Multiscale evaluation of asphalt binder-aggregate interface exposed to sodium chloride deicer

Sodium chloride (NaCl) is widely used in roadways' winter maintenance operations. Despite its effectiveness, NaCl solution is known to accelerate the moisture-induced damage process in asphalt mixes. This study aimed to identify the mechanisms involved in the deterioration of adhesive and cohesive bonds in asphalt and aggregate interfaces due to the NaCl deicer and freeze–thaw (F-T) action. A multiscale material characterisation approach and evaluation of fundamental intrinsic material properties were applied to achieve this goal. Adhesive properties of aggregate-binder systems subjected to aqueous NaCl concentrations and F-T cycles were characterised by conducting binder bond strength tests. The surface free energy technique was also employed to evaluate the impact of salt concentration and moisture on the different energy parameters and moisture-induced damage potential. Furthermore, the influence of salt concentration and F-T cycles on the surface nanostructure and adhesion of the asphalt binder was evaluated using atomic force microscopy. The multiscale characterisation approach presented in this study provided significant insights into the physio-chemical mechanisms involved in the deterioration of the bonds in aggregate-binder systems exposed to different aqueous NaCl concentrations. A fundamental understanding of the damage mechanisms is necessary to develop counteracting measures that extend the life of asphalt pavements in cold climates.