Three-dimensional micromechanical pavement model development for the study of block cracking

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Block cracking in asphalt pavements is a primary form of surface cracking but has been the subject of very few scientific investigations. Although this deterioration mode is covered in many pavement evaluation guides and condition rating systems, the underlying mechanisms of block cracking have not been fully investigated. Therefore, understanding the mechanisms behind block cracking and tailoring preventive solutions merits rigorous investigation. In this paper, a 3D discrete element viscoelastic and inhomogeneous microstructure-based pavement model subjected to thermal straining was introduced. A typical PG 64-22, dense-graded Illinois asphalt surface mixture was adopted as the baseline material because it typically experiences block cracking later in its service life. The mechanisms of block cracking patterns were investigated as a function of the dimension of pavement segments, relaxation capacity and aging state of materials, including spatial gradients, cooling rate and pre-existing crack presence using the aforementioned discrete element models. Discrete element simulations showed that initial block cracking primarily occurred in the upper one-to-two centimeters of the surface, which agreed with field observations. In addition, it was found that block cracks formed at a warmer temperature than that associated with the onset of thermal cracking. This implied that current test criteria for thermal cracking mitigation may need to be updated or supplemented in order to control block cracking. Finally, the techniques presented herein can be extended to identify candidates for preventive maintenance, and in developing tailored maintenance techniques.