First, the basic methods of pavement disease maintenance
In view of various diseases of asphalt pavement in expressway, different maintenance methods should be adopted according to different damage forms and reasons. The main methods can be summarized as local maintenance, coverage and modification.
(1) local maintenance
Local maintenance mainly refers to the small or scattered area where diseases occur, which accounts for a small proportion in the whole road section. Through small-scale treatment, the damaged pavement can be restored to normal use. Common methods are as follows:
1. Maintenance of asphalt pavement cracks. At present, there are few pavement cracks in newly-built expressway, but there are many expressway in early construction, which are mainly temperature cracks, semi-rigid base reflection cracks and mesh cracks caused by insufficient base strength. Because expressway has high requirements for asphalt pavement, the treatment of cracks must be carried out according to high standards. For transverse cracks, if the crack width is less than 5mm, hot asphalt should be poured; When the crack width is greater than 5mm, mechanical slotting should be adopted first, and fine-grained asphalt mixture should be used to fill it tightly. If there are many cracks, emulsified asphalt slurry seal coat should be adopted; For the mesh cracks caused by insufficient strength of the base, the asphalt surface should be milled or roughed, and then a layer of asphalt concrete should be paved for sealing.
2. Maintenance of rutting on asphalt pavement. When rutting occurs on asphalt pavement, we must first analyze the causes of rutting and what kind of rutting it belongs to. If the rut is caused by excessive surface wear, use a milling machine to remove the surface, and then resurface asphalt concrete. Rutting in expressway of our province is mainly caused by insufficient strength of pavement base and poor gradation of asphalt mixture. If the strength of the base is insufficient, the surface layer should be ground off, and the pavement base should be prepared before paving; If rutting is caused by asphalt mixture, the surface layer with unreasonable gradation should be ground off and the rutting resistant asphalt mixture (such as SMA) should be paved instead.
3. Maintenance of frost heaving and frost boiling. Frost heaving and frost boiling often occur in expressway built in the early days. Frost heave usually occurs in the excavation section of Kaishan Road, and the water in the lower part of subgrade cannot be discharged. In such a road section, horizontal and vertical blind ditches should be set at the lower part of subgrade, or collecting wells should be set and then paved. When boiling, all the original pavement should be dug to the top of subgrade, the gravel cushion should be re-filled, the semi-rigid base (cement stabilized macadam) should be redone, and then the asphalt concrete surface should be paved.
4. Maintenance of damaged bridge deck pavement. When the bridge deck is damaged in a large area, it should be treated in two ways. One is that only the asphalt surface layer is damaged, and the cement concrete under the surface layer is intact. In this case, the asphalt surface should be ground off to expose cement concrete, then emulsified asphalt should be sprayed, and then asphalt concrete should be paved. If the cement concrete under the asphalt pavement is also damaged, the cement concrete should be treated first. If the damaged area is small, it should be treated locally. If the damaged area is large, it is best to redo the cement concrete pavement. Under normal circumstances, the original cement concrete pavement will be completely chiseled to the top of the beam, and then steel mesh will be laid, cement concrete will be poured again, and emulsified asphalt adhesive layer oil will be sprinkled. Finally, pave asphalt pavement. At present, the thickness of asphalt pavement is mostly 9cm, which is paved in two layers.
(2) Covering the surface
In order to eliminate the damage, improve the smoothness of pavement and restore the anti-skid performance, expressway pavement overlay adopts AK- 13a or AK- 16a. In recent years, with the maturity of SMA pavement structure technology, SMA is the most ideal pavement structure, and the thickness of overlay should generally be 4~5cm, generally not less than 4 ~ 5 cm. SBS modified asphalt is the best road asphalt.
(3) Renovation
When the pavement in expressway is seriously damaged, the pavement can not be restored to a good state of use by overlay maintenance, or the bearing capacity of the pavement is seriously insufficient, it should be renovated. Renovation needs to redo the cushion and base and resurface the surface.
Second, the road maintenance construction method
When the maintenance plan is determined for the pavement that needs maintenance, it will enter the implementation stage of the plan. The specific steps are as follows:
(A) according to the maintenance design to do a good job of preparation before construction.
1. Check the diseases of the maintenance section, and measure the pavement elevation and basic data required for construction.
2. Investigate and test all kinds of materials needed for construction, test technical indicators, select materials that meet the requirements, and ensure the quality of construction materials.
3. Conduct a comprehensive maintenance inspection of all kinds of machinery and tools required for construction, so that their performance is in good use, the number of machinery must be sufficient, and important machinery should have spare equipment.
(2) Road milling and planing
1. Construction lofting. Determine the milling depth according to the pavement damage and design elevation, and mark the pavement to ensure good "flatness" after milling.
2. Milling and planing wastes should come out of the field at the historic moment, and it is not allowed to throw them away at will to pollute the environment.
(3) Pavement base construction
1. For the road section that needs to be redone at the grass-roots level, before laying the new pavement cushion, the road groove should be rolled for 3 ~ 4 times with a three-wheel roller of 12 ~ 15t or an equivalent roller. If the surface layer is found to be too dry and loose, a proper amount of water should be sprayed. If the surface layer is too wet and "spring phenomenon" occurs, measures such as turning over the sun or mixing lime (or cement) should be taken to deal with it. And in accordance with the provisions, check whether the elevation, width, transverse slope of road arch, flatness, compactness and rebound modulus of subgrade surface meet the requirements.
2. During the construction of semi-rigid base, the pavement base and subbase should be mixed by BMW mixer, and it is forbidden to leave a plain soil interlayer at the bottom of the mixing layer. When mixing, the ingredients should be accurate and uniform, and the particle gradation should meet the design requirements. The construction temperature should be above 5℃, and the delay time from adding water to mixing to the end of rolling should not exceed 2 hours. Rolling should be carried out when the mixture reaches or is slightly higher than the optimal water content. The roller shall be a heavy-duty vibratory roller with a weight of 12t or more. After the completion of rolling, sprinkler should be used for maintenance, and the maintenance time should be more than 7 days. During the whole curing period, the surface of the base or subbase must always be moist. Traffic should be closed except for sprinklers.
(4) Seal coat and adhesive coat construction
After the semi-rigid base is completed, seal asphalt shall be applied. Before pouring sealing asphalt, the pavement should be cleaned, kerbs and artificial structures should be properly protected to prevent pollution; Seal asphalt should not flow after paving, and penetrate into the base to a certain depth, and no oil film should be formed on the surface; No construction is allowed in windy or rainy days, and no seal coat is allowed when the temperature is lower than 10℃. In the construction process of adhesive layer, before pouring adhesive layer oil, the dirt on the road surface must be cleaned up. When there are sticky clods, wash them with water and pour them after the surface is dry. The asphalt in the bonding layer should be evenly distributed. After the asphalt pouring of the bonding layer, no other vehicles and pedestrians are allowed to pass except the asphalt mixture transport vehicle.
Three. conclusion
According to the above investigation and analysis of diseases in expressway, the following conclusions are drawn from the prevention and maintenance countermeasures of pavement diseases:
1. The expressway pavement built in the early days was seriously damaged because the overall strength of the pavement could not meet the use requirements. That is, the design thickness of semi-rigid base is too thin, which leads to bending and tensile failure and seriously reduces the deflection value of pavement. Such a structure must be strengthened at the grassroots level of the whole bank.
2. From the appearance of pavement diseases, most serious diseases are caused by water, so we must attach great importance to pavement drainage design when designing pavement. Especially the drainage of the cutting section and the central separation area.
3. Adhesion and anti-stripping performance of asphalt and aggregate are one of the main reasons for water damage. Aggregates with poor adhesion (such as granite) can be soaked in 1% and 2% lime water, which can achieve good results.
4. AK-A anti-skid surface or SMA structure is recommended for asphalt pavement surface to increase the service life of pavement. On the basis of I-type dense gradation, adjust the middle asphalt concrete appropriately, increase the content of crushed stone and mineral powder, and improve the deformation resistance and compactness. Dense asphalt concrete is selected for the bottom layer to improve the load fatigue resistance.
Four. discuss
According to the comprehensive evaluation index PQI of asphalt pavement, it is difficult to objectively and accurately reflect the damage of asphalt pavement in expressway. It is only a reference index, and different maintenance methods are adopted for different reasons of pavement damage. The maintenance measures taken must be targeted. If the pavement is damaged in a small area, it shall be maintained in accordance with the methods and requirements of Technical Specification for Asphalt Pavement Maintenance. If the damage is large and cannot be completed within the scope of minor repairs and maintenance, then a reasonable maintenance scheme should be selected according to the actual situation.
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