Integration of laboratory testing, field performance data and numerical simulations for the study of low-temperature cracking

Low temperature cracking remains one of the major pavement distresses in asphalt concrete pavements in cold regions. An integrated laboratory testing, field performance data, and numerical simulation approach was used to study thermal cracking as part of a US National Pooled Fund Study on Low-Temperature Cracking. This paper focuses on testing, analysis, and field data from five controlled test sections at the Minnesota Road Research Program facility (MnROAD). Low temperature viscoelastic relaxation modulus master curves and tensile strength were obtained from indirect tension testing conducted at three temperatures. Fracture energy of field samples were obtained using the disc-shaped compact tension (DC[T]) test. Temperature-dependent thermal coefficient data was collected by one of the research partners (the University of Wisconsin) for each of the five field mixtures. A bi-linear cohesive zone model was used in the simulation of thermal cracking in five MnROAD pavement sections. Four custom-designed user subroutines were employed in the commercial finite element program ABAQUS, including: a bi-linear cohesive zone fracture model, a temperature shift factor routine, a time- and depth-dependent temperature profile algorithm, and a bi-linear thermal coefficient routine. The temperature boundary conditions were generated using the Enhanced Integrated Climatic Model (EICM) available in the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) using air temperatures obtained from National Weather Service databases. Detailed field performance crack maps were used to compare actual field cracking against numerical simulation results. This paper describes how this comprehensive, integrated testing and modeling program provided new insights towards the mechanisms of thermal cracking in asphalt pavements.