EFFECT OF SEGREGATION ON PERFORMANCE OF HOT-MIX ASPHALT

Segregation of hot mix asphalt (HMA) pavements has been one problem that has resulted in poor performance in many pavements. There is currently no procedure available for quantifying segregation to determine how much segregation is too much, or in other words, how much coarser the gradation must be before a reduction in performance is expected. Therefore, the objective of this study was to determine how much segregation can be tolerated before premature raveling is the likely result. Five pavements from the Alabama Highway Department Divisions 4 and 6 were selected for inclusion in the study. Visual estimation of the severity of raveling and segregation were made and cores from the pavements were obtained. The density was measured with a thin-lift nuclear gauge and the macro-texture of the pavement surface in the segregated area was determined. A detailed laboratory testing program was performed on the cores and evaluated to characterize the mixture properties and their effect on raveling. Traffic data and mix design information was obtained for each pavement. Briefly, the conclusions from this study were as follows: (1) A variation in the percent passing the No. 4 sieve greater than 10 to 12% can lead to significant raveling; (2) Segregated areas of a pavement have lower asphalt content than that of the average asphalt content of the test section; (3) Segregated areas of a pavement have lower in-place density than the average density of the pavement; (4) Segregated areas of a pavement after 2-3 years have smaller sand patch diameters than the average sand patch diameter of the pavement indicating raveling and some differences in surface texture; (5) Traffic as measured by age and AADT has an effect on the sand patch diameter and hence raveling; and (6) The sand patch diameter which can be quantified correlates to the amount of raveling.