Critical factors affecting thermal cracking of asphalt pavements: towards a comprehensive specification

Thermal cracking remains one of the most challenging distresses to predict and reduce in pavements constructed in cold regions. The research community after more than 40 years of extensive research has gained significant understanding of the mechanisms and factors affecting this distress. Current specifications and testing methods used for the selection of materials are a good starting point for the minimisation of this distress. However, there are critical factors and properties not addressed in current specifications that if considered could further improve the performance of asphalt pavements to thermal loading. This paper provides a critical review of the main factors affecting low-temperature cracking and the current analyses and testing methods used for the design. Analysis of thermo-volumetric and fracture properties from a multi-scale perspective (i.e. Binder→Mastic→Mixture) is used to suggest the addition of key performance parameters that can complement current specification parameters (e.g. S and m-value at 60 s in the bending beam rheometer). Furthermore, this paper discusses the pros and cons of the traditional methods used for thermal stress–strain analysis when designing pavements to resist thermal cracking: (a) continuous approach and (b) fracture mechanics approach (i.e. inclusion of a pre-determined flaw). Based on recent findings and testing results from major research activities as part of the Asphalt Research Consortium and two pooled-fund studies on low-temperature cracking (Phase I and Phase II), recommendations are made with regard to the analysis framework and to the mechanical characterisation of asphalt materials. Suggestions are made for the development of a more comprehensive specification that includes fracture and thermo-volumetric properties not accounted for in current practice.