Influence of Buton Rock Asphalt on the Physical and Mechanical Properties of Asphalt Binder and Asphalt Mixture

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. .e results show that the activation treatment can effectively enhance the molecular polarity of Buton rock asphalt. .e “wet process” was used to prepare the Buton rock asphalt-modified asphalt binder, and the high-temperature performance and aging resistance were significantly improved. .e modified asphalt prepared by mixing 30% rock asphalt shows the optimum balance between service performance and segregation. .e on-site full-scale application of the Buton rock asphalt-modified asphalt pavement showed the good workability and service performance. .is 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.


Introduction
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.
e 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 [1][2][3][4][5].It is added to ordinary asphalt mixture as external admixture at home and abroad so as to improve the high-temperature performance and water stability performance of the asphalt mixture. is method is commonly known as "dry process."However, as seen from the application effect, the Buton rock asphalt cannot play its maximum role due to construction variability such as the mixing uniformity of construction [6][7][8][9][10].
Zhong et al. found that the addition of rock asphalt improved the high-temperature performance of petroleum bitumen binders and mixtures.
e moisture damage resistance, tensile strength, and fatigue performance of petroleum mixture were enhanced as well.
e lowtemperature performance was slightly weakened [11].Li et al. evaluated the potential impact of different types of rock asphalts on the performance of asphalt composites.ey avoided the extraction of the asphalt binder from rock asphalt and simplified the process of evaluating the potential impact of rock asphalts on mixture performance.ey found that addition of rock asphalts increases material stiffness and slightly reduces relaxation potential of asphalt composites at low-temperatures [12].Zou and Wu studied the rheological properties and field applications of the Buton rock asphalt.ey found that with increasing BRA content, the binder's penetration decreased, softening point increased, dynamic viscosity at 60 °C increased, and complex modulus increased.
e BRA-modified asphalt concrete mixtures had better rutting performance as compared to the control asphalt concrete mixture sample [13].Li et al. investigated the relationship between the microstructure and the performance of the Buton rock asphalt by using surface free energy and an infrared spectrum analysis.ey found that mixing the BRA was a physical modification.An increase of rocking asphalt content can result in the increase of the hydrophobicity of the asphalt mixtures [14].Rock asphalt can be seen as a composite consisting of asphalt binder and fillers.erefore, for the interfacial behavior between rock asphalt and asphalt binder (or aggregate), refer Guo et al.'s research [15][16][17][18].
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."e rock asphalt is firstly pretreated by the activation process for preliminary grinding and activation.en, 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. is 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.

Raw Materials.
e raw material of the Buton rock asphalt (BRA) is the rock asphalt powder produced by Hubei Zhengkang Asphalt Technology Co., Ltd. e specific performance indicators are shown in Table 1, and all technical indicators meet the specification requirements [19].

Activation Pretreatment.
e 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 [13].e concrete process is as follows.e rock asphalt is firstly broken up and dehydrated and then is grinded at high temperature.According to microscopic image characterization, the rock asphalt molecules have extremely strong polarity after hightemperature "activation."ey connect the asphalt molecules in the matrix asphalt and the resin and ash content in the rock asphalt together to form a stable multidimensional net structure which effectively improves the performance of the matrix asphalt, as shown in Figures 1 and 2.

"Wet
Process" of the Buton 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.en, 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.e 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.e specific equipment design drawings and the entity diagram of the equipment are shown in Figures 3 and 4.

Sample Preparation.
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."e performance of modified asphalt and modified asphalt mixture is tested.

Testing Protocols
2.5.1.Asphalt Binder.Penetration test, softening point test, and ductility test were conducted according to the Test Specification of Asphalt and Asphalt Mixture (JTG E20-2011) [20]. 2 Advances in Materials Science and Engineering e 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.e more viscous the asphalt, the longer it will take to ow through a capillary under the in uence of gravity alone.ere are several standardized capillaries in use today.Most laboratory instruments employ glass capillaries or "tubes."A more recent advancement for eld 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.e suction was then released, and the asphalt binder owed 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 nal mark.e tubes were selected such that the test would take a minimum of 200 secs to complete.is made it easier for manual timekeeping.More details can be found in ASTM D445.

Asphalt
Mixture.Dynamic stability and residual stability can be obtained from the basic Marshall tests of asphalt mixtures [20].Regarding freeze-thaw splitting tests, the compaction method of the specimen of the freeze-thaw cycle test was gyratory compacting.
e diameter of the specimen was 100 mm, and the height was 63.5 mm ± 1.3 mm. e procedure of the free-thaw cycle is as follows: (1) e specimens were randomly divided into two groups.
e rst 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.
(2) e 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.(3) e 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.
e 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.e loading rate is 50 mm/min.e indirect tensile strength is calculated according to the following equation, and the TSR is calculated according to (2):  Advances in Materials Science and Engineering 3 where R T is the indirect tensile strength (MPa), P T is the maximum value of the test load (N), and h is the specimen height (mm). TSR where TSR is the tensile strength ratio (%), R T1 is the indirect tensile strength before freeze-thaw cycle (MPa), and R T2 is the indirect tensile strength after freeze-thaw cycle (MPa).is study used the low-temperature blending test to evaluate the low-temperature anticracking performance of asphalt mixtures.e blending failure strain was selected as the evaluation index of low-temperature performance of asphalt mixtures.e bigger the blending failure strain, the better the low-temperature performance of asphalt mixtures.
e diameter of specimens was 250 mm × 30 mm × 35 mm. e test temperature was −10 °C, and the loading rate was 1 mm/min.

In uence of Di erent Rock Asphalt Contents on the Physical and Mechanical Properties of Asphalt Binder.
Related tests are carried out on the No. 70 road petroleum asphalt and modi ed rock asphalt with di erent mixing amounts according to the Test Speci cation of Asphalt and Asphalt Mixture (JTG E20-2011) [20].e test results are shown in Table 2.
It can be seen from Table 2 that the penetration value decreased and the softening point increased with the increase of BRA content.It indicates that BRA can improve the permanent deformation resistance of the asphalt binder, further to improve the high-temperature service performance of BRA-modi ed asphalt pavement.Table 2 also shows that the ductility decreased dramatically after BRA modi cation.It means the elongation ability of asphalt approached a limit, and most probably it was the same for elasticity of asphalt that was a fundamental property for lasting serving life of exible pavement.Regarding viscosity, the more viscous asphalt requires more energy consumption in every single process of asphalt industry including storage, transporting, placing, and compacting.erefore, a greater viscosity could be disadvantageous for construction of asphalt pavement.However, a greater viscosity also can help the asphalt pavement resisting the high-temperature rutting.Selecting a proper BRA/asphalt binder ratio to obtain a suitable viscosity to balance the workability and service performance of asphalt pavement is a key of BRA application.At the same time, after the aging of the rotating lm, the residual penetrations of the modi ed Buton rock asphalt with ve di erent mixing amounts are all higher than that of the matrix asphalt, indicating that the antiaging performance of the modi ed Buton rock asphalt has obvious improvement.In addition, the storage stability of the modi ed Buton rock asphalt decreases with the increase of rock asphalt content.After mixing 40% and 50% of rock asphalt, the di erences of softening points of BRA-modi ed asphalt between 0 and 48 hours were 2.5 °C and 4 °C, respectively.It indicates that the modi ed Buton rock asphalt has relatively serious segregation.According to the requirement of Technical Speci cations for Construction of Highway Asphalt Pavements (JTG F40-2004), the di erence of softening points of modi ed asphalt between 0 and 48 hours should be less than 2.5 °C [21].us, 40% and 50% are not recommended as the best mixing amount of rock asphalt.

In uence of Di erent Rock Asphalt Contents on the
Physical and Mechanical Properties of Asphalt Mixture.Advances in Materials Science and Engineering According to the above analysis, the modi ed Buton rock asphalt with a mixing amount of 40% or 50% has more serious segregation.erefore, in the performance analysis of the modi ed Buton rock asphalt, this paper only compares the performances of the modi ed Buton rock asphalt mixture with a mixing amount of 10%, 20%, and 30%, respectively.And based on this, the best mixing amount of the modi ed Buton rock asphalt is determined.e AC-13-type asphalt mixture is selected as the test object with gradation shown in Figure 5.
e Marshall test is carried out to determine the best asphalt-aggregate ratio of the modi ed Buton rock asphalt with di erent mixing amounts.In addition, the hightemperature rutting test, low-temperature beam bending test, immersion Marshall test, and freeze-thaw splitting test are also carried out according to the speci cation [20].e detailed test procedure can be found at Section 2.5.According to the technical speci cations for modi ed asphalt pavements, the dynamic stability should be larger than 2400 time/mm, the residual stability should be larger than 80%, and the TSR value should be larger than 75% [21].e detailed tests results are shown in Figure 6.
It can be seen from Figure 6 that the dynamic stability and residual stability of the Buton rock asphalt mixture increase with the increase of the mixing amount of rock asphalt, and the beam bending failure and freeze-thaw splitting strength ratio increase with the increase of the mixing amount of rock asphalt, indicating that the high-temperature resistance and antistrip performance of modi ed asphalt mixture increase signi cantly with the increase of rock asphalt content, and its low-temperature crack resistance and low-temperature freezing resistance decrease with the increase of the mixing amount of rock asphalt.When the mixing amount of rock asphalt reaches 30%, the modi ed Buton asphalt mixture has the best high-temperature antirutting performance and antistrip  performance, and its low-temperature crack resistance and low-temperature freezing resistance also meet the regulatory requirements.us, it is recommended to set 30% as the best mixing amount of the rock asphalt.

Case Application.
e 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.is 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.e asphalt is the Ssangyong asphalt produced in Jiangyin, South Korea e 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. e connection between the rock asphalt modification equipment and the mixing plant is shown in Figure 7.
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 [21].e specific properties are shown in Table 3.
According to the Marshall test, the best asphaltaggregate ratio was determined.And the related road performance is tested.e specific data are shown in Tables 4  and 5. e test methods were all standard procedure.ey can be found in Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40-2004) [21].As can be seen from the tables, the design requirements are met.
According to the test results, the heating temperature of the modified Buton rock asphalt is 140 °C to 150 °C.e aggregate heating temperature is 170 °C to 180 °C.e dry mixing time of the aggregate is 7 s, and the wet mixing time is 42 s.e out-feeding temperature is determined as 150 °C to 160 °C.e 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.
e mixture paved on the site is uniform without segregation, and the cored sample demonstrates that the compaction degree can reach 98%.

Conclusions
e 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.e following is a summary of conclusions that can be drawn based on the aforementioned results and discussion: (1) e 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.
(2) In this study, the self-developed on-site modification equipment is innovatively adopted.e 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.(3) e 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.us, 30% is recommend as the best mixing amount for the production of modified rock asphalt by "wet process."6 Advances in Materials Science and Engineering (4) 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.e long-term performance observation of the test section will be carried out in the further work.

Figure 4 :Figure 1 :Figure 2 :
Figure 4: Picture of the device used for preparation of the rock asphalt-modi ed asphalt binder.

Figure 6 :
Figure 6: E ect of di erent 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.

Figure 7 :
Figure 7: e connection between the rock asphalt modi cation equipment and the mixing plant.

Table 1 :
Properties of the BRA used in this research.

Table 2 :
In uence of di erent rock asphalt contents on the properties of the asphalt binder.

Table 3 :
Properties of the rock asphalt-modified asphalt binder in the field.

Table 4 :
Physical properties of rock asphalt-modified asphalt mixture in the field.

Table 5 :
Mechanical properties of rock asphalt-modified asphalt mixture in the field.