Performance of Asphalt Concrete Pavements

The performance of asphalt concrete, cement stabilized granular materials, and unstabilized aggregates are reviewed. Cracking of primary pavements was found to be a more important distress mechanism than rutting. Frost susceptible subbases and bases, low percentages of stabilizing agents and unstabilized base materials having poor gradations and low densities, or both, are important factors resulting in poor performance of pavements. The basic CBR design assumption requiring a minimum depth of material of only gradually increasing CBR value above the subgrade is shown not to be valid for high quality materials. Surface cracking can usually be controlled by attaining low air voids in the asphalt concrete through the use of higher asphalt contents, closer control during mixing and field compaction, and the use of lower viscosity asphalts. The required structural section should probably be selected using the lower measured subgrade strengths particularly for poor subgrade conditions.