Repeatability and Reproducibility of Low-Temperature Testing of Asphalt Mixtures Using a Modified Bending Beam Rheometer

Abstract

Low-temperature cracking is one of the major causes of pavement distress during the winter season. Research has shown that measuring the flexural stiffness of asphalt mixture beams using a bending beam rheometer (BBR) is a good way to control the low temperature properties of asphalt mixtures. However, before such a test is adopted as a specification, the repeatability and reproducibility of the testing protocol need to be verified. This study uses the draft American Association of State Highway and Transportation Officials protocol established by Marasteanu et al. to evaluate the variability of results from two separate laboratories, one at the University of Utah and one at the Utah Department of Utah central laboratory. The purpose of this research is to examine the reproducibility of test results across different laboratories. A series of gyratory asphalt mixture samples were examined based on mixture designs from Utah highways; each of the samples was cut into thin asphalt mixture beams and divided evenly between the two laboratories. Each set of tests shared the same variables for both laboratories and were conducted on the same day. The testing was performed at a temperature of -18°C, which corresponds to the low temperature performance grade plus 10°C. One variable was altered between each pair of tests, namely the amount of time between cutting of the gyratory asphalt mixture sample and running of the test. The variations in time conducted after cutting included four intervals: two days, three days, one week, and two weeks after cutting, which highlight the effects of any steric hardening for both short and long periods on the repeatability of results. The results of these tests demonstrated consistency across both laboratories. These results also indicate that steric hardening has no effect on testing samples after 48 hours and that the test results are repeatable for the same asphalt mixture specimen. Therefore, the BBR test can be used as a low-temperature specification for asphalt mixtures.