MECHANISTIC CHARACTERIZATION OF ANTI-STRIPPING ADDITIVES IN SASKATCHEWAN ASPHALT MIXES

Saskatchewan Highways and Transportation commonly uses hydrated lime and liquid anti-stripping additives to mitigate asphalt-aggregate stripping susceptibility of hot mix asphalt mixes. Based on empirical experience of observed field performance in Saskatchewan, the addition of lime is thought to not only improve stripping resistance, but also the mechanical behaviour of the mix. However, the addition of lime requires adequate voids in the mineral aggregate of the mix, and contractors have the added difficulty of handling lime during construction, making liquid anti-stripping products more appealing. Although the influence lime has on Saskatchewan mixes has been evaluated in the past, none of the investigations involved determining its effect in terms of fundamental mechanistic mix behaviour. In addition, the long-term performance of liquid anti-stripping additives has not been well established in Saskatchewan field state conditions. This laboratory study investigated the mechanistic behaviour of a typical Saskatchewan hot mix asphalt concrete modified with hydrated lime, with a liquid anti-stripping additive, and without any anti-stripping treatment as control. Specifically, triaxial frequency sweep characterization was performed to evaluate the various mixes. The mechanistic properties of the various asphalt mixes considered in this research were characterized across dynamic stress states, across a range of load frequencies, at 20°C. In summary, this research found that hydrated lime improved the mechanistic behaviour of asphalt concrete mixes relative to the unmodified specimens and the samples modified with liquid anti-stripping additive at 20°C. Minimal difference was observed in the mechanistic behaviour of the unmodified asphalt concrete specimens and the specimens modified with liquid anti-stripping additive. However, liquid anti-stripping additive appeared to increase the radial strain behaviour of the asphalt mix considered in this study. This increase in radial strain resulted in a similar Poisson’s ratio behaviour to that of the lime-treated mix.