Backcalculation of asphalt concrete Poisson’s ratio using the ultrasonic pulse velocity test

Abstract

For asphalt mixtures, it is widely known that Poisson’s Ratio (PR) varies according to several parameters, and it is a temperature and loading frequency-dependent property. However, measuring PR at different temperatures and frequencies during mechanical tests is not commonly done. For that, a complex arrangement of fixtures and instruments would be necessary, and still likely not compatible with typical cylindrical specimens. This work aimed to combine the simple and practical Ultrasonic Pulse Velocity (UPV) test with the conventional Dynamic Modulus (\(|E^*|\)) test used for determining pavement design inputs related to asphalt mixtures. To do this, four typical lower binder asphalt concrete mixes were selected, having different levels of Asphalt Binder Replacement (ABR), given the presence of RAP/RAS, and covering seven different asphalt binders in terms of Performance Grade (PG). Additionally, a baseline mixture with no recycled material was used for comparison. Results show that estimating \(|E^*|\) via UPV assuming a typical PR value may be inaccurate. Once reference experimental modulus values were available, PR was backcalculated using the UPV theory, showing that this property increases as temperature increases, while it decreases as ABR and air voids increases. This indicates that PR can be a source of significant variability when it comes to the use of recycled materials. Therefore, UPV emerges as a low-cost, practical, and reasonably accurate piece of equipment (compared to state-of-practice assumptions) with potential to be integrated with traditional \(|E^*|\) testing for an assessment of PR sensitivity according to different mixes’ properties.