Abstract:
Premature asphalt rutting, due to high temperatures and heavy loads, has been a major
distress on flexible pavements in Pakistan. One of the main causes of this early rutting is the
available asphalt binders, which are still graded by using penetration grading system. The
primary objective of this study is to study the high temperature susceptibility of the available
asphalt binders in Pakistan. This was accomplished by collecting the temperature data from
twenty-one meteorological stations from several geographical locations in the country.
Based on the temperature variations, the country was divided into different climatic regions.
The Superpave procedure was adopted to establish PG grade requirements for these regions.
The country was then divided into different PG grade zones. Subsequently, it was observed
that PG grades 70-10, 6 4-10, and 76-10 were the three critical binder grades required in
Pakistan. Later, all available asphalt binders, typically used in the highway construction,
were obtained from two refineries —Attock Refinery Limited (ARL) and National Refinery
Limited (NRL). The binders were then subjected to performance testing using the state-ofthe-
art equipment to determine the critical high temperatures. It was found that the ARL
binders having a penetration grade 60/70 is being used in PG 76-10 and PG 70-10 zones and
have a high temperature performance grade of only 58. Moreover, NRL 60/70 and NRL
80/100 grades were found to have same high temperature PG grade. To characterize the
rheology of available binders, master curves were developed by using dynamic shear
rheometer (DSR) and performing frequency sweep tests. The rheological parameters form the
developed master curves showed the superiority of polymer modified binder ARL60/70 (P)
over rest of the asphalt binders. These results show that the existing asphalt binder grades
will be very susceptible to high temperatures as being used in Pakistan. It is therefore
recommended that harder asphalt binder should be used in the country and the PG grading
systems should be adopted to mitigate asphalt-related rutting in Pakistan.
