This paper mainly analyzes the causes of asphalt pavement aging and the situation of asphalt recycling at home and abroad.
Keywords: asphalt aging and regeneration
1 Foreword China's highway construction has developed rapidly. By 2005, the national highway mileage exceeded 40,000 kilometers, ranking second in the world. The main and secondary roads are nearly 200,000 kilometers, most of which are asphalt pavements. How to manage and maintain these expressways well is an important topic facing the highway departments in China at present. Expressway consumes about 350 ~ 400 tons of asphalt per kilometer. By 2004, the demand for road asphalt in China has exceeded100000 tons.
2 asphalt aging analysis "aging" refers to the process that asphalt is refined from the refinery, and in the process of storage, transportation, construction and use, due to long-term exposure to air, environmental factors such as heating, oxygen and polymerization, even the internal structure of asphalt changes, and at the same time its properties change, resulting in the deterioration of road performance. Asphalt aging is a gradual process, and its speed directly affects the service life of pavement, which is a rich and important factor affecting the durability of asphalt pavement. The essence of asphalt aging process is that the chemical structure of each component compound in asphalt changes, which leads to the change of solubility parameters of asphaltene and soft asphaltene in asphalt, which leads to the increase of solubility parameters difference between asphaltene and soft asphaltene, which leads to the decrease of compatibility and ultimately leads to the decline of asphalt pavement performance.
3. 1 Research Status of Asphalt Pavement Recycling at Home and Abroad 1982. The Ministry of Communications issued asphalt concrete pavement recycling as a key scientific and technological project, Tongji University was responsible for the research of this topic, and Shanxi, Hubei, Henan, Hebei and other provinces and cities participated in it, and carried out systematic experimental research on asphalt concrete pavement recycling technology. Since 1990s, some highway maintenance units have tried to simply recycle old materials and use them in low-grade highways or road bases.
Road recycling has become a common practice in the United States. At present, its recycling rate is as high as 80%, which saves the cost 10% ~ 30% compared with the pavement made of new asphalt materials. Western European countries also attach great importance to asphalt recycling technology. The former Federal Republic of Germany is the first country to use recycled materials for highway pavement maintenance. 1978 All waste asphalt pavement materials are recycled and implemented according to law.
3.2 asphalt regeneration mechanism The regeneration of asphalt pavement is mainly asphalt regeneration. Based on the migration of chemical components, the colloidal structure of asphalt has changed after aging due to the migration of components. Some ingredients are more than others, while others are less. The comparison examples between the components are not harmonious, and the road performance of asphalt is reduced. Based on the colloidal structure theory of recycled asphalt from old asphalt materials, a quantitative recycling agent is added to the old asphalt to redistribute the chemical components in the old asphalt and restore its original properties, which meet the technical requirements specified in the specification. The function of regenerant is to make asphalt meet the viscosity requirements of construction and final road use; Improve the recycled asphalt mixture to achieve the best durability, provide enough asphalt binder to wrap additional new aggregate, and provide binder needed for mixture design. 3.3 Performance Analysis of Regenerator Regenerator must be conducive to improving the redistribution of chemical components of IEt asphalt, have good compatibility with old asphalt, and have the ability to dissolve and disperse asphaltene, so as to change the chemical components and rheological properties of old asphalt and meet the technical index requirements specified by road asphalt. There are two kinds of regenerants, A and B, which are added to the old asphalt in the proportions of 2%, 3%, 4%, 5% and 6% respectively. The penetration, ductility and softening point of recycled asphalt were measured. The penetration of asphalt is closely related to the performance of asphalt pavement, which is the most important basis for choosing asphalt label in China. For asphalt with the same oil source or temperature sensitivity, asphalt with large penetration, that is, thinner asphalt, has lower stiffness modulus and fewer cracks than asphalt with thick asphalt. The aging needle degree is also closely related to the crack resistance of asphalt pavement. The analysis data show that the crack resistance and high temperature stability of asphalt pavement increase with the increase of recycled agent content and penetration. The ductility of asphalt is determined by stretching the ends of standard samples at a specific speed and temperature until they break. Ductility reflects the temperature sensitivity of asphalt, and the test results also reflect the internal relationship of asphalt components, which is an important pillar to determine the performance of asphalt. For materials with the same penetrating power, the obvious use effect with large ductility is better. The softening point of asphalt is a performance index at high temperature, and the measurement method is the ring and ball method. The analysis data show that with the increase of the content of recycling agent, the ductility of asphalt gradually increases and the softening point gradually decreases, which shows that adding recycling agent to aging asphalt is effective to improve the performance of asphalt. When type B regenerant is used, the mass fraction of asphalt is 5% or
When the mass fraction of A-type recycled asphalt is 6%, the penetration, ductility, softening point and other road performance indexes of old asphalt are greatly improved, which basically meet the requirements of the specification:
Conclusion The world oil resources are limited and will not be regenerated. Overexploitation will inevitably lead to resource depletion. China's highway construction, especially the large-scale construction of expressways, has experienced more than ten years of development and made great achievements. At present, some expressways have entered the period of large and medium-sized repair. According to the design life of asphalt pavement (1.5-20 years), from now on, 1.2% of asphalt pavement needs to be renovated every year, and the waste of old asphalt will reach 2.2 million tons every year. If it can be used, the economic benefits will be considerable, and the research on asphalt recycling technology is of far-reaching significance.
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