Micromechanical description of bitumen aging behavior

Abstract

For the design of durable pavement constructions, considering the change of material properties of hot mix asphalt over time is essential. Hardening and embrittlement of bitumen lead to a reduced resistance against cryogenic cracks and the premature formation of fatigue cracks in bituminous layers. This phenomenon called aging is induced by environmental impacts. Within this work, a micromechanical model extending an existing multiscale model for hot mix asphalt is proposed, which allows a prediction of the consequences of microstructural changes observed as a result of aging effects. On the basis of AFM and ESEM images, a microstructure of bitumen consisting of a contiguous matrix with an embedded micelle-like structure can be identified. Hence, a structural concept based on SARA fractions arranged in a representative volume element is suggested. Static shear creep tests on artificially composed bitumen with asphaltene contents varying between 0 and 30 wt% in aged and laboratory-aged (RTFOT+PAV) conditions were conducted to identify the properties of material phases as well as to validate the presented model assumptions. A very good accordance between model predictions and experimental results indicates that the model is able to reproduce as well as to describe significant microstructural effects related to aging.