Temperature Zoning of Pakistan for Asphalt Mix Design

M. Waseem Mirza, Zahid Abbas, Mujasim Ali Rizvi

Abstract


The current asphalt binder specifications in Pakistan are based on the Penetration Grade: penetration test is performed at 25oC. Penetration is an empirical measure of the consistency that is used as an empirical indicator of the rutting and fatigue susceptibility of asphalt binder, and is not related to pavement performance. The new mix design methodology developed under the Strategic Highway Research Program (SHRP), called the SUPERPAVE is a performance-based approach. The first step in the implementation of SUPERPAVE methodology is to establish high and low pavement temperatures for a location. The temperatures define the required Performance Grade (PG) of asphalt binder. This paper documents the initial ground work towards implementation of SUPERPAVE mix design for establishing high and low geographical temperature zones. The temperature zoning of Pakistan was carried out by using temperature data obtained from 64 weather stations. The SHRP and LTPP prediction models were utilized for predicting pavement temperatures. A significant difference was observed between the predicted pavement temperatures from both the models. The SHRP model gives higher, high temperature PG grade providing additional protection against rutting. Since rutting is the most common distress on flexible pavements in Pakistan, the SHRP models at 98% level of reliability is recommended. PG 70-10 binder seems to be the most common grade that encompasses more than 70% area of Pakistan. However, currently none of the two local refineries produce PG 70-10 binder, thus it should be a concern for the highway agencies. The polymer modified asphalt binder produced by Attock refinery (A-PMB) corresponds to harder PG 76-16 while A-60/70 (PG 58-22) or K-60/70 (PG 64-22) produced at Attock and National refineries respectively are softer compared to the PG 70-10. Harder grade is more prone to cracking, whereas softer grade of more prone to rutting. Consequently, the current construction practices which utilize A-60/70 or K-60/70 may be prone to excessive rutting.

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References


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