With the rapid development of asphalt pavement, the drainage capacity of asphalt pavement is becoming more and more demanding. Therefore, it is imperative to study the permeable asphalt mixture. The air voids and the connected air voids are the main factors affecting the drainage function and low-temperature performance of asphalt pavement. In order to solve the drainage and low-temperature cracking problem, it is proposed to incorporate a certain amount of polyester fiber into the permeable asphalt mixture. This paper studies the air voids and low-temperature performance of asphalt mixture with different polyester fiber contents. It is concluded that with the increase of polyester fiber content, both the air voids and the connected air voids decrease first and then increase and reach the minimum value when the polyester fiber content is 0.4%. At this time, the low-temperature crack resistance of the permeable polyester fiber asphalt mixture is also the best.
Asphalt pavement has the advantages of smooth surface, comfortable driving, low noise, and no dust. It has become the main form of high-grade road pavement. However, the ordinary asphalt pavement has poor water permeability and the road surface-gathered water cannot be eliminated in time, which leads to a decline of road surface antisliding performance and affects driving safety [
In permeable asphalt mixture, it is difficult to satisfy the high viscosity requirement by using ordinary modified asphalt alone, but the viscosity can be increased by incorporating with polyester fiber [
The permeable asphalt mixture is a kind of special hot asphalt mixture, which has the characteristics of high voids, high content coarse aggregate, and good aggregate contact performance. Compared with densely packed asphalt mixtures, permeable asphalt mixtures have a higher proportion of voids, which is obtained by reducing sand and mineral fillers [
The permeable asphalt mixture can quickly remove the road surface water due to the existence of more connected voids, but the semiclosed voids will leave some water in the voids, which will cause frost heaving damage of asphalt pavement at low temperature. Low-temperature cracking is one of the main diseases of asphalt pavement, which greatly affects the function of pavement. Some studies have shown that polyester fiber has a certain effect on the low-temperature crack resistance of the asphalt mixture [
In summary, the research on permeable asphalt mixture mostly focuses on the analysis of the aggregate contact surface of the mixture and some literatures have studied the high-temperature performance and water stability of permeable asphalt mixture. However, little research has reported the effect of polyester fiber on the porosity and low-temperature properties of permeable asphalt mixtures. Therefore, this paper gives reasonable polyester fiber content and void content by analyzing the influence of polyester fiber content on air voids and low-temperature performance and provides guidance for paving permeable asphalt mixture pavement.
The coarse and fine aggregates are, respectively, rolled limestone gravel and mechanical limestone sand produced by Huainan, which are clean, dry, nonweathered, and free of impurities. They have enough strength and wear resistance, the needle-like content is small, and the particles are angular. Filler refers to mineral powder with a particle size of less than 0.075 mm. The mineral powder must be grounded from the hydrophobic stone, such as strong-basic rock in limestone or magmatic rock, and can flow freely from the silo. The physical properties and chemical composition of the mineral powder are shown in Tables
Physical properties of mineral powder.
Project | Measured value |
---|---|
Apparent density (g·cm−3) | 2.15 |
Water content (%) | 0.92 |
Hydrophilic coefficient | 0.90 |
Plasticity index | 3.60 |
Chemical composition of mineral powder.
Chemical constituents | Si2O | Al2O3 | Fe2O3 | MgO | CaO | K2O | Na2O | Other |
---|---|---|---|---|---|---|---|---|
Content (%) | 4.38 | 1.56 | 0.76 | 0.49 | 48 | 0.14 | 0.03 | 44.64 |
In the design of permeable asphalt pavement materials, the requirements for asphalt are high and high viscosity-modified asphalt should be selected. At present, there are two types of high viscosity-modified asphalts used in China: one is finished high viscosity-modified asphalt and the other is directly adding modifier into the asphalt mixture. However, due to the relatively high cost of the two types of asphalt, the promotion and application of permeable asphalt pavement is greatly limited. Therefore, the test uses the SBS-modified asphalt [
Technical indexes of SBS-modified asphalt.
Technical index | Measured values |
---|---|
Penetration (25°C, 100 g, 5 s)/0.1 mm | 48.1 |
Ductility (25°C, 5 cm/min)/cm | >100 |
Softening point (°C) | 81.5 |
Relative density | 1.043 |
In asphalt mixture, the polyester fiber forms a three-dimensional network structure which mainly plays a reinforcing role in increasing the asphalt film thickness of the aggregate surface and enhances the adhesion between the aggregate and the asphalt [
Polyester fiber.
Technical indexes of polyester fiber.
Project | Performance | Pavement requirements |
---|---|---|
Length (mm) | 12 ± 2 | ≥3 |
Diameter ( |
20 ± 2.5 | 20 ± 5 |
Strength (MPa) | 500∼680 | ≥500 |
Elongation at break (%) | 15∼35 | ≥15 |
Young’s modulus (GPa) | >13.5 | — |
Proportion | 1.36 | 1.36 ± 0.05 |
Melting point (°C) | 259 | ≥258 |
Air void is an important indicator that affects the structural function of the permeable asphalt mixture. However, the air voids of the permeable asphalt mixture are closely related to the rainfall intensity. Table
Air void requirement in different rainfall intensities.
Rainfall intensity | Rainfall (mm·h−1) | Air voids (%) |
---|---|---|
Rainstorm | ≥16.0 | ≥22.0 |
Heavy | 8.1∼15.9 | 18.7∼21.6 |
Moderate | 2.6∼8.0 | 14.1∼18.6 |
Light | ≤2.6 | — |
It can be seen from Table
The air voids of the permeable asphalt mixture directly affect the drainage function, but the choice of mineral aggregate gradation determines the air voids [
Aggregate gradation.
The fiber can improve the water immersion stability of the asphalt mixture, and the enhancement effect is related to the fiber type. In the experiment of the influence of salt on water stability of the fiber asphalt mixture, Ji [
Although the Marshall test is commonly used to determine the mix proportion of the asphalt mixture [
Comparing (a) before and (b) after the beaker test.
Schellenberg binder drainage test results.
Polyester fiber content (%) | Run-off loss at different asphalt content (%) | ||||
---|---|---|---|---|---|
3.9 | 4.4 | 4.9 | 5.4 | 5.9 | |
0 | 0.037 | 0.040 | 0.043 | 0.057 | 0.063 |
0.3 | 0.023 | 0.027 | 0.033 | 0.033 | 0.060 |
0.35 | 0.020 | 0.027 | 0.037 | 0.040 | 0.043 |
0.4 | 0.020 | 0.027 | 0.033 | 0.040 | 0.053 |
0.45 | 0.020 | 0.023 | 0.027 | 0.033 | 0.043 |
0.5 | 0.043 | 0.047 | 0.053 | 0.057 | 0.060 |
According to the results of the Schellenberg binder drainage test, the smaller the draindown of binder, the larger the film thickness of the asphalt on the aggregate surface and the better the bond performance between the aggregates. The incorporation of polyester fiber can reduce the draindown of binder of asphalt and enhance the adhesion between aggregate and asphalt. The main reason for this phenomenon is that the polyester fiber has the characteristics of lipophilicity and large specific surface area and can adsorb the free asphalt to form the asphalt film and reduce the loss of binder drainage. However, in the case of a certain amount of fiber, the adsorption of the fiber on the asphalt is basically the same as the effect of obstructing the flow. As the amount of the asphalt increases, the leakage loss increases. Therefore, there is a certain relationship between the amount of polyester fiber and the amount of asphalt. Combined with the test results of Zhang and Wu [
The relation between the fiber content and optimum asphalt content.
There are three types of air voids, connected air voids, semiconnected air voids, and closed air voids. As shown in Figure
Air void types in the permeable polyester fiber asphalt mixture.
The size of connected air voids directly determines the strength and the drainage capacity of the permeable polyester fiber asphalt mixture [
Bending test is one of the main methods for evaluating the low-temperature performance of the asphalt mixture. The size of the beam specimen is 250 mm × 30 mm × 50 mm, which is cut from a 300 mm × 300 mm × 50 mm plate specimen formed by a wheel rolling method, as shown in Figure
Specimen.
The test results of air voids and connected air voids of the permeable asphalt mixture with different polyester fiber contents are shown in Table
Connected air voids and air voids relationship under different polyester fiber dosage.
Fiber content (%) | Asphalt content (%) | Test piece height (%) | Air voids (%) | Connected air voids (%) | ||
---|---|---|---|---|---|---|
Single value | Average value | Single value | Average value | |||
0 | 4.95 | 64.8 | 19.8 | 19.7 | 15.1 | 15.4 |
64.6 | 20.3 | 14.8 | ||||
64.3 | 19.2 | 14.6 | ||||
63.7 | 19.6 | 17.1 | ||||
|
||||||
0.3 | 5.0 | 64.8 | 19.5 | 19.4 | 15.2 | 15.1 |
64.8 | 19.2 | 15.0 | ||||
64.6 | 19.5 | 14.8 | ||||
64.7 | 19.5 | 15.3 | ||||
|
||||||
0.35 | 5.05 | 64.5 | 19.2 | 19.3 | 14.6 | 15.0 |
64.9 | 19.6 | 15.4 | ||||
64.6 | 19.3 | 14.8 | ||||
64.3 | 19.1 | 15.0 | ||||
|
||||||
0.4 | 5.1 | 64.2 | 18.4 | 19.1 | 14.0 | 14.9 |
63.7 | 19.5 | 15.4 | ||||
63.5 | 19.6 | 15.1 | ||||
63.4 | 19.0 | 15.2 | ||||
|
||||||
0.45 | 5.15 | 64.6 | 19.3 | 19.6 | 14.5 | 15.2 |
63.6 | 19.9 | 15.5 | ||||
63.6 | 20.0 | 16.3 | ||||
64.2 | 19.1 | 14.3 | ||||
|
||||||
0.5 | 5.2 | 63.7 | 18.3 | 19.7 | 14.0 | 15.3 |
64.2 | 21.1 | 17.1 | ||||
64.7 | 19.6 | 15.0 | ||||
64.8 | 19.8 | 15.0 |
It can be seen from Table
According to Table
Relation between total air voids and polyester fiber content.
Relation between connected air voids and polyester fiber content.
It can be seen from Figures
The major reason for this phenomenon is that, in the case where the content of the polyester fiber is little, it can be uniformly distributed in the mixture to fill the internal void of the mixture. When the polyester fiber content increases to 0.4%, the uniform distribution of the polyester fiber in the asphalt mixture reaches a maximum, and the number of filled voids also reaches a maximum, and the corresponding air voids and connected air voids reach a minimum. However, with the polyester fiber content exceeding 0.4%, the air voids of the asphalt mixture gradually increase [
Bending test is used to analyze the effect of polyester fiber on the low-temperature crack resistance of the permeable asphalt mixture. The test results are shown in Table
Bending testing results at low temperature.
Fiber content (%) | Asphalt content (%) | Air voids (%) | Flexural tensile strength (MPa) | Maximum flexure tensile strain ( |
Flexural stiffness modulus (MPa) | |||
---|---|---|---|---|---|---|---|---|
Single value | Average value | Single value | Average value | Single value | Average value | |||
0 | 4.95 | 19.7 | 2.34 (−) | 3.57 | 1785 (−) | 1575 | 1311 (−) | 2273 |
3.60 | 1575 | 2286 | ||||||
3.87 | 1523 | 2542 | ||||||
3.24 | 1682 | 1991 | ||||||
|
||||||||
0.3 | 5.0 | 19.4 | 5.19 | 5.02 | 3045 (−) | 2538 | 1704 | 1896 |
4.93 | 2573 | 1916 | ||||||
5.06 | 2415 | 2095 | ||||||
4.91 | 2625 | 1870 | ||||||
|
||||||||
0.35 | 5.05 | 19.3 | 6.02 | 5.87 | 3203 | 3308 | 1880 | 1777 |
5.84 | 3518 | 1660 | ||||||
5.70 | 3098 | 1840 | ||||||
5.90 | 3413 | 1729 | ||||||
|
||||||||
0.4 | 5.1 | 19.1 | 6.82 | 6.66 | 4043 | 4174 | 1687 | 1594 |
8.19 (−) | 4148 | 1975 (−) | ||||||
6.84 | 4305 | 1589 | ||||||
6.32 | 4200 | 1505 | ||||||
|
||||||||
0.45 | 5.15 | 19.6 | 4.60 | 4.48 | 2258 | 2014 | 2038 | 2121 |
4.61 | 1756 | 2625 | ||||||
4.33 | 1890 | 2291 | ||||||
4.38 | 2153 | 2035 | ||||||
|
||||||||
0.5 | 5.2 | 19.7 | 4.26 | 4.24 | 2100 | 2266 | 2029 | 1886 |
4.37 | 2553 | 1712 | ||||||
3.95 | 2363 | 1672 | ||||||
4.36 | 2048 | 2129 |
It can be seen from Table
The maximum flexure tensile strain is an index to measure the low-temperature deformation ability of the asphalt mixture. The larger the maximum flexure tensile strain, the larger the deformation range of the asphalt mixture and the better the low-temperature crack resistance. It can be seen from Table
The drainage effect of permeable asphalt pavement depends on the content of air voids. The higher the air void content, the better the drainage effect and the poorer low-temperature crack resistance. As can be seen from Table
According to the low-temperature bending test results, the relationship among the flexural tensile strength, the flexural stiffness modulus, and the polyester fiber content of the permeable asphalt mixture are shown in Figures
Relation between flexural tensile strength and polyester fiber content.
Relation between flexural stiffness modulus and polyester fiber content.
The bending failure of asphalt mixture girders is mainly caused by cracking along the interface of aggregate. The encountered large particles during cracking produce extrusion and shear and cause damage to the SBS-modified asphalt mixture under low-temperature conditions. It can be seen that good interface strength is an important guarantee to prevent cracking of the mixture [
It can be seen from Figure
Through the comprehensive analysis of Figures
It can also be seen from Table
The relationship between the connected air voids and air voids of the permeable polyester fiber asphalt mixture and the relationship between the air voids and the flexural tensile strength are shown in Figures
Relation between connected air voids and air voids.
Relation between flexural tensile strength and air voids.
It can be seen from Figure
It can be seen from Figure
This paper mainly analyzes the influence of the polyester fiber content on the low-temperature crack resistance and air voids of the permeable asphalt mixture and obtains the following main conclusions. The air voids and connected air voids of the permeable polyester fiber asphalt mixture decrease first and then increase with the increase of the polyester fiber content; the air voids and connected air voids reach the minimum values of 19.1% and 14.9% when the polyester fiber content is 0.4%. The flexural tensile strength of the permeable polyester fiber asphalt mixture reaches the maximum value when the content of polyester fiber is 0.4%, indicating that the mixture has the strongest resistance to low-temperature damage and the best crack resistance at low temperature. Air void is an important factor affecting the flexural tensile strength of the permeable polyester fiber asphalt mixture. The flexural tensile strength decreases with the increase of air voids. At the air void of 19.1%, the flexural tensile strength reaches the maximum value. Adding proper amount of polyester fiber and choosing reasonable air voids can improve the low-temperature crack resistance of the permeable polyester fiber asphalt mixture.
The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.
The authors declare that they have no conflicts of interest.
This research was funded by the Natural Science Research Project of Colleges and Universities in Anhui Province (no. KJ2017A096).