Evaluating suitability of energy efficient and anti-stripping additives for polymer and Polyphosphoric acid modified asphalt binder using surface free energy approach

Polyphosphoric acid (PPA) along with reactive elastomeric terpolymer (RET) are being used to enhance rheological performance of asphalt binders. However, PPA+RET modified asphalt binders results in higher working temperature, thus difficult to use it in practice. Therefore, some energy efficient warm mix additives (WMA) are used to decrease working temperature, to saving of energy and fuel. However, suitability of varieties of energy efficient additives for PPA+RET modified asphalt binders has not been evaluated so far. Similarly, performance of PPA+RET modified asphalt binder may deteriorate with addition of anti-stripping agent such as hydrated lime (HL), because acidic effects of PPA may be neutralized with basic nature of HL. The present study contributes to understand suitability of energy efficient additives and HL on bonding and debonding potential of PPA+RET asphalt binder (called Control binder) with two types of aggregates (basalt and granite) using surface chemistry based approach. The Control binder was blended with three different energy efficient WMA additives namely, Wax based (WB), chemical based (CB), and foam based (FB) along with HL. First contact angle of Control binder with WMA additives with and without HL was measured using Wilhelmy plate. Thereafter, acidic and basic surface free energy (SFE) components of selected asphalt binders were determined using acid-base theory. The SFE components of asphalt binders and aggregates were used to evaluate adhesion bond energies in dry and wet condition. Overall, the results showed that bonding potential of Control binder with selected aggregates decreased after addition of WMA additives. In fact, addition of HL with WMA additives further degraded the bonding potential of asphalt binders, thus nullifying the effects of anti-stripping agent. Out of three WMA additives, FB showed good results with HL compared to WB and CB. Basalt aggregates (basic) showed relatively better bonding behavior with Control asphalt after addition of WMA and HL additives as compared to granite (acidic) aggregates.