Application of Calibrated Mechanistic Fatigue Analysis with Aging Effects

The work contained in this report constitutes Phase II of TxDOT Project 0-4468. Phase I is documented in Reports 0-4468-1 and 0-4468-2. The primary objective of Phase II was to provide additional laboratory validation and sensitivity analysis of the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements fatigue analysis approaches recommended in Report 0-4468-2. The second objective was to provide a better understanding of the binder-mixture relationships and effects of binder oxidative aging on both mixture fracture properties and fatigue life (Nf). The third objective was to explore the possibility of establishing a surrogate fatigue test protocol based on the CMSE approach. These objectives were achieved through fatigue characterization of additional hot-mix asphalt concrete (HMAC) mixtures with different mix-design parameters and materials under varying laboratory aging exposure conditions. Analysis of the results indicated that the CMSE approach provides a promising and rational methodology for fundamentally characterizing the fatigue resistance of HMAC mixtures. The results obtained were reasonable and exhibited low statistical variability. Compared to the CMSE, the simplified CM approach has a reduced laboratory test program and analysis time, but it is less versatile. For the materials and test conditions considered in the project, Nf was observed to be dependent on both mix-design parameters and material properties. Generally, an increase in binder content improved the mixture fracture properties and Nf. The results further indicated that binders and mixtures do stiffen due to oxidative aging and that the Nf decline is characteristic of each mixture type. The application of Miners¿ cumulative damage concept also provided a fundamentally promising basis for quantifying Nf decline as a function of both aging and traffic loading effects and should be explored further. With respect to CMSE laboratory testing, although the repeated direct-tension test provided the best correlation with CMSE Nf predictions, the tensile strength test was preliminarily proposed as the surrogate fatigue test protocol based on practicality and simplicity. However, additional validation of the CMSE and CM approaches together with the surrogate fati.ue test orotocols and software develot,ment are recommended.