The application technology of trenchless asphalt pavement comprehensive maintenance vehicles

At present, there are many types of specialized equipment on the market for small-scale repair of asphalt pavement. According to different repair processes, they can be divided into two categories: excavation type and trenchless type operation machinery. According to the temperature state of the old road surface at the time of repair, excavation and trenchless repair are also called cold repair and hot repair. The obvious feature of trenchless operation machinery is that it is equipped with a working device at the rear that can heat the road surface on the spot. Due to the characteristics of trenchless repair such as low labor intensity, good operation quality, on-site recycling of old materials, repeated correction of filled potholes, and no seasonal restrictions, the trenchless asphalt pavement comprehensive maintenance vehicle has always been determined as the preferred model in the equipment purchase and selection of the Shanxi Provincial Expressway Administration Bureau.

Although the trenchless asphalt pavement comprehensive maintenance vehicle can complete the repair work of various small-scale asphalt pavement diseases, it does not always demonstrate its advantages of high speed and low cost in all cases. The most suitable working condition for it is generally a depth not exceeding 60mm. Therefore, when using trenchless asphalt pavement comprehensive maintenance vehicles, it is also necessary to establish a scientific management mechanism and adopt necessary detection methods to promptly identify potential diseases, providing a guarantee for scientific decision-making, rapid handling, and the efficient completion of pavement repair under the most economical conditions. The following are some specific practices of the trenchless asphalt pavement comprehensive maintenance vehicle in practical applications.

Preparation before homework

1. Reserve of repair materials

To ensure the quality of the repair, the asphalt concrete materials used for the repair are generally still provided by large mixing plants. However, it is neither economical nor realistic for a small amount of asphalt concrete to be provided by the mixing plant. Therefore, the trenchless comprehensive maintenance vehicle is usually equipped with a silo with heating and insulation functions, which can heat the cold materials that have been mixed in advance.

When using a trenchless comprehensive maintenance vehicle, a certain amount of mixture should be reserved based on the actual amount of asphalt concrete materials required and the production conditions of the surrounding asphalt concrete mixing plants. However, asphalt concrete materials should not be stored in excessive amounts or for too long; otherwise, their quality will deteriorate due to oxidation, affecting the lifespan of pothole repair.

To facilitate the loading of materials into the insulation silo, after the asphalt mixture is transported back, a clean and flat site should be found in advance. The rear guard of the dump truck should be fixed and opened at an appropriate Angle. While moving, the asphalt mixture should be naturally spread out according to a certain thickness (60mm), and then manually trimmed and cut into small pieces of about 500mm×500mm. After condensation, they should be stored in a centralized manner for future use. In addition, the centralized storage areas should be kept away from direct sunlight and rain as much as possible.

The material gradation should mainly focus on the upper layer. According to actual needs, some middle and lower layer materials can be appropriately prepared.

2 Heating of asphalt mixture

When it is inconvenient or insufficient to provide the mixture from the asphalt concrete mixing plant to meet the demand, the pre-stored finished mixture should be used. Due to the poor thermal conductivity of the asphalt mixture, it needs to be heated for a long time and gradually increased in temperature; otherwise, it will cause the aging of the asphalt material near the box wall. Generally, the heating of the mixture should start the night before the construction. Before loading the stored asphalt mixture into the material box, it should be crushed into small pieces to prevent damage to the material box during pouring and to facilitate heating. The amount of mixed materials to be added should be estimated in advance and not added blindly. The heated mixed materials should be used up as much as possible on the same day to avoid repeated heating and reduce the quality of the mixed materials. The unused mixture can be reheated at most twice.

3 Allocation of operation personnel

To ensure the need for rapid operation, generally more than four operation personnel are equipped. One construction manager is needed, mainly responsible for handling various construction issues on site and ensuring construction quality. One driver is required, responsible for driving the comprehensive maintenance vehicle and operating various supporting machinery. Two technical workers are needed, responsible for heating, digging, filling and leveling operations. One traffic safety officer is needed to be responsible for traffic safety duty at the operation site. The number of officers can be increased on special sections as the situation requires.

Repair work

1. Treatment of abscesses, cracks and depressions

For diseases such as abscesses, cracks and depressions that only involve the surface layer, the repair operation is relatively simple. The operation procedures are as follows.

Traffic control. Traffic safety is a prerequisite for highway construction operations. Before treating pavement diseases, construction signboards must be placed strictly in accordance with relevant national regulations. There are also full-time safety officers on duty for traffic safety.

(2) Determine the scope of disease treatment. Use a 3-meter ruler to measure the flatness of the affected area. Based on the test results, mark the range of diseases that need to be treated with chalk. Then define the range of diseases that need to be dealt with. To facilitate the operation, they should be organized into a relatively regular shape. Finally, draw symmetrical cross lines to facilitate the determination of the placement position of the heating plate.

(3) Heat the diseased road surface. The heating plates of comprehensive maintenance vehicles usually have multiple zones, which can meet the needs of different heating areas. Operators should be familiar with the areas of each zone and select the appropriate zone when heating. Move the comprehensive maintenance vehicle, position the heating device above the diseased area, and then fine-tune the control system to adjust the position and height of the heating device to start heating.

(4) Raking and trimming. After the heating is completed, use an iron rake to loosen the designated repair area. Then, spray an appropriate amount of emulsified asphalt or hot asphalt as needed. At the same time, add or remove materials appropriately according to the flatness for further finishing.

(5) Initial compaction. ① Static pressure: Use the built-in hand-held roller to conduct static pressure twice, first along the edges and then in the middle. Then, use a 3-meter straightedge to check the flatness and the corners. If necessary, adjust the height and fill in the gaps according to the loose paving coefficient. The start, stop and change of the compaction direction of the roller should be carried out on the old road surface. ② Vibration rolling: Start the vibrator. The rolling process should be no less than two times. After rolling, no flatness adjustment is allowed.

(6) Final compaction. After static compaction with a roller twice, the surface should be finished. The temperature after final compaction should not be lower than 70℃.

(7) Open up transportation. After compaction, isolation measures should be taken to divert traffic. If it is indeed necessary to open traffic, water should be sprinkled to quickly cool down.

2 Pit. Patching operation

When the damaged parts of the road surface have already shown signs of mud heaving or potholes, the repair work becomes relatively more complicated. The specific operation procedures are as follows.

(1) Define the scope of disease treatment. Use a 3-meter straightedge to check the flatness at the pothole and damaged positions on the asphalt pavement. Based on the flatness test results, use chalk to mark the range of diseases that need to be treated and the approximate range of excavation.

(2) Eliminate pavement diseases. The above-mentioned diseases have caused varying degrees of pollution to the asphalt concrete and must be removed before repair. Use the electric pick or hydraulic pick that comes with the comprehensive maintenance vehicle to successively remove and destroy the designated diseased area layer by layer according to the upper layer, middle layer and lower layer. The trench wall should be as vertical as possible to the bottom surface, and leave a 100mm gap between each surface layer of the road surface. A simple indicator to distinguish whether the strength of asphalt concrete has been damaged during the process of removing asphalt pavement diseases; The cross-section should be visually inspected. If the asphalt concrete cross-section around the pickaxe appears "white", it indicates that the strength of the asphalt concrete meets the requirements. Otherwise, the range of disease removal should be further expanded until the stable part is reached. The removal operation generally does not need to pay attention to the shape. The main purpose is to remove the failed concrete and slurry to reach the part that meets the strength requirements. At the same time, it is necessary to avoid small areas, dead corners and other shapes that are not convenient for compaction, and try to achieve a smooth transition as much as possible.

(3) Clean the pits and trenches. After removal, shape the serrated pit wall into a smooth vertical surface and remove the loose parts. Clear the debris, soil and loose parts at the bottom of the pit. If there is water at the bottom of the pit, use a blowtorch or heating plate to heat and dehumidify.

(4) Spray bonding asphalt. After cleaning the pits and trenches thoroughly, spray a layer of emulsified asphalt or hot asphalt on the walls and the bottom of the pits.

(5) Spread the mixture. The hot asphalt mixture unloaded from the comprehensive maintenance vehicle is first initially spread with an iron rake, and then finely leveled with a manual leveler at a loose paving coefficient of 1.3 to 1.5.

(6) Initial compaction. ① Manual assisted compaction: If the asphalt mixture is laid in multiple layers, the corners and edges that the roller cannot reach during the compaction of the lower layer should be compacted manually with a tamper. ② Static compaction: Use the built-in hand-held vibratory roller to conduct static compaction twice, first along the edge and then in the middle. After that, use a 3-meter straightedge to check the flatness. If necessary, adjust the height by lifting or lowering according to the loose paving coefficient. ③ Vibration compaction: Start the vibrator and conduct vibration compaction for no less than two times.

(7) Recheck the flatness and seamless treatment. After deep repair, due to the difficulty in controlling the loose paving coefficient, the flatness after compaction may not meet the requirements. At this time, it is necessary to conduct a re-inspection and rectification of the pavement flatness. Meanwhile, in order to make the joint between the newly laid mixture and the original asphalt pavement dense, seamless treatment should also be carried out. These two operations can be conducted simultaneously. When the flatness meets the requirements, only seamless treatment should be carried out. The specific operations are as follows: After the compaction is completed, use a 3-meter straightedge to check the flatness of the repaired area. ② Heat the repaired part with a heating plate. The heating depth should be ensured to be around 30mm, and the heating width should exceed the joint by 100mm. ③ Loosen the heated part to make its shape as regular as possible, remove the surface oxide layer appropriately, correct the flatness or fill it with the same new material, and then level it.

(8) Re-pressing. Re-compact with a vibratory roller according to the compaction procedure.

3 Treatment of other diseases

For damage caused by fire or fuel leakage, the charred parts should be peeled off after heating according to the treatment process for cracking and sinking. For damage caused by fuel leakage, the loose materials should also be peeled off before heating.

Bridgehead jumping is a relatively common disease on highways, with a large area. However, compared with other methods, it is relatively simple, quick and effective to deal with it with a comprehensive maintenance vehicle. The treatment method can be carried out in accordance with the subsidence repair process, but it needs to be completed in several stages.

There are two problems with the joints after large-scale road surface repair. One is that the flatness is difficult to guarantee. Second, the joints are prone to cracking and water seepage, causing premature damage. By adopting the method of staged heating treatment, the flatness of the repaired joints can be enhanced and seamless treatment can be carried out, thereby improving the repair quality and service life of the road surface.