Effect of Asphalt Binder Aging on Thermodynamic Parameters and Its Relationship with Moisture Sensitivity of Asphalt Mixes

In the existent methods for investigating the potential of moisture damage based on thermodynamic concepts in asphalt mixes, the role of asphalt binder aging on thermodynamic parameters has not been considered. The current method described in this paper was developed to investigate the effect of asphalt binder aging on moisture sensitivity of asphalt mixes using mechanical and thermodynamic tests. Eight different asphalt mixes, including two types of asphalt binder with different penetration grades (60-70 and 85-100) and two types of aggregates (limestone and granite), were investigated using a liquid antistripping additive in two controlled and aged states. Thermodynamic parameters related to moisture sensitivity of asphalt mixes were calculated using surface free energy (SFE) components of aggregate, asphalt binder, and water (with and without considering aging). Then the relationship between debonding energy and the indirect tensile strength ratio of different specimens was investigated via statistical analyses. Results of SFE parameters of the aged and controlled asphalt binder showed that asphalt binder aging causes an increase in absolute value of debonding energy, adhesion free energy, and cohesion free energy of compounds made with Asphalt Binder 85-100 and leads to the reduction of adhesion free energy and cohesion free energy of compounds made with Asphalt Binder 60-70. The relationship between results of debonding energy in two controlled and aged asphalt binder states and the indirect tensile ratio showed that these two indicators are strongly correlated. The correlation coefficient between the moisture sensitivity indicator and debonding energy of specimens in two controlled and aged states was 0.65 and 0.77, respectively. The high correlation between results of the tensile strength ratio (TSR) and debonding energy with aged asphalt binder indicates the necessity of using SFE components of asphalt binder after aging in thermodynamic calculations.