Double-layer asphalt paving, also known as "hot-to-hot" paving abroad and "double-layer integrated paving" in China, was patented by a German professor in 1993. What are the technical characteristics of double-layer paving? A comparison of traditional asphalt paving and double-layer integrated paving reveals that traditional asphalt pavement is layered, compacted layer by layer, and a tack coat is sprayed between the two layers. Disadvantages of this technology include: rapid cooling of the wearing layer, which affects compaction quality; susceptibility to environmental contamination between layers; increased costs associated with spraying tack coats; long construction times, and low equipment utilization.

ompared to traditional asphalt paving processes, double-layer integrated paving offers several advantages. Because the tack coat and wearing layer are connected hot-to-hot during paving, there is no clear boundary between the layers during compaction. This results in better interlocking between the wearing layer and the tack coat, and the two asphalt mixtures with different mix ratios blend together at the interface, creating a stronger bond between the layers. Double-layer paving technology optimizes the pavement structure by reducing the thickness of the wearing course and increasing the thickness of the asphalt mixture in the bonding course (intermediate layer). This improves the rutting resistance of the asphalt pavement and correspondingly extends its service life. Because the wearing course and the bonding course are in thermal contact and cool down more slowly, this overcomes the drawback of traditional asphalt paving, which suffers from rapid cooling due to a thin wearing course. It also allows for optimal temperature and time for rolling the wearing course, facilitating more efficient rolling process planning and achieving optimal compaction density.
A section of the Phase II expressway was tested using the double-layer asphalt paving process. The wearing course was constructed with two thicknesses: 3cm and 2.5cm. Initial compaction after paving was achieved using sand injection. Testing after screeding revealed compaction levels of 89.5% for the intermediate course and 80.5% for the wearing course. Final compaction levels were 99% for the wearing course and 98% for the intermediate course. The smoothness ranged from 0.49 to 0.79mm, and the texture depth exceeded 0.6mm, meeting pavement acceptance standards. At present, the construction of expressways in the country has developed by leaps and bounds. Through understanding the technical characteristics of double-layer paving, if one-tenth of the newly built and overhauled provincial highways and expressways suitable for double-layer asphalt paving adopt double-layer paving every year, it will not only shorten the construction and maintenance cycle of the highways, but also save a lot of asphalt pavement raw materials.