Properties of Bituminous Mixtures Containing Different Fillers
A. Kavussi and R.G. Hicks
Abstract
In severe winter conditions, the interaction between thermal and load stresses may result in early cracking of bituminous surfacings. This is mainly due to the increased stiffness of the mix. Besides parameters such as aggregate grading and binder type which affect mix stiffness, there are also the effects of the filler present on the mix behavior. This latter component, in addition to filling the voids, interacts with the binder present in the mix making it stiff and brittle. The change in mix properties is very much related to the properties of the filler.
This paper is aimed at characterizing the role of fillers in bituminous mixtures. Emphasis is mainly given to the low temperature properties of bituminous mixes. Four types of filler (limestone, quartz, fly ash, and kaolin) with different physical properties were evaluated. The characteristics of the fillers were determined using several different physical tests. It was found that the dry compacted filler test method is a good test method for filler characterization. Some modifications in the test procedure were made in order to produce more repeatable results. The four fillers were combined with one type of bitumen at different filler levels and routine bitumen tests were carried out. The temperature susceptibility of the various filler-bitumen mixes were determined using the penetration index values. The results of the viscosity testing showed how the fillers stiffened the filler-bitumen mixes. The filler-bitumen ratios used in the study were evaluated in a typical dense-graded asphaltic concrete mix. Marshall testing was performed at different temperatures ranging from 30 to 70Cand two Marshall test parameters, namely, Marshall temperature index of stability and Marshall temperature index of stiffness, were determined. Flexural testing was also carried out at a range of different low temperatures to determine the flexural properties of mixes containing different types and amounts of fillers.
A toughness parameter (i.e., the area under stress-strain curve in flexural testing) was evaluated at different low temperatures. It was found that, for each mix, there is an optimum filler content corresponding to maximum toughness. For the fillers tested in this research, the maximum toughness corresponded to a region of filler/bitumen ratio between 0.25 and 0.75.