Volume 40, Issue 4 (July 2012)
Correlation of Flow Number with Stiffness Obtained from Dynamic Shear Rheometer Testing of Extracted Binder from Asphalt Concrete Containing Recycled Asphalt Pavement
This paper describes the results of a study that used the flow number (FN) test to evaluate the rutting susceptibility of asphalt concrete (AC) mixtures containing recycled asphalt pavement (RAP). The study compared the rut depths determined using an asphalt pavement analyzer (APA) (APA rut depth) with binder stiffness test data obtained with a dynamic shear rheometer. Both APA rut depths and binder stiffness are used to evaluate the rutting susceptibility of AC mixtures in Virginia. However, recent studies suggest that the results of the FN test might correlate better with field rutting than most existing rut tests. In addition, because currently almost all AC mixtures produced in Virginia contain RAP, extraction and recovery (ER) tests are required to obtain binder for testing. Therefore, another objective of the study was to determine whether the correlation between FN and the stiffness of recovered asphalt binders would allow the FN test to be used as a surrogate for the recovered binder stiffness. For the mixtures evaluated, the APA rut depth ranged from 0.61 to 1.99 mm, the FN from about 700 to 7500 cycles, and the binder stiffness from 1.637 to 8.498 kPa. The results show that FN was positively correlated with binder stiffness (r = 0.8507, p < 0.0001) but not correlated with APA rut depth (r = −0.2666, p = 0.3010). The results also show that APA rut depth and binder stiffness were not correlated (r = 0.01829, p = 0.944). The study concluded that FN is sensitive to binder stiffness for the mixtures considered. This suggests that the FN test could be used as a new approach for evaluating the effect of RAP on asphalt mixtures and thereby replace or minimize the use of binder ER test methods.