Experimental research on combined effects of flame retardant and warm mixture asphalt additive on asphalt binders and bituminous mixtures

The application of bituminous mixture modified by flame retardant (FR) and warm mixture asphalt additive (WMAA) (BMMFW) is becoming a trend in tunnel pavements. When FR improves the flame retardancy of asphalt binder and WMAA reduces the construction temperatures of bituminous mixture, the combined effects of the two additives on pavement performances need to be studied. In this study, two types of original asphalt, FR (ZIR®) and WMAA (Sasobit®) were chosen. Through conventional performance tests and high and low temperature rheological tests, the experimental research was focused on the pavement performance investigation of original asphalt binder, asphalt binder modified by FR and WMAA (ABMFW), base bituminous mixture and BMMFW. The results show that the used FR and WMAA can improve the high temperature properties of asphalt binder and bituminous mixture, reduce the low temperature performance but have slight negative effects on water stability. The effects of WMAA on reducing viscosity are related with asphalt species, and whether the influence of the FR and WMAA on the absolute value of viscosity–temperature index is increasing or decreasing also depends on the type of original asphalt. An interesting and important phenomenon is founded, which is that using the creep rate m(t) to describe the low temperature performance of asphalt binder or bituminous mixture may sometimes be insufficient or unreliable, while employing the m(t)/S(t) (ratio of creep rate to the stiffness at time t), stress-relaxation time and Wd(t)/Ws(t) (ratio of dissipated energy to stored energy at time t) may be reasonable and accurate.