Application of Direct Tension Testing to Field Samples to Investigate the Effects of HMA Aging

Abstract

There are many factors which contribute to fatigue failure in HMA. While studies have been made with respect to binder aging, little has been done to investigate the effect of aging on the fatigue failure of asphalt mixtures. The lack of an effective and efficient method of testing field samples has contributed to this deficiency. This study focused on the development of a method for preparing and testing field samples in direct tension. This methodology was then be employed in combination with the VEC and RDT* tests to investigate several factors that affect fatigue in HMA. Particular emphasis was placed on the role of aging in the fatigue process.

A method of testing field samples in direct tension was successfully developed. Results from the VEC and RDT* tests performed on several field samples collected from across the state of Texas were analyzed. US 277 field sample results were compared to laboratory mixed and compacted (LMLC) sample results as well as results obtained from extracted binder testing. Findings show that oxidative aging has an impact on the stiffness and performance of HMA. Chip seal surface treatments can extend the life of the pavement, but their affects are found primarily at the surface.

Two additional field sites were tested, analyzed, and compared to LMLC results. These comparisons verified the effects of aging and show that a relationship between LMLC samples and field samples can be developed. Modulus values for one month of artificial aging of LMLC samples is equivalent to 10.5 months of aging in the field.

Finally, 21 Texas sites used for the study were analyzed and a multivariate linear regression was performed to determine the factors that play the most significant role in the aging process. A linear regression model was constructed to determine the number of loads to failure from fatigue cracking due, primarily, to aging.