In order to study the effect of different rock asphalt contents on the physical and mechanical properties of an asphalt binder and asphalt mixture, the physical and mechanical tests and analysis were conducted. An on-site case was investigated to verify the effectiveness of rock asphalt-modified pavement. The results show that the activation treatment can effectively enhance the molecular polarity of Buton rock asphalt. The “wet process” was used to prepare the Buton rock asphalt-modified asphalt binder, and the high-temperature performance and aging resistance were significantly improved. The modified asphalt prepared by mixing 30% rock asphalt shows the optimum balance between service performance and segregation. The on-site full-scale application of the Buton rock asphalt-modified asphalt pavement showed the good workability and service performance. This research demonstrated the ability of rock asphalt improving asphalt pavement on multiscales. It is helpful for the broader application of rock asphalt in asphalt pavement.
Rock asphalt (RA) is a kind of asphalt coming from the petroleum flowing into the split cracks of rock. It is formed after billions of years of accumulation and changes under the combined action of heat, pressure, oxidation, catalyst, and bacteria. As a kind of natural asphalt, it is a kind of green, energy saving, environmental new pavement material because it has high degree of fusion with asphalt and does not require chemical processing. When it is used in the modified asphalt, it can improve the road performance of the modified asphalt, especially high-temperature stability, water resistance, and durability, with remarkable social and economical benefits. The Buton rock asphalt (BRA), as a representative product of rock asphalt, is produced in the Buton island of Indonesia. It comes from the sedimentation of the Jurassic marine animal fossils and is characterized by high asphalt content and high nitrogen content, being resiniferous and nonwaxy [
Zhong et al. found that the addition of rock asphalt improved the high-temperature performance of petroleum bitumen binders and mixtures. The moisture damage resistance, tensile strength, and fatigue performance of petroleum mixture were enhanced as well. The low-temperature performance was slightly weakened [
In view of the construction variability which is inevasible for the production of the Buton rock asphalt-modified asphalt by “dry process,” this research innovatively put forward the “wet process.” The rock asphalt is firstly pretreated by the activation process for preliminary grinding and activation. Then, the activated rock asphalt is mixed with the matrix asphalt. Finally, the mix asphalt is grinded by colloid mill to produce the modified rock asphalt. This process can fully integrate the rock asphalt with the matrix asphalt, thus effectively promoting the cross-linking polymerization of the polar functional groups in the rock asphalt and the active groups (carboxyl, aldehyde, carbonyl, and naphthalene) in the matrix asphalt, improving the arrangement mode and net structure (node and strength) of the matrix asphalt molecules and enhancing the asphalt cohesion. In this way, it significantly improves the antifluidity, antioxidation, adhesion, and temperature susceptibility of the modified asphalt, thus improves the high-temperature resistance, water damage resistance, and fatigue performance of the mixture of rock asphalt and modified asphalt, and makes the mixture more suitable for large-scale production.
The raw material of the Buton rock asphalt (BRA) is the rock asphalt powder produced by Hubei Zhengkang Asphalt Technology Co., Ltd. The specific performance indicators are shown in Table
Properties of the BRA used in this research.
Items | Unit | Test results | Technical requirements |
---|---|---|---|
Colour character | — | Brown powder | Black or brown powder |
Ash content | % | 61.7 | ≤80 |
Moisture content | % | 2 | ≤2 |
Asphalt content | % | 27 | — |
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Particle size range | — | — | — |
4.75 mm | % | 100 | 100 |
2.36 mm | % | 95.8 | 95∼100 |
1.18 mm | % | 82.8 | >80 |
The activation pretreatment aims at improving the degree of fusion between the rock asphalt and the matrix asphalt and thus fully exerts the modification ability of the rock asphalt [
Rock asphalt after activation pretreatment.
Multidimensional network of rock asphalt.
Specifically, the “wet process” of the Buton rock asphalt developed in this paper includes the following: the matrix asphalt is firstly preheated from 150°C to 160°C by a heating system and is then pumped to the asphalt tank. At the same time, the Buton asphalt mixture, which has been broken and dehydrated, is added to the feed inlet and is slowly added to the matrix asphalt. Then, the mixing device is started. After stirring for 0.5 h to 1 h, the premix is pumped into the self-developed colloid mill for full grinding. The rock asphalt particles are grinded to less than 100 mesh. When they uniformly suspend in the matrix asphalt, the modified rock asphalt can be obtained. Finally, the prepared modified Buton rock asphalt is stored in the storage tank for proper storage. The specific equipment design drawings and the entity diagram of the equipment are shown in Figures
Schematic of the device used for preparation of rock asphalt-modified asphalt binder. 1: agitator tank; 2: feed port; 3: discharge port; 4: mixing motor; 5: reducer; 6: stirring shaft; 7: helical blade; 8: thermometer; 9: first high-temperature gate valve; 10: second high-temperature gate valve; 11: service port; 12: production delivery pump; 13: baseboard; 14: first side plate; 15: second side plate; 16: man way; 17: ladder stand; 18: insulation two-way; 19: distribution box.
Picture of the device used for preparation of the rock asphalt-modified asphalt binder.
In order to compare the influence of different mixing amounts of the Buton rock asphalt on the performance of modified asphalt and asphalt mixture and determine the optimum mixing amount of rock asphalt, 10%, 20%, 30%, 40%, and 50% of the activated rock asphalt are, respectively, added to the No. 70 road petroleum asphalt to produce the modified Buton rock asphalt according to the “wet process.” The performance of modified asphalt and modified asphalt mixture is tested.
Penetration test, softening point test, and ductility test were conducted according to the Test Specification of Asphalt and Asphalt Mixture (JTG E20–2011) [
The gravimetric capillary method was used to measure the kinematic viscosity of the asphalt binder at 135°C. Measurements using capillary viscometers were based on the relation between viscosity and time. The more viscous the asphalt, the longer it will take to flow through a capillary under the influence of gravity alone. There are several standardized capillaries in use today. Most laboratory instruments employ glass capillaries or “tubes.” A more recent advancement for field measure of kinematic viscosity employs a split aluminum cell capillary. In this research, the manual constant temperature bath system consisting of a very precise temperature-controlled bath was used. A sample of the asphalt binder was suctioned into the tube until it reaches the start point. The suction was then released, and the asphalt binder flowed by gravity through the controlled capillary section of the tube. Two or three marks were visible on the tube. We watched the meniscus of the asphalt binder as it passes the start point. At this point, we recorded the time it took the asphalt binder to pass the final mark. The tubes were selected such that the test would take a minimum of 200 secs to complete. This made it easier for manual timekeeping. More details can be found in ASTM D445.
Dynamic stability and residual stability can be obtained from the basic Marshall tests of asphalt mixtures [ The specimens were randomly divided into two groups. The first group of the specimen was kept on the platform at room temperature; the second group of the specimen was immersed in water with 97.3∼98.7 kPa for 15 minutes, then the valve was opened, and the specimen was kept in the water without pressure for 0.5 hours. The second group of specimens was removed into a plastic bag with 10 ml of water, and then the condition temperature was maintained at −18°C ± 2°C for 16 hours. The specimens removed from the low-temperature case were immediately put in the water tank at the temperature of 60°C ± 0.5 °C for 24 hours.
The specimens were kept in 25°C ± 0.5°C constant temperature water tank for 2 hours and then were removed, and immediately splitting loading by the MTS machine was applied. The loading rate is 50 mm/min. The indirect tensile strength is calculated according to the following equation, and the TSR is calculated according to (
This study used the low-temperature blending test to evaluate the low-temperature anticracking performance of asphalt mixtures. The blending failure strain was selected as the evaluation index of low-temperature performance of asphalt mixtures. The bigger the blending failure strain, the better the low-temperature performance of asphalt mixtures. The diameter of specimens was 250 mm × 30 mm × 35 mm. The test temperature was −10 °C, and the loading rate was 1 mm/min.
Related tests are carried out on the No. 70 road petroleum asphalt and modified rock asphalt with different mixing amounts according to the Test Specification of Asphalt and Asphalt Mixture (JTG E20–2011) [
Influence of different rock asphalt contents on the properties of the asphalt binder.
Test items | Sample types | |||||
---|---|---|---|---|---|---|
Pure asphalt | Pure asphalt + 10% BRA | Pure asphalt + 20% BRA | Pure asphalt + 30% BRA | Pure asphalt + 40% BRA | Pure asphalt + 50% BRA | |
Penetration (25°C, 100 g, 5 s) (0.1 mm) | 73 | 66 | 58 | 55 | 46 | 32 |
Softening point (°C) | 46 | 48 | 50 | 52 | 58 | 60 |
Ductility (15°C, 5 cm/min) (cm) | 100 | 68 | 42 | 34 | 21 | 12 |
Kinematic viscosity at 135°C (Pa·s) | 0.452 | 0.476 | 0.512 | 0.625 | 0.856 | 1.343 |
Difference of softening points between 0 and 48 hours (°C) | — | 0.5 | 1 | 1.5 | 2.5 | 4 |
Ratio of penetrations before and after RTFOT test | 71 | 75 | 81 | 86 | 83 | 82 |
It can be seen from Table
According to the above analysis, the modified Buton rock asphalt with a mixing amount of 40% or 50% has more serious segregation. Therefore, in the performance analysis of the modified Buton rock asphalt, this paper only compares the performances of the modified Buton rock asphalt mixture with a mixing amount of 10%, 20%, and 30%, respectively. And based on this, the best mixing amount of the modified Buton rock asphalt is determined. The AC-13-type asphalt mixture is selected as the test object with gradation shown in Figure
Gradation of selected AC-13 asphalt mixture.
The Marshall test is carried out to determine the best asphalt-aggregate ratio of the modified Buton rock asphalt with different mixing amounts. In addition, the high-temperature rutting test, low-temperature beam bending test, immersion Marshall test, and freeze-thaw splitting test are also carried out according to the specification [
Effect of different rock asphalt contents on the performance of asphalt mixture. (a) Dynamic stability. (b) Residual stability. (c) Freeze-thaw split strength ratio TSR. (d) Low-temperature bending failure strain.
It can be seen from Figure
The rock asphalt-modified asphalt pavement was implemented in the major maintenance project of asphalt pavement of the Huoqiu section of S310 Linye Road within Lian City of Anhui Province. This section was built according to the secondary highway standard, with a design speed of 60 kilometers per hour. After milling, the AC-13 asphalt mixture with a thickness of 4 cm was paved. The asphalt is the Ssangyong virgin asphalt produced in Jiangyin, South Korea The coarse and fine aggregates come from the Chaohu Zhongcai Limestone Gravel Plant, and it is composed of limestone; the mineral powder is produced by Lvan Traffic Industry Co., Ltd. The connection between the rock asphalt modification equipment and the mixing plant is shown in Figure
The connection between the rock asphalt modification equipment and the mixing plant.
According to the local climate and traffic characteristics, 30% rock asphalt was mixed in the matrix asphalt for processing modified rock asphalt. More details can be found in Technical Specifications for Construction of Highway Asphalt Pavements. JTG F40-2004 [
Properties of the rock asphalt-modified asphalt binder in the field.
Test items | Penetration (25°C, 100 g, 5 s) (0.1 mm) | Softening point (°C) | Ductility (15°C, 5 cm/min) (cm) | Kinematic viscosity at 135°C (Pa·s) | Difference of softening point between 0 and 48 hours (°C) | Ratio of penetrations before and after RTFOT test (%) |
---|---|---|---|---|---|---|
Value | 53 | 51 | 33 | 0.575 | 1.5 | 83 |
According to the Marshall test, the best asphalt-aggregate ratio was determined. And the related road performance is tested. The specific data are shown in Tables
Physical properties of rock asphalt-modified asphalt mixture in the field.
Test items | Asphalt-aggregate ratio (%) | Theoretical maximum relative density | Bulk relative density | Void content (VV) (%) | Voids in mineral aggregate (VMA) (%) | Voids of mineral aggregate that are filled with asphalt (VFA) (%) |
---|---|---|---|---|---|---|
Value | 4.8 | 2.544 | 2.451 | 3.7 | 14.1 | 74.2 |
Mechanical properties of rock asphalt-modified asphalt mixture in the field.
Test items | Stability (MS) (kN) | Flow number (FL) (mm) | Dynamic stability (time/mm) | Residual stability (%) | Freeze-thaw split strength ratio (%) | Low-temperature bending failure strain ( |
---|---|---|---|---|---|---|
Value | 12.64 | 3.5 | 3376 | 91 | 81 | 2683 |
According to the test results, the heating temperature of the modified Buton rock asphalt is 140°C to 150°C. The aggregate heating temperature is 170°C to 180°C. The dry mixing time of the aggregate is 7 s, and the wet mixing time is 42 s. The out-feeding temperature is determined as 150°C to 160°C. The on-site construction technology includes two times of rolling by the single vibratory road roller with a weight of 13 tons, 6 times of rolling by the rubber-tired roller with a weight of 26 tons and one time of rolling for leveling carried out by the single vibratory road roller with a weight of 11 tons.
The mixture paved on the site is uniform without segregation, and the cored sample demonstrates that the compaction degree can reach 98%.
The objective of this study was to investigate the effect of different rock asphalt contents on the physical and mechanical properties of the asphalt binder and asphalt mixture by conducting mechanical tests and microstructure analyzation. The following is a summary of conclusions that can be drawn based on the aforementioned results and discussion: The activation treatment is carried out on the Buton rock asphalt powder, which effectively enhances the molecular polarity of rock asphalt, promotes the coupling of resin and ash content in the rock asphalt and the matrix asphalt, and thus forms a stable multidimensional net structure to improve the performance of the matrix asphalt. In this study, the self-developed on-site modification equipment is innovatively adopted. The activated Buton rock asphalt is added to the matrix asphalt by “wet process” to prepare the modified Buton rock asphalt which has significantly improved high-temperature resistance and aging resistance. The modified asphalt prepared by mixing 40% rock asphalt has more serious segregation. According to the comparison test of road performance, it is concluded that the modified asphalt prepared by mixing 30% rock asphalt has more balanced properties. Thus, 30% is recommend as the best mixing amount for the production of modified rock asphalt by “wet process.” According to the verification of entity engineering, the modified Buton rock asphalt mixture prepared by “wet process” has better application property and workability and is suitable for large-scale production. However, due to the short completion time of the test section, the long-term performance of pavement cannot be reflected completely. The long-term performance observation of the test section will be carried out in the further work.
The authors declare no conflicts of interest.
Yafei Li and Jing Chen conceived and designed the experiments; Yafei Li performed the experiments; Yafei Li and Meng Guo analyzed the data; Jin Yan contributed reagents/materials/analysis tools; Meng Guo wrote the paper.
This study was supported by Beijing Natural Science Foundation (8174071) and Quota Funds for Promoting the Connotation Development of Universities, Beijing University of Technology (004000514118017).