The high-performance asphalt materials are used to replace the ordinary road asphalt that cannot meet the requirements of natural environment and traffic situation, which is the effective way to solve poor asphalt pavement durability. In this paper, polyphosphoric acid- (PPA-) modified asphalt and polyphosphoric acid (PPA)/styrene-butadiene-styrene (SBS) composite-modified asphalt with different PPA content were prepared by using two-type asphalt. The effect of PPA modifier on asphalt was analyzed by using the creep elastic recovery rate, accumulating strain and creep modulus tests. The results showed that asphalt types and the PPA could significantly improve the elastic recovery rate of asphalt, reduce the cumulative strain and creep stiffness of the viscosity part, improve the high-temperature performance, and reduce the permanent deformation of the asphalt under repeated load. The high-temperature performance and low-temperature performance of PPA-modified asphalt were studied by the chemical and physical modification techniques. The advantages of modified asphalt are well developed while reducing the price of it, which has important technical and economic significance.
The main tasks of contemporary highway construction study are to optimize pavement structure, apply high-performance materials, improve construction technology, and decrease risk assessment [
According to the modification principle of polymer on asphalt performance, modified asphalt can be divided into reactive-modified asphalt and swelling dispersing-modified asphalt [
PPA has been used as a modifying agent to produce modified asphalt for decades [
Masson used the methods of gel permeation chromatography, nuclear magnetic resonance, and thin-layer chromatography to study the evolution process of chemical reaction of PPA in asphalt. During the reaction of PPA with asphalt, esters and salts are produced in the active part of asphalt, which ionizes saturated aromatic aromatization, aromatic cyclization, and colloidal components in asphalt. Several possible reaction mechanism hypotheses are proposed, and new asphaltene micelles were prepared. In addition, PPA had the effect of activating a part of asphalt double bond to have cross-bonding, extending, and strengthening asphaltene network structure [
Different base asphalts were used to study the influence of PPA addition on asphalt PG high temperature grade and four components. Experimental data indicated that the addition of 2% PPA could improve the high temperature grade of asphalt. The addition of PPA could increase the content of asphaltene by over 50% [
The rheological performance and aging resistance of PPA/SBS-modified asphalt were studied. Compared with sulfur/SBS composite-modified asphalt, PPA/SBS composite-modified asphalt has better high temperature stability, but poor low temperature performance. This phenomenon can be improved by increasing the content of SBS-modifying agent [
The effects of PPA modification on asphalt binders had been studied [
Therefore, different contents of PPA were added to SBS-modified asphalt in this paper. Combined with chemical modification and physical modification technology, the high-temperature performance and low-temperature performance of PPA-modified asphalt and PPA/SBS composite-modified asphalt were studied. In terms of reducing the price of modified asphalt and giving full play to the advantages of modified asphalt, this study has important technical and economic significance.
Experimental method: different proportions of SBS or SBS + PPA material were added to SK90 and ZH90 bitumen to produce SBS-modified bitumen or SBS/PPA composite bitumen. Through high temperature test and low temperature test, the material property changes of SBS-modified asphalt or SBS/PPA composite asphalt could be obtained after the corresponding test. The experimental process is shown in Figure
Whole experimental process.
The SK90 and Zhenhai 90 (ZH90) were selected as two asphalt binders in this paper. According to
The results of performance tests and four component analysis of asphalt binders.
Physical properties and chemical component | SK90 | ZH90 |
---|---|---|
Penetration (25°C, 0.1 mm) | 86.5 | 81.0 |
Softening point (°C) | 45.5 | 46.0 |
Ductility (15°C, cm) | >100 | >100 |
Penetration ratio (%) | 72.0 | 70.6 |
Ductility (cm) | 9.3 | 8.0 |
Mass loss (%) | 0.9 | 1.0 |
Performance grade (°C) | 58–22 | 58–22 |
Stiffness modulus (MPa, −12°C) | 231 | 243 |
Creep rate (MPa/S, −12°C) | 0.351 | 0.342 |
Asphaltene (%) | 8.63 | 7.34 |
Resin (%) | 17.40 | 29.28 |
Aromatics (%) | 44.78 | 36.62 |
Saturates (%) | 24.20 | 23.41 |
Industrial PPA with H2PO3 content of 105% was selected as a modifying agent in this research. Its main technical indexes are shown in Table
Technical index of PPA.
Technical index | 105% H2PO3 |
---|---|
P2O5 concentration | 74.2 |
Surface tension (N/cm2) | 74 × 10−5 |
Specific heat capacity (J/g·°C) | 1.498 |
Boiling point (°C) | 354 |
Yueyang Petrochemical 1301 (YH791) was selected as an SBS-modifying agent in this research. Its main performance indexes are shown in Table
Performance index of YH791 modifying agent.
Item | YH791 |
---|---|
Structure | Line-type |
PS/PB | 30/70 |
Percentage of liquid volume (%) | 0 |
300% stretching stress (MPa) | 1.90 |
Elongation (%) | 700 |
Permanent deformation (%) | 45 |
Hardness | 60 |
Total ash (%) | 0.20 |
When base asphalt was heated to 160°C, PPA-modifying agent which accounted for 1%, 1.5%, 2%, and 2.5% of the asphalt mass was added. FLUCK high-speed shearing emulsifying machine was used to shear it at the speed of 1000 r/min for 20 minutes, and then PPA-modified asphalt with different PPA contents was prepared, as shown in Figure
Preparation of PPA-modified asphalt.
The base asphalt was heated up to 180°C; solubilizer and SBS-modifying agent which accounted for 4.5% of base asphalt mass were added. FLUCK high-speed shearing emulsifying machine was used to operate at the speed of 4000 r/min for 40 min, and then stabilizer was added to shear for 5 min. Finally, it was put into a constant temperature oven at 160°C to grow for 2 hours, as shown in Figure
Preparation of SBS-modified asphalt.
The base asphalt was heated up to 180°C; solubilizer and SBS-modifying agent which accounted for 3.5% of base asphalt mass were added. FLUCK high-speed shearing emulsifying machine was used to operate at the speed of 4000 r/min for 40 min, and then stabilizer was added to shear for 5 min. It was put into a constant temperature oven at 160°C to grow for 1.5 hours. Then, PPA which accounted for 0.5%, 1.0%, 1.5%, and 2.0% of asphalt mass was added to it to be sheared at the speed of 1000 r/min for 10 min, as shown in Figure
Preparation of PPA/SBS compound-modified asphalt.
Dynamic shearing rheometer was applied to PPA-modified asphalt with different modifying agent contents, SBS-modified asphalt, and PPA/SBS compound-modified asphalt with different PPA contents to carry out high-temperature repeated creep test. The test temperature of modified asphalt was 60°C, load intensity was 100 kPa, load was 1 s, unload was 9 s, and repetitive cycle quantity 100 times.
SK90 base asphalt and ZH90 base asphalt were selected. PPA that was 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% of asphalt mass was added to record the accumulated strain values of load and unload on 10 times, 20 times, 30 times, 40 times, 50 times, 60 times, 70 times, 80 times, 90 times, and 100 times, as shown in Figure
Whole process of high-temperature test.
Strain-controlled mode was used in this paper. The test frequency was 10 rad/s and test temperature was from 20°C to 60°C. Temperature sweep test was conducted to PPA-modified asphalt with different modifying agent contents, SBS-modified asphalt, and PPA/SBS compound-modified asphalt with different PPA contents to record the complex modulus and phase angle under every test temperature.
To study the effect of raw materials on the low-temperature performance of PPA-modified asphalt and PPA/SBS compound-modified asphalt, the bending beam rheological (BBR) test was used to test the stiffness modulus
PPA-modifying agent that was 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% of asphalt mass was added to prepare PPA-modified asphalt and compare with base asphalt in terms of the low-temperature performance. First, it was placed in the rolling thin film oven for aging. The aging temperature was 163°C and aging time was 85 min. PAV pressure aging was conducted to the asphalt that had short-term aging to simulate the long-term aging condition of pavement using process. The aging temperature was 100°C, pressure was 2.1 MPa, and aging time was 20 h. Temperature was increased until the flow condition for the specimen with pressure aging and casting was conducted to the asphalt beam test specimen to test the stress-strain characteristics at −6°C, −12°C, −18°C, and −24°C, as shown in Figure
Whole process of low-temperature test.
To study the low-temperature performance of PPA/SBS compound-modified asphalt, SBS-modified asphalt with 3.5% and 4.5% SBS-modifying agent was prepared. In the 3.5% SBS-modified asphalt, PPA modifier that was 0.5%, 1.0%, 1.5%, and 2.0% of asphalt mass was added to prepare PPA/SBS compound-modified asphalt. RTFOT short-term aging test was conducted to SBS-modified asphalt and PPA/SBS compound-modified asphalt with swelling development first, and further PAV pressure aging test was performed on it. Then, asphalt beam specimen was formed. Stiffness modulus
Figure
Accumulated strain of PPA-modified asphalt with the change of load times.
Figure
Influence of PPA mixing amount on the elastic recovery rate of modified asphalt.
The constitutive equation of Burgers model was used to fit stress and strain relationship in the 50th and 51st times of repeated creep-recovery tests to obtain generalized Voigt (Gv) from average values, which was used as the viscous part of creep stiffness modulus and evaluating high-temperature permanent deformation characteristics of asphalt. The test results of two asphalts with different PPA mixing amounts are as shown in Figure
Influence of PPA mixing amount on the Gv value of PPA-modified asphalt.
It can be found by analyzing Figure
Figure
Accumulated strain for PPA/SBS compound-modified asphalt.
Figure
Influence of PPA mixing amount on the elastic recovery rate of PPA/SBS-modified asphalt.
It can be seen from Table
Influence of PPA mixing amount on Gv of PPA/SBS compound-modified asphalt.
PPA mixing amount | Gv (Pa) | |
---|---|---|
SK90 | ZH90 | |
3.5% SBS | 4998 | 5370 |
0.5% PPA + 3.5% SBS | 9531 | 9682 |
1.0% PPA + 3.5% SBS | 10257 | 10092 |
1.5% PPA + 3.5% SBS | 13814 | 13420 |
2.0% PPA + 3.5% SBS | 14432 | 13996 |
4.5% SBS | 10041 | 9985 |
Figure
The storage modulus and loss modulus for PPA-modified asphalt.
Under the same temperature, the
Figure
The storage modulus and loss modulus for PPA/SBS compound-modified asphalt.
Figure
Influence of PPA on the phase angle of PPA-modified asphalt.
It can be seen from Figure
It can be seen by analyzing Figure
Influence of PPA mixing amount on creep stiffness modulus of PPA-modified asphalt.
It can be seen from the modification effect of PPA on ZH90 asphalt in Figure
Figure
Influence of PPA mixing amount on stiffness modulus of PPA/SBS-modified asphalt.
As shown in Figure
It can be found by comparing the influence of PPA and SBS modifier on the low-temperature performance of SK90 and ZH90 asphalts under different temperatures that the influence of two selected base asphalts on the test results of stiffness modulus of PPA/SBS compound-modified asphalt was not significant.
It can be seen by analyzing Figure
Influence of PPA mixing amount on the creep rate of PPA-modified asphalt.
Compared with Figure
Figure
Influence of PPA mixing amount on creep rate of PPA/SBS-modified asphalt.
With the increase of PPA content, the recovery rate of asphalt increased obviously. When repeated creep-recovery test effect was less than 50 times, the fluctuation of elastic recovery value of asphalt was significant, but when creep-recovery effect was over 50 times, the deformation recovery rate tended to be stable. With the increase of PPA content, the Gv value of modified asphalt increased continuously. But when PPA content was over 1.5%, the slope of PPA content-Gv curve slowed down obviously. The high temperature performance of SK90 asphalt was always better than that of modified ZH90 asphalt. The creep performance of 3.5% SBS + 1% PPA composite-modified asphalt was almost the same as that of 4.5% SBS-modified asphalt. When the PPA content exceeded 1%, the improvement effect of it on repeated creep recovery performance was not significant. Temperature sweeping results showed that the storage modulus and loss modulus of PPA-modified asphalt increased with the increase of PPA content. When the test temperature was low, the performance difference of modified asphalt with different modifying agent content was more obvious. The phase angle of PPA-modified asphalt decreased with the increase of modifying agent content and increased with the increase of test temperature. From the analysis of the rate at which the phase angle increases with the increase of temperature, the addition of PPA improves the high temperature stability of asphalt. The low-temperature stiffness modulus of PPA-modified asphalt increased obviously with temperature decreasing. The stiffness modulus of modified asphalt increased with the increase of PPA content, but with the further decrease of test temperature, the influence of PPA content on the stiffness of modified asphalt decreased. With the decrease of test temperature, the creep rate
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this article.
This work was supported by the Special Fund for Basic Scientific Research of Central College of Chang’an University (nos. 300102218413, 310821153502, and 300102218405) and the Department of Science &Technology of Shaanxi Province (nos. 2016 ZDJC-24 and 2017KCT-13).