Comparison of moduli for asphalt binders obtained from different test devices

Tests performed using Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), and Direct Tension (DT) device can be used to generate various linear viscoelastic functions. According to the theory of viscoelasticity, any viscoelastic function can be converted into any other viscoelastic function. The behavior of these conversions when applied to test data for four unmodified asphalt binders was investigated, to compare moduli generated by the three test devices. Inter-conversion methods available in polymer literature were successfully used to inter-relate viscoelastic moduli determined from laboratory tests. From a selected number of methods that could be applied to asphalt binder rheological data, the methods with the least degree of error were: dynamic shear moduli to creep compliance, dynamic shear moduli to relaxation modulus, creep compliance to relaxation modulus, and constant strain rate stress-strain to relaxation modulus. Significant differences were found between moduli generated from the DSR and BBR test devices, attributed to the influence of cooling rate on physical hardening and the sample size. Smaller differences were observed between DT and BBR data. However, after approximately 10 sec, DT relaxation modulus began to decrease, suggesting that nonlinear effects occurred in the test sample at large strains.