Thin Overlay and Ultra-Thin Overlay

Thin overlay is a thinner overlay compared to traditional overlay (usually more than 40 mm thick). Generally, the hot-mixed asphalt concrete cover with a compacted thickness of 30 mm ± 5 mm is called a thin overlay. The main functions of the thin cover are to improve the flatness, restore the surface roughness, make the original surface damage (such as potholes, cracks, ruts, etc.) of the pavement to a certain extent, and extend the service life of the pavement. The ultra-thin overlay is an upgraded version of the technology of the thin overlay. The ultra-thin overlay can greatly reduce the cost of pavement maintenance engineering under the premise of achieving the same performance of the road surface, so it has gradually replaced the thin overlay technology. At present, the ultra-thin overlay commonly used in China can be divided into three categories, including:1.Ultra-thin overlay technology using modified emulsified asphalt and open grading (represented by Shell Novachip);2.Using warm mixing technology and dense grading Ultra-thin overlay;3.Ultra-thin overlay with rubber asphalt. This chapter mainly introduces materials, design, construction, construction quality control, quality inspection and acceptance of the thin overlay and ultra-thin overlay.