Performance of Hot Mix Asphalt Using Coarse and Skip Graded Aggregates

The aggregate gradation of the hot mix asphalts (HMA) used in southern Nevada before 1989 generally fell above the maximum density line (fine graded aggregate mix). Various asphaltic concrete pavements using an aggregate gradation curve that resides below the maximum density line for any nominal size aggregate have been placed in the southern Nevada area over the past few years. These pavements have shown improved resistance to rutting and permanent deformation. This paper presents mix design and performance (rutting) data of four (post-1990) projects in which the gradations range from continuous coarse graded to skip coarse graded aggregates (gradation curves that dropped sharply from the 3/4 in. sieve to the 1/2 in. sieve size then continued in a well-graded fashion). Maximum rut depths were measured for all traffic lanes at major intersections, and average rut depths were then calculated for each project. Rutting measurements were made after at least one annual cycle of operation. These measurements show a 50% rutting reduction when the continuous coarse graded aggregate HMA was used instead of the pre-1989 fine graded aggregate HMA. The rutting was further reduced by 50% when skip graded aggregate HMA was used instead of the continuous coarse graded HMA.