INTRODUCTION OF PERFORMANCE BASED SPECIFICATIONS FOR ASPHALT BINDERS IN PAKISTAN

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.