Evaluation of the effects of aggregate gradation and compaction effort on the voids in mineral aggregate in asphalt concrete.

摘要

Asphalt concrete should resist short-term rutting, provide resistance to thermal cracking, and maintain structural integrity through the design life of the structure. Balancing these factors is achieved by ensuring adequate asphalt binder in a strong aggregate structure. The design asphalt content is decreased by applying additional compaction effort in the form of increased gyrations in the Superpave Gyrator Compactor. The mixes that undergo increased compaction effort present decreased fatigue life, although they resist short-term rutting. Mixes that undergo less compaction effort contain more binder and have long fatigue lives, although they are susceptible to rutting.;Two hypotheses were tested to determine the effects of compaction effort, and gradation on the voids in mineral aggregate. Three gradations were tested to simulate the range of aggregate gradations allowed within the West Virginia Department of Highways control points for 9.5mm asphalt concrete at compaction levels of 80, and 100 gyrations. The reduction in the number of design gyrations for asphalt concretes in West Virginia does not create significant differences in the design parameter, voids in mineral aggregate (VMA). At a given compaction level, moving away from the maximum density line, either coarse- or fine-graded, creates statistically different VMA.;Additionally, the bulk specific gravity samples were tested for indirect tensile (IDT) strength, and fracture energy. The 80 gyration mixes presented higher IDT strength than the 100 gyration mixes. Mixes with high compaction slopes presented the lowest IDT strength. Using the load-deflection curves from the IDT test, the fracture energy was calculated. The 80 gyration mixes had fracture energy 32% greater than the 100 gyration mixes, indicating an increased fatigue life. The coarse graded mix has the largest increase in fracture energy when reducing compaction effort, although it had the lowest IDT strength.