# Study on Properties of Drainage SBS Modified Asphalt Mixture with Fiber

Authors: Zhenxia Li; Tengteng Guo; Yuanzhao Chen; Menghan Zhang; Qingyu Xu; Jing Wang; Lihui Jin
Journal: Advances in Civil Engineering
 (2021)

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## Abstract

In order to improve the road performance of drainage SBS modified asphalt mixture, basalt fiber was added to prepare drainage styrene-butadiene-styrene (SBS) modified asphalt mixture. The viscosity-toughness, toughness, and 60°C dynamic viscosity of SBS modified asphalt were tested. The modification effect was evaluated from the perspective of high and low temperature rheological properties by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The high temperature stability, water stability, low temperature crack resistance, and drainage of basalt fiber SBS drainage asphalt mixture were evaluated and compared with nonfiber SBS drainage asphalt mixture and TPS drainage asphalt mixture. The morphology characteristics of asphalt mixture and the distribution of basalt fiber in the mixture were analyzed from a micro perspective. The results showed the following: the overall performance of basalt fiber is better than that of lignin fiber. SBS modifier content in 7% can meet the requirements of drainage asphalt pavement on asphalt binder. The optimum asphalt content of SBS modified asphalt mixture with basalt fiber content of 0, 0.15, 0.25, and 0.35% is 4.9, 5.05, 5.15, and 5.2%. The fiber is irregularly distributed in the mixture to form a three-dimensional network structure, which has a series skeleton function. It plays a tensile role in the initial cracking of asphalt mixture and prevents further expansion of cracks.


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## Body

## 1. Introduction

With the proposal of ‘sponge city’ construction in China, drainage asphalt pavement has attracted more and more attention [1–3]. The drainage asphalt pavement surface layer adopts large void open graded asphalt mixture, and the middle and lower layers adopt dense graded asphalt mixture. It has good noise reduction, drainage, and antiskid performance, which can effectively improve the safety of travel in rainy days and reduce noise pollution to a certain extent [4, 5]. Due to the small content of fine aggregate and mineral powder in the drainage asphalt pavement mixture, there are a large number of communicating interstices, air and rainwater are easy to penetrate into the internal structure, and they are prone to aging and reduce the service life; drainage asphalt mixture is an open-graded skeleton void structure with more coarse aggregate and less adhesive force, so the asphalt binder used in drainage asphalt pavement should have strong adhesion, antistripping, and water resistance to aggregate [6–13].In order to strengthen the high and low temperature performance, skid resistance, and water stability of drainage pavement, many related studies have been conducted in China and abroad. In the 1960s, Germany first proposed the “large void asphalt pavement,” namely, petroleum asphalt (spraying anionic emulsified asphalt) pavement, which was developed and applied to airport runways. The purpose is to enhance the skid resistance of runways and reduce and avoid the water drift generated by aircraft during the taxiing in rainy days [14]. In the 1990s, the paving test of porous asphalt pavement was carried out in Britain. The asphalt mixture used in the test section is rubber asphalt or No. 100 matrix asphalt, and fiber and 2% lime are added. It is proved that the pavement has the effect of reducing noise and rainwater film [15]. In 1999, fiber was introduced into China for the first time, and some highway projects began to use fiber as additive to improve the road performance of asphalt mixture. Through exploring the mechanism of basalt fiber in asphalt mixture [16, 17], it is found that basalt fiber has the best high temperature stability and shear strength among several fibers, which can significantly improve the rutting resistance factor and water stability of asphalt mortar [18–22]. Toughened polystyrene (TPS) is a high viscosity asphalt additive, which can significantly improve the high and low temperature performance of asphalt and improve the fatigue performance of asphalt pavement. However, due to the high price of TPS high viscosity asphalt modifier, it is difficult to promote it [23, 24]. Later, SBS modifier was widely used in China. SBS is a kind of thermoplastic elastomer, which has the elasticity of rubber at room temperature and can melt and flow at high temperature. The incorporation of SBS modifier into asphalt mixture can greatly improve the rutting resistance, and the high temperature stability is also better, and the water stability of drainage asphalt mixture is effectively improved [25–29].Basalt fiber can improve the dispersion of mineral powder, has toughening and reinforcing effect, and can improve pavement performance and prolong service life; SBS modifier has the advantages of high softening point, high viscosity, large elongation, and strong antistripping property. Adding SBS modifier into asphalt mixture can make it have good high temperature stability and durability. Therefore, both of them are used for drainage asphalt mixture to further enhance the high and low temperature stability and water damage resistance of drainage asphalt pavement. To this end, this paper intends to prepare the drainage SBS modified asphalt mixture with basalt fiber and puts forward the preparation method of high-speed shear SBS modified asphalt. The rheological properties of modified asphalt are analyzed by DSR test and BBR test. The high temperature stability, low temperature crack resistance, water stability, and drainage performance are comprehensively studied through rutting test, immersion Marshall test, freeze-thaw splitting test, and low temperature bending test. The mechanism of basalt fiber reinforced asphalt mixture on road performance is further studied from the micro level by scanning electron microscopy, so as to promote the development of drainage asphalt pavement in China.


## 2. Raw Material

### 2.1. Asphalt

In this test, 70# A grade asphalt is selected, and its basic performance is tested according to the requirements ofTest procedures for asphalt and asphalt mixture in highway engineering JTGE20-2011. The test results are shown in Table 1.Table 1
Technical indicators of 70 matrix asphalt.
Test metricTest resultSpecification requirementTest methodNeedle penetration (25°C, 100 g, 5 s) (0.1 mm)68.260∼80T0604Softening point (ball and ring method) (°C)57.2≥46.0T0606Ductility (5 cm/min, 15°C) (cm)106.3≥100T0605Flash point (°C)268≥260T0611Density (g·cm−3)1.025Actual measurementT0603Solubility (%)99.7≥99.5T0607After RTFOTMass variation (%)−0.1−0.8∼+0.8T0610Penetration ratio (%)72.1≥61T0604Ductility (5 cm·min−1, 15°C) (cm)7≥6T0605


### 2.2. Coarse Aggregate

The selection of coarse aggregate should meet the requirements of dry and clean, small crushing value, and less needle flake content. According to the specificationHighway engineering aggregate test procedures JTG E42-2005 requirements for coarse aggregate test, the test results of each specification are shown in Table 2.Table 2
Main technical index of coarse aggregate.
Pilot projectTest resultTechnical standardTest methodCrushing value of stone (%)13.2 mm～16 mm15.8≤26T03169.5 mm～13.2 mm16.74.75 mm～9.5 mm18.92.36 mm～4.75 mm22.5Los Angeles wear value (%)13.2 mm～16 mm14.7≤28T03179.5 mm～13.2 mm15.14.75 mm～9.5 mm18.62.36 mm～4.75 mm16.5Apparent specific gravity13.2 mm～16 mm2.81≥2.60T03049.5 mm～13.2 mm2.784.75 mm～9.5 mm2.752.36 mm～4.75 mm2.69Water absorption (%)13.2 mm～16 mm1.2≤2.0T03049.5 mm～13.2 mm1.44.75 mm～9.5 mm0.82.36 mm～4.75 mm1.1Water washing method ＜0.075 mmParticles content (%)13.2 mm～16 mm0.5≤1T03109.5 mm～13.2 mm0.84.75 mm～9.5 mm0.72.36 mm～4.75 mm0.8Soft stone content (%)13.2 mm～16 mm2.2≤3T03209.5 mm～13.2 mm1.74.75 mm～9.5 mm2.52.36 mm～4.75 mm1.9


### 2.3. Fine Aggregate

According to the specificationHighway engineering aggregate test procedures JTG E42-2005 requirements for fine aggregate test, the test results of each specification are shown in Table 3.Table 3
Main technical index of fine aggregate.
Pilot projectTest resultTechnical standardTest methodApparent specific gravity1.18 mm～2.36 mm2.81≥2.50T03280.6 mm～1.18 mm2.80Sand equivalent (%)1.18 mm～2.36 mm72≥60T03440.6 mm～1.18 mm68Angularity (s)1.18 mm～2.36 mm31≥30T03450.6 mm～1.18 mm32


### 2.4. Mineral Fines

The technical indicators of ore powder are shown in Table4.Table 4
Main technical indexes of mineral powder.
Pilot projectTest resultTechnical standardTest methodApparent density (t·m−3)0.3 mm～0.6 mm2.81≥2.50T03520.15 mm～0.3 mm2.830.075 mm～0.15 mm2.84＜0.075 mm2.93Moisture content (%)0.3 mm～0.6 mm0.1≤1T01030.15 mm～0.3 mm0.10.075 mm～0.15 mm0.1＜0.075 mm0.1Appearance0.3 mm～0.6 mmwithoutNo agglomeratesT03510.15 mm～0.3 mmwithout0.075 mm～0.15 mmwithout＜0.075 mmwithoutHydrophilic coefficient0.3 mm～0.6 mm0.1＜1T03530.15 mm～0.3 mm0.10.075 mm～0.15 mm0.1＜0.075 m0.1Plasticity index (%)0.3 mm～0.6 mm2.2＜4T03540.15 mm～0.3 mm2.10.075 mm～10.15 mm2.2＜0.075 mm2.2


### 2.5. Fiber

The drainage asphalt mixture has large void ratio and low aggregate specific surface area, which may lead to segregation of mixture during paving and rolling. Therefore, the pavement performance of the mixture can be improved by adding fiber to increase the thickness of asphalt film and the grip strength between asphalt and mineral. The nominal length of basalt fiber and wood fiber is 6 mm, and the diameter of single fiber is 16μm, and the technical indexes are shown in Table 5.Table 5
Technical specifications for different types of fibers.
Fiber classBreaking strength (MPa)Elastic modulus (GPa)Oil absorption ratio (%)Water absorption (%)Mass loss (%)Basalt fiber30001104.20.61.1Lignin fiber<300338.84.75.7


### 2.6. Modifier

#### 2.6.1. The SBS Modifier

SBS modifier is provided by Ningbo Yinzhou Pott Polymer New Materials limited company, is a thermoplastic rubber material, styrene butadiene ethylene block, and has a linear structure, as shown in Figure1.Figure 1
The SBS modifier.


#### 2.6.2. The TPS Modifier

TPS modifier is provided by Shanghai Qunkang Company; the composition is mainly thermoplastic rubber, adhesive resin, as shown in Figure2.Figure 2
The TPS modifier.


## 2.1. Asphalt

In this test, 70# A grade asphalt is selected, and its basic performance is tested according to the requirements ofTest procedures for asphalt and asphalt mixture in highway engineering JTGE20-2011. The test results are shown in Table 1.Table 1
Technical indicators of 70 matrix asphalt.
Test metricTest resultSpecification requirementTest methodNeedle penetration (25°C, 100 g, 5 s) (0.1 mm)68.260∼80T0604Softening point (ball and ring method) (°C)57.2≥46.0T0606Ductility (5 cm/min, 15°C) (cm)106.3≥100T0605Flash point (°C)268≥260T0611Density (g·cm−3)1.025Actual measurementT0603Solubility (%)99.7≥99.5T0607After RTFOTMass variation (%)−0.1−0.8∼+0.8T0610Penetration ratio (%)72.1≥61T0604Ductility (5 cm·min−1, 15°C) (cm)7≥6T0605


## 2.2. Coarse Aggregate

The selection of coarse aggregate should meet the requirements of dry and clean, small crushing value, and less needle flake content. According to the specificationHighway engineering aggregate test procedures JTG E42-2005 requirements for coarse aggregate test, the test results of each specification are shown in Table 2.Table 2
Main technical index of coarse aggregate.
Pilot projectTest resultTechnical standardTest methodCrushing value of stone (%)13.2 mm～16 mm15.8≤26T03169.5 mm～13.2 mm16.74.75 mm～9.5 mm18.92.36 mm～4.75 mm22.5Los Angeles wear value (%)13.2 mm～16 mm14.7≤28T03179.5 mm～13.2 mm15.14.75 mm～9.5 mm18.62.36 mm～4.75 mm16.5Apparent specific gravity13.2 mm～16 mm2.81≥2.60T03049.5 mm～13.2 mm2.784.75 mm～9.5 mm2.752.36 mm～4.75 mm2.69Water absorption (%)13.2 mm～16 mm1.2≤2.0T03049.5 mm～13.2 mm1.44.75 mm～9.5 mm0.82.36 mm～4.75 mm1.1Water washing method ＜0.075 mmParticles content (%)13.2 mm～16 mm0.5≤1T03109.5 mm～13.2 mm0.84.75 mm～9.5 mm0.72.36 mm～4.75 mm0.8Soft stone content (%)13.2 mm～16 mm2.2≤3T03209.5 mm～13.2 mm1.74.75 mm～9.5 mm2.52.36 mm～4.75 mm1.9


## 2.3. Fine Aggregate

According to the specificationHighway engineering aggregate test procedures JTG E42-2005 requirements for fine aggregate test, the test results of each specification are shown in Table 3.Table 3
Main technical index of fine aggregate.
Pilot projectTest resultTechnical standardTest methodApparent specific gravity1.18 mm～2.36 mm2.81≥2.50T03280.6 mm～1.18 mm2.80Sand equivalent (%)1.18 mm～2.36 mm72≥60T03440.6 mm～1.18 mm68Angularity (s)1.18 mm～2.36 mm31≥30T03450.6 mm～1.18 mm32


## 2.4. Mineral Fines

The technical indicators of ore powder are shown in Table4.Table 4
Main technical indexes of mineral powder.
Pilot projectTest resultTechnical standardTest methodApparent density (t·m−3)0.3 mm～0.6 mm2.81≥2.50T03520.15 mm～0.3 mm2.830.075 mm～0.15 mm2.84＜0.075 mm2.93Moisture content (%)0.3 mm～0.6 mm0.1≤1T01030.15 mm～0.3 mm0.10.075 mm～0.15 mm0.1＜0.075 mm0.1Appearance0.3 mm～0.6 mmwithoutNo agglomeratesT03510.15 mm～0.3 mmwithout0.075 mm～0.15 mmwithout＜0.075 mmwithoutHydrophilic coefficient0.3 mm～0.6 mm0.1＜1T03530.15 mm～0.3 mm0.10.075 mm～0.15 mm0.1＜0.075 m0.1Plasticity index (%)0.3 mm～0.6 mm2.2＜4T03540.15 mm～0.3 mm2.10.075 mm～10.15 mm2.2＜0.075 mm2.2


## 2.5. Fiber

The drainage asphalt mixture has large void ratio and low aggregate specific surface area, which may lead to segregation of mixture during paving and rolling. Therefore, the pavement performance of the mixture can be improved by adding fiber to increase the thickness of asphalt film and the grip strength between asphalt and mineral. The nominal length of basalt fiber and wood fiber is 6 mm, and the diameter of single fiber is 16μm, and the technical indexes are shown in Table 5.Table 5
Technical specifications for different types of fibers.
Fiber classBreaking strength (MPa)Elastic modulus (GPa)Oil absorption ratio (%)Water absorption (%)Mass loss (%)Basalt fiber30001104.20.61.1Lignin fiber<300338.84.75.7


## 2.6. Modifier

### 2.6.1. The SBS Modifier

SBS modifier is provided by Ningbo Yinzhou Pott Polymer New Materials limited company, is a thermoplastic rubber material, styrene butadiene ethylene block, and has a linear structure, as shown in Figure1.Figure 1
The SBS modifier.


### 2.6.2. The TPS Modifier

TPS modifier is provided by Shanghai Qunkang Company; the composition is mainly thermoplastic rubber, adhesive resin, as shown in Figure2.Figure 2
The TPS modifier.


## 2.6.1. The SBS Modifier

SBS modifier is provided by Ningbo Yinzhou Pott Polymer New Materials limited company, is a thermoplastic rubber material, styrene butadiene ethylene block, and has a linear structure, as shown in Figure1.Figure 1
The SBS modifier.


## 2.6.2. The TPS Modifier

TPS modifier is provided by Shanghai Qunkang Company; the composition is mainly thermoplastic rubber, adhesive resin, as shown in Figure2.Figure 2
The TPS modifier.


## 3. Test Method

### 3.1. Preparation Method of Modified Asphalt

SBS modified asphalt with 7% SBS modifier and TPS modified asphalt with 12% TPS modifier were prepared by high-speed shearing method. The specific preparation process of modified asphalt is as follows:


#### 3.1.1. Title of Raw Materials

According to the amount and blending ratio of modified asphalt required in the test, the amount of matrix asphalt and modifier was determined. The modifier is slowly and evenly added to the matrix asphalt heated to 160°C.


#### 3.1.2. Preswelling

The research shows that the polymer is uniformly distributed in the base asphalt, and the improvement effect of asphalt performance will be more significant when the volume is expanded to 10 times the original volume, and then the high-speed shear is carried out. That is, after the modifier is added to asphalt, the polymer is preswelling, which makes it easier to shear and grind. Therefore, this experiment first sheared at a low speed of 600 r/min for 15 min to ensure the full swelling of the modifier.


#### 3.1.3. High-Speed Shearing

After the modifier is fully swelling, the shear rate is increased to 4500 r/min under the condition of high-speed shear 40 min, so that the different components of asphalt are redistributed to prepare the required modified asphalt.


### 3.2. Determination Method of Optimum Dosage Combination

#### 3.2.1. Determination of Mineral Grading

According to the recommended grading range of OGFC-13 for drainage asphalt mixture in the specification, the pass rate of 2.36 mm sieve hole is adjusted, and three initial grading schemes are selected based on the grading median, as shown in Table6.Table 6
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Grading typeThrough the following sieve hole (mm) mass percentage (%)1613.29.54.752.361.180.60.30.150.075Upper limit10010080302218151286Lower limit1009060121064332Median10095702116129.57.55.54Gradation 110095.274.126.918.212.89.86.75.14.1Gradation 210094.670.823.315.611.28.76.24.94.1Gradation 310093.967.420.213.29.47.35.243.3The initial asphalt contents of the three groups of gradations are obtained by theoretical calculation, which are 4.9%, 4.7%, and 4.3%, respectively. Then, the Marshall specimens of SBS drainage asphalt mixture and TPS drainage asphalt mixture are formed by the target gradation and the corresponding initial asphalt content, and the void ratio of the specimens is measured. Studies have shown that when the target porosity is about 20%, the drainage asphalt pavement can not only ensure excellent drainage performance, but also ensure good structural performance. Therefore, 20% was selected as the target porosity for this topic. The test results are shown in Table7.Table 7
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Mixture typeGrading schemeAsphalt-stone ratio (%)Percentage of void (%)SBS bituminous mixtureGradation 14.917.7Gradation 24.719.4Gradation 34.321.7TPS bituminous mixtureGradation 14.917.6Gradation 24.719.2Gradation 34.322.3The analysis in Table7 shows that the void ratio of gradation 1 is small, and the void ratio of gradation 3 is large. The void ratio of SBS drainage asphalt mixture and TPS drainage asphalt mixture at gradation 2 is closer to the target void ratio of 20%. So, choose gradation 2 as target gradation.


#### 3.2.2. Determination of Optimum Asphalt Content

(1) Drain-Down Test. Leakage test is using asphalt mixture test procedures T0732 beaker method for testing; the specific steps are as follows: 1 kg of asphalt mixture will be mixed into the mass of 800 ml dry clean beaker, called the total mass of m1. The glass cover was added to the beaker and placed in an oven at 170°C. After 1 h, the beaker was removed, and the mixture was poured onto the glass plate. The total mass of the beaker and the adhesive was recorded as m2. The leakage loss is calculated according to Formula (1). The specification requires that, for the drainage asphalt mixture, the leakage loss in the leakage test should be ≤0.8%. TPS drainage asphalt mixture and SBS drainage asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% were made with 0.5% oil-aggregate ratio in the range of 4%∼6% oil-aggregate ratio. The inflection point of the curve in the leakage loss-oil-aggregate ratio diagram was taken as the maximum asphalt content.(1)Δm=m2−m0m1−m0×100.In the formula:Δm——loss rate of leakage, %; m0——cup quality, g; m1——total quality of beaker and asphalt mixture, g.(2) Leakage Test Results. The results of leakage test are shown in Table 8 and Figure 3. Taking the inflection point of the curve in the leakage loss-oil ratio diagram as the maximum asphalt content, the maximum asphalt content of SBS modified asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% is 5.0%, 5.1%, 5.2%, and 5.25%, respectively. The maximum asphalt content of TPS modified asphalt mixture is 4.9%. With the increase of fiber content, asphalt content increases accordingly. The reason is that the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film, so the higher the fiber content, the higher the maximum asphalt content of asphalt mixture.Table 8
The leakage test results of different drainage asphalt mixtures are summarized.
Asphalt-stone ratio (%)Δm (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.00.050.0310.0250.0290.0714.50.160.0520.0450.0490.1725.00.540.0810.0710.0750.3885.51.460.1270.1140.1181.0146.02.780.0310.1750.1821.672Figure 3
Leakage loss-whetstone ratio diagram. (a) Leakage loss-oil-aggregate ratio diagram of fiber-less SBS. (b) The leakage loss-oil-aggregate ratio diagram of 0.15% SBS fiber. (c) The leakage loss-oil-aggregate ratio diagram of 0.25% SBS fiber. (d) The leakage loss-oil-aggregate ratio diagram of 0.35% SBS fiber. (e) TPS leakage loss-oil-rock ratio diagram.
(a)(b)(c)(d)(e)(3) CANTABRO Test. The specific steps of the Scattering loss test are as follows: Marshall specimens were placed in a constant temperature water bath at 20°C and 0.5°C for 20 h. The specimen was taken out and weighed as m0. Put it into the Los Angeles wear testing machine, without steel ball, set the speed of 30∼33 r/min, and the revolution is 300 r. Then, the broken specimen was taken out, and the maximum test block in the residual test block was selected for weighing, denoted as m1. Calculate the dispersion loss rate, as shown in formula (2). Within the range of 4%–6% of the oil-stone ratio, TPS modified asphalt Marshall specimens and SBS modified asphalt Marshall specimens with 0%, 0.15%, 0.25%, and 0.35% basalt fiber content were prepared with 0.5% of the oil-stone ratio to conduct the dispersion test. The minimum asphalt content takes the inflection point of the curve in the dispersion loss-oil ratio diagram.(2)ΔS=m0−m1m0×100.In the formula:ΔS——scattering loss, %; m0——quality of specimen before test, g; m1——maximum residual mass after test, g.(4) Results of Scattering Loss Test. The results of scattering loss test are shown in Table 9 and Figure 4, The maximum asphalt content of SBS modified asphalt mixture with 0%, 0.15%, 0.25%, and 0.35% basalt fiber is 5.0%, 5.1%, 5.2%, and 5.25%, respectively; The minimum asphalt content is 4.8%, 5.0%, 5.1%, and 5.15%, respectively. The maximum asphalt content of TPS drainage asphalt mixture is 4.9%, and the minimum asphalt content is 4.7%. With the increase of fiber content, the amount of asphalt also increases accordingly, because the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film. The leakage loss rate and dispersion loss rate of SBS drainage asphalt mixture with basalt fiber are significantly lower than those of SBS drainage asphalt mixture without basalt fiber. With the increase of fiber content, the leakage loss rate and dispersion loss rate show a trend of first decreasing and then increasing. The reason is that after the fiber is mixed with the asphalt mixture, it produces physical infiltration or even chemical bond with the surface active substances in the asphalt. The asphalt is wrapped on the surface of the fiber to inhibit its free flow and reduce the leakage loss and dispersion loss; however, when the fiber content exceeds a certain amount, it is difficult for the fiber to be uniformly dispersed, and it will be intertwined or even agglomerated. The asphalt mixture in the agglomerated part will gather more free asphalt, and the leakage loss and dispersion loss will increase instead.Table 9
Comparison of test results of different drainage asphalt mixtures.
Asphalt-stone ratio (%)ΔS (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.018.8316.5413.3614.8617.124.514.3212.439.6711.0312.635.010.889.366.978.129.455.57.756.514.265.256.846.05.354.353.183.874.65Figure 4
Scatter loss-whetstone ratio diagram. (a) Float loss-oil-aggregate ratio diagram of fiberless SBS. (b) Float loss-oil-petroleum ratio diagram of 0.15% fiber SBS. (c) Float loss-oil-petroleum ratio diagram of 0.25% fiber SBS. (d) Float loss-oil-petroleum ratio diagram of 0.35% fiber SBS. (e) TPS float loss-oil-petroleum ratio diagram.
(a)(b)(c)(d)(e)


#### 3.2.3. Determination of Fiber Content

The test results are shown in Table10 and Figures 5–7.Table 10
Marshall test results of SBS asphalt mixture with different content of fiber.
Fiber content (%)Asphalt-stone ratio (%)Degree of stability (kN)Flow value (10−1 mm)VV (%)VMA (%)VFA (%)04.906.0222.720.128.830.50.155.056.8520.419.928.331.10.255.157.7627.519.627.931.40.355.206.9323.219.227.631.6Figure 5
Basalt fiber content-asphalt mixture volume index diagram.Figure 6
Basalt fiber content-Marshall stability relationship diagram.Figure 7
Relationship diagram of basalt fiber content and flow value.The analysis of the test results shows the following:With the increase of fiber content, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. Because the increase of fiber content will increase the asphalt content and occupy more voids, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. However, the three changes are not significant, because the drainage asphalt mixture is the skeleton void structure, and the gradation type is the decisive factor affecting the void ratio. The fiber content and asphalt content have little effect on it. It can be seen from Figure8 that Marshall stability increases with the increase of fiber content. When the basalt fiber content is 0.25%, the stability has a peak value of 7.76 kN. The reason is that the high tensile strength of basalt fiber can improve the strength of drainage asphalt mixture, thus improving the stability and the ability to resist deformation. However, when the fiber content is too high, the fiber is difficult to be evenly distributed in the mixture, entangled together, and the fiber cannot give full play to its role. When subjected to load, stress concentration may occur, resulting in local damage and Marshall stability decreases. The stability reaches the peak when the basalt fiber content is 0.25%, and the leakage loss rate and dispersion loss rate are the smallest when the basalt fiber content is 0.25%, indicating that the fiber can play a better role and enhance the performance of the mixture. Therefore, 0.25% basalt fiber is selected as the best dosage.Figure 8
Gaps of drained asphalt mixture.


### 3.3. Test Method for Rheological Properties

#### 3.3.1. Dynamic Shear Test

Using dynamic shear rheometer: According to the specification JTG E20-2011, T0628-2011, in the temperature range of 58°C–82°C, the temperature of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt was scanned for each increase of 6°C. The control strain mode was selected, and the loading strain was uniformly selected as 10%. The loading frequency was 10 rad/s, and the sample size was 25 mm × 2 mm. The complex shear modulusG∗, phase angle δ, rutting factor G∗/sinδ and other parameters of the matrix asphalt before and after aging and the composite modified asphalt before and after aging were tested by dynamic shear rheometer to study the high-temperature performance of the composite modified asphalt.


#### 3.3.2. Flexural Creep Stiffness Test

Using bending beam rheometer: The BBR test of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt at −12°C, −18°C and −24°C was carried out to determine the bending creep stiffness modulusS and creep curve slope m, and the low temperature crack resistance of asphalt was studied.


### 3.4. Road Performance Test Method

#### 3.4.1. High-Temperature Stability

The YLDCX-6 automatic wheel milling machine is used. Three rut boards of fiber-free SBS drainage asphalt mixture, 0.25% basalt fiber content SBS drainage asphalt mixture, and TPS drainage asphalt mixture are formed, respectively, with the volume of 300 mm × 300 mm × 50 mm. Then, the YLDCZ-8S rut tester is used, and the test is carried out at 60°C, 42 times/min and 0.7 MPa.


#### 3.4.2. Water Stability

(1) Immersion Marshall Test. Eight standard Marshall specimens of three kinds of drainage asphalt mixtures were formed, respectively, and the residual stability, namely, the ratio of the stability of the specimen soaked for 48 h and 0.5 h at 60°C, was used as the evaluation standard. The larger the value was, the stronger the ability of the mixture to resist water damage was. In this experiment, the DF stability tester was used to measure the stability, and then the residual stability was obtained.(2) Freeze-Thaw Splitting Test. Marshall specimens of three kinds of drainage asphalt mixtures were formed in two groups, and the first group was subjected to splitting test after water bathing at 25°C for 2 h. The second group was saturated for 15 min under the condition of 97.3∼98.7 kPa vacuum degree. The specimens were placed in a plastic bag, and 10 mL water was added. The specimens were placed at −18°C for 16 h and then bathed at 60°C for 24 h. Finally, the splitting test was carried out at 25°C for 2 h.(3) Immersion and Scattering Test. The Marshall specimen was placed at 60°C for 48 h and then placed at room temperature for 24 h. The mass of the specimen was weighed, and then the specimen was put into the Los Angeles testing machine to rotate 300 revolutions at a speed of 33 r/min. The mass of the specimen was taken out, and the dispersion loss was calculated and compared with the standard dispersion loss.


#### 3.4.3. Low Temperature Crack Resistance

The low temperature bending test of the beam was used to evaluate the low temperature crack resistance of the drainage asphalt mixture. In other words, the vertical pressure was applied in the middle of the beam until the beam was damaged. The ability of the mixture to resist deformation under low-temperature conditions was simulated. The evaluation indexes were flexural tensile strength, maximum flexural tensile strain, and flexural stiffness modulus.The rutting plates of SBS drainage asphalt mixture with basalt fiber, TPS drainage asphalt mixture, and nonfiber SBS drainage asphalt mixture were cut into small beams with a volume of 30 mm × 35 mm × 250 mm, respectively. The asphalt mixture multifunctional dynamic test system was used to load at the midpoint under the conditions of −10°C of test temperature and 50 mm·min−1 of loading speed, and the required data for the test were calculated.


### 3.5. Test Method for Drainage Performance

The basic steps of seepage test are as follows: the asphalt mixture specimen was formed by wheel milling method. The steel ring was placed in the central position of the specimen, and the lines were marked along the inner ring and the outer ring by chalk. Take off the steel ring, the two-ring clamp part with waterproof putty; ’/’mm for sealing treatment. Place the pavement water seepage meter at the measuring point and press down the base of the water seepage meter to enhance the water tightness and prevent water from flowing out of the gap or other gap between the water seepage meter and the sealing material. Exhaust the air in the water meter and fill the water, open the switch, and when the water surface drops to 100 mL, start timing. When the water surface drops to 500 mL, stop counting and calculate the seepage coefficient.


### 3.6. Microanalysis

#### 3.6.1. Scanning Electron Microscope Test

JSM-7500F scanning electron microscope (SEM) was used to observe the microscopic characteristics of splitting failure of basalt fiber SBS drainage asphalt mixture and fiber-less SBS drainage asphalt mixture and the distribution of basalt fiber in the mixture. The length, width, and height of the specimen are 2 cm × 2 cm × 1 cm, and the automatic magnetron sputtering instrument is used to spray gold for 15 s at 40 mA current, so that the specimen has enough conductivity.


## 3.1. Preparation Method of Modified Asphalt

SBS modified asphalt with 7% SBS modifier and TPS modified asphalt with 12% TPS modifier were prepared by high-speed shearing method. The specific preparation process of modified asphalt is as follows:


### 3.1.1. Title of Raw Materials

According to the amount and blending ratio of modified asphalt required in the test, the amount of matrix asphalt and modifier was determined. The modifier is slowly and evenly added to the matrix asphalt heated to 160°C.


### 3.1.2. Preswelling

The research shows that the polymer is uniformly distributed in the base asphalt, and the improvement effect of asphalt performance will be more significant when the volume is expanded to 10 times the original volume, and then the high-speed shear is carried out. That is, after the modifier is added to asphalt, the polymer is preswelling, which makes it easier to shear and grind. Therefore, this experiment first sheared at a low speed of 600 r/min for 15 min to ensure the full swelling of the modifier.


### 3.1.3. High-Speed Shearing

After the modifier is fully swelling, the shear rate is increased to 4500 r/min under the condition of high-speed shear 40 min, so that the different components of asphalt are redistributed to prepare the required modified asphalt.


## 3.1.1. Title of Raw Materials

According to the amount and blending ratio of modified asphalt required in the test, the amount of matrix asphalt and modifier was determined. The modifier is slowly and evenly added to the matrix asphalt heated to 160°C.


## 3.1.2. Preswelling

The research shows that the polymer is uniformly distributed in the base asphalt, and the improvement effect of asphalt performance will be more significant when the volume is expanded to 10 times the original volume, and then the high-speed shear is carried out. That is, after the modifier is added to asphalt, the polymer is preswelling, which makes it easier to shear and grind. Therefore, this experiment first sheared at a low speed of 600 r/min for 15 min to ensure the full swelling of the modifier.


## 3.1.3. High-Speed Shearing

After the modifier is fully swelling, the shear rate is increased to 4500 r/min under the condition of high-speed shear 40 min, so that the different components of asphalt are redistributed to prepare the required modified asphalt.


## 3.2. Determination Method of Optimum Dosage Combination

### 3.2.1. Determination of Mineral Grading

According to the recommended grading range of OGFC-13 for drainage asphalt mixture in the specification, the pass rate of 2.36 mm sieve hole is adjusted, and three initial grading schemes are selected based on the grading median, as shown in Table6.Table 6
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Grading typeThrough the following sieve hole (mm) mass percentage (%)1613.29.54.752.361.180.60.30.150.075Upper limit10010080302218151286Lower limit1009060121064332Median10095702116129.57.55.54Gradation 110095.274.126.918.212.89.86.75.14.1Gradation 210094.670.823.315.611.28.76.24.94.1Gradation 310093.967.420.213.29.47.35.243.3The initial asphalt contents of the three groups of gradations are obtained by theoretical calculation, which are 4.9%, 4.7%, and 4.3%, respectively. Then, the Marshall specimens of SBS drainage asphalt mixture and TPS drainage asphalt mixture are formed by the target gradation and the corresponding initial asphalt content, and the void ratio of the specimens is measured. Studies have shown that when the target porosity is about 20%, the drainage asphalt pavement can not only ensure excellent drainage performance, but also ensure good structural performance. Therefore, 20% was selected as the target porosity for this topic. The test results are shown in Table7.Table 7
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Mixture typeGrading schemeAsphalt-stone ratio (%)Percentage of void (%)SBS bituminous mixtureGradation 14.917.7Gradation 24.719.4Gradation 34.321.7TPS bituminous mixtureGradation 14.917.6Gradation 24.719.2Gradation 34.322.3The analysis in Table7 shows that the void ratio of gradation 1 is small, and the void ratio of gradation 3 is large. The void ratio of SBS drainage asphalt mixture and TPS drainage asphalt mixture at gradation 2 is closer to the target void ratio of 20%. So, choose gradation 2 as target gradation.


### 3.2.2. Determination of Optimum Asphalt Content

(1) Drain-Down Test. Leakage test is using asphalt mixture test procedures T0732 beaker method for testing; the specific steps are as follows: 1 kg of asphalt mixture will be mixed into the mass of 800 ml dry clean beaker, called the total mass of m1. The glass cover was added to the beaker and placed in an oven at 170°C. After 1 h, the beaker was removed, and the mixture was poured onto the glass plate. The total mass of the beaker and the adhesive was recorded as m2. The leakage loss is calculated according to Formula (1). The specification requires that, for the drainage asphalt mixture, the leakage loss in the leakage test should be ≤0.8%. TPS drainage asphalt mixture and SBS drainage asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% were made with 0.5% oil-aggregate ratio in the range of 4%∼6% oil-aggregate ratio. The inflection point of the curve in the leakage loss-oil-aggregate ratio diagram was taken as the maximum asphalt content.(1)Δm=m2−m0m1−m0×100.In the formula:Δm——loss rate of leakage, %; m0——cup quality, g; m1——total quality of beaker and asphalt mixture, g.(2) Leakage Test Results. The results of leakage test are shown in Table 8 and Figure 3. Taking the inflection point of the curve in the leakage loss-oil ratio diagram as the maximum asphalt content, the maximum asphalt content of SBS modified asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% is 5.0%, 5.1%, 5.2%, and 5.25%, respectively. The maximum asphalt content of TPS modified asphalt mixture is 4.9%. With the increase of fiber content, asphalt content increases accordingly. The reason is that the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film, so the higher the fiber content, the higher the maximum asphalt content of asphalt mixture.Table 8
The leakage test results of different drainage asphalt mixtures are summarized.
Asphalt-stone ratio (%)Δm (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.00.050.0310.0250.0290.0714.50.160.0520.0450.0490.1725.00.540.0810.0710.0750.3885.51.460.1270.1140.1181.0146.02.780.0310.1750.1821.672Figure 3
Leakage loss-whetstone ratio diagram. (a) Leakage loss-oil-aggregate ratio diagram of fiber-less SBS. (b) The leakage loss-oil-aggregate ratio diagram of 0.15% SBS fiber. (c) The leakage loss-oil-aggregate ratio diagram of 0.25% SBS fiber. (d) The leakage loss-oil-aggregate ratio diagram of 0.35% SBS fiber. (e) TPS leakage loss-oil-rock ratio diagram.
(a)(b)(c)(d)(e)(3) CANTABRO Test. The specific steps of the Scattering loss test are as follows: Marshall specimens were placed in a constant temperature water bath at 20°C and 0.5°C for 20 h. The specimen was taken out and weighed as m0. Put it into the Los Angeles wear testing machine, without steel ball, set the speed of 30∼33 r/min, and the revolution is 300 r. Then, the broken specimen was taken out, and the maximum test block in the residual test block was selected for weighing, denoted as m1. Calculate the dispersion loss rate, as shown in formula (2). Within the range of 4%–6% of the oil-stone ratio, TPS modified asphalt Marshall specimens and SBS modified asphalt Marshall specimens with 0%, 0.15%, 0.25%, and 0.35% basalt fiber content were prepared with 0.5% of the oil-stone ratio to conduct the dispersion test. The minimum asphalt content takes the inflection point of the curve in the dispersion loss-oil ratio diagram.(2)ΔS=m0−m1m0×100.In the formula:ΔS——scattering loss, %; m0——quality of specimen before test, g; m1——maximum residual mass after test, g.(4) Results of Scattering Loss Test. The results of scattering loss test are shown in Table 9 and Figure 4, The maximum asphalt content of SBS modified asphalt mixture with 0%, 0.15%, 0.25%, and 0.35% basalt fiber is 5.0%, 5.1%, 5.2%, and 5.25%, respectively; The minimum asphalt content is 4.8%, 5.0%, 5.1%, and 5.15%, respectively. The maximum asphalt content of TPS drainage asphalt mixture is 4.9%, and the minimum asphalt content is 4.7%. With the increase of fiber content, the amount of asphalt also increases accordingly, because the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film. The leakage loss rate and dispersion loss rate of SBS drainage asphalt mixture with basalt fiber are significantly lower than those of SBS drainage asphalt mixture without basalt fiber. With the increase of fiber content, the leakage loss rate and dispersion loss rate show a trend of first decreasing and then increasing. The reason is that after the fiber is mixed with the asphalt mixture, it produces physical infiltration or even chemical bond with the surface active substances in the asphalt. The asphalt is wrapped on the surface of the fiber to inhibit its free flow and reduce the leakage loss and dispersion loss; however, when the fiber content exceeds a certain amount, it is difficult for the fiber to be uniformly dispersed, and it will be intertwined or even agglomerated. The asphalt mixture in the agglomerated part will gather more free asphalt, and the leakage loss and dispersion loss will increase instead.Table 9
Comparison of test results of different drainage asphalt mixtures.
Asphalt-stone ratio (%)ΔS (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.018.8316.5413.3614.8617.124.514.3212.439.6711.0312.635.010.889.366.978.129.455.57.756.514.265.256.846.05.354.353.183.874.65Figure 4
Scatter loss-whetstone ratio diagram. (a) Float loss-oil-aggregate ratio diagram of fiberless SBS. (b) Float loss-oil-petroleum ratio diagram of 0.15% fiber SBS. (c) Float loss-oil-petroleum ratio diagram of 0.25% fiber SBS. (d) Float loss-oil-petroleum ratio diagram of 0.35% fiber SBS. (e) TPS float loss-oil-petroleum ratio diagram.
(a)(b)(c)(d)(e)


### 3.2.3. Determination of Fiber Content

The test results are shown in Table10 and Figures 5–7.Table 10
Marshall test results of SBS asphalt mixture with different content of fiber.
Fiber content (%)Asphalt-stone ratio (%)Degree of stability (kN)Flow value (10−1 mm)VV (%)VMA (%)VFA (%)04.906.0222.720.128.830.50.155.056.8520.419.928.331.10.255.157.7627.519.627.931.40.355.206.9323.219.227.631.6Figure 5
Basalt fiber content-asphalt mixture volume index diagram.Figure 6
Basalt fiber content-Marshall stability relationship diagram.Figure 7
Relationship diagram of basalt fiber content and flow value.The analysis of the test results shows the following:With the increase of fiber content, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. Because the increase of fiber content will increase the asphalt content and occupy more voids, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. However, the three changes are not significant, because the drainage asphalt mixture is the skeleton void structure, and the gradation type is the decisive factor affecting the void ratio. The fiber content and asphalt content have little effect on it. It can be seen from Figure8 that Marshall stability increases with the increase of fiber content. When the basalt fiber content is 0.25%, the stability has a peak value of 7.76 kN. The reason is that the high tensile strength of basalt fiber can improve the strength of drainage asphalt mixture, thus improving the stability and the ability to resist deformation. However, when the fiber content is too high, the fiber is difficult to be evenly distributed in the mixture, entangled together, and the fiber cannot give full play to its role. When subjected to load, stress concentration may occur, resulting in local damage and Marshall stability decreases. The stability reaches the peak when the basalt fiber content is 0.25%, and the leakage loss rate and dispersion loss rate are the smallest when the basalt fiber content is 0.25%, indicating that the fiber can play a better role and enhance the performance of the mixture. Therefore, 0.25% basalt fiber is selected as the best dosage.Figure 8
Gaps of drained asphalt mixture.


## 3.2.1. Determination of Mineral Grading

According to the recommended grading range of OGFC-13 for drainage asphalt mixture in the specification, the pass rate of 2.36 mm sieve hole is adjusted, and three initial grading schemes are selected based on the grading median, as shown in Table6.Table 6
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Grading typeThrough the following sieve hole (mm) mass percentage (%)1613.29.54.752.361.180.60.30.150.075Upper limit10010080302218151286Lower limit1009060121064332Median10095702116129.57.55.54Gradation 110095.274.126.918.212.89.86.75.14.1Gradation 210094.670.823.315.611.28.76.24.94.1Gradation 310093.967.420.213.29.47.35.243.3The initial asphalt contents of the three groups of gradations are obtained by theoretical calculation, which are 4.9%, 4.7%, and 4.3%, respectively. Then, the Marshall specimens of SBS drainage asphalt mixture and TPS drainage asphalt mixture are formed by the target gradation and the corresponding initial asphalt content, and the void ratio of the specimens is measured. Studies have shown that when the target porosity is about 20%, the drainage asphalt pavement can not only ensure excellent drainage performance, but also ensure good structural performance. Therefore, 20% was selected as the target porosity for this topic. The test results are shown in Table7.Table 7
Mineral aggregate gradation of OGFC-13 asphalt mixture.
Mixture typeGrading schemeAsphalt-stone ratio (%)Percentage of void (%)SBS bituminous mixtureGradation 14.917.7Gradation 24.719.4Gradation 34.321.7TPS bituminous mixtureGradation 14.917.6Gradation 24.719.2Gradation 34.322.3The analysis in Table7 shows that the void ratio of gradation 1 is small, and the void ratio of gradation 3 is large. The void ratio of SBS drainage asphalt mixture and TPS drainage asphalt mixture at gradation 2 is closer to the target void ratio of 20%. So, choose gradation 2 as target gradation.


## 3.2.2. Determination of Optimum Asphalt Content

(1) Drain-Down Test. Leakage test is using asphalt mixture test procedures T0732 beaker method for testing; the specific steps are as follows: 1 kg of asphalt mixture will be mixed into the mass of 800 ml dry clean beaker, called the total mass of m1. The glass cover was added to the beaker and placed in an oven at 170°C. After 1 h, the beaker was removed, and the mixture was poured onto the glass plate. The total mass of the beaker and the adhesive was recorded as m2. The leakage loss is calculated according to Formula (1). The specification requires that, for the drainage asphalt mixture, the leakage loss in the leakage test should be ≤0.8%. TPS drainage asphalt mixture and SBS drainage asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% were made with 0.5% oil-aggregate ratio in the range of 4%∼6% oil-aggregate ratio. The inflection point of the curve in the leakage loss-oil-aggregate ratio diagram was taken as the maximum asphalt content.(1)Δm=m2−m0m1−m0×100.In the formula:Δm——loss rate of leakage, %; m0——cup quality, g; m1——total quality of beaker and asphalt mixture, g.(2) Leakage Test Results. The results of leakage test are shown in Table 8 and Figure 3. Taking the inflection point of the curve in the leakage loss-oil ratio diagram as the maximum asphalt content, the maximum asphalt content of SBS modified asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% is 5.0%, 5.1%, 5.2%, and 5.25%, respectively. The maximum asphalt content of TPS modified asphalt mixture is 4.9%. With the increase of fiber content, asphalt content increases accordingly. The reason is that the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film, so the higher the fiber content, the higher the maximum asphalt content of asphalt mixture.Table 8
The leakage test results of different drainage asphalt mixtures are summarized.
Asphalt-stone ratio (%)Δm (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.00.050.0310.0250.0290.0714.50.160.0520.0450.0490.1725.00.540.0810.0710.0750.3885.51.460.1270.1140.1181.0146.02.780.0310.1750.1821.672Figure 3
Leakage loss-whetstone ratio diagram. (a) Leakage loss-oil-aggregate ratio diagram of fiber-less SBS. (b) The leakage loss-oil-aggregate ratio diagram of 0.15% SBS fiber. (c) The leakage loss-oil-aggregate ratio diagram of 0.25% SBS fiber. (d) The leakage loss-oil-aggregate ratio diagram of 0.35% SBS fiber. (e) TPS leakage loss-oil-rock ratio diagram.
(a)(b)(c)(d)(e)(3) CANTABRO Test. The specific steps of the Scattering loss test are as follows: Marshall specimens were placed in a constant temperature water bath at 20°C and 0.5°C for 20 h. The specimen was taken out and weighed as m0. Put it into the Los Angeles wear testing machine, without steel ball, set the speed of 30∼33 r/min, and the revolution is 300 r. Then, the broken specimen was taken out, and the maximum test block in the residual test block was selected for weighing, denoted as m1. Calculate the dispersion loss rate, as shown in formula (2). Within the range of 4%–6% of the oil-stone ratio, TPS modified asphalt Marshall specimens and SBS modified asphalt Marshall specimens with 0%, 0.15%, 0.25%, and 0.35% basalt fiber content were prepared with 0.5% of the oil-stone ratio to conduct the dispersion test. The minimum asphalt content takes the inflection point of the curve in the dispersion loss-oil ratio diagram.(2)ΔS=m0−m1m0×100.In the formula:ΔS——scattering loss, %; m0——quality of specimen before test, g; m1——maximum residual mass after test, g.(4) Results of Scattering Loss Test. The results of scattering loss test are shown in Table 9 and Figure 4, The maximum asphalt content of SBS modified asphalt mixture with 0%, 0.15%, 0.25%, and 0.35% basalt fiber is 5.0%, 5.1%, 5.2%, and 5.25%, respectively; The minimum asphalt content is 4.8%, 5.0%, 5.1%, and 5.15%, respectively. The maximum asphalt content of TPS drainage asphalt mixture is 4.9%, and the minimum asphalt content is 4.7%. With the increase of fiber content, the amount of asphalt also increases accordingly, because the huge specific surface area of fiber can become the interface of asphalt infiltration, so as to adsorb asphalt, increase the amount of asphalt, and increase the thickness of asphalt structural film. The leakage loss rate and dispersion loss rate of SBS drainage asphalt mixture with basalt fiber are significantly lower than those of SBS drainage asphalt mixture without basalt fiber. With the increase of fiber content, the leakage loss rate and dispersion loss rate show a trend of first decreasing and then increasing. The reason is that after the fiber is mixed with the asphalt mixture, it produces physical infiltration or even chemical bond with the surface active substances in the asphalt. The asphalt is wrapped on the surface of the fiber to inhibit its free flow and reduce the leakage loss and dispersion loss; however, when the fiber content exceeds a certain amount, it is difficult for the fiber to be uniformly dispersed, and it will be intertwined or even agglomerated. The asphalt mixture in the agglomerated part will gather more free asphalt, and the leakage loss and dispersion loss will increase instead.Table 9
Comparison of test results of different drainage asphalt mixtures.
Asphalt-stone ratio (%)ΔS (%)Fiber-free SBS0.15% fiber SBS0.25% fiber SBS0.35% fiber SBSTPS4.018.8316.5413.3614.8617.124.514.3212.439.6711.0312.635.010.889.366.978.129.455.57.756.514.265.256.846.05.354.353.183.874.65Figure 4
Scatter loss-whetstone ratio diagram. (a) Float loss-oil-aggregate ratio diagram of fiberless SBS. (b) Float loss-oil-petroleum ratio diagram of 0.15% fiber SBS. (c) Float loss-oil-petroleum ratio diagram of 0.25% fiber SBS. (d) Float loss-oil-petroleum ratio diagram of 0.35% fiber SBS. (e) TPS float loss-oil-petroleum ratio diagram.
(a)(b)(c)(d)(e)


## 3.2.3. Determination of Fiber Content

The test results are shown in Table10 and Figures 5–7.Table 10
Marshall test results of SBS asphalt mixture with different content of fiber.
Fiber content (%)Asphalt-stone ratio (%)Degree of stability (kN)Flow value (10−1 mm)VV (%)VMA (%)VFA (%)04.906.0222.720.128.830.50.155.056.8520.419.928.331.10.255.157.7627.519.627.931.40.355.206.9323.219.227.631.6Figure 5
Basalt fiber content-asphalt mixture volume index diagram.Figure 6
Basalt fiber content-Marshall stability relationship diagram.Figure 7
Relationship diagram of basalt fiber content and flow value.The analysis of the test results shows the following:With the increase of fiber content, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. Because the increase of fiber content will increase the asphalt content and occupy more voids, the porosity and mineral gap rate decrease accordingly, and the asphalt saturation increases. However, the three changes are not significant, because the drainage asphalt mixture is the skeleton void structure, and the gradation type is the decisive factor affecting the void ratio. The fiber content and asphalt content have little effect on it. It can be seen from Figure8 that Marshall stability increases with the increase of fiber content. When the basalt fiber content is 0.25%, the stability has a peak value of 7.76 kN. The reason is that the high tensile strength of basalt fiber can improve the strength of drainage asphalt mixture, thus improving the stability and the ability to resist deformation. However, when the fiber content is too high, the fiber is difficult to be evenly distributed in the mixture, entangled together, and the fiber cannot give full play to its role. When subjected to load, stress concentration may occur, resulting in local damage and Marshall stability decreases. The stability reaches the peak when the basalt fiber content is 0.25%, and the leakage loss rate and dispersion loss rate are the smallest when the basalt fiber content is 0.25%, indicating that the fiber can play a better role and enhance the performance of the mixture. Therefore, 0.25% basalt fiber is selected as the best dosage.Figure 8
Gaps of drained asphalt mixture.


## 3.3. Test Method for Rheological Properties

### 3.3.1. Dynamic Shear Test

Using dynamic shear rheometer: According to the specification JTG E20-2011, T0628-2011, in the temperature range of 58°C–82°C, the temperature of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt was scanned for each increase of 6°C. The control strain mode was selected, and the loading strain was uniformly selected as 10%. The loading frequency was 10 rad/s, and the sample size was 25 mm × 2 mm. The complex shear modulusG∗, phase angle δ, rutting factor G∗/sinδ and other parameters of the matrix asphalt before and after aging and the composite modified asphalt before and after aging were tested by dynamic shear rheometer to study the high-temperature performance of the composite modified asphalt.


### 3.3.2. Flexural Creep Stiffness Test

Using bending beam rheometer: The BBR test of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt at −12°C, −18°C and −24°C was carried out to determine the bending creep stiffness modulusS and creep curve slope m, and the low temperature crack resistance of asphalt was studied.


## 3.3.1. Dynamic Shear Test

Using dynamic shear rheometer: According to the specification JTG E20-2011, T0628-2011, in the temperature range of 58°C–82°C, the temperature of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt was scanned for each increase of 6°C. The control strain mode was selected, and the loading strain was uniformly selected as 10%. The loading frequency was 10 rad/s, and the sample size was 25 mm × 2 mm. The complex shear modulusG∗, phase angle δ, rutting factor G∗/sinδ and other parameters of the matrix asphalt before and after aging and the composite modified asphalt before and after aging were tested by dynamic shear rheometer to study the high-temperature performance of the composite modified asphalt.


## 3.3.2. Flexural Creep Stiffness Test

Using bending beam rheometer: The BBR test of matrix asphalt, 7% SBS modified asphalt, and 12% TPS modified asphalt at −12°C, −18°C and −24°C was carried out to determine the bending creep stiffness modulusS and creep curve slope m, and the low temperature crack resistance of asphalt was studied.


## 3.4. Road Performance Test Method

### 3.4.1. High-Temperature Stability

The YLDCX-6 automatic wheel milling machine is used. Three rut boards of fiber-free SBS drainage asphalt mixture, 0.25% basalt fiber content SBS drainage asphalt mixture, and TPS drainage asphalt mixture are formed, respectively, with the volume of 300 mm × 300 mm × 50 mm. Then, the YLDCZ-8S rut tester is used, and the test is carried out at 60°C, 42 times/min and 0.7 MPa.


### 3.4.2. Water Stability

(1) Immersion Marshall Test. Eight standard Marshall specimens of three kinds of drainage asphalt mixtures were formed, respectively, and the residual stability, namely, the ratio of the stability of the specimen soaked for 48 h and 0.5 h at 60°C, was used as the evaluation standard. The larger the value was, the stronger the ability of the mixture to resist water damage was. In this experiment, the DF stability tester was used to measure the stability, and then the residual stability was obtained.(2) Freeze-Thaw Splitting Test. Marshall specimens of three kinds of drainage asphalt mixtures were formed in two groups, and the first group was subjected to splitting test after water bathing at 25°C for 2 h. The second group was saturated for 15 min under the condition of 97.3∼98.7 kPa vacuum degree. The specimens were placed in a plastic bag, and 10 mL water was added. The specimens were placed at −18°C for 16 h and then bathed at 60°C for 24 h. Finally, the splitting test was carried out at 25°C for 2 h.(3) Immersion and Scattering Test. The Marshall specimen was placed at 60°C for 48 h and then placed at room temperature for 24 h. The mass of the specimen was weighed, and then the specimen was put into the Los Angeles testing machine to rotate 300 revolutions at a speed of 33 r/min. The mass of the specimen was taken out, and the dispersion loss was calculated and compared with the standard dispersion loss.


### 3.4.3. Low Temperature Crack Resistance

The low temperature bending test of the beam was used to evaluate the low temperature crack resistance of the drainage asphalt mixture. In other words, the vertical pressure was applied in the middle of the beam until the beam was damaged. The ability of the mixture to resist deformation under low-temperature conditions was simulated. The evaluation indexes were flexural tensile strength, maximum flexural tensile strain, and flexural stiffness modulus.The rutting plates of SBS drainage asphalt mixture with basalt fiber, TPS drainage asphalt mixture, and nonfiber SBS drainage asphalt mixture were cut into small beams with a volume of 30 mm × 35 mm × 250 mm, respectively. The asphalt mixture multifunctional dynamic test system was used to load at the midpoint under the conditions of −10°C of test temperature and 50 mm·min−1 of loading speed, and the required data for the test were calculated.


## 3.4.1. High-Temperature Stability

The YLDCX-6 automatic wheel milling machine is used. Three rut boards of fiber-free SBS drainage asphalt mixture, 0.25% basalt fiber content SBS drainage asphalt mixture, and TPS drainage asphalt mixture are formed, respectively, with the volume of 300 mm × 300 mm × 50 mm. Then, the YLDCZ-8S rut tester is used, and the test is carried out at 60°C, 42 times/min and 0.7 MPa.


## 3.4.2. Water Stability

(1) Immersion Marshall Test. Eight standard Marshall specimens of three kinds of drainage asphalt mixtures were formed, respectively, and the residual stability, namely, the ratio of the stability of the specimen soaked for 48 h and 0.5 h at 60°C, was used as the evaluation standard. The larger the value was, the stronger the ability of the mixture to resist water damage was. In this experiment, the DF stability tester was used to measure the stability, and then the residual stability was obtained.(2) Freeze-Thaw Splitting Test. Marshall specimens of three kinds of drainage asphalt mixtures were formed in two groups, and the first group was subjected to splitting test after water bathing at 25°C for 2 h. The second group was saturated for 15 min under the condition of 97.3∼98.7 kPa vacuum degree. The specimens were placed in a plastic bag, and 10 mL water was added. The specimens were placed at −18°C for 16 h and then bathed at 60°C for 24 h. Finally, the splitting test was carried out at 25°C for 2 h.(3) Immersion and Scattering Test. The Marshall specimen was placed at 60°C for 48 h and then placed at room temperature for 24 h. The mass of the specimen was weighed, and then the specimen was put into the Los Angeles testing machine to rotate 300 revolutions at a speed of 33 r/min. The mass of the specimen was taken out, and the dispersion loss was calculated and compared with the standard dispersion loss.


## 3.4.3. Low Temperature Crack Resistance

The low temperature bending test of the beam was used to evaluate the low temperature crack resistance of the drainage asphalt mixture. In other words, the vertical pressure was applied in the middle of the beam until the beam was damaged. The ability of the mixture to resist deformation under low-temperature conditions was simulated. The evaluation indexes were flexural tensile strength, maximum flexural tensile strain, and flexural stiffness modulus.The rutting plates of SBS drainage asphalt mixture with basalt fiber, TPS drainage asphalt mixture, and nonfiber SBS drainage asphalt mixture were cut into small beams with a volume of 30 mm × 35 mm × 250 mm, respectively. The asphalt mixture multifunctional dynamic test system was used to load at the midpoint under the conditions of −10°C of test temperature and 50 mm·min−1 of loading speed, and the required data for the test were calculated.


## 3.5. Test Method for Drainage Performance

The basic steps of seepage test are as follows: the asphalt mixture specimen was formed by wheel milling method. The steel ring was placed in the central position of the specimen, and the lines were marked along the inner ring and the outer ring by chalk. Take off the steel ring, the two-ring clamp part with waterproof putty; ’/’mm for sealing treatment. Place the pavement water seepage meter at the measuring point and press down the base of the water seepage meter to enhance the water tightness and prevent water from flowing out of the gap or other gap between the water seepage meter and the sealing material. Exhaust the air in the water meter and fill the water, open the switch, and when the water surface drops to 100 mL, start timing. When the water surface drops to 500 mL, stop counting and calculate the seepage coefficient.


## 3.6. Microanalysis

### 3.6.1. Scanning Electron Microscope Test

JSM-7500F scanning electron microscope (SEM) was used to observe the microscopic characteristics of splitting failure of basalt fiber SBS drainage asphalt mixture and fiber-less SBS drainage asphalt mixture and the distribution of basalt fiber in the mixture. The length, width, and height of the specimen are 2 cm × 2 cm × 1 cm, and the automatic magnetron sputtering instrument is used to spray gold for 15 s at 40 mA current, so that the specimen has enough conductivity.


## 3.6.1. Scanning Electron Microscope Test

JSM-7500F scanning electron microscope (SEM) was used to observe the microscopic characteristics of splitting failure of basalt fiber SBS drainage asphalt mixture and fiber-less SBS drainage asphalt mixture and the distribution of basalt fiber in the mixture. The length, width, and height of the specimen are 2 cm × 2 cm × 1 cm, and the automatic magnetron sputtering instrument is used to spray gold for 15 s at 40 mA current, so that the specimen has enough conductivity.


## 4. Results and Discussion

### 4.1. Determination of Modifier Dosage

The comparison results of main performance indexes are shown in Table11. It can be seen from Table 11 that the decrease of penetration of the two modified asphalts indicates that the viscosity of asphalt increases and the road performance is improved. The low temperature ductility of modified asphalt has been further improved. SBS modifier exceeds the modification effect of TPS modifier, indicating that SBS modified asphalt has better low temperature crack resistance. The modified asphalt with high dynamic viscosity at 60°C can form thick asphalt film and has good adhesion performance, thus improving the water stability and durability of the mixture.Table 11
Experimental results of modified asphalt.
Test metric7% SBS12% TPSSpecification requirementPenetration (25°C, 0.1 mm)45.343.7＞40Softening point (°C)83.689.7＞80Ductility (5 cm·min−1, 15°C) (cm)57.852.3＞50Toughness (N·m)21.724.6＞20Tenacity (N·m)16.318.8＞15Dynamic viscosity at 60°C (Pa·s)2057824984＞20000


### 4.2. Analysis of Rheological Properties

#### 4.2.1. Dynamic Shear Test

The test results are shown in Figures9 and 10, and the analysis in Figures 9 and 10 shows that, with the increase of temperature, the phase angle of matrix asphalt increases, indicating that the proportion of viscoelastic components has changed, and the matrix asphalt is transformed from elasticity to viscosity. However, SBS modified asphalt showed a trend of first increase and then decrease, because with the increase of temperature, the activity of modifier increased with the increase of temperature, which increased the proportion of elastic components in modified asphalt. The phase angle of TPS modified asphalt was lower than that of SBS modified asphalt, indicating that the proportion of elastic components was large, the ability to restore deformation was stronger, and the ability to resist high temperature deformation was stronger. Peng et al. studied the performance of modified lignocellulose and SMA-13 asphalt mixture and concluded that when the yield of modified lignocellulose ranged from 0.3% to 0.5%, the rutting resistance was the best [30]. In this experiment, with the increase of temperature, the complex shear modulus and rutting factor of the three asphalts show a decreasing trend, indicating that the antirutting deformation ability is reduced. Meanwhile, because the rutting factor of TPS modified asphalt is higher than that of SBS modified asphalt, TPS modified asphalt has better rutting resistance.Figure 9
Temperature-phase angle diagram.Figure 10
Temperature-rutting factor diagram.


#### 4.2.2. Flexural Creep Stiffness Test

The test results are shown in Figures11 and 12; by analyzing Figures 11 and 12, it can be seen that the stiffness modulus of the three kinds of asphalt increases with the decrease of temperature, which reflects that the brittleness of asphalt increases with the decrease of temperature, and it is easy to crack at low temperature. Huang et al. in the study of basalt fiber asphalt mixture fatigue properties obtained 0.4% dosage of 9 mm basalt fiber asphalt mixture, and low temperature crack resistance is the best, 1.3 times for ordinary asphalt mixture [31]. The smaller the stiffness modulus, the greater the energy required for material failure, and the better the crack resistance, and the SBS modified asphalt has better low temperature crack resistance. With the decrease of temperature, the creep rate of three kinds of asphalt is also reduced. The maximum creep rate of SBS modified asphalt is m, and the stiffness modulus S changes faster with time. Under low temperature environment, the stiffness modulus S value decreases rapidly, which reduces the possibility of cracking of drainage asphalt pavement. SBS modified asphalt has better low temperature crack resistance. Therefore, SBS modified asphalt has the minimum stiffness modulus, the maximum creep rate, and the best low temperature crack resistance at the same temperature.Figure 11
Stiffness modulus-temperature diagram.Figure 12
Relationship between creep rate and temperature.


### 4.3. Analysis on Road Performance

#### 4.3.1. High-Temperature Stability

The rutting test results are shown in Table12. The deformation of basalt fiber SBS drainage asphalt mixture is the smallest, and the DS value is increased by 0.5% and 14.3%, respectively, compared with TPS drainage asphalt mixture and nonfiber SBS drainage asphalt mixture. It shows that adding fiber under high temperature can improve the stability of the material, mainly reflected in two aspects: firstly, the reason of rutting is largely due to the decrease of asphalt viscosity under high temperature conditions, showing plastic characteristics. The addition of basalt fiber will adsorb more free asphalt, and the proportion of structural asphalt with strong adhesion will increase. Therefore, the adhesion of the mixture is enhanced, and the high temperature stability of the drainage asphalt mixture is improved; secondly, the fibers are evenly distributed in the mixture and overlap with each other to form a fiber skeleton network, which plays a role of reinforcement, restricting the free movement of aggregates and playing the role of hooping. Thus, the antideformation ability of the mixture is improved, so as to improve the high-temperature stability of the drainage asphalt mixture. Studies have shown that when the basalt content reaches 0.4%, the high temperature stability of the 6 mm chopped basalt fiber mixture is the best, which is 1.8 times that of the ordinary asphalt mixture [31].Table 12
Result of rutting test.
Mixture type45 min deflection (mm)60 min deflection (mm)Dynamic stability (times·mm−1)Fiber-free SBS1.771.992884Basalt fiber SBS1.551.743316TPS1.621.813298Technical standard－－≥3000


#### 4.3.2. Water Stability

Relevant research shows that the water stability of 6 mm fiber asphalt mixture with 0.2% content is the best [31]. The water stability test results of three asphalt mixtures in this test are shown in Tables 13–15. Tables 13–15 show that the three performances of 0.25% basalt fiber SBS drainage asphalt mixture are the best. The residual stability, freeze-thaw splitting strength ratio, and immersion dispersion loss of 0.25% basalt fiber SBS drainage asphalt mixture are 2.7%, 5.6%, and 4.9% higher than those of TPS drainage asphalt mixture, respectively, and 8.6%, 8.5%, and 8.5% higher than those of nonfiber SBS drainage asphalt mixture. The reason is that, similar to the high temperature stability of fiber reinforced drainage asphalt mixture, the addition of fiber increases the proportion of structural asphalt, the adhesion between asphalt and aggregate is enhanced, and the erosion of water is weakened. In addition, the network structure formed by fiber in the mixture increases the strength of the mixture. In addition, the raw material test shows that the moisture absorption of basalt fiber is poor, which can avoid its expansion at the interface and improve the water stability of drainage asphalt mixture.Table 13
Results of immersion Marshall test.
Mixture typeFlood 0.5 h degree of stability (kN)Flood 48Hd degree of stability (kN)Residual stability (%)Fiber-free SBS6.024.9181.60.25% fiber SBS7.767.090.2TPS6.575.7587.5Technical standard－－≥75Table 14
Test results of freeze-thaw splitting.
Mixture typeSplitting strength of unfrozen specimen (MPa)Splitting strength of freeze-thaw specimens (MPa)Splitting intensity ratio (%)Fiber-free SBS0.600.4778.2Basalt fiber SBS0.730.6386.7TPS0.670.5481.1Technical standard－－≥75Table 15
Flight test results.
Mixture typeStandard dispersion loss (%)Loss of immersion dispersion (%)Fiber-free SBS11.120.00.25% fiber SBS6.711.5TPS9.816.4


#### 4.3.3. Low Temperature Crack Resistance

Low temperature crack resistance test results are shown in Table16; the analysis in Table 16 shows that the flexural stiffness modulus of basalt fiber SBS drainage asphalt mixture is the smallest, which is 5.7% and 10.2% lower than that of fiber-less SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. This shows that the greater the energy required for material failure, the better the crack resistance at low temperature. The maximum flexural tensile strain of basalt fiber SBS drainage asphalt mixture is the largest, which is 9.5% and 15.3% higher than that of nonfiber SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. It shows that the higher the strain is, the better the resistance to low temperature deformation is. Cheng et al. studied the effect of basalt fiber content on the pavement performance of large-porosity asphalt mixture and found that basalt fiber could improve the splitting tensile strength of large-porosity asphalt mixture before and after freezing and thawing, indicating that basalt fiber had excellent low-temperature crack resistance [32]. The low temperature crack resistance of basalt fiber SBS drainage asphalt mixture is the best, and TPS drainage asphalt mixture is the worst. The low temperature crack resistance of SBS modified asphalt is better than that of TPS modified asphalt. Basalt fiber SBS drainage asphalt mixture has the best low temperature crack resistance. Analyzing the reasons, the fibers overlap with each other in the mixture space to form a fiber grid. Under low temperature conditions, it plays a role of tackifying, inhibits the flow of free asphalt, and enhances the bonding with aggregate. The elastic modulus of fiber is high, and the tensile strength is large, which can improve the overall performance of the mixture. In addition, fiber grid can spread the pavement load inside the mixture, reduce stress concentration, and prevent pavement cracking.Table 16
Test results of low temperature bending.
Type of asphalt mixtureFlexural tensile strength (MPa)Maximum bending strength (με)Bending stiffness modulus (%)Fiber-free SBS7.353197.32298.6Basalt fiber SBS7.593503.52166.4TPS7.333037.12413.7Technical standard——≥2000


### 4.4. Drainage Performance Analysis

#### 4.4.1. Connecting Void

The voids of drainage asphalt mixture include connected voids, semiconnected voids, and closed voids, as shown in Figure8. The semiconnected voids can store water but cannot drain. The closed voids can neither store water nor drain. Only the connected voids can play the role of drainage. Therefore, it is extremely important to study the connected voids for drainage asphalt pavement.The analysis of the test results is shown in Table17. The void ratios of the three kinds of drainage asphalt mixtures are maintained at about 20%, which meets the requirements of the initial void ratio of the drainage pavement. The connectivity porosity is above 15%, so the three drainage asphalt mixtures all meet the requirements of drainage function of drainage pavement.Table 17
Connected void fraction test results.
Type of asphalt mixturePercentage of void (%)Connecting porosity (%)Fiber-free SBS20.117.34Basalt fiber SBS19.615.97TPS19.916.45


#### 4.4.2. Analysis of Seepage Test

The seepage test results are shown in Table18. The analysis of the test results shows that the seepage coefficient of basalt fiber drainage asphalt mixture is the smallest. The reason for the analysis is that the incorporation of fibers reduces the void ratio of the mixture. At the same time, the adsorption of fibers on asphalt increases the amount of asphalt and decreases the void ratio. However, the main factor affecting the void ratio is the gradation type, so the number of fibers and asphalt have little effect on the results, which also meets the specification requirements and has good drainage performance.Table 18
Seepage test results.
Type of asphalt mixtureThe first timing (s)The second timing (s)Water permeability coefficient (mL·min−1)Fiber-free SBS1.47.24137.9Basalt fiber SBS1.27.53809.5TPS1.4 y7.44000.0Specification requirement－－>3600


### 4.5. Microscopic Mechanism Analysis

#### 4.5.1. Scanning Electron Microscope Analysis

(1) Analysis on Strengthening Effect of Bonding Interface between Fiber and Asphalt. The OGFC-13 asphalt mixture belongs to the skeleton void structure, and the interlocking force of mineral particles is not strong, mainly relying on the bonding effect of binder. In related studies, it is proposed that the combination mode between fiber and asphalt mixture is mainly mechanical connection and infiltration adsorption. Since the fiber surface is not smooth but has a certain roughness, convex and concave, the pits on the surface of asphalt and fiber form a more compact combination [33]. It can be seen from Figure 13 that the mineral aggregate in the nonfiber SBS drainage asphalt mixture is not closely bonded to the asphalt, and there are a large number of voids. Therefore, with the increase of temperature and the erosion of water, the mineral aggregate is easy to peel off from the asphalt surface, resulting in rutting, pits, and other damage. The fiber diameter is small, and the mixed mixture has a huge specific surface area. The fiber surface is adsorbed by a large amount of asphalt, and the root is closely bonded with the asphalt mixture. This shows that the infiltration between fiber and asphalt liquid is great, and the bonding degree of the interface between the two is significantly greater than that between the mineral aggregate of nonfiber asphalt mixture and asphalt.Figure 13
Bonding interface between asphalt and ore in fiber free asphalt mixture.Figure14 shows that fiber and mixture are combined by mechanical connection and infiltration adsorption. Basalt fiber has a certain roughness and unevenness. Asphalt phase extends to the pits on the surface of fiber phase, forming a closer combination. When asphalt phase contacts with fiber, it is surface contact, resulting in the effect equivalent to mechanical anchor sum. It has a large bite force and improves the high temperature stability of drainage asphalt mixture by improving the bond strength. Transition layer refers to the structural asphalt layer, and the transition layer between free asphalt and fiber can connect two phases. There are two forms of asphalt in the mixture. One is the constrained structural asphalt, and the other is the free asphalt without contact with the entity. The constrained structural asphalt has stronger bonding force. The adsorption of fiber makes free asphalt transform into transition layer structure asphalt at the contact point of the two. The fiber with large specific surface area will form a large number of transition layers in the mixture, and the proportion of structural asphalt with higher cohesive force increases. Therefore, the addition of fiber can improve the high and low temperature stability and water stability of drainage asphalt mixture. The incorporation of basalt fiber changes the effect of each phase interface of drainage asphalt mixture and improves the road performance of drainage asphalt mixture.Figure 14
The bonding interface between basalt fibers and bitumen.(2) Effect of Fiber on Reinforcement and Crack Resistance of Drainage Asphalt Mixture. It can be seen from Figure 15 that the splitting failure surface of fiber-free SBS drainage asphalt mixture has many cracks and different stripping levels. The mineral material is in a state of separation, and the connection is extremely weak. The microscopic picture of drainage asphalt mixture with basalt fiber is shown in Figure 16.Figure 15
Breakdown of asphalt mixture without fiber drainage.
(a)(b)Figure 16
Fracture of basalt fiber drainage asphalt mixture.
(a)(b)The main failure mode of asphalt mixture in use is shear failure, which starts from the internal voids of asphalt mixture and spreads along the original voids, especially the interface between asphalt and mineral [33]. The basalt overlaps vertically and horizontally in the mixture to form a spatial network structure. When the asphalt pavement is subjected to load, the spatial network structure can transfer stress and reduce stress concentration, which is similar to the role of reinforcement in reinforced concrete. It can also inhibit the free movement of particles, play a ‘hoop’ role in the mixture, and improve the overall mechanical properties of drainage asphalt pavement. It can be seen from the photographs of the fiber fracture that the fiber is interspersed in the asphalt mixture, and the root is absorbed by the asphalt and buried in the internal of the asphalt mixture, indicating that the basalt fiber and the asphalt mixture have strong adhesion and crack resistance.


## 4.1. Determination of Modifier Dosage

The comparison results of main performance indexes are shown in Table11. It can be seen from Table 11 that the decrease of penetration of the two modified asphalts indicates that the viscosity of asphalt increases and the road performance is improved. The low temperature ductility of modified asphalt has been further improved. SBS modifier exceeds the modification effect of TPS modifier, indicating that SBS modified asphalt has better low temperature crack resistance. The modified asphalt with high dynamic viscosity at 60°C can form thick asphalt film and has good adhesion performance, thus improving the water stability and durability of the mixture.Table 11
Experimental results of modified asphalt.
Test metric7% SBS12% TPSSpecification requirementPenetration (25°C, 0.1 mm)45.343.7＞40Softening point (°C)83.689.7＞80Ductility (5 cm·min−1, 15°C) (cm)57.852.3＞50Toughness (N·m)21.724.6＞20Tenacity (N·m)16.318.8＞15Dynamic viscosity at 60°C (Pa·s)2057824984＞20000


## 4.2. Analysis of Rheological Properties

### 4.2.1. Dynamic Shear Test

The test results are shown in Figures9 and 10, and the analysis in Figures 9 and 10 shows that, with the increase of temperature, the phase angle of matrix asphalt increases, indicating that the proportion of viscoelastic components has changed, and the matrix asphalt is transformed from elasticity to viscosity. However, SBS modified asphalt showed a trend of first increase and then decrease, because with the increase of temperature, the activity of modifier increased with the increase of temperature, which increased the proportion of elastic components in modified asphalt. The phase angle of TPS modified asphalt was lower than that of SBS modified asphalt, indicating that the proportion of elastic components was large, the ability to restore deformation was stronger, and the ability to resist high temperature deformation was stronger. Peng et al. studied the performance of modified lignocellulose and SMA-13 asphalt mixture and concluded that when the yield of modified lignocellulose ranged from 0.3% to 0.5%, the rutting resistance was the best [30]. In this experiment, with the increase of temperature, the complex shear modulus and rutting factor of the three asphalts show a decreasing trend, indicating that the antirutting deformation ability is reduced. Meanwhile, because the rutting factor of TPS modified asphalt is higher than that of SBS modified asphalt, TPS modified asphalt has better rutting resistance.Figure 9
Temperature-phase angle diagram.Figure 10
Temperature-rutting factor diagram.


### 4.2.2. Flexural Creep Stiffness Test

The test results are shown in Figures11 and 12; by analyzing Figures 11 and 12, it can be seen that the stiffness modulus of the three kinds of asphalt increases with the decrease of temperature, which reflects that the brittleness of asphalt increases with the decrease of temperature, and it is easy to crack at low temperature. Huang et al. in the study of basalt fiber asphalt mixture fatigue properties obtained 0.4% dosage of 9 mm basalt fiber asphalt mixture, and low temperature crack resistance is the best, 1.3 times for ordinary asphalt mixture [31]. The smaller the stiffness modulus, the greater the energy required for material failure, and the better the crack resistance, and the SBS modified asphalt has better low temperature crack resistance. With the decrease of temperature, the creep rate of three kinds of asphalt is also reduced. The maximum creep rate of SBS modified asphalt is m, and the stiffness modulus S changes faster with time. Under low temperature environment, the stiffness modulus S value decreases rapidly, which reduces the possibility of cracking of drainage asphalt pavement. SBS modified asphalt has better low temperature crack resistance. Therefore, SBS modified asphalt has the minimum stiffness modulus, the maximum creep rate, and the best low temperature crack resistance at the same temperature.Figure 11
Stiffness modulus-temperature diagram.Figure 12
Relationship between creep rate and temperature.


## 4.2.1. Dynamic Shear Test

The test results are shown in Figures9 and 10, and the analysis in Figures 9 and 10 shows that, with the increase of temperature, the phase angle of matrix asphalt increases, indicating that the proportion of viscoelastic components has changed, and the matrix asphalt is transformed from elasticity to viscosity. However, SBS modified asphalt showed a trend of first increase and then decrease, because with the increase of temperature, the activity of modifier increased with the increase of temperature, which increased the proportion of elastic components in modified asphalt. The phase angle of TPS modified asphalt was lower than that of SBS modified asphalt, indicating that the proportion of elastic components was large, the ability to restore deformation was stronger, and the ability to resist high temperature deformation was stronger. Peng et al. studied the performance of modified lignocellulose and SMA-13 asphalt mixture and concluded that when the yield of modified lignocellulose ranged from 0.3% to 0.5%, the rutting resistance was the best [30]. In this experiment, with the increase of temperature, the complex shear modulus and rutting factor of the three asphalts show a decreasing trend, indicating that the antirutting deformation ability is reduced. Meanwhile, because the rutting factor of TPS modified asphalt is higher than that of SBS modified asphalt, TPS modified asphalt has better rutting resistance.Figure 9
Temperature-phase angle diagram.Figure 10
Temperature-rutting factor diagram.


## 4.2.2. Flexural Creep Stiffness Test

The test results are shown in Figures11 and 12; by analyzing Figures 11 and 12, it can be seen that the stiffness modulus of the three kinds of asphalt increases with the decrease of temperature, which reflects that the brittleness of asphalt increases with the decrease of temperature, and it is easy to crack at low temperature. Huang et al. in the study of basalt fiber asphalt mixture fatigue properties obtained 0.4% dosage of 9 mm basalt fiber asphalt mixture, and low temperature crack resistance is the best, 1.3 times for ordinary asphalt mixture [31]. The smaller the stiffness modulus, the greater the energy required for material failure, and the better the crack resistance, and the SBS modified asphalt has better low temperature crack resistance. With the decrease of temperature, the creep rate of three kinds of asphalt is also reduced. The maximum creep rate of SBS modified asphalt is m, and the stiffness modulus S changes faster with time. Under low temperature environment, the stiffness modulus S value decreases rapidly, which reduces the possibility of cracking of drainage asphalt pavement. SBS modified asphalt has better low temperature crack resistance. Therefore, SBS modified asphalt has the minimum stiffness modulus, the maximum creep rate, and the best low temperature crack resistance at the same temperature.Figure 11
Stiffness modulus-temperature diagram.Figure 12
Relationship between creep rate and temperature.


## 4.3. Analysis on Road Performance

### 4.3.1. High-Temperature Stability

The rutting test results are shown in Table12. The deformation of basalt fiber SBS drainage asphalt mixture is the smallest, and the DS value is increased by 0.5% and 14.3%, respectively, compared with TPS drainage asphalt mixture and nonfiber SBS drainage asphalt mixture. It shows that adding fiber under high temperature can improve the stability of the material, mainly reflected in two aspects: firstly, the reason of rutting is largely due to the decrease of asphalt viscosity under high temperature conditions, showing plastic characteristics. The addition of basalt fiber will adsorb more free asphalt, and the proportion of structural asphalt with strong adhesion will increase. Therefore, the adhesion of the mixture is enhanced, and the high temperature stability of the drainage asphalt mixture is improved; secondly, the fibers are evenly distributed in the mixture and overlap with each other to form a fiber skeleton network, which plays a role of reinforcement, restricting the free movement of aggregates and playing the role of hooping. Thus, the antideformation ability of the mixture is improved, so as to improve the high-temperature stability of the drainage asphalt mixture. Studies have shown that when the basalt content reaches 0.4%, the high temperature stability of the 6 mm chopped basalt fiber mixture is the best, which is 1.8 times that of the ordinary asphalt mixture [31].Table 12
Result of rutting test.
Mixture type45 min deflection (mm)60 min deflection (mm)Dynamic stability (times·mm−1)Fiber-free SBS1.771.992884Basalt fiber SBS1.551.743316TPS1.621.813298Technical standard－－≥3000


### 4.3.2. Water Stability

Relevant research shows that the water stability of 6 mm fiber asphalt mixture with 0.2% content is the best [31]. The water stability test results of three asphalt mixtures in this test are shown in Tables 13–15. Tables 13–15 show that the three performances of 0.25% basalt fiber SBS drainage asphalt mixture are the best. The residual stability, freeze-thaw splitting strength ratio, and immersion dispersion loss of 0.25% basalt fiber SBS drainage asphalt mixture are 2.7%, 5.6%, and 4.9% higher than those of TPS drainage asphalt mixture, respectively, and 8.6%, 8.5%, and 8.5% higher than those of nonfiber SBS drainage asphalt mixture. The reason is that, similar to the high temperature stability of fiber reinforced drainage asphalt mixture, the addition of fiber increases the proportion of structural asphalt, the adhesion between asphalt and aggregate is enhanced, and the erosion of water is weakened. In addition, the network structure formed by fiber in the mixture increases the strength of the mixture. In addition, the raw material test shows that the moisture absorption of basalt fiber is poor, which can avoid its expansion at the interface and improve the water stability of drainage asphalt mixture.Table 13
Results of immersion Marshall test.
Mixture typeFlood 0.5 h degree of stability (kN)Flood 48Hd degree of stability (kN)Residual stability (%)Fiber-free SBS6.024.9181.60.25% fiber SBS7.767.090.2TPS6.575.7587.5Technical standard－－≥75Table 14
Test results of freeze-thaw splitting.
Mixture typeSplitting strength of unfrozen specimen (MPa)Splitting strength of freeze-thaw specimens (MPa)Splitting intensity ratio (%)Fiber-free SBS0.600.4778.2Basalt fiber SBS0.730.6386.7TPS0.670.5481.1Technical standard－－≥75Table 15
Flight test results.
Mixture typeStandard dispersion loss (%)Loss of immersion dispersion (%)Fiber-free SBS11.120.00.25% fiber SBS6.711.5TPS9.816.4


### 4.3.3. Low Temperature Crack Resistance

Low temperature crack resistance test results are shown in Table16; the analysis in Table 16 shows that the flexural stiffness modulus of basalt fiber SBS drainage asphalt mixture is the smallest, which is 5.7% and 10.2% lower than that of fiber-less SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. This shows that the greater the energy required for material failure, the better the crack resistance at low temperature. The maximum flexural tensile strain of basalt fiber SBS drainage asphalt mixture is the largest, which is 9.5% and 15.3% higher than that of nonfiber SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. It shows that the higher the strain is, the better the resistance to low temperature deformation is. Cheng et al. studied the effect of basalt fiber content on the pavement performance of large-porosity asphalt mixture and found that basalt fiber could improve the splitting tensile strength of large-porosity asphalt mixture before and after freezing and thawing, indicating that basalt fiber had excellent low-temperature crack resistance [32]. The low temperature crack resistance of basalt fiber SBS drainage asphalt mixture is the best, and TPS drainage asphalt mixture is the worst. The low temperature crack resistance of SBS modified asphalt is better than that of TPS modified asphalt. Basalt fiber SBS drainage asphalt mixture has the best low temperature crack resistance. Analyzing the reasons, the fibers overlap with each other in the mixture space to form a fiber grid. Under low temperature conditions, it plays a role of tackifying, inhibits the flow of free asphalt, and enhances the bonding with aggregate. The elastic modulus of fiber is high, and the tensile strength is large, which can improve the overall performance of the mixture. In addition, fiber grid can spread the pavement load inside the mixture, reduce stress concentration, and prevent pavement cracking.Table 16
Test results of low temperature bending.
Type of asphalt mixtureFlexural tensile strength (MPa)Maximum bending strength (με)Bending stiffness modulus (%)Fiber-free SBS7.353197.32298.6Basalt fiber SBS7.593503.52166.4TPS7.333037.12413.7Technical standard——≥2000


## 4.3.1. High-Temperature Stability

The rutting test results are shown in Table12. The deformation of basalt fiber SBS drainage asphalt mixture is the smallest, and the DS value is increased by 0.5% and 14.3%, respectively, compared with TPS drainage asphalt mixture and nonfiber SBS drainage asphalt mixture. It shows that adding fiber under high temperature can improve the stability of the material, mainly reflected in two aspects: firstly, the reason of rutting is largely due to the decrease of asphalt viscosity under high temperature conditions, showing plastic characteristics. The addition of basalt fiber will adsorb more free asphalt, and the proportion of structural asphalt with strong adhesion will increase. Therefore, the adhesion of the mixture is enhanced, and the high temperature stability of the drainage asphalt mixture is improved; secondly, the fibers are evenly distributed in the mixture and overlap with each other to form a fiber skeleton network, which plays a role of reinforcement, restricting the free movement of aggregates and playing the role of hooping. Thus, the antideformation ability of the mixture is improved, so as to improve the high-temperature stability of the drainage asphalt mixture. Studies have shown that when the basalt content reaches 0.4%, the high temperature stability of the 6 mm chopped basalt fiber mixture is the best, which is 1.8 times that of the ordinary asphalt mixture [31].Table 12
Result of rutting test.
Mixture type45 min deflection (mm)60 min deflection (mm)Dynamic stability (times·mm−1)Fiber-free SBS1.771.992884Basalt fiber SBS1.551.743316TPS1.621.813298Technical standard－－≥3000


## 4.3.2. Water Stability

Relevant research shows that the water stability of 6 mm fiber asphalt mixture with 0.2% content is the best [31]. The water stability test results of three asphalt mixtures in this test are shown in Tables 13–15. Tables 13–15 show that the three performances of 0.25% basalt fiber SBS drainage asphalt mixture are the best. The residual stability, freeze-thaw splitting strength ratio, and immersion dispersion loss of 0.25% basalt fiber SBS drainage asphalt mixture are 2.7%, 5.6%, and 4.9% higher than those of TPS drainage asphalt mixture, respectively, and 8.6%, 8.5%, and 8.5% higher than those of nonfiber SBS drainage asphalt mixture. The reason is that, similar to the high temperature stability of fiber reinforced drainage asphalt mixture, the addition of fiber increases the proportion of structural asphalt, the adhesion between asphalt and aggregate is enhanced, and the erosion of water is weakened. In addition, the network structure formed by fiber in the mixture increases the strength of the mixture. In addition, the raw material test shows that the moisture absorption of basalt fiber is poor, which can avoid its expansion at the interface and improve the water stability of drainage asphalt mixture.Table 13
Results of immersion Marshall test.
Mixture typeFlood 0.5 h degree of stability (kN)Flood 48Hd degree of stability (kN)Residual stability (%)Fiber-free SBS6.024.9181.60.25% fiber SBS7.767.090.2TPS6.575.7587.5Technical standard－－≥75Table 14
Test results of freeze-thaw splitting.
Mixture typeSplitting strength of unfrozen specimen (MPa)Splitting strength of freeze-thaw specimens (MPa)Splitting intensity ratio (%)Fiber-free SBS0.600.4778.2Basalt fiber SBS0.730.6386.7TPS0.670.5481.1Technical standard－－≥75Table 15
Flight test results.
Mixture typeStandard dispersion loss (%)Loss of immersion dispersion (%)Fiber-free SBS11.120.00.25% fiber SBS6.711.5TPS9.816.4


## 4.3.3. Low Temperature Crack Resistance

Low temperature crack resistance test results are shown in Table16; the analysis in Table 16 shows that the flexural stiffness modulus of basalt fiber SBS drainage asphalt mixture is the smallest, which is 5.7% and 10.2% lower than that of fiber-less SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. This shows that the greater the energy required for material failure, the better the crack resistance at low temperature. The maximum flexural tensile strain of basalt fiber SBS drainage asphalt mixture is the largest, which is 9.5% and 15.3% higher than that of nonfiber SBS drainage asphalt mixture and TPS drainage asphalt mixture, respectively. It shows that the higher the strain is, the better the resistance to low temperature deformation is. Cheng et al. studied the effect of basalt fiber content on the pavement performance of large-porosity asphalt mixture and found that basalt fiber could improve the splitting tensile strength of large-porosity asphalt mixture before and after freezing and thawing, indicating that basalt fiber had excellent low-temperature crack resistance [32]. The low temperature crack resistance of basalt fiber SBS drainage asphalt mixture is the best, and TPS drainage asphalt mixture is the worst. The low temperature crack resistance of SBS modified asphalt is better than that of TPS modified asphalt. Basalt fiber SBS drainage asphalt mixture has the best low temperature crack resistance. Analyzing the reasons, the fibers overlap with each other in the mixture space to form a fiber grid. Under low temperature conditions, it plays a role of tackifying, inhibits the flow of free asphalt, and enhances the bonding with aggregate. The elastic modulus of fiber is high, and the tensile strength is large, which can improve the overall performance of the mixture. In addition, fiber grid can spread the pavement load inside the mixture, reduce stress concentration, and prevent pavement cracking.Table 16
Test results of low temperature bending.
Type of asphalt mixtureFlexural tensile strength (MPa)Maximum bending strength (με)Bending stiffness modulus (%)Fiber-free SBS7.353197.32298.6Basalt fiber SBS7.593503.52166.4TPS7.333037.12413.7Technical standard——≥2000


## 4.4. Drainage Performance Analysis

### 4.4.1. Connecting Void

The voids of drainage asphalt mixture include connected voids, semiconnected voids, and closed voids, as shown in Figure8. The semiconnected voids can store water but cannot drain. The closed voids can neither store water nor drain. Only the connected voids can play the role of drainage. Therefore, it is extremely important to study the connected voids for drainage asphalt pavement.The analysis of the test results is shown in Table17. The void ratios of the three kinds of drainage asphalt mixtures are maintained at about 20%, which meets the requirements of the initial void ratio of the drainage pavement. The connectivity porosity is above 15%, so the three drainage asphalt mixtures all meet the requirements of drainage function of drainage pavement.Table 17
Connected void fraction test results.
Type of asphalt mixturePercentage of void (%)Connecting porosity (%)Fiber-free SBS20.117.34Basalt fiber SBS19.615.97TPS19.916.45


### 4.4.2. Analysis of Seepage Test

The seepage test results are shown in Table18. The analysis of the test results shows that the seepage coefficient of basalt fiber drainage asphalt mixture is the smallest. The reason for the analysis is that the incorporation of fibers reduces the void ratio of the mixture. At the same time, the adsorption of fibers on asphalt increases the amount of asphalt and decreases the void ratio. However, the main factor affecting the void ratio is the gradation type, so the number of fibers and asphalt have little effect on the results, which also meets the specification requirements and has good drainage performance.Table 18
Seepage test results.
Type of asphalt mixtureThe first timing (s)The second timing (s)Water permeability coefficient (mL·min−1)Fiber-free SBS1.47.24137.9Basalt fiber SBS1.27.53809.5TPS1.4 y7.44000.0Specification requirement－－>3600


## 4.4.1. Connecting Void

The voids of drainage asphalt mixture include connected voids, semiconnected voids, and closed voids, as shown in Figure8. The semiconnected voids can store water but cannot drain. The closed voids can neither store water nor drain. Only the connected voids can play the role of drainage. Therefore, it is extremely important to study the connected voids for drainage asphalt pavement.The analysis of the test results is shown in Table17. The void ratios of the three kinds of drainage asphalt mixtures are maintained at about 20%, which meets the requirements of the initial void ratio of the drainage pavement. The connectivity porosity is above 15%, so the three drainage asphalt mixtures all meet the requirements of drainage function of drainage pavement.Table 17
Connected void fraction test results.
Type of asphalt mixturePercentage of void (%)Connecting porosity (%)Fiber-free SBS20.117.34Basalt fiber SBS19.615.97TPS19.916.45


## 4.4.2. Analysis of Seepage Test

The seepage test results are shown in Table18. The analysis of the test results shows that the seepage coefficient of basalt fiber drainage asphalt mixture is the smallest. The reason for the analysis is that the incorporation of fibers reduces the void ratio of the mixture. At the same time, the adsorption of fibers on asphalt increases the amount of asphalt and decreases the void ratio. However, the main factor affecting the void ratio is the gradation type, so the number of fibers and asphalt have little effect on the results, which also meets the specification requirements and has good drainage performance.Table 18
Seepage test results.
Type of asphalt mixtureThe first timing (s)The second timing (s)Water permeability coefficient (mL·min−1)Fiber-free SBS1.47.24137.9Basalt fiber SBS1.27.53809.5TPS1.4 y7.44000.0Specification requirement－－>3600


## 4.5. Microscopic Mechanism Analysis

### 4.5.1. Scanning Electron Microscope Analysis

(1) Analysis on Strengthening Effect of Bonding Interface between Fiber and Asphalt. The OGFC-13 asphalt mixture belongs to the skeleton void structure, and the interlocking force of mineral particles is not strong, mainly relying on the bonding effect of binder. In related studies, it is proposed that the combination mode between fiber and asphalt mixture is mainly mechanical connection and infiltration adsorption. Since the fiber surface is not smooth but has a certain roughness, convex and concave, the pits on the surface of asphalt and fiber form a more compact combination [33]. It can be seen from Figure 13 that the mineral aggregate in the nonfiber SBS drainage asphalt mixture is not closely bonded to the asphalt, and there are a large number of voids. Therefore, with the increase of temperature and the erosion of water, the mineral aggregate is easy to peel off from the asphalt surface, resulting in rutting, pits, and other damage. The fiber diameter is small, and the mixed mixture has a huge specific surface area. The fiber surface is adsorbed by a large amount of asphalt, and the root is closely bonded with the asphalt mixture. This shows that the infiltration between fiber and asphalt liquid is great, and the bonding degree of the interface between the two is significantly greater than that between the mineral aggregate of nonfiber asphalt mixture and asphalt.Figure 13
Bonding interface between asphalt and ore in fiber free asphalt mixture.Figure14 shows that fiber and mixture are combined by mechanical connection and infiltration adsorption. Basalt fiber has a certain roughness and unevenness. Asphalt phase extends to the pits on the surface of fiber phase, forming a closer combination. When asphalt phase contacts with fiber, it is surface contact, resulting in the effect equivalent to mechanical anchor sum. It has a large bite force and improves the high temperature stability of drainage asphalt mixture by improving the bond strength. Transition layer refers to the structural asphalt layer, and the transition layer between free asphalt and fiber can connect two phases. There are two forms of asphalt in the mixture. One is the constrained structural asphalt, and the other is the free asphalt without contact with the entity. The constrained structural asphalt has stronger bonding force. The adsorption of fiber makes free asphalt transform into transition layer structure asphalt at the contact point of the two. The fiber with large specific surface area will form a large number of transition layers in the mixture, and the proportion of structural asphalt with higher cohesive force increases. Therefore, the addition of fiber can improve the high and low temperature stability and water stability of drainage asphalt mixture. The incorporation of basalt fiber changes the effect of each phase interface of drainage asphalt mixture and improves the road performance of drainage asphalt mixture.Figure 14
The bonding interface between basalt fibers and bitumen.(2) Effect of Fiber on Reinforcement and Crack Resistance of Drainage Asphalt Mixture. It can be seen from Figure 15 that the splitting failure surface of fiber-free SBS drainage asphalt mixture has many cracks and different stripping levels. The mineral material is in a state of separation, and the connection is extremely weak. The microscopic picture of drainage asphalt mixture with basalt fiber is shown in Figure 16.Figure 15
Breakdown of asphalt mixture without fiber drainage.
(a)(b)Figure 16
Fracture of basalt fiber drainage asphalt mixture.
(a)(b)The main failure mode of asphalt mixture in use is shear failure, which starts from the internal voids of asphalt mixture and spreads along the original voids, especially the interface between asphalt and mineral [33]. The basalt overlaps vertically and horizontally in the mixture to form a spatial network structure. When the asphalt pavement is subjected to load, the spatial network structure can transfer stress and reduce stress concentration, which is similar to the role of reinforcement in reinforced concrete. It can also inhibit the free movement of particles, play a ‘hoop’ role in the mixture, and improve the overall mechanical properties of drainage asphalt pavement. It can be seen from the photographs of the fiber fracture that the fiber is interspersed in the asphalt mixture, and the root is absorbed by the asphalt and buried in the internal of the asphalt mixture, indicating that the basalt fiber and the asphalt mixture have strong adhesion and crack resistance.


## 4.5.1. Scanning Electron Microscope Analysis

(1) Analysis on Strengthening Effect of Bonding Interface between Fiber and Asphalt. The OGFC-13 asphalt mixture belongs to the skeleton void structure, and the interlocking force of mineral particles is not strong, mainly relying on the bonding effect of binder. In related studies, it is proposed that the combination mode between fiber and asphalt mixture is mainly mechanical connection and infiltration adsorption. Since the fiber surface is not smooth but has a certain roughness, convex and concave, the pits on the surface of asphalt and fiber form a more compact combination [33]. It can be seen from Figure 13 that the mineral aggregate in the nonfiber SBS drainage asphalt mixture is not closely bonded to the asphalt, and there are a large number of voids. Therefore, with the increase of temperature and the erosion of water, the mineral aggregate is easy to peel off from the asphalt surface, resulting in rutting, pits, and other damage. The fiber diameter is small, and the mixed mixture has a huge specific surface area. The fiber surface is adsorbed by a large amount of asphalt, and the root is closely bonded with the asphalt mixture. This shows that the infiltration between fiber and asphalt liquid is great, and the bonding degree of the interface between the two is significantly greater than that between the mineral aggregate of nonfiber asphalt mixture and asphalt.Figure 13
Bonding interface between asphalt and ore in fiber free asphalt mixture.Figure14 shows that fiber and mixture are combined by mechanical connection and infiltration adsorption. Basalt fiber has a certain roughness and unevenness. Asphalt phase extends to the pits on the surface of fiber phase, forming a closer combination. When asphalt phase contacts with fiber, it is surface contact, resulting in the effect equivalent to mechanical anchor sum. It has a large bite force and improves the high temperature stability of drainage asphalt mixture by improving the bond strength. Transition layer refers to the structural asphalt layer, and the transition layer between free asphalt and fiber can connect two phases. There are two forms of asphalt in the mixture. One is the constrained structural asphalt, and the other is the free asphalt without contact with the entity. The constrained structural asphalt has stronger bonding force. The adsorption of fiber makes free asphalt transform into transition layer structure asphalt at the contact point of the two. The fiber with large specific surface area will form a large number of transition layers in the mixture, and the proportion of structural asphalt with higher cohesive force increases. Therefore, the addition of fiber can improve the high and low temperature stability and water stability of drainage asphalt mixture. The incorporation of basalt fiber changes the effect of each phase interface of drainage asphalt mixture and improves the road performance of drainage asphalt mixture.Figure 14
The bonding interface between basalt fibers and bitumen.(2) Effect of Fiber on Reinforcement and Crack Resistance of Drainage Asphalt Mixture. It can be seen from Figure 15 that the splitting failure surface of fiber-free SBS drainage asphalt mixture has many cracks and different stripping levels. The mineral material is in a state of separation, and the connection is extremely weak. The microscopic picture of drainage asphalt mixture with basalt fiber is shown in Figure 16.Figure 15
Breakdown of asphalt mixture without fiber drainage.
(a)(b)Figure 16
Fracture of basalt fiber drainage asphalt mixture.
(a)(b)The main failure mode of asphalt mixture in use is shear failure, which starts from the internal voids of asphalt mixture and spreads along the original voids, especially the interface between asphalt and mineral [33]. The basalt overlaps vertically and horizontally in the mixture to form a spatial network structure. When the asphalt pavement is subjected to load, the spatial network structure can transfer stress and reduce stress concentration, which is similar to the role of reinforcement in reinforced concrete. It can also inhibit the free movement of particles, play a ‘hoop’ role in the mixture, and improve the overall mechanical properties of drainage asphalt pavement. It can be seen from the photographs of the fiber fracture that the fiber is interspersed in the asphalt mixture, and the root is absorbed by the asphalt and buried in the internal of the asphalt mixture, indicating that the basalt fiber and the asphalt mixture have strong adhesion and crack resistance.


## 5. Conclusion

(1)
Compared with TPS drainage asphalt mixture and nonfiber SBS drainage asphalt mixture, basalt fiber SBS drainage asphalt mixture can better improve the high temperature stability of drainage asphalt mixture. 0.25% basalt fiber SBS drainage asphalt mixture has the best three properties, indicating that its water stability is the best; the maximum bending strain of basalt fiber SBS drainage asphalt mixture is the largest, which shows that its resistance to low temperature deformation is better than the other two kinds of drainage asphalt mixture.(2)
The optimum asphalt content of BS drainage asphalt mixture with basalt fiber content of 0%, 0.15%, 0.25%, and 0.35% is 4.9%, 5.05%, 5.15%, and 5.2%, respectively. When the content of basalt fiber is 0.25%, the stability reaches the peak, and the leakage loss rate and the dispersion loss rate reach the minimum. Therefore, 0.25% is selected as the optimal content of basalt fiber.(3)
The high temperature performance, water stability, low temperature performance, and drainage performance of 0.25% basalt fiber SBS drainage asphalt mixture can meet the specification requirements, and the performance is better. Compared with no fiber SBS drainage asphalt mixture and TPS drainage asphalt mixture, the dynamic stability, residual stability, and freeze-thaw splitting strength are improved. Dip loss and bending stiffness modulus decrease. The connectivity porosity of basalt fiber SBS drainage asphalt Marshall specimen is 15.97%, and the permeability coefficient is 3809.5 mL/min, which meets the requirements of the specification. Therefore, SBS drainage asphalt mixture with basalt fiber has good performance and can be applied in drainage pavement.(4)
The root of basalt fiber mixed with asphalt mixture is closely bonded with the mixture, and the bonding degree of the interface between basalt fiber and asphalt mixture is significantly greater than that of the mineral aggregate and asphalt mixture without basalt fiber, which has a large bite force and improves the bonding strength, indicating that the infiltration effect between basalt fiber and asphalt is good; and the bonding interface bonding degree of the two is significantly greater than that of the fiber-free asphalt mixture mineral and asphalt joint. The formation of network structure in the mixture inhibits the further diffusion of cracks and improves the high and low temperature performance and water stability of drainage asphalt mixture.



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*Source: 7846499-2021-12-13.xml*