In highway construction, asphalt concrete pavements are widely used due to their superior performance. To achieve higher quality, the roadbed, pavement, and their structural components have been meticulously optimized and improved. Improving the pavement's bearing capacity, durability, and resistance to water damage are key objectives. To this end, the treatment between the various layers of asphalt concrete pavements has become particularly important, and the role of the permeate coat, tack coat, and seal coat, as key links, has become increasingly prominent. Each of these three layers has its own unique functions and should not be confused. Below, we will explore these key steps in depth.
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1. Key Steps in Asphalt Pavement Construction
1.1 ▲ The Role and Construction Techniques of the Permeate Coat
The permeate coat plays a crucial role in asphalt pavement construction. The penetration layer, an organic binder penetrating layer on the surface of an inorganic binder base course, is primarily used in pavement construction as an interlayer treatment between the underlying course and the surface course. It performs multiple functions: penetrating the pores of the base course surface, strengthening the bond between the base course and the surface course; promoting the binding of fine particles in the aggregate on the surface of the base course; reducing the cost of curing the base course and improving its quality; and, when applied promptly after the base course is laid, the penetration of the penetration layer fills the open pores on the surface of the base course, forming a waterproof layer. If the surface course is delayed for some reason, the penetration layer can provide temporary protection against damage from rainfall and traffic.
▲ Process Requirements for Penetration Layer Construction
During construction, the penetration layer is typically made of kerosene-diluted asphalt, requiring precise control of the mix ratio, temperature, and dosage. Intelligent equipment is used during application to ensure uniformity, ensuring that the penetration layer penetrates 5 to 10 mm into the base course and is fully penetrated and consolidated.
In highway construction, we use kerosene-diluted No. 90 asphalt as the penetration layer material. The technical specifications of this material must meet the AL(H)-2 standard for liquid petroleum asphalt for road use. The kerosene-to-asphalt ratio is crucial, as the kerosene content directly affects the penetration rate, while the asphalt content is crucial for the consolidation, stabilization, bonding, and waterproofing of the permeable layer to the base layer.
Because kerosene readily dissolves asphalt, we utilize specialized mixing tanks to produce kerosene-diluted asphalt. Under strict control of asphalt temperature and kerosene content, flow meters precisely meter the mixture to ensure thorough mixing of the asphalt and kerosene. After mixing, the finished liquid asphalt is transported to an asphalt distributor for application. It is important to note that to prevent separation of the kerosene and asphalt, it is best to use all the finished product within the same day.

Before spreading, the base layer must be thoroughly cleaned to remove debris and dust. During spreading, intelligent asphalt spreaders are used, and a microcomputer control system accurately controls the spread rate. For areas where mechanical construction is inconvenient, such as road widening and bridge approaches, manual spray guns are used for supplementary spreading.
1.2 ▲ The Importance of Tack Coat and Construction Techniques
The tack coat plays a crucial role in road construction, serving to firmly bond the various layers and the surface layer to the structure. This bonding primarily relies on the adhesive strength of the tack coat, making the selection of tack coat material crucial, particularly its bond strength and shear resistance. During construction, we typically use emulsified asphalt or modified emulsified asphalt as the tack coat material. Compared to standard emulsified asphalt, modified emulsified asphalt offers significantly improved strength, making it more suitable for road construction. 
▲ Tack Coat Construction Process Requirements
The tack coat should be made of modified SBR emulsified asphalt, a sprayable cationic medium- or fast-cracking emulsified asphalt whose technical specifications must meet the standards for PC-3 road emulsified asphalt. Before spreading, the underlying subgrade must be thoroughly cleaned to remove debris and dust. Spreading is performed using an intelligent spreader, with microcomputers precisely controlling the amount of sprayed asphalt. Modified emulsified asphalt must be spread in clear weather to ensure construction quality and avoid contamination.
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▲ The Importance of Seal Coats and Construction Techniques
▲ The Importance of Seal Coats
Seal coats play a crucial role in road construction and are divided into upper and lower seal coats. The upper seal coat, typically applied above the asphalt concrete surface course, seals out any moisture and protects against wheel wear. The lower seal coat, located between the base course and surface course, forms a solid barrier to protect against water damage. This design effectively seals out moisture and prevents contamination of the applied upper seal coat. 
▲ Process Requirements for Seal Coat Construction
Use high-quality SBS modified asphalt and single-size crushed stone to ensure the longevity and waterproofing of the asphalt surface layer. Maintain good environmental conditions during construction to prevent contamination. The underlying layer must be thoroughly cleaned before applying the modified asphalt. During application, use intelligent equipment to ensure uniformity. Any contamination must be immediately removed to ensure smooth construction.
In short, to ensure the structural bearing capacity, durability, and water damage resistance of asphalt concrete pavements, we must pay close attention to the construction techniques between each treatment layer and strictly adhere to the "Technical Specifications for Asphalt Pavement Construction" to ensure that construction quality meets standards.