As the most frequently used transportation hub, highway is an indispensable transportation facility for the rapid development of social economy, which is directly related to economic development and people's lives. Asphalt pavement is widely used in urban road construction because of its advantages of low investment cost, strong wear resistance, smoothness and easy repair. However, with the development of economy and the increase of road service life, many diseases such as cracks, grooves and ruts will appear on the pavement due to long-term external force, which seriously reduces the service performance and service life of the pavement. At the same time, if these diseases are not repaired and rectified in time, it may damage the internal structure of the highway and have a serious impact on traffic. Therefore, at present, the maintenance of asphalt pavement has become an increasingly important topic.
First, the types and causes of asphalt highway diseases
1. Cracks appeared on the sidewalk.
Asphalt pavement cracks are one of the most common highway diseases. Pavement cracks can be divided into mesh cracks, longitudinal cracks and transverse cracks. After the completion of asphalt highway, cracks usually appear soon after use because of the weak overall strength of asphalt pavement. The main reasons for the cracks are that the asphalt highway base is wet and soft, and its stability is poor, or the pavement becomes brittle due to aging, and a large area of cracks are formed under the action of gravity, thus forming network cracks. The longitudinal cracks are mainly due to the imperfect construction of highway joints, or the uneven pavement at the junction of old and new pavements after highway expansion, and the cracks formed along the junction after being squeezed by vehicles. The transverse cracks are mainly caused by the change of pavement structure, and the transverse cracks caused by the change of temperature and humidity are unbearable because of the expansion and contraction caused by climate.
2. Rutting on the road surface
The main form of rutting is belt groove, and there are a lot of cracks inside and outside the groove. The cause of rutting is mainly attributed to the repeated action of overloaded vehicles. Before the construction of asphalt road, there are clear restrictions on the bearing capacity of institutions and materials. However, due to the acceleration of urbanization, some construction vehicles have to transport materials through existing roads. Therefore, the extrusion of a large number of transport vehicles far exceeds the bearing weight and time of asphalt pavement, and the long-term repeated action causes pavement damage and forms a large number of ruts. In addition, the internal structure of expressway is uneven. When it is squeezed by huge force, the relatively loose structure first forms cracks, then forms long ruts, and after a long time, it forms permanent band grooves.
3. Forming pits and grooves
The main forms of potholes are local potholes, middle potholes and grass-roots potholes. Local potholes are mainly potholes formed on the road surface, mainly because the early cracks of the road were not treated in time, and the mixture on the asphalt road surface was infiltrated by rain water under the long-term vehicle load. The potholes in the middle layer are mainly caused by potholes between the pavement and the middle layer. The main reason is that the internal structure of asphalt concrete will gradually deepen with the destruction of the surface, leading to the destruction of the internal structure and the formation of serious pits and grooves. However, the pits and grooves at the base directly affect the interior of subgrade. Because the pit and groove are easy to form a large amount of accumulated water, impurities such as accumulated water and engine oil penetrate into the highway from cracks, resulting in loose structure of the internal mixture. Under the rolling of vehicles, grass-roots diseases are gradually reflected on the surface particles, causing serious damage and seriously affecting traffic and speed. The serious loose internal structure of highway may also lead to traffic accidents and threaten personal safety. Secondly, another reason for the formation of pits and grooves is caused by pavement design, such as improper mixture ratio and temperature of asphalt mixture, which makes asphalt aging and viscosity decrease, changes the best performance of asphalt and reduces the service life of asphalt highway.
4. Flooding
Flooding mainly occurs in summer, asphalt softens, and a large part of the upper asphalt stone is easy to overflow more asphalt during extrusion, which forms pavement flooding with the increase of load. Floods are easy to cause slippery roads, especially in rainy days, which pose a safety threat to driving. Secondly, due to the high asphalt content in the upper asphalt mixture, the compressive capacity of the highway will be reduced.
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Pavement wrapping is mainly caused by uneven asphalt pavement, and its flexibility decreases. The original reason may be that the asphalt content in asphalt pavement is too high and the viscosity is low, which makes the pavement material have insufficient high temperature resistance and is pushed to form a group when the vehicle is driving; Secondly, the high amount of water at the base affects the effective viscosity of the surface layer and the base layer, and under the action of external force, uneven cohesion is formed.
Second, the maintenance measures of asphalt highway
Highway maintenance is an important method to maintain and extend the service life of highway. In order to achieve the real-time effect of highway maintenance, when there are early diseases on the highway, corresponding measures should be taken in time to prevent minor diseases from spreading into serious diseases, which will bring inconvenience to economy, transportation and life.
1. Preventive maintenance
Preventive maintenance is the initial maintenance of asphalt highway, which is suitable for pavement repair, but it can't solve the diseases inside the highway. Usually, preventive maintenance is carried out in the early stage of highway diseases, and a series of protective measures are taken before the performance of highway declines.
2. Daily maintenance
(1) joint filling. When cracks (less than 5mm) appear on the highway, joint filling measures are a common repair technology. After the impurities in the pavement cracks are cleaned up, the corresponding hot asphalt mixture is poured into the cracks, and the cracks are sealed with repair glue to prevent the infiltration of accumulated water from causing further damage to the highway. Usually, joint filling requires a professional pressure joint filling machine to fill hot asphalt mixture into the depth of large cracks, so that uneven filling will not occur and good sealing and waterproof effect will be achieved.
(2) Maintenance of depressed pavement
Grooves have damaged the roadbed to a certain extent, so it is necessary not only to repair the cracks simply, but also to rebuild the damaged roadbed at the grass-roots level. It mainly deals with the soil foundation of subgrade depression section and frost boiling section, and uses cement stabilized gravel sand (6%) as cushion at the bottom, which is repeatedly rolled until it is shaped. Then, after the base is repaired, the surface layer can be treated with recycled asphalt to achieve better repair effect.
(3) Micro-surfacing maintenance technology
The main function of micro-surfacing technology is to restore the surface function of the road, so that the road can be put into use in a short time after repair, which has great advantages in time. In addition, the maintenance of highway pavement is a refined process, because the damage of highway pavement is mainly reflected in cracks, so the maintenance of highway pavement is mainly micro-treatment. Micro-crack is a kind of highway disease that is not easy to be found, and it is often ignored in highway repair work. Once the micro-cracks on the pavement surface spread, it will destroy the pavement and even the internal structure of expressway on a large scale. Therefore, emulsified asphalt can be used to seal the irregular cracks on asphalt pavement, so as to enhance the waterproof performance of kilometer pavement and prevent the expansion of micro-cracks.
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