A? Iaj? r typ~ of asphaltic concrete pavement failure is rutting, which is mamfested at the surface. Rutting may originate in any of th~ pavement layers; rutting that originates in the upper asphalt1c concrete layers of surface or binder course is discussed. Recently researchers have recommended the computer program ASPHALT for estimating a design asphalt content for paving mixtures. Its basis is described and its use illustrated. The results~ f a comparison of laboratory designs for asphalt content with field performance related to rutting are described.

The objectives of the computer program ASPHALT are to estimate the design of asphalt content for paving mixtures to minimize the possibility of a rutting failure (by flow) and to have sufficient asphalt for good durability (1). Basically, rutting is minimized with a low asphalt content and durability is enhanced with a high asphalt content. The paving mixture is envisioned as having been on the roadway under traffic for about 5 years so that its physical characteristics have become stabilized. The age of the mixture is important to the concepts of the program. The experience of the author has indicated that by the age of about 5 years the asphalt layer must have (a)~ ore than 2 percent air voids to not show bleeding or ruttmg and (b) a so-called asphalt film thickness ranging from-6 to 12 µm to show good resistance to cracking and stripping. The failures mentioned are those that would have originated in the asphaltic course. Rutting that originates by shear failure of a soil course is not a part of the asphaltic concrete mixture design.