Michael J. Farrar

Bio: Michael J. Farrar is an academic researcher from Wyoming Department of Transportation. The author has contributed to research in topics: Dynamic shear rheometer & Test method. The author has an hindex of 11, co-authored 19 publications receiving 569 citations.

New Low-Temperature Performance-Grading Method: Using 4-mm Parallel Plates on a Dynamic Shear Rheometer

Abstract: Mechanical measurements on asphalt binders to determine the performance grade of the low-temperature specification are typically carried out with a bending beam rheometer (BBR). The BBR test requires considerable material to fabricate a specimen (approximately 15 g per beam). The relatively large amount of asphalt binder required for the BBR limits its applications. The BBR is difficult to apply to extracted asphalt binder or to other situations in which there is a limited amount of binder, for example, residue from emulsions. This paper proposes an alternate mechanical test to the BBR to determine low-temperature PG. Only approximately 25 mg of asphalt binder are required to perform a test. The test employs 4-mm-diameter parallel plates on a dynamic shear rheometer (DSR) and includes a correction for machine compliance. This correction allows testing to -40°C. A low-temperature specification from the 4-mm rheometry is suggested by the establishment of a correlation between BBR creep stiffness data and DS...

New Technique for Measuring Low-Temperature Properties of Asphalt Binders with Small Amounts of Material

Abstract: A new technique, which uses 4-mm parallel plates on a dynamic shear rheometer (DSR) with machine compliance corrections, was developed to measure low-temperature properties of asphalts. Good results have been achieved at test temperatures as low as -40°C. The test method requires only about 25 mg of material instead of 15 g for the bending beam rheometer (BBR). Also, no specimen premolding is needed, and a relatively low temperature (60°C to 70°C) is required to load the samples into the measuring system. The key to the new technique is correction for errors due to machine compliance. Two types of machine compliance correction were applied to the dynamic frequency sweep data in this work. The following areas were investigated: effects of machine compliance on the measured low-temperature properties, reproducibility of data, consistency among data collected on different sizes of plates after machine compliance corrections, and comparison between the corrected data from DSR and converted BBR data. Results s...

Evolution of the Crossover Modulus with Oxidative Aging: Method to Estimate Change in Viscoelastic Properties of Asphalt Binder with Time and Depth on the Road

Abstract: This study is based on recovered binders from a hot-mix asphalt comparative test site constructed in Arizona in 2001 with mix collected during construction and cores collected in 2005 and 2010. The intent of the study is to evaluate the potential of using the evolution of the binder crossover modulus with time and depth in the pavement to determine the change in linear viscoelastic properties of the binder during the life of the pavement. The crossover modulus is one of three parameters in the Christensen-Anderson (CA) complex shear modulus model. The CA model is used in this study to develop complex modulus and phase angle master curves of the binder as a function of field time, depth, and temperature. The master curves generated demonstrate the change in SHRP specification parameters, such as m-value and creep stiffness, as well as in the mix dynamic modulus with time and depth on the road. In addition, although asphalt dependent, a linear relationship between oxygen uptake and the log of the crossover ...