Use of the Hirsh Model to Back Calculate the Performance Characteristics of the Blended Binder in Superpave Recycled Hot Mixtures

摘要

When Reclaimed Asphalt Pavement (RAP) is incorporated into hot mix asphalt the characteristics of the resulting binder are uncertain. It is anticipated that some degree of blending occurs between the aged asphalt contained in the RAP and the virgin asphalt. Considering that the use of recycled hot mixtures is an extended practice in Ontario, this paper explores the behaviour of laboratory-prepared mixtures combining different RAP content and virgin asphalt Performance Grade (PG). The mixture proportions were adjusted in order to make the mix volumetric properties meet the requirements and to retain similar mix gradations. Dynamic modulus testing was conducted on replicated specimens using the Asphalt Mixture Performance Tester (AMPT) following the AASHTO TP79 standard. The resulting complex modulus of the mix (E~*) was used to estimate the complex modulus of the binder (G~*) through the Hirsch Model, and the resulting master curves were compared with the results from direct testing using the Dynamic Shear Rheometer (DSR) on the extracted and recovered binder. From the results it can be concluded that it is possible to estimate the performance of the blended binder from the performance of the mix. The analyses also allowed verifying that the blending between the old and new binders occurring in the mix is incomplete.