There is a common belief that concrete pavements are stronger than asphalt pavements. The reason for this misconception is that comparisons are not made on equivalent designs. The traffic-carrying ability of asphalt or concrete pavement is approximately the same for each inch of pavement thickness.
To illustrate how this relates to pavement design, the concept of Structural Number must be considered. The Structural Number (SN) is an empirical strength value assigned to a particular material. The SN has no units. It is a relative number that is used to compare different materials.
To establish a standard with which to compare the structural numbers, the strength of a graded aggregate base is assigned a value of 1.0 for each inch of thickness. On this scale a 6-inch thick base would have a Structural Number of 6.0 and a 10-inch thick base would have a SN of 10.
A flexible pavement of full depth asphalt or rock and asphalt will often flex and rebound rather than break under a single heavy load. However, an asphalt pavement will fail relatively quickly under a series of loads that exceed its design capacity. The proper way to determine the design is to calculate the correct SN for the traffic and convert to the required layer thickness that meets the need.