Low temperature behavior of very hard bituminous binder material for road applications

Very hard bituminous binders are becoming popular in pavement design. Mixtures with very high stiffness are used already for a number of years in the Netherlands as base course materials. Asphalt mixtures containing these hard bituminous binders are very stable but at lower temperatures the material can become very brittle. This brittle behavior can result in premature cracking during early service life. At the laboratory of Road and Railway Engineering of Delft University of Technology a special very hard binder called C-fix was investigated. Different low temperature tests were performed on this hard binder as well as the mixture containing this material. The relaxation behavior of the material provides insight into the low temperature behavior of hard binder material. First frequency sweeps were done with the dynamic shear rheometer (DSR) at a range of temperatures. The tests were performed to determine the stiffness and phase angle of the material. With the dynamic mechanical analysis (DMA) on beams of both binder and mastic (bitumen and filler) glass transition temperatures were determined. The filler influenced the results considerably. Direct tensile tests were performed on samples of bitumen and mastic. Both failure tests and relaxation tests were done. The results showed that the filler type could influence the behavior considerably. Finally relaxation tests were performed on a porous asphalt mixture in a specially designed tension test set-up. From the results it became clear that already at 0 degrees C the relaxation capacity of the porous mixture with C-fix binder was strongly reduced. In all cases the C-fix binder was compared with a 70-100 pen grade bitumen.