Effects of warm mix asphalt additives on bonding potential and failure pattern of asphalt-aggregate systems using strength and energy parameters

The present study was undertaken to evaluate the effects of different warm mix asphalt (WMA) additives on bonding behaviour of asphalt binder and aggregates using two different approaches: (i) The surface free energy (SFE) method and (ii) The asphalt bond strength (ABS) test. The study involved two phases, the first phase involved measurement of the SFE of control, and WMA (Sasobit, Advera, and Rediset) modified asphalt binders by the Wilhelmy plate method, and aggregate's (limestone and granite) SFE by the dynamic vapour sorption (DVS) method. Thereafter, bond energies were computed using SFE method for understanding the bonding behaviour of WMA modified binders with different aggregates in dry and wet conditions. The second phase involved direct measurement of bond strength and failure pattern between asphalt binder and aggregate combinations by the ABS test in both dry and wet conditions. Furthermore, bond strength of all combination of asphalt binder and aggregates were compared by SFE and ABS methods. The results indicated that Sasobit and Advera effectively contributed in enhancing the cohesive energy of control binder, whereas Rediset decreased the cohesive energy of control binder. Bond strength of WMA modified binder depends on both aggregate type and WMA additives. The results show that asphalt binder with Sasobit can have better bonding performance with limestone (basic) aggregate, whereas, asphalt binder after addition of Advera showed better bonding performance with granite (acidic) aggregate. After wet conditioning, asphalt binders with limestone (basic) aggregate combinations exhibited cohesive failure showing minimal effect of water on bond strength compared to binders with granite (acidic) aggregate combinations which showed adhesive failure. The comparison of bond strength by mechanical ABS test and energy based SFE methods have shown a fair correlation between bond strength ratio (BSR) and energy ratio (ER).