectively. Observations indicate that rubber powder plays an active and significant role in improving the low-temperature crack resistance of QRA-modified asphalt.
The reasons for the improvement of its low-temperature crack resistance are as follows: Due to the different material properties of rubber powder particles and matrix asphalt, the degree of deformation is not the same when subjected to load. Among them, the deformation of matrix asphalt will be greater than that of rubber powder particles. The degree of deformation will induce the rubber powder to appear crazing and the energy brought by the wear stress, thereby improving the low-temperature crack resistance of the asphalt. The existence of Qingchuan rock asphalt reduces the distance between the colloidal structure centered on rubber powder particles and the asphalt colloid, and gradually becomes a stable three-dimensional network structure with Qingchuan rock asphalt as the core and connected with rubber powder. When subjected to tensile load, the interaction force of this stable network structure increases, and it can better resist the tension, thus improving the tensile deformation ability of asphalt as a whole. In a word, the incorporation of rubber powder has the effect of improving the flexibility of asphalt in a low-temperature environment and endows asphalt with better stress relaxation characteristics.
Figure 13b illustrates that the creep rate, denoted by m, for QRA/RP compound-modified asphalt surpasses that of the other two asphalt types when evaluated at identical temperature settings, indicating that the addition of composite modifier improves the brittleness and reduces the probability of the low-temperature stress of asphalt. Under the temperature conditions of −6 °C, −12 °C, and−18 °C, among the m of the three asphalts, QRA-modified asphalt exhibits the lowest m, suggesting that the inclusion of QRA could potentially undermine the ductile characteristics of the asphalt. QRA/RP composite-modified asphalt reached the maximum. Among them, the m of QRA/RP composite-modified asphalt is 0.137, 0.082, and 0.054 higher than that of QRA-modified asphalt, and the growth ratio is 23.9%, 23.0%, and 20.9%, which indicates that under the temperature condition of −6 °C, RP has the most significant effect on the low-temperature function of QRA-modified asphalt.

4.4.2. Analysis of Low-Temperature Creep Performance of Aged Asphalt

For the three kinds of asphalt after RTFOT, the equal test analysis method as before aging is adopted, and the results are shown in Figure 14.
From Figure 14a, it is evident that after RTFOT, the S of the three asphalt samples is increased compared with those before aging; that is, aging has a certain degree of weakening effect on the low-temperature characteristics of bitumen. After aging, under the low-temperature conditions of−6 °C, −12 °C, and−18 °C, the S of QRA/RP composite-modified asphalt is still smaller than the other two bitumen samples, indicating that the aging effect does not affect the modification efficiency of rubber powder and the RP compensates for the weakness of low-temperature performance of QRA.
From Figure 14b, it is evident that after RTFOT, the creep rate m of the three asphalt samples shows a downward tendency with the decrease in temperature. At the same temperature, the m value of matrix asphalt is the largest and slightly higher than that of Qingchuan rock asphalt-modified asphalt, indicating that the matrix asphalt is subjected to aging. After aging, the deterioration trend is significant. Qingchuan rock asphalt has a good ability to resist the adverse effects of aging. Therefore, after short-term aging, its low-temperature crack resistance is marginally improved over that of matrix asphalt, which alleviates some of the detrimental impacts on the low-temperature characteristics of asphalt.

4.5. Micro-Morphology Characterization Analysis

4.5.1. Micro-Morphology Analysis of Raw Materials

(1)
Microscopic morphology characterization analysis of Qingchuan rock asphalt
The QRA powder was magnified by 10,000 and 25,000 times, as shown in Figure 15. It illustrates that Qingchuan rock asphalt is presented in granular form at room temperature. The surface is rough and staggered, and the structure is loose. The special structural system makes it form a stable and solid ‘mineral powder–asphalt’ mixed structure after adsorbing small molecules of asphalt.
(2)
Micro-morphology analysis of rubber powder
The RP was magnified by 3000 and 5000 times, and the results are shown in Figure 16. It illustrates that the surface of the RP particles is rough and irregularly shaped, and there is a fluffy microporous pore structure similar to ‘sponge’. In the process of swelling and degradation of RP, the light components in bitumen are more easily embedded, the modified asphalt system gradually reaches a stable state.

4.5.2. Characterization Analysis of Asphalt Microstructure

(1)
Microstructure of matrix asphalt
The morphology of the matrix asphalt was characterized by magnification of 500 and 2000 times, as shown in Figure 17. It illustrates that when magnified by 500 times, mild texture can still be observed on the surface of matrix asphalt, but no other impurities or particles appear. After being magnified 2000 times, some textures on the surface of the base asphalt image disappear, showing a smooth and flat texture on the whole, and its microscopic morphology is evenly distributed asphalt phase.
(2)
Microstructure of QRA-modified asphalt
The microstructure of QRA-modified asphalt was analyzed by amplifying 100 and 2000 times, as shown in Figure 18. It illustrates that the distribution of Qingchuan rock asphalt in matrix asphalt is more regular, showing a three-dimensional reticular spatial structure interlaced in vertical and horizontal directions, with no obvious particulate matter prominent, and no agglomeration and agglomeration.
The specific analysis reveals that the porous structure of Qingchuan rock asphalt will closely adsorb the light oil and saturated ingredients in the matrix asphalt, so that the contact interface between the particles and the asphalt is firmly combined. On the macro level, QRA is evenly distributed in the matrix asphalt, and there is a high degree of compatibility achieved between them. After the adsorption is completed, there are many small particles wrapped with asphalt film on the surface of QRA-modified asphalt. These particles will decrease in volume as the temperature decreases. Finally, the properties gradually become fixed and become spherical bodies with stable state energy.
(3)
Microstructure of QRA/RP composite-modified asphalt
The QRA/RP composite-modified asphalt was magnified 500 and 5000 times, as shown in Figure 19. It illustrates that after the addition of RP to Qingchuan rock asphalt-modified asphalt, the RP swells and desulfurizes in the bitumen, and the volume of the RP particles increases and gradually develops into a saturated state. At this time, many textures on the surface of the QRA-modified asphalt are disrupted, and the QRA/RP composite-modified asphalt exhibits a more complex three-dimensional network structure and wave structure. At the beginning of entering the matrix asphalt, the large particles of RP exist in the base asphalt in the form of discrete suspension and connect with the micelle structure of the matrix asphalt after closely adsorbing light oil, forming an interface layer with viscous characteristics with the large particles of rubber powder as the core, and initially forming a three-dimensional network structure. After contact with Qingchuan rock asphalt, the core of the system is transferred to the macromolecular Qingchuan rock asphalt. Many rubber powder particles are attracted by the larger Qingchuan rock asphalt micelle system and then connected, filling in the matrix asphalt in a more uniform and dense form. It provides an important force in improving the common problems of insufficient swelling and uneven agglomeration of polymer rubber powder and asphalt.

4.6. Infrared Spectrum Analysis

The wavenumber transparency test was carried out on three asphalts in turn, and the resultant data are illustrated in Figure 20.
It can be found from the infrared spectrum of QRA-modified asphalt that it has a wide O-H bond stretching vibration peak at 3500 cm−1, indicating that the adhesion of asphalt is enhanced. Because the composition of N element in Qingchuan rock asphalt is high, and it exists in the form of amide group or cyano compound, the absorption peak at 3208 cm−1 band is attributed to the stretching vibration of N-H bond in amide structure-CO-NH-. The absorption peaks at 2865 cm−1 and 2781 cm−1 are stronger than that of base asphalt, and the intensity is strengthened in this wave number range. Further analysis shows that the vibration peak generated by the stretching vibration of the benzene ring conjugated C=C skeleton is found at about 1712 cm−1. The larger the peak value, the stronger the benzene ring skeleton vibration in asphaltene, and the higher the condensation degree of aromatic ring structure in asphaltene than that of matrix asphalt, indicating that the high-temperature characteristics of matrix asphalt modified by QRA are improved. On the whole, the shape and change trends of the characteristic peaks of the infrared spectrum of QRA-modified asphalt are close to those of the matrix asphalt, and the modification of the matrix asphalt by QRA is only a physical mixing that changes the content of functional groups.
Through comparative analysis of the infrared spectra depicted for QRA/RP composite-modified asphalt in Figure 20, one observes that the coordinates of each absorption peak in the functional group area and the fingerprint area are basically corresponding to the matrix asphalt, and the graphic trend is also roughly the same. This phenomenon shows that the main reaction between RP and matrix asphalt is still a physical reaction; at the same time, it can be obtained that it is also similar to the infrared spectrum trend of QRA-modified asphalt, but the intensity of individual absorption peaks changed. QRA/RP composite-modified asphalt produced a weak new characteristic peak at 2243 cm−1, which was due to the stretching vibration of the P-H chemical bond in rubber powder. At 1687 cm−1, the absorption peak of QRA/RP composite-modified asphalt changed slightly compared with that of QRA-modified asphalt. The analysis may be due to the fact that under high-speed shear, the C=C double bond in the RP particles was opened, and the broken chemical bond was recombined with the asphalt to form a new solid construction, resulting in a slow absorption peak here. Further analysis shows that the absorption peak at 1485 cm−1 indicates that it contains more methylene groups. The symmetrical stretching vibration peak of S=O appears at 1004 cm−1, which is the product of the oxidation reaction of the thioether group in the RP.
In summary, in QRA/RP composite-modified asphalt, Qingchuan rock asphalt does not chemically interact with matrix asphalt, but only physically blends. Rubber powder and matrix asphalt are mainly physical modification, supplemented by chemical modification. Through these chemical and physical effects, Qingchuan rock asphalt, rubber powder, and matrix asphalt are integrated into a whole, so that the mechanical properties of QRA/RP composite-modified asphalt are enhanced as a whole.

5. Conclusions

(1) By adding QRA to the matrix asphalt, the mass loss and viscosity ratio decreased by 12.6% and 0.426, and the residual penetration ratio increased by 10.4%. On the basis of QRA-modified asphalt, the mass loss and viscosity ratio of QRA/RP composite-modified asphalt decreased by 3.8% and 0.118, and the residual penetration ratio increased by 11.6%. QRA and RP can reduce the effects of aging on asphalt.
(2) Before and after aging, the G* and G*/sinδ of QRA/RP composite-modified asphalt are the largest, and the δ is the smallest, which indicates that QRA and RP enhance the ability of asphalt to resist plastic deformation, and also shows that the aging effect does not change the role of modifier. After aging, the G*/sinδ of the three asphalts increases, indicating that aging can increase the consistency of asphalt, and aging has a positive effect on the improvement of high-temperature characteristics of asphalt.
(3) There is a positive correlation between the G* and shear frequency of asphalt before and after aging. Under the same test conditions, the G* of the two modified asphalts is higher than that of the matrix asphalt, and in the main curve, the QRA/RP composite-modified asphalt curve is at the highest position, indicating that QRA and RP significantly improve the high-temperature rheological properties. The G* value of the three species of asphalt after aging is increased compared with that before aging, and the curve generally shows an upward tendency, which once again verifies the accuracy of temperature scanning.
(4) The cumulative strain of matrix asphalt is great. The R (0.1) of QRA-modified asphalt is 58.612 percentage points higher than that of matrix asphalt, and the composite-modified asphalt is 24.423 percentage points higher than that of QRA-modified asphalt, indicating that QRA plays an important role in improving the permanent deformation resistance of asphalt.
(5) The m value of QRA-modified asphalt is small. After adding rubber powder, at −6 °C, the S of QRA/RP composite-modified asphalt is 30.5% lower than that of QRA-modified asphalt, and the m value is increased by 23.9%, indicating that rubber powder can effectively improve the low-temperature flexibility of QRA-modified asphalt. After aging, the change range of the m value of the two modified asphalts slows down, indicating that QRA improves the permanent deformation resistance of asphalt.
(6) After Qingchuan rock asphalt and rubber powder are mixed with matrix asphalt, a three-dimensional network structure supported by cross-linking is formed, which improves the segregation and agglomeration of RP and asphalt. QRA and matrix asphalt are physically blended. The addition of rubber powder makes the symmetric stretching vibration peak of S=O appear at 1004 cm−1 of QRA/RP composite-modified asphalt, indicating that rubber powder has a weak chemical reaction in asphalt, but the main reaction between the two is still a physical reaction.

Author Contributions

Writing—original draft preparation, W.L. and X.J.; writing—review and editing, W.L., Y.C. and Z.L.; investigation, T.G. and Y.C.; discussion, T.G., Z.L. and X.J. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Planned project supported by science and technology innovation team of universities and colleges in Henan province: [Grant Number 24IRTSTHN011]; the Central Plains Science and Technology Innovation Leader Project [Grant Number 244200510031].

Institutional Review Board Statement

No applicable.

Informed Consent Statement

No applicable.

Data Availability Statement

Some or all data, models, or code that support the findings of thisstudy are available from the corresponding author upon reasonable request.

Conflicts of Interest

Author Wuan Li was employed by the company Zhengzhou Yellow River Engineering Co., Ltd. Author Yukun Chen was employed by the company China Construction Second Engineering Bureau Limited. Author Tengteng Guo and Zhenxia Li were employed by the company North China University of Water Resources and Electric Power-Henan Provincial Institute of Transportation Planning and Design Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Coatings 14 01246 g001
Figure 1. Original asphalt temperature scanning test results.
Figure 1. Original asphalt temperature scanning test results.
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Figure 2. Aging asphalt temperature scanning test results.
Figure 2. Aging asphalt temperature scanning test results.
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Figure 3. G*/sinδ-temperature curve before aging.
Figure 3. G*/sinδ-temperature curve before aging.
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Figure 4. G*/sinδ-temperature curve after aging.
Figure 4. G*/sinδ-temperature curve after aging.
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Figure 5. G*-angular frequency change diagram of matrix asphalt before and after aging.
Figure 5. G*-angular frequency change diagram of matrix asphalt before and after aging.
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Figure 6. G*-angular frequency change diagram of QRA-modified asphalt before and after aging.
Figure 6. G*-angular frequency change diagram of QRA-modified asphalt before and after aging.
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Figure 7. G*-angular frequency change diagram of QRA/RP composite-modified asphalt before and after aging.
Figure 7. G*-angular frequency change diagram of QRA/RP composite-modified asphalt before and after aging.
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Figure 8. Principle diagram of the main curve.
Figure 8. Principle diagram of the main curve.
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Figure 9. Three asphalts G*-angular frequency main curves.
Figure 9. Three asphalts G*-angular frequency main curves.
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Figure 10. MSCR test data diagram.
Figure 10. MSCR test data diagram.
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Figure 11. R and Jnr of three kinds of asphalt at 0.1 kPa.
Figure 11. R and Jnr of three kinds of asphalt at 0.1 kPa.
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Figure 12. R and Jnr of three kinds of asphalt at 3.2 kPa.
Figure 12. R and Jnr of three kinds of asphalt at 3.2 kPa.
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Figure 13. The data of S and m with temperature change.
Figure 13. The data of S and m with temperature change.
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Figure 14. Aging S and m with temperature change data map.
Figure 14. Aging S and m with temperature change data map.
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Figure 15. Scanning electron microscopy of Qingchuan rock asphalt.
Figure 15. Scanning electron microscopy of Qingchuan rock asphalt.
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Figure 16. Scanning electron microscopy of rubber powder.
Figure 16. Scanning electron microscopy of rubber powder.
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Figure 17. Scanning electron microscopy of matrix asphalt.
Figure 17. Scanning electron microscopy of matrix asphalt.
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Figure 18. Scanning electron microscopy of Qingchuan rock asphalt-modified asphalt.
Figure 18. Scanning electron microscopy of Qingchuan rock asphalt-modified asphalt.
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Figure 19. Scanning electron microscopy of QRA/RP composite-modified asphalt.
Figure 19. Scanning electron microscopy of QRA/RP composite-modified asphalt.
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Figure 20. Infrared spectra of asphalt.
Figure 20. Infrared spectra of asphalt.
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Table 1. Basic performance index of 70 a asphalt.
Table 1. Basic performance index of 70 a asphalt.
Test IndexUnitTest ResultTechnical RequirementTest Method
Penetration (25 °C, 100 g, 5 s)0.1 mm65.260~80T0640
Ductility (5 cm/min, 5 °C)cm16.8≥0T0605
Softening point (global method)°C151.0≥46T0606
Flash point°C270≥260T0611
Density (25 °C)g/cm31.159Measured valueT0603
After RTFOTMass variation%0.232−0.8~+0.8T0610
Residual penetration ratio%66.4≥61T0604
Ductility (5 cm/min, 5 °C)cm9.3≥15T0605
Table 2. Technical Indicators of QRA.
Table 2. Technical Indicators of QRA.
Test ProjectAppearanceAsphalt Content (%)Density (g/cm³)Water Content (%)Ash Content (%)
Test resultBlack brown powder89.21.171.018.9
Table 3. Performance index of rubber powder.
Table 3. Performance index of rubber powder.
Test ProjectRelative DensitySieve Residue (%)Ash (%)Tenor (%)Rubber Hydrocarbon Content (%)
Test result1.22.63.30.0358
Table 4. Short-term aging test results of three kinds of asphalt.
Table 4. Short-term aging test results of three kinds of asphalt.
Asphalt
Type		Before AgingAfter Aging
Quality (g)25 °C Penetration (0.1 mm)Viscosity (135 °C, Pa·s)Quality
Loss (%)		Residual Penetration Ratio (%)Ratio of Viscosity
Matrix asphalt34.95264.30.4570.23266.41.643
QRA-modified asphalt34.89439.21.6810.10678.61.217
QRA/RP
Composite-modified asphalt		35.16732.76.7530.06888.41.099
Table 5. Matrix asphalt fitting curve table.
Table 5. Matrix asphalt fitting curve table.
Test Temperature (°C)Fitting EquationR2
40lgG* = 0.9017lgω + 3.60680.9994
52lgG* = 0.9405lgω + 2.86040.9997
64lgG* = 0.9718lgω + 2.24660.9990
76lgG* = 0.9168lgω + 1.65720.9981
88lgG* = 0.8218lgω + 1.05920.9933
Table 6. Matrix asphalt shift factor table.
Table 6. Matrix asphalt shift factor table.
Test Temperature (°C)Lgω (rad/s)Shift Factors
40−0.67300
520.1484−0.8214
640.7753−1.4483
761.4647−2.1377
882.3616−3.0346
Table 7. Two modified asphalt fitting curve table.
Table 7. Two modified asphalt fitting curve table.
Asphalt TypeTest Temperature (°C)Fitting EquationR2
QRA -modified asphalt40lgG* = 0.8374lgω + 4.17820.9990
52lgG* = 0.8995lgω + 3.37270.9997
64lgG* = 0.9502lgω + 2.66670.9998
76lgG* = 0.9222lgω + 2.08370.9986
88lgG* = 0.8960lgω + 1.65200.9964
QRA/RP
Composite-modified
asphalt		40lgG* = 0.7120lgω + 4.79150.9978
52lgG* = 0.7383lgω + 4.17100.9952
64lgG* = 0.7415lgω + 3.57530.9985
76lgG* = 0.7054lgω + 3.05160.9984
88lgG* = 0.7525lgω + 2.59010.9988
Table 8. Two modified asphalt displacement factor table.
Table 8. Two modified asphalt displacement factor table.
Asphalt TypeTest Temperature (°C)Lgω (rad/s)Shift Factors
QRA-modified
asphalt		40−1.40700
52−0.4143−0.9927
640.3508−1.7578
760.9936−2.4006
881.5045−2.9115
QRA/RP
composite-modified asphalt		40−2.51620
52−1.5861−0.9301
64−0.7759−1.7403
76−0.0731−2.4431
880.5447−3.0609
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Li, W.; Chen, Y.; Guo, T.; Li, Z.; Jiang, X. Study on the Performance of Modified Qingchuan Rock/Rubber Asphalt. Coatings 2024, 14, 1246. https://doi.org/10.3390/coatings14101246

AMA Style

Li W, Chen Y, Guo T, Li Z, Jiang X. Study on the Performance of Modified Qingchuan Rock/Rubber Asphalt. Coatings. 2024; 14(10):1246. https://doi.org/10.3390/coatings14101246

Chicago/Turabian Style

Li, Wuan, Yukun Chen, Tengteng Guo, Zhenxia Li, and Xiaoxiao Jiang. 2024. "Study on the Performance of Modified Qingchuan Rock/Rubber Asphalt" Coatings 14, no. 10: 1246. https://doi.org/10.3390/coatings14101246

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