added asphalt layer的用法和样例：
- tension strain at base of asphalt layer
- A 10% service charge is added on to the bill.
- They are used in road construction in various ways. They may be laid over the soil and rock base to help segregate the subsoil and the fill, and they may be laid over the base directly under the surface asphalt layers.
- bonding condition between asphalt layer and semi-rigid layer