Abstract
A novel Three-Point Bending Beam Test (3-PBT) using a Dynamic Shear Rheometer (DSR) with linear drive motor is introduced for testing asphalt binder at low temperature conditions. This 3-PBT in DSR can be used as surrogate for Bending Beam Rheometer (BBR) tests. Advantages in comparison to BBR are that (i) 3-PBT works without harmful cooling medium ethanol, (ii) the amount of asphalt binder for testing is significantly lower (using material equivalent of 10% of BBR tests), (iii) a silicone rubber mold is used for specimen preparation instead of standard aluminum mold for BBR tests, which makes handling easier, and (iv) the loading protocol is more practical without applying contact load manually. The novel 3-PBT in DSR is presented with respect to preparation, installation, and conditioning of specimens, as well as to the loading protocol. Tests were conducted at temperatures of −10, −16, and −20°C. For the purpose of comparison to BBR tests, and of identifying most suitable testing conditions from alternative setups, a test series was run including 9 different asphalt binders. As to BBR tests, two different cooling media were used, i.e., ethanol and air. Finally, all test results obtained from DSR and BBR tests were analyzed in view of precision and correlation. DSR results correlated well with BBR results, while precision of 3-PBT in DSR was found to be satisfying.
Highlights
Thermal cracking is known as a major mode of deterioration in poorly designed asphalt pavements (Arand, 1983; Arand, 1998; Bouldin et al, 2000; Wistuba et al, 2009; Wistuba, 2019)
(iii) the amount of asphalt binder for specimen fabrication is around 1.2 g and significantly lower, using a material equivalent of 10% of Bending Beam Rheometer (BBR) tests only, (iv) a silicone rubber mold is used for specimen preparation instead of standard aluminum mold for BBR tests, which makes handling easier and saves time, (v) the loading protocol is more practical without any need to apply contact load manually, the effect of which on the test specimen is unknown, (vi) one and the same Dynamic Shear Rheometer (DSR) instrument can be used for the determination of characteristic rheological binder properties in shear mode and in bending mode
Depending on the accessories and the manufacturer of each device, the price of a DSR including an axial system for 3-PBT can range from two to three times the price of a BBR
Summary
Thermal cracking is known as a major mode of deterioration in poorly designed asphalt pavements (Arand, 1983; Arand, 1998; Bouldin et al, 2000; Wistuba et al, 2009; Wistuba, 2019). The resistance of asphalt binder to low-temperature is usually addressed via Bending Beam Rheometer (BBR) tests (AASTHO T313-12, 2012; EN 14771, 2012). In BBR tests, the low-temperature flexural creep stiffness and the relaxation properties of the asphalt binder are addressed. For this purpose, an asphalt binder prismatic beam (125 mm in length, 6.25 mm in height, and 12.5 mm in width) is horizontally placed in a cold fluid bath, and is loaded by applying a constant load of 980 mN to the midpoint of the beam. BBR has developed as the primary testing tool for measuring low-temperature characteristics of asphalt binders (mostly long-term aged prior to BBR testing). Various authors have reported significant drawbacks of BBR testing related to specimen preparation and testing conditions, i.e.,
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