The asphalt pavement of expressway bears the influence of vehicle load, rain erosion, temperature change and other external factors for a long time, and is easy to appear cracks, pits, ruts, subsidence and other diseases, which directly affect the driving safety and road traffic efficiency.In order to ensure the flatness, durability and driving comfort of expressway pavement, pavement maintenance construction shall strictly comply with national and industry specifications, implement standardized and refined construction requirements, and comprehensively control the quality of each link of maintenance.Combined with the current highway maintenance specification, this paper expounds the core specification requirements of asphalt pavement maintenance of expressway in detail.
I. General basic principles of maintenance
Expressway asphalt pavement maintenance must strictly follow the core principles of "prevention first, combination of prevention and treatment, minimally invasive repair, and quality first".Before maintenance, comprehensive road condition inspection shall be completed to accurately determine the type, cause, scope and depth of diseases and eliminate blind construction.Targeted repair technology is adopted for different diseases, taking into account the stability of pavement structure and traffic safety, while minimizing the construction period and reducing traffic interference.All maintenance operations shall comply with the Technical Specification for Highway Asphalt Pavement Maintenance, Inspection and Evaluation Standard for Expressway Maintenance Quality and other industry standards to ensure that the pavement performance and service life after maintenance meet the standards.
II. Classification and maintenance specifications for common diseases
(I) Crack maintenance specification
Crack is the most common disease of asphalt pavement, which can be divided into three types: transverse crack, longitudinal crack and network crack. The maintenance standards are different.For fine cracks with width less than 3mm, dust and sundries in the cracks shall be cleaned, and sealant shall be used to fill the cracks to ensure that the filling joints are full, free of gaps and smooth without overflow.Medium cracks with width of 3- 10mm shall be filled with high-performance hot pouring joint glue after joint expansion and cleaning to ensure tight adhesion, waterproof and impervious.For wide cracks and network cracks with width greater than 10mm, the damaged pavement base shall be removed, asphalt mixture shall be re-paved for compaction and repair to prevent continuous spread of diseases, and the flatness of repaired pavement shall be consistent with that of original pavement.

(II) Pit maintenance specifications
Pit maintenance follows the specification requirements of "round hole square repair, shallow hole deep repair".Firstly, accurately delimit the repair range of pit groove, cut regular rectangular groove body, thoroughly remove loose mixture, dust and accumulated water in groove, and ensure solid and dry groove wall and groove bottom.Asphalt mixture shall be selected according to pit depth, paving and compaction shall be carried out in layers when depth is greater than 5cm, and compaction degree shall be ≥98%.After repair, the road surface shall be smooth without jumping, the joints shall be tight without water seepage, and the appearance shall be coordinated with the original road surface.
(III) Rutting and subsidence maintenance specifications
Mild rutting (depth ≤ 10 mm) can be leveled and repaired by micro-surface treatment and slurry sealing; moderate and severe rutting shall be milled and damaged surface course, asphalt surface course shall be re-paved and compacted.The stability of the base and subgrade shall be tested first for road subsidence diseases. If the base is damaged, the base material shall be replaced thoroughly. After compaction reaches the standard, the asphalt surface shall be paved to prevent secondary subsidence. The elevation and flatness of the repaired road shall meet the traffic standards of high-speed road surface.
III. Core specification requirements for construction technology
Before maintenance and construction, traffic arrangement shall be well controlled, warning, speed limit and diversion signs shall be set in strict accordance with the construction specifications for high-speed maintenance to ensure construction and driving safety.During the construction process, the paving temperature, compaction temperature and paving speed of asphalt mixture shall be strictly controlled to eliminate problems such as low temperature paving and incomplete compaction.Joints between new and old pavement shall be treated with seam cutting and adhesive layer, and adhesive layer asphalt shall be sprayed to ensure firm bonding and prevent cracking and seepage in later period.At the same time, the construction shall avoid severe weather such as rain, snow, strong wind and low temperature to ensure that the construction environment meets the requirements of asphalt pavement technology.
IV. Quality acceptance and maintenance specification road
After the surface maintenance is completed, the quality acceptance shall be strictly carried out, focusing on the core indicators such as pavement flatness, compaction, joint quality, appearance quality, water seepage coefficient, etc. All indicators shall meet the acceptance standards for high-speed pavement maintenance.After acceptance, it is necessary to conduct post-curing, close traffic and stand for curing, and open the asphalt mixture to traffic only after the asphalt mixture is completely cured and the temperature drops to normal temperature.At the same time, maintenance accounts shall be established to record the position of diseases, maintenance technology, construction parameters and acceptance results, so as to provide data support for subsequent normal maintenance.
V. Conclusion
Highway asphalt pavement maintenance is the key work to ensure road capacity and prolong road service life.The whole construction process must strictly abide by the industry specifications, accurately study and judge diseases, standardize construction, fine acceptance, control maintenance quality from the source, effectively solve various road diseases, and continuously ensure the safe, stable and efficient passage of expressways.