Experimental investigation of the impact of using SBR nanocomposite on moisture damage of asphalt mixtures using surface free energy theory

Moisture damage is one of the common damages of asphalt mixtures due to the deteriorating effect of moisture on asphalt cement cohesion and asphalt cement-aggregate adhesion. Anti-stripping additives are used to enhance the strength of asphalt mixtures against this damage in order to increase the asphalt cement-aggregate adhesion and asphalt cement cohesion. In the present study, it has been tried to examine the effect of the nano clay/styrene-butadiene rubber (SBR) nanocomposite as asphalt cement modifier on the moisture susceptibility of asphalt mixtures using thermodynamic and mechanical technics. The asphalt specimens were placed under 1, 3, and 5 freeze-thaw cycles in order to simulate environmental conditions. The findings of this study indicated that the application of SBR nanocomposite has led to the improvement of the strength of the asphalt mixtures to moisture damage, particularly in specimens made using granite aggregates. In addition, the results of the surface free energy theory showed that asphalt cement modification using SBR nanocomposite increased and decreased the basic and acidic components of the base asphalt cement, respectively. This improved the adhesion between asphalt cement and acidic aggregates, which are prone to moisture damage. Moreover, the SBR nanocomposite use increased the cohesion free energy, hence increasing the resistance of asphalt film against the cohesion-type rupture. Furthermore, calculations based on thermodynamic concepts revealed that the asphalt cement modification has led to a reduction in the de-bonding energy in the stripping event; this event indicates a decrease in the tendency of the system to stripping from the thermodynamics view.