Low-temperature performance prediction of asphalt mixtures used for LLP—new approach based on fundamental test methods and numerical modeling

Abstract

A major mode of deterioration in fully-flexible long-life pavements (LLP) is surface-initiated top–down cracking. If surface maintenance is suspended, surface-initiated cracks may conflict the long-life concept, as they will propagate into the structural layers and structural deterioration will start. The risk of surface-initiated top–down cracking is influenced by a number of interacting factors. Critical stresses may result, e.g. from the 3D loading situation at or near the pavement surface due to contact stresses between the tire and the pavement surface, from a sudden change in the asphalt layer temperature gradient, from traffic loading at low-temperatures and from material related factors like asphalt ageing and particle segregation due to stripping of the binder. Cracks may also be initiated by early construction micro-cracks induced by the asphalt roller. Depending on the respective mechanism of initiation, surface cracks are observed to be orientated in both directions, transversally to the road axis and longitudinally and longitudinal cracks are found inside as well as outside the wheel-path.

In this study, the combined effect of tensile stresses resulting from both traffic and thermal loading in a typical fully-flexible LLP structure is investigated. Supposed that the risk of surface-initiated cracking can be minimized by using an appropriate asphalt material, the main objective of this paper is to find important missing links between the characterization of fundamental low-temperature properties of an asphalt mixture, on the one hand, and its in-service behaviour with special regard to the risk of surface-initiated top–down cracking at low-temperatures, on the other hand. Based on fundamental test methods, material modeling and numerical simulation, an overall concept is presented that will enable a better prediction of the low-temperature performance and a better risk evaluation of surface-initiated cracking at low-temperatures. First promising results are given for a typical fully-flexible LLP structure that is exposed to prescribed temperature and loading scenarios. Realistic critical stress distributions at the road surface in consequence of combined thermal and traffic loading are found that allow assessment of the risk of longitudinal surface-initiated top–down cracking at low-temperatures.

Keywords:

• Surface-initiated top–down cracking
• Low-temperature cracking
• Long-life pavement
• Performance prediction