Asphalt pavement hot recycling technology has been widely used in China because of its excellent performance and stable quality, and scholars have mainly carried out relevant research on the problem of primary aging and regeneration of asphalt, and the problem of multiple aging and regeneration of asphalt is rarely involved. No. 70 matrix asphalt was selected as the research object, and the laboratory test was used to simulate the three aging and regeneration processes of asphalt, and the variation law of the road performance of matrix asphalt for multiple regeneration was tested through the penetration degree, softening point, ductility and Brinell viscosity. The results show that the matrix asphalt undergoes multiple aging and regeneration, and the high temperature performance is improved, the rheological properties are deteriorated, and the low temperature performance is attenuated when the regenerant content is the same during regenerationWhen adding regenerant, we should focus on the recovery of the low-temperature performance of the aging asphalt.
Keywords: asphalt |Multiple aging |Multiple regeneration |Performance test
With the further extension of China's road network, the periodic renovation and maintenance tasks of roads during the operation period have risen rapidly, and the scale of large and medium road repairs will continue to operate at a high level. Among the large and medium-sized road repair and maintenance of a large number of waste pavement materials, only the trunk highway produces more than 1 asphalt pavement material every year600 million tons. It is of great significance to efficiently regenerate the waste pavement materials generated by road maintenance during the operation period, so that the road traffic infrastructure can provide safe and convenient services for economic and social development, reduce resource occupation and environmental damage, and better serve the construction of a resource-saving and environment-friendly society.
Asphalt pavement hot recycling technology has been widely used at home and abroad because of its excellent performance and stable quality. Whether the hot recycling pavement can be reused for the second or more times has attracted widespread attention. Judging from the existing research, European and American countries (regions) have mainly carried out fruitful research on the regeneration effect of regenerator and the evaluation method of physical and mechanical properties of recycled asphalt mixture, which provides a scientific basis for the practical application of asphalt mixture recycling technology, but the problem of multiple aging and regeneration of asphalt is still rarely involved. Domestic scholars have also carried out a lot of research on asphalt recycling technology, Huang Xiaoming et al. on the basis of referring to the current design method of matrix asphalt mixture in China and the design method of foreign recycled mixture, and put forward the design method of the mix ratio of recycled asphalt and recycled mixture.
Ji Xiaoping measured the viscosity of recycled asphalt under different conditions of new and old asphalt blending, established and verified the composite viscosity temperature curve of recycled asphalt and the calculation formula of new aggregate heating temperature based on heat conduction, and verified the reliability of the calculation formula through physical engineering. Qi Wenxiang et al. designed a test scheme to simulate the diffusion process of regenerant in aged asphalt, and carried out regression analysis based on the softening point test results, and pointed out that the increase of ambient temperature and diffusion time can significantly improve the diffusion degree of regenerantThe full diffusion of regenerant in aging asphalt is conducive to the improvement of the strength of recycled asphalt mixture. Only consider the problem of primary regeneration, ignore its long-term recycling, is not conducive to the maximization of economic and social benefits, resulting in asphalt pavement recycling application technology has "worries at the same time, with the continuous advancement of China's highway infrastructure construction, the demand for natural resources is increasing, so it is necessary to consider the research and development of asphalt pavement multiple regeneration technology, which is related to the balance of the ecological environment, is the inevitable requirement of the long-term development of human beings.
In this paper, matrix asphalt was selected as the research object to study the performance differences of matrix asphalt under the action of different amounts of regenerant, and the variation law of performance indexes of multi-recycled asphalt was revealed.
1. Raw materials and test schemes
1.1 Raw materials
In this paper, Tepuck No. 70 matrix asphalt was used for the test. According to the "Highway Engineering Asphalt and Asphalt Mixture Test Regulations" (JTG E20-2011), the main performance indicators of asphalt were tested and tested, and the results are shown in Table 1.
The regenerant was tested according to the indicators required by the Technical Specification for Highway Asphalt Pavement Recycling (JTG T5521-2019), and the test results are shown in Table 2.
1.2 Test protocol
1) At present, the entity engineering generally only involves the initial regeneration of asphalt mixture recovering material (RAP), and the RAP that has been used for many years after recycling cannot be obtained from the site. This study investigates the technical indicators of domestic asphalt, combined with the "Technical Specification for Highway Asphalt Pavement Recycling" (JTG T5521-2019) stipulates that when using in-situ thermal recycling technology, the 25 penetration degree of the original pavement asphalt should not be less than 20 (0.).1mm）。According to the previous test experience, the htfot method was used to prepare the aging asphalt in the laboratory, and the penetration degree of the aging asphalt was 30 (01mm), which is approximately the penetration of rap** asphalt that has been used for 10 years.
2) Test the road performance indicators of aged asphalt, including penetration (25), softening point, ductility (15) and Brinell viscosity (135).
3) The aging asphalt was regenerated by adding different amounts of regenerant, and the performance indexes of asphalt under different amounts of regenerant were tested respectively.
4) According to the recovery of asphalt properties under different regenerant dosages, a suitable regenerant dosage is determined to prepare recycled asphalt.
The above 4 steps are all the links of a regeneration, and these 4 steps are repeated with the recycled asphalt prepared in step (4) to complete the process of aging and regeneration again. In this study, three asphalt recycling processes were completed, and the performance indexes of asphalt binder were tested separately at different steps of each recycling process.
2. Asphalt aging and regeneration test
2.1. Asphalt primary aging and regeneration test
After the new asphalt of No. 70 was aged by TFOT at 163P and 10 h, the regenerant was added to the aged asphalt according to the preset dosage % (mass fraction), and after slowly stirring evenly, the penetration level, softening point, ductility and Brinell viscosity tests were carried out. The test results are shown in Table 3.
It can be seen from Table 3 that with the increase of regenerant content, asphalt penetration, ductility increase, softening point and viscosity decrease, indicating that regenerant can effectively improve the performance of primary aging asphalt.
According to the Technical Specification for Highway Asphalt Pavement Recycling (JTG T5521-2019) and engineering experience, the new asphalt is reduced by one grade as the target number of recycled asphalt, so the target penetration degree of recycled asphalt proposed in this study is 50 (01mm), 15p ductility is not less than 30cm. According to the regeneration effect of the primary recycled asphalt, in order to prevent the aging asphalt from being excessively softened and affecting the high-temperature performance of the asphalt mixture, the reasonable dosage of the regenerating agent of the primary recycled asphalt is 6%.
2.2. The 2nd and 3rd aging and regeneration tests of asphalt
The asphalt binder after the initial regeneration is subjected to TFOT aging of H, and then the regenerant is added to the second aging asphalt according to the preset dosage % respectively, and the mold is poured after slowly stirring evenly, and the penetration degree, softening point, ductility and Brinell viscosity test are carried out. The test results show that with the increase of regenerant content, the penetration and ductility of asphalt increase, and the softening point and viscosity decrease, indicating that the regenerant can still effectively improve the performance of twice-aged asphalt.
The target penetration of recycled asphalt is 50 (0.).1 mm), 15 ductility is not less than 30 cm, combined with the regeneration effect of the second aging asphalt, the regenerating agent content of the second recycled asphalt is 6%.
The above steps were repeated for the third aging and regeneration, and the test results were similar to those of the first and second aging and regeneration, and the test data of the three aging and regeneration were summarized in Table 4.
3 Test results and analysis
In order to horizontally compare the differences in asphalt performance under different regeneration times, the regenerant content should be as consistent as possible, and the performance index of matrix asphalt should be comprehensively analyzed when the matrix asphalt undergoes three times of aging and regeneration, and the regenerant content is 6%, see Figure 1
1) After aging, the penetration degree of matrix asphalt is significantly reduced. After adding 6% regenerant, there was no obvious difference in the penetration of the three recycled asphalt, and the penetration level of the asphalt after the third regeneration was even higher than that of the primary recycled asphalt, indicating that the penetration index of the asphalt could be restored to the primary regeneration level after multiple aging and regeneration of the matrix asphalt.
2) With the increase of the aging times of matrix asphalt, the softening point of the aging asphalt increased, but the increase was small, and the softening point of the recycled asphalt showed an upward trend after adding 6% regenerant, indicating that the high temperature performance of the asphalt was partially improved after many times of aging and regeneration, but the improvement was not large.
3) Compared with the recovery effect of regenerant on the ductility of matrix asphalt, the initial regeneration effect was the best, and the ductility of recycled asphalt gradually decreased from the second regenerationOn the third regeneration, the ductility is 241cm, can no longer meet the ductility requirements of the target grade of recycled asphalt. The results showed that the substrate asphalt attenuated at low temperature ductility with the increase of regeneration times. When the amount of regenerant is increased to 9% in the third regeneration, the ductility index can meet the performance requirements of the target label of recycled asphalt.
4) With the aging and regeneration times of matrix asphalt, the viscosity of the aged asphalt gradually increased, and the viscosity was improved after adding 6% regenerant, but the viscosity of the recycled asphalt showed an overall upward trend, indicating that the matrix asphalt became viscous and the rheological properties became worse after multiple aging and regeneration.
4. Conclusion
1) The matrix asphalt has undergone many times of aging, and the penetration and ductility are significantly reduced, and the softening point and viscosity are increased.
2) The road performance of asphalt can still be partially restored under the action of regenerant, and under the condition of adding the same amount of regenerant, with the increase of regeneration times, the softening point and viscosity show an upward trend, the ductility gradually decreases, and the penetration degree does not change significantly.
3) after the matrix asphalt undergoes multiple regeneration, the high-temperature performance is improved, the rheological properties become poor, and the low-temperature properties are attenuated, so the recovery of the low-temperature properties of the aging asphalt should be focused on when adding recycler.
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