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Influence of Waxes on Bitumen and Asphalt Concrete Mixture Performance

ABSTRACT This paper deals with scientific work carried out to study the influence of different kinds of wax on bitumen and asphalt concrete mixture properties. Experimental parts involve base bitumens from different sources, isolated bitumen waxes and commercial waxes. Asphalt concrete slabs, containing base or wax modified bitumen were prepared and tested. Binder properties were evaluated using different types of laboratory equipment, such as dynamic shear rheometer (DSR), bending beam rheometer (BBR), differential scanning calorimeter (DSC), as well as equipment for determining more conventional parameters. Asphalt concrete properties were evaluated at low temperatures using the tensile strain restrained specimen test (TSRST) and creep test at −25°C. At higher temperatures, dynamic creep testing was performed at 40°C, and complex modulus tests between 0 and 20°C. Binder test results indicated that the magnitude and type of effect on bitumen rheology depend on the bitumen itself, type of crystallizing fraction in the bitumen and/or type and amount of additive used. Adding polyethylene wax, showed no or positive effects on the rheological behaviour at low temperatures (decrease in stiffness) as well as medium and high temperatures (increase in complex modulus and decrease in phase angle). However, the corresponding positive effects could not be shown in dynamic creep testing (at 40°C) of asphalt concrete mixtures containing these modified binders. Adding FT-paraffin decreased the physical hardening index (obtained using BBR) for all bitumens. Also polyethylene wax and montan wax showed this effect for some bitumens. Slack wax showed a large increasing effect on physical hardening. No correlation between physical hardening index (PHI) and wax content by DSC was found in this study. Addition of commercial waxes used showed no or marginally positive influence on bitumen ageing properties for bitumens and test conditions used. Asphalt mixture test results were compared to the corresponding binder test results, and found to be less evident. Significant physical hardening by BBR could not be confirmed by TSRST.