An evaluation of the use of WMA wax additives in the production of unconventional bituminous mixtures

Abstract

There are several technologies for the production of Warm Mix Asphalts (WMA), namely by using water, some form of organic additive or surface agents to affect the temperature reduction. Another methodology for achieving that goal is by the use of paraffin wax additives that allow the production temperature to be reduced (i.e. reducing the viscosity binder at mixing temperatures) without compromising the viscosity of the binder at operating temperatures. In this study a particular wax additive (Sasobit®) was studied, which melts at approximately 100 °C and reduces the viscosity of the base bitumen at temperatures above that value, while significantly increases the stiffness of the binder at the operating temperature range. In fact, the penetration grade of a bitumen is frequently changed into a harder one after the modification with the studied wax additive. The main objective of this study was to assess whether it would be possible to use this additive in order to produce both high modulus bituminous mixtures (HMBM) and high flexibility bituminous mixtures (HFBM) by using base bitumens softer than those normally applied in such mixtures. This would allow the use of a lower production temperature (further reduced by the use of the wax additive) and would result in an improved performance of the mixtures at the typical operating temperatures. Thus, a paraffin wax modified 35/50 pen bitumen was used in comparison to a conventional 10/20 pen bitumen for the production of the HMBM. In order to produce the HFBM, a paraffin wax modified 160/220 pen bitumen was used in comparison to a conventional 50/70 pen bitumen. The results obtained in the penetration and R&B tests allowed selecting the optimum additive content, while the reduction of temperature of the WMA mixtures was based on the results of viscosity tests. Performance tests, including water sensitivity, wheel tracking tests, stiffness modulus and fatigue tests were performed on the four different mixtures studied, being possible to conclude that the use of paraffin waxes reduced the production temperature of the WMA mixtures by 30-40 ºC, maintaining or even improving some properties of the studied mixtures, namely the fatigue cracking resistance.