Pavement cores were collected from rutting asphalt concrete pavements less than 2 years old. Laboratory tests revealed common causes of rutting, such as excessive asphalt content, excessive fine-grained aggregate, and high percentages of natural, rounded aggregate particles. A test program was designed and initiated to quantify the contribution to plastic deformation in laboratory-prepared asphalt concrete mixtures when increasing amounts of natural (uncrushed) aggregate particles are added to replace crushed particles. The objective is to generate supporting data and prepare specifications for maximum quantity of certain natural sands, minimum top-size aggregate, and minimum voids in mineral aggregate in paving mixtures to be placed on high traffic volume roadways. Tests on asphalt mixtures included unconfined compression, static and dynamic creep, and indirect tension; the particle index test was used on the aggregate. Results to date have indicated that susceptibility to plastic deformation increases dramatically whennatural fine aggregate particles replace crushed particles in a given aggregategradation. A new theoretical approach that includes the aggregate's influence on rutting is being considered. In this analysis the aggregate's characteristics are studied by using a factor in the creep-recovery performance of the mixture. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Abstract