Nanoindentation Characterization of Moisture Damage in Different Phases of Asphalt Concrete

Abstract Traditional microscale testing cannot be performed on asphalt binder, mastic, or aggregate, while they are an integral part of asphalt concrete (AC). Recently, nanoindentation has created an opportunity to characterize mastic and asphalt binder while they reside in an AC sample. In the study, laboratory nanoindentation testing is carried out to characterize moisture-induced damage in different phases of AC. A moisture-induced sensitivity testing (MIST) device is used for moisture conditioning of AC. In the MIST device, an AC sample is fully submerged under water and all-around cyclic pressure is applied through the pores inside an AC sample to cause damage. Damaged AC samples are indented for an extended dwell time of 200 s using an unloading rate of 0.02 mN/s to minimize viscous effects of asphalt on test results. The indentation load-displacement curve is analyzed by the Oliver–Pharr method to obtain elastic modulus and hardness. When comparing wet and dry sample indentation test results, it is observed that the modulus of the wet mastic reduces to 60 % of dry mastic modulus. Overall moisture conditioning reduces the modulus of AC by 70 %. In addition, the creep response of the mastic phase is modeled by a viscoelastic Burger model. The creep compliance value of wet mastic is 42 % higher than that of dry mastic.