Comparative Study of the Effects of Physical and Chemical Aging on Extracted and Recovered Asphalt Binders from Some Municipal and Provincial Roads in Canada
It has been reported that estimated pavement lifecycles have been reduced by 50-60 % in Ontario over the last 25 years (Auditor General of Ontario, 2016). This raises issues of concern with respect to durability and performance among others. This document aims to comparatively study the effects of physical and chemical aging on the performance of extracted and recovered loose-mix and core mix samples from some provincial and municipal contracts in Ontario. In this study, four loose-mix (plant-aged) and eight core-mix (field-aged, 4 - 5 years) samples were cautiously extracted and recovered using dichloromethane and standard rotary evaporation in a moderate to high vacuum, nitrogen atmosphere and final bath temperature of 160 °C for one hour. The binders recovered from the loose-mix samples were taken through laboratory aging using the standard Superpave® pressure aging vessel method and all the samples were evaluated for their performance using conventional Superpave® methods such as Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) and the improved Ministry of Transportation of Ontario methods (LS-308 Extended Bending Beam Rheometer (eBBR) and LS-299 Double-Edge Notched Tension (DENT) test). Chemical test methods like Fourier Transform Infra-red (FTIR) spectroscopy and X-ray Fluorescence (XRF) analysis were used to determine the presence of carbonyls, sulfoxides, zinc and molybdenum which result from chemical oxidation and the addition of recycled engine oil bottoms (REOB). The significant amount of zinc and molybdenum found in all the samples could be a result of addition of REOB, which is known to accelerate the process of physical and chemical aging. All the binders recovered from the loose-mix samples showed better performance based on their performance grading using the dynamic shear rheometer, extended bending beam rheometer and double-edge notched tension test at low, intermediate and high temperatures. Their durability is however suspect since they contained significant amounts of zinc, molybdenum, carbonyls and sulfoxides known to be ‘aging accelerators’. All the field-aged (4-5 yrs.) samples but one showed poor performance at low, intermediate and high temperature which is explained by the comparatively higher amount of zinc, molybdenum, carbonyls and sulfoxides found in them. The extended bending beam rheometer (eBBR) method was seen as a more efficient quality control indicator since some of the samples which passed the regular bending beam rheometer method failed the extended bending beam rheometer test based on the grade losses.