The thickness of asphalt pavement on highways is a key factor in ensuring road quality and durability. As an asphalt mixture layer laid on a flexible or semi-rigid base course, the thickness of the asphalt pavement directly affects the road's service life and safety. So, how thick is the asphalt pavement on highways? Let's find out.
Road Grade and Thickness Standards
The asphalt thickness of highways and Class I roads is typically between 12 and 18 centimeters. Highways are usually designed with an 18-centimeter asphalt layer, employing a three-layer structure: an 8-centimeter lower layer, a 6-centimeter middle layer, and a 4-centimeter upper layer. Class II roads have asphalt layer thicknesses between 6 and 12 centimeters, while Class III roads have asphalt layer thicknesses between 3 and 5 centimeters.
Furthermore, beneath the asphalt layer in the subgrade section, two layers of cement-stabilized crushed stone, also known as "water-stabilized," are typically laid, with a total thickness of 36 centimeters. This is done in two stages, each 18 centimeters thick, called the lower base course and the upper base course. Of course, newer techniques now use a double-layer continuous paving method. Below the 36 cm water-stabilized layer, a 20 cm layer of graded crushed stone is usually laid; this is called the subbase.

These factors together constitute the thickness of the pavement structure. It's worth noting that different design institutes and regions may have differences in pavement structure design, but the total thickness of the pavement layers for expressways and Class I highways is generally controlled within the range of 68 to 76 cm.
Layers of the Pavement Structure
Do you know how thick the asphalt pavement of expressways is? The thickness of the asphalt pavement is a key indicator for measuring the performance of expressways, Class I highways, and other types of roads. This thickness varies depending on the highway's grade and design requirements. Next, we will explore the thickness of asphalt pavement and its components in detail.
First, let's understand the basic composition of asphalt pavement. From bottom to top, asphalt pavement generally includes the following layers:
Subgrade and base course: As the foundation of the asphalt pavement, they are usually composed of a mixture of soil and aggregates, bearing the heavy responsibility of supporting traffic flow. In specific situations, such as within bridges or tunnels, the subgrade may be omitted.
Cement-stabilized crushed stone layer (referred to as "water-stabilized"): Following the subgrade, the water-stabilized layer appears with a thickness of 36 cm. It is constructed in two layers: a lower base course and an upper base course, each 18 cm thick.
Asphalt layer: Located above the water-stabilized layer, this is the main traffic area in the asphalt pavement. Its thickness varies depending on the highway grade, but the thickness of the asphalt layer for expressways and Class I highways typically falls within the range of 12 to 18 cm. A common structure is 8+6+4 cm, i.e., an 8 cm lower layer, a 6 cm middle layer, and a 4 cm upper layer. However, when laying asphalt in bridges or tunnels, only a 6+4 cm thick asphalt layer may be needed, without a lower layer.
Furthermore, there may be slight differences in the design of pavement structure thickness between different regions and design institutes. But generally speaking, the total thickness of the pavement layers for expressways and Class I highways is usually between 68 and 76 cm.