Study on the use of a WMA surface agent additive on recycled and asphalt rubber mistures

In the last few years, several studies have been carried out with the objective of lowering the production temperature of bituminous mixtures, thus resulting in a product entitled warm mix asphalt (WMA). In the present study, a particular surface agent additive (Cecabase®) was used for that purpose in two different bituminous mixtures (a recycled bituminous mixture and an asphalt rubber mixture). Hot recycling of bituminous mixtures is generally seen as a complex operation in terms of technological procedures. In fact, the amount of reclaimed material incorporated into new bituminous mixtures is most of the times limited to 20-30%, by mass, due to the reduction in the plant capacity if higher values are used. This is related to the time that is necessary to transfer the temperature of the overheated aggregates to the reclaimed material before the mixing process is finished. Thus, significant savings could be obtained in terms of energy consumption and emissions to the environment if it was possible to improve the workability of the mixture without the need to overheat the new aggregates, and without compromising the performance of the mixture. Similarly, in the production of asphalt rubber (AR) mixtures, which are produced at elevated temperatures (usually above 170 ºC) due to the higher viscosity of the AR binder, significant savings would be obtained if the mixing temperature could be lowered by 20 or 30 ºC. The present paper shows a series of test results obtained from a recycled mixture with a 50% recycling ratio and an asphalt rubber mixture, both produced with conventional binders and with binders modified with Cecabase®, allowing for a direct comparison of their properties. A compactability test (EN 12697-10) was carried out to determine the temperature reduction that could be achieved without compromising the volumetric properties of the mixtures. Performance tests, including water sensitivity, wheel tracking tests, stiffness modulus and fatigue tests were performed on the four different mixtures studied and the results and main conclusions obtained are analysed in the present paper