Abstract Manager

The AASHTOWare Pavement ME Design (PMED) software is a comprehensive design and analysis tool based on mechanistic-empirical approach. The software can predict various distresses in pavements for varied traffic loads, layer materials, subgrade and climate. However, its widespread adoption is facing challenges because of inadequate, inconsistent or unrealistic responses to some key inputs. Asphalt binder grade (or properties) is one of such key inputs into the PMED software for the design and analysis of flexible pavements.

The TAC ME Design Subcommittee conducted a series of design trials using the new version (v3.0) of the PMED software to evaluate the predicted performance of new flexible pavements for varied asphalt binder performance grade (PG) under varied climatic conditions (11 weather stations) across Canada. These trials aimed to assess the impacts of asphalt binder grade selection on key pavement performance measures such as smoothness (IRI), permanent deformations, thermal cracks and fatigue cracks. The selected (nine) asphalt binder grades included PG 58-22, 58-28, 58-34 and 58-40 to assess the impact of low temperature and PG 52-28, (58-28), 64-28, 70-28, 64-34 and 70-34 to assess the impact of high temperature grades.

The preliminary analyses of results indicates that softer binders in terms of reduced low temperature grades reduce the predicted thermal cracks in some climatic areas. Increased high temperature grades generally result in reduction of thermal cracks despite that the low temperature grade of asphalt binders remains unchanged, which requires further investigation. The predicted asphalt concrete layer and total rutting depths increase with decreased low temperature grades and reduce with increased high temperature grades, as expected. The predicted bottom-up fatigue cracking and top-down fatigue cracking (TDFC) increase with decreased low temperature grades and reduce with increased high temperature grades, which are unexpected. Some inconsistencies in predicted distresses including the predicted IRI among the climatic areas were also observed. Asphalt binder with decreased low temperature grades resulted in increase in the predicted IRI in relatively warmer climates and reduction in IRI in relatively colder climates. An increased high temperature grade resulted in a reduction of the predicted IRI. The sensitivity of climatic conditions on the predicted TDFC was low.

The objective of this paper is to present the above specified trial results including detailed analyses and findings. The presented information may help agencies and interested individuals in assessing the suitability of the PMED software and the impact of selecting an asphalt binder grade on pavement performance.