Investigation of bitumen rheological properties measured at different rheometer gap sizes

The dynamic Shear Rheometer (DSR) test is a standard method used to characterize the rheological properties of bitumen binders. Prior research substantiates the belief that, given that measured results are dependent on the rheometer gap size, currently recommended rheometer gap sizes (1 mm/2mm) cannot represent the mechanical properties of bitumen in asphalt mixtures. This study focused on the effect of gap size on the rheological property of bitumen binders. To this end, three bitumen binders were measured at different rheometer gap sizes (10 ~ 1000 μm). Subsequently, the rheological properties, including the complex modulus, phase angle, master curve, black diagram, were discussed. The results indicated that the measured rheological properties of bitumen binders are related to the testing gap size. In particular, as the gap size decreases, the complex modulus tends to decrease. Due to the presence of modifiers, the effect of the rheometer gap size also depends on the type of bitumen. The selective adsorption and colloidal theories were introduced to understand the effect of gap size. Additionally, a mathematical relationship called Temperature-Gap Superposition Principle (TGSP) was proposed to establish the relationship between the measured complex moduli in the standard state and the thin state.