WHEN CAN BITUMEN RHEOLOGICAL PROPERTIES BE USED SUCCESSFULLY TO PREDICT ASPHALT MIX PERFORMANCE

With the advent of higher axle loads and increasing traffic densities, the use of polymer modified bitumen (PMBs) and other speciality binders is increasing. Such modification of the binder is intended to change its rheological properties, for example decrease the temperature susceptibility, enhance elasticity and increase viscosity. These enhancements, which improve pavement performance, are not necessarily characterised by conventional binder properties. As a result, correlations with asphalt performance may break down. In recognition of the short-comings of these traditional tools, BP has conducted an extensive research programme to investigate the benefit of using fundamental binder rheological measurements to predict asphalt pavement performance. Performance of dense mix asphalts were investigated as follows: (1) Permanent Deformation (Rutting) at high service temperatures (40 to 60 degrees C); (2) Fatigue at intermediate service temperatures (0 to 20 degrees C); (3) Brittle Fracture at low service temperatures (-40 to 0 degrees C). From data presented in the paper it may be concluded that compared to standard, empirical binder properties, carefully selected rheological criteria can provide a more reliable prediction of asphalt performance for modified, unmodified and speciality binders. At high and low temperatures it appears that binder rheological measures may be used as indicators of mix performance for the purposes of comparing binders in a given mix. Loading and temperature conditions under which measurements are made are critical. However, the issue of fatigue is more complex and it may be necessary to use other binder and/or mix measurements to predict fatigue performance. (A) For the covering abstract see IRRD 885061.