Date of this Version
Kommidi, S. R. and Kim, Y-R. (2019). "Investigation of DSR Test Methods to Determine Binder Low Temperature Properties". NDOT Research Report #SPR-1 (18) M073.
The low temperature rheology of bituminous binders is of great interest because low temperature cracking is one of the primary asphalt pavement failure modes observed in cold-climate places such as Nebraska. Low temperature binder characterization/grading has been primarily conducted using the bending beam rheometer (BBR), while the dynamic shear rheometer (DSR) can alternatively be used to characterize the low temperature properties of binders with the recent advancement of DSR equipment that can cover a wide range of testing temperatures. This study investigates alternative testing-analysis methods using the DSR to determine low temperature asphalt binder properties that have been measured by the BBR. Toward that end, twelve different binders from four sources satisfying three different PG grading criterion common in Nebraska were selected. The binder samples were tested in the frequency domain at temperatures ranging from 60°C to -30°C under PAV-aged conditions using DSR. The 8-mm parallel plate geometry was primarily employed for the testing, while four binders were randomly selected and tested using the 4-mm parallel plate to investigate the influence of geometry on the results. BBR experiments were also performed as a parallel for each binder. Three methods were used to analyze and compare the data from the two different experiments (i.e., DSR and BBR) where each method utilizes a different scheme for converting the frequency domain results to time domain data to compare with the BBR results. The three methods are: (1) Western Research Institute’s (WRI) methodology; (2) NCHRP methodology; and (3) UNL’s mechanistic approach. It was observed that the DSR testing is quite promising, and sample preparation is crucial to obtain reliable-repeatable results. Moreover, in the proposed UNL’s mechanistic approach, it was observed that a single shift factor for creep compliance may account for different testing conditions, differences in physical hardening and temperature-dependent effects. The approach was then extended to seven additional binders to further examine its feasibility, and it was observed that the predictions from the proposed approach match well with the experimental values.