In this paper, the influence of the performance changes of SBS modified asphalt before and after aging, such as penetration, 5-ductility, softening point, 135 dynamic viscosity and elastic recovery, was experimentally studied under different aging methods such as film oven aging, P** aging and ultraviolet aging. The results show that the 5 ductility and 135 kinematic viscosity of SBS modified asphalt change significantly after aging, and the aging effect has a significant effect on the high and low temperature properties of SBS modified asphaltAfter the short-term aging of TFOT, the performance of SBS modified asphalt has decreased significantly, and the attenuation range of SBS modified asphalt gradually decreases with the extension of aging time in the long-term use process (ultraviolet aging, P** aging).
Keywords:
Aging method |SBS Modified Asphalt |Ultraviolet aging |Performance Impact.
High-grade asphalt pavement generally gives priority to SBS modified asphalt pavement, because SBS modified asphalt has excellent road properties such as high temperature rutting resistance, low temperature crack resistance, water stability, fatigue resistance and aging resistance. However, SBS modified asphalt pavement will still have a variety of diseases after several years of service, such as rutting, network cracks, etc. The occurrence of these diseases is caused by heavy traffic on the one hand, and the aging of the modified asphalt itself on the other hand. Therefore, it is necessary to study the aging phenomenon of SBS modified asphalt, especially the influence of different aging modes on the performance of SBS modified asphalt.
Based on the aging mechanism theory and the generation and development process of SBS modified asphalt, three laboratory test methods were designed to simulate three different asphalt aging modes: short-term aging, long-term aging and ultraviolet aging, the effects of three different aging methods on the performance of SBS modified asphalt were studied, and the performance change law of SBS modified asphalt under different aging modes was analyzed.
Aging mechanism and process of SBS modified asphalt
Aging mechanism. The preparation process of SBS modified asphalt is mixed with SBS modifier (star or linear) and matrix asphalt and a small amount of other admixtures in a certain proportion, and finally made into SBS modified asphalt after high-speed shearing and development. Focusing on matrix asphalt and SBS modifier, the two main raw materials of SBS modified asphalt, it is generally believed that the aging of SBS modified asphalt is due to the oxidation reaction of the matrix asphalt itself to form an unstable structureSecond, the chemical structure of SBS modifier contains double bonds, which are broken and oxidized under the action of light, heat and oxygen. In the long-term aging process of SBS modified asphalt, the long-chain SBS molecule breaks and becomes a small molecule short chain, which leads to the decomposition of the spatial network structure of SBS-modified asphalt, and the modification effect of SBS-modified asphalt is attenuated.
Aging process. It is generally believed that the main aging methods of SBS modified asphalt are mainly divided into two types, one is short-term aging, and the other is long-term aging. Among them, the short-term aging phenomenon mainly occurs in the heating, mixing and rolling process of SBS modified asphalt mixture in constructionLong-term aging refers to the gradual aging of SBS modified asphalt due to the exposure of SBS modified asphalt pavement to natural light during long-term use. In the whole long-term photo-oxygen aging process, the aging caused by ultraviolet radiation accounts for the largest proportion compared with other aging forms, so this paper takes ultraviolet aging as the third aging mode to study its influence on the performance of SBS modified asphalt.
Simulation test design and test methods for different aging methods
Short-term aging simulation test.
At present, there are two standard test methods for the short-term aging test of indoor simulated asphalt in ASTM, AASTO and the current technical specifications of China: one is the film oven aging test (TFOT), and the other is the rotary film oven aging test (RTFOT). However, a large number of physical engineering application experience shows that the actual application effect of the aging test of the rotary film oven is not as good as that of the aging test of the film oven. Therefore, the 173 TFOT film oven aging test in the previous research conclusion of the project was used to simulate the short-term aging process of SBS modified asphalt.
Long-term aging simulation test.
When carrying out the indoor simulation test of the long-term aging process, this test refers to the current specification, adopts the requirements of the pressure aging test (P**) proposed by the SHRP in the United States, and modifies the P** aging test conditions as follows
1) Carry out 173 thin film oven aging test (TFOT) on the sample, after 5 hours, pour the 50g sample after TFOT aging into the stainless steel disc;
2) Put the 173 TFOT aging specimen into the P** pressure aging utensils, and release 2The air pressure was 1MPa, and the temperature was set to 100 for 20 hours. At the end of p** pressure aging, the residue after vacuum degassing was detected.
Ultraviolet aging simulation test.
In this experiment, an ultraviolet aging chamber was designed to simulate the aging of the pavement during long-term outdoor use.
The ultraviolet aging test process in this laboratory is as follows:
1) At the aging temperature of 173, the TFOT test was carried out on the SBS modified asphalt, and the performance index of the SBS modified asphalt before and after aging was detected.
2) The SBS modified asphalt after the 173 TFOT aging test was put into the ultraviolet aging box, and the indoor ultraviolet aging tests of 3D, 6D, 9D, 12D, 15D and 18D were carried out, and the performance index of the SBS modified asphalt after ultraviolet aging was detected.
Experiment with raw materials
The raw material matrix asphalt adopts South Korean SK-90;SBS modified asphalt is made of Yanshan Petrochemical 4303SBS modifier in accordance with 45% of the dosage is mixed with SK-90 high-speed shearing preparation. The performance indicators of raw materials and prepared SBS modified asphalt were tested, and the results met the requirements of the specification. The test results of matrix asphalt and SBS modified asphalt are shown in Table 1 and Table 2.
Test results and analysis
Effect of short-term aging on the performance of SBS modified asphalt.
The results of short-term aging simulation test of SBS modified asphalt are shown in Table 3.
It can be seen from Table 3 that after the aging of 173 TFOT, the performance of SBS modified asphalt has no uniform change law, and the indicators of penetration, ductility and elastic recovery are attenuated, while the softening point and kinematic viscosity increase, and the ductility index changes the most significantly, indicating that SBS modified asphalt becomes hard, brittle and weakens its fluidity after aging with 173 TFOT, but the indexes of its aging residue can still meet the requirements of the current specification. The reasonableness of setting the TFOT aging temperature to 173 is verified.
Effect of long-term aging on the properties of SBS-modified asphalt.
The results of the long-term aging simulation test (P** test) of SBS modified asphalt are shown in Table 4.
It can be seen from Table 4 that after the SBS modified asphalt undergoes P** aging, compared with the non-aging, the attenuation ratio of penetration, ductility, kinematic viscosity, elastic recovery and other indicators is basically more than 50%, and the performance is seriously attenuatedThe performance indexes of SBS modified asphalt after aging can no longer meet the requirements of the specification, indicating that the performance of SBS modified asphalt is attenuated under the action of long-term light and oxygen, resulting in frequent pavement diseases, which directly affects the performance of pavement.
Effect of ultraviolet aging on the properties of SBS-modified asphalt.
Follow this article 23. The proposed ultraviolet aging indoor simulation test method is shown in Table 5 and Figure 1.
Combined with Table 5 and Figure 1, it can be seen that:
1) After 173 TFOT aging, the penetration and softening point of SBS modified asphalt were significantly reduced, and the viscosity increased, indicating that the performance of SBS modified asphalt had been greatly attenuated during the heating and mixing process of SBS modified asphalt mixture. In the subsequent aging process, the penetration and ductility of SBS-modified asphalt continued to decrease, the kinematic viscosity continued to increase, and the asphalt hardened, thickened and the ductility deteriorated, indicating that the performance of asphalt continued to decline in the subsequent ultraviolet aging process.
2) In the second half of ultraviolet aging (12D and 18D), the performance indexes of SBS modified asphalt tended to be flat. With the increasing aging time, the performance change rate of asphalt will slowly decrease to flat, and the performance of SBS-modified asphalt will no longer continue to decay rapidly.
Comparison of performance of SBS modified asphalt under different aging methods.
In this paper, three different laboratory tests were used to test the performance of SBS modified asphalt under different aging methods, and the simulation test correspondence of the three aging methods was as follows
1) 173 Film Oven Aging (TFOT) is used to simulate short-term aging
2) Pressure aging (P**) is used to simulate the long-term aging process of pavement
3) Ultraviolet aging is used to simulate the aging of SBS modified asphalt pavement during actual long-term use.
The indoor ultraviolet aging test of 18 days using the ultraviolet aging box can be equivalent to the aging degree of the outdoor aging of the asphalt pavement for 1 year, and the p** aging test can be equivalent to the aging degree of the surface layer of the asphalt pavement for 5 years, so the test results are summarized in Table 6 according to the time order of aging. A comparison of the performance degradation is shown in Figure 2.
As can be seen from Table 6 and Figure 2:
1) General trend: SBS modified asphalt has undergone three different aging processes, and its performance continues to decay in turn, and the softening point index changes irregularly.
2) Specific index: Compared with the non-aging, no matter what kind of aging it undergoes, the 5 ductility and 135 kinematic viscosity of SBS modified asphalt after aging have changed significantly. The results of P** aging test show that the 5 ductility of SBS modified asphalt after aging is about 74% lower than that of non-aging, and the kinematic viscosity of 135 is about 96% higher than that of non-aging. The results showed that the aging effect had a significant effect on the high and low temperature properties of SBS-modified asphalt.
3) Short-term and long-term changes: From the analysis of the whole aging process, the performance attenuation of SBS modified asphalt is the most obvious after the short-term aging of 173 TFOT: the attenuation amplitude of penetration accounts for about 63% of the attenuation amplitude of the whole aging process, the attenuation amplitude of ductility accounts for about 44%, and the attenuation amplitude of kinematic viscosity accounts for about 26%, indicating that the performance of SBS modified asphalt is greatly attenuated in the process of mixture mixing and long-term use (ultraviolet aging, P** aging) Medium performance degradation will continue to occur, but the decay will gradually decrease.
Conclusion
In this paper, the effects of different aging methods on the performance of SBS modified asphalt are studied by simulating three different aging methods, including short-term aging, long-term aging and ultraviolet aging
1) Under the action of different aging modes, the changes of the performance indexes of SBS modified asphalt after aging showed a decrease in penetration, 5 ductility, and an increase in 135 kinematic viscosity, and the properties of asphalt were attenuated.
2) No matter what kind of aging is undergone, compared with other performance indexes, the 5 ductility and 135 kinematic viscosity of SBS-modified asphalt change significantly after aging, indicating that the aging effect has a great influence on the high and low temperature properties of SBS-modified asphalt.
3) In the process of asphalt mixture heating and mixing, that is, in the short-term aging process (173 TFOT short-term aging simulation is used indoors), the performance of SBS modified asphalt has been greatly reduced, and in the long-term use process (indoor ultraviolet aging and P** aging simulation), with the continuous extension of aging time, the performance of SBS modified asphalt will continue to decay, but the attenuation amplitude gradually decreases.
The full text was first published in the 9th issue of the Technical Application Technology Edition of Highway Transportation Technology, 2019.
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