Rheological behaviour of n-alkane modified bitumen in aspect of Warm Mix Asphalt technology

•Wax additives hardens modified bitumen in the intermediate service temperature.•Viscosity curve as a tool allows to select the additive dedicated for WMA technology.•Bitumen and bitumen modified with wax additives present similar rheological behaviour. In this paper, there are presented properties of bituminous binder modified with new generation of various n-alkane additives used in Warm Mix Asphalt (WMA) technology. Laboratory tests were focused on properties of neat bitumen blended with 18 different n-alkane additives. Based on conventional in Europe binder tests such as penetration, softening point and Fraass breaking point, consistency at service temperature was analysed. Various modifiers with different melting point temperature used in WMA technology are described together with their influence on the binder dynamic viscosity and on rheological properties such as complex modulus and phase angle. In addition dispersion of n-alkane additives in bitumen was examined based on the UV microscopy and binder morphology. It can be found that based on the comparison of the viscosity curves for neat bitumen and bitumen modified with n-alkane additives, it is possible to make first selection of the optimal additive in aspect of the WMA technology. Based on the viscosity curve analysis, for the WMA technology effective additives should present melting temperature in the range of temperature between 90°C and 130°C. At this temperature, n-alkane modified bitumen should be more viscosity susceptible, which mean that viscosity should faster decrease with the temperature change, as compared to the neat bitumen. Based on the rheological and morphological assessment, it can be stated that too high melting point of n-alkane additives generate some problem with additive dissolving and homogeneity of binder and does not compensate beneficial changes in bitumen rheological properties.