Use of Black Diagrams to Identify Inconsistencies in Rheological Data

ABSTRACT This paper describes the use of Black diagrams of complex modulus versus phase angle to detect the occurrence of inconsistencies in rheological data caused by testing irregularities and distinctive material properties. In general, conventional penetration grade bitumens can be classified as “thermo-rheologically simple” materials with their rheological properties being temperature and time equivalent provided that they are determined within the binder's linear viscoelastic region and by suitable testing procedures. In the paper, Black diagrams have been successfully used to identify compliance (testing) errors in rheological data associated with the inappropriate use of various dynamic shear rheometer spindle geometries. The results indicate that using a 25 mm diameter testing geometry at complex modulus values greater than 105 Pa leads to an overestimation of elastic response and an underestimation of binder stiffness. As Black diagrams do not require any manipulation of rheological data prior to data presentation, they provide a convenient means of assessing the effect of polymer modification and oxidative ageing on the rheological properties of bituminous binders. In general, semi-crystalline EVA PMBs tend to show unique rheological characteristics at intermediate temperatures due to the occurrence of different crystalline structures at different temperatures. Elastomeric SBS PMBs tend to produce a distinctive elastic response at high temperatures/low frequencies as a result of their dominant polymer network. Finally, Black diagrams have been used to identify discrepancies in rheological data due to non-linear effects before attempts are made to shift the data to produce smooth, continuous master curves.