Quantitative relationship of fundamental rheological properties of bitumen with the empirical Ring and Ball softening point

This paper employs the linear viscoelastic parameter G′/tanδ as the quantitative criterion for identifying a common relationship with the Ring and Ball softening point of both unmodified and polymer-modified bitumen (PMB). Temperature sweep was conducted at 10 rad/s with dynamic shear rheometer to determine the complex shear modulus G* and phase angle δ of bitumen. The parameter G′/tanδ could be obtained. Logarithmic interpolation was applied for G′/tanδ to determine the equivalent softening temperature Ts _G′/tanδ at which G′/tanδ equals the proposed criterion values. With this method, a good agreement could be reached between Ts _G′/tanδ and the softening point for both unmodified bitumen and PMB. While keeping high accuracy for unmodified bitumen, the accuracy of Ts _G′/tanδ as an estimation of the softening point of PMB was largely improved when compared to the iso-modulus approach. The reliability of this quantitative relationship is preliminarily verified and its implementation is discussed in the Black space.