Investigation of top-down cracking mechanisms using the viscoelastic continuum damage finite element program

This dissertation presents an advanced analysis tool for predicting top-down cracking (TDC) of hot-mix asphalt (HMA) pavements in a realistic manner. TDC is known to involve a complicated set of interactive mechanisms, perhaps more so than other HMA distresses. Such complexity makes it difficult to predict TDC reliably using conventional material models and analysis tools. Over the years, the viscoelastoplastic continuum damage (VEPCD) model has been improved to better understand and predict the behavior of asphalt concrete materials. The ability of the VEPCD model to accurately capture various critical phenomena has been demonstrated. For fatigue cracking evaluation of pavement structures, the viscoelastic damage (VECD) model has been incorporated into a finite element code as VECD-FEP++. To use this code in the prediction of TDC requires the enhancement and incorporation of additional sub-models to account for the effects of aging, healing, thermal stress, viscoplasticity and mode of loading. Although some of these models are not fully refined due to incomplete knowledge of the underlying physics of the process, placeholder models are incorporated into the framework so that they can be easily replaced when more fundamental approaches are identified. Within this VECD-FEP++ framework, a systematic parametric study is performed to identify the role of various mechanisms in TDC under certain specific conditions. Analysis using the enhanced VECD-FEP++ is found to capture some intuitive and important phenomena of TDC. Finally, to assess the capability of the VECD-FEP++ framework, the Federal Highway Administration Accelerated Load Facility (FHWA ALF) pavements are simulated and the results is found to agree well with the measured field performance. After proper calibration, this tool could provide quantitative predictions of the extent and severity of TDC.