Parking Lot Structural Numbers vs. Asphalt

35 year old McKay Road intersecting 22 year old Miller Street, both are heavy use concrete streets in Shelbyville

Concrete is considered a structural pavement while asphalt is not. For this reason it is difficult to compare the two. Asphalt is very dependent on the strength and stability of the base underneath it and it cannot bridge soft spots. Soils have variable load carrying ability and when soil becomes wet, it is not as strong. When water falls in the cracks of asphalt, the area around the crack becomes saturated and less able to support the asphalt. The soft area widens, there are more cracks, and soon there is mud pumping up from the cracks, and the process continues.

This is not true with concrete. Concrete is far less dependent on the ground it rests on. When comparing asphalt to concrete, it is wise to use agreed upon Structural Numbers per inch of material. Concrete is 0.5/inch of concrete. A five inch thick slab of concrete has a structural number of 2.5 (0.5 x 5 = 2.5)