Laboratory Performance Evaluation of Fine and Coarse-Graded Asphalt Concrete Mix

During the last 20 years, Superpave pavements were built using mostly coarse-graded mixes as opposed to fine-graded mixes. This is because coarse mix requires less asphalt binder than a fine mix, whereas both mixes fulfill the Superpave criteria. Recently, it was observed nationally that the Superpave mixes have good field rutting performances but poor cracking performances. A common belief now is that fine mixes could have solved this cracking issue of Superpave. The idea is that the fine mixes would have less air voids which would transmit less air and water, and thereby, fine mixes would have less aging/cracking and moisture damage, respectively. To this end, this study evaluates whether a fine-graded mix has better performances than a coarse-graded mix. Both mixes have identical performance grade binder, reclaimed asphalt pavement (RAP) content, and aggregate source and were collected from a road site on New Mexico (NM) 14, where they were applied side-by-side to construct two-lane 2-mile sections in each direction. Both mixes were tested for dynamic modulus, Hamburg wheel tracking device (HWTD) rutting, beam fatigue (BF), thermal stress restrained specimen test (TSRST), and semicircular bending (SCB). The coarse mix shows higher dynamic moduli and better rutting performances than the fine mix, which were expected. The fine mix failed (more than 12.5 mm rutting for 10,000 passes) in HWTD rutting. The coarse mix shows better fatigue performance than the fine mix. Critical fracture energy release rate ($J_C$-integral) from the SCB test demonstrates that both mixes have similar crack resistance properties. TSRST test results demonstrate higher failure strength and lower failure temperature for coarse mix compared with fine mix. Therefore, simply replacing coarse mix with fine mix cannot resolve Superpave’s cracking issue.