Real-Time Ultrasonic Monitoring to Understand Damage in Asphalt Mixes Under Uniaxial Loading

Abstract: Asphalt pavements are subjected to vehicular loads and environmental stresses during their design life, leading to distresses such as fatigue cracking and rutting. This necessitates an understanding of crack growth and damage in asphalt pavements in order to plan preventive maintenance activities. Non-destructive methods such as ultrasonic pulse testing have been employed to assess damage within conventional asphalt mix samples. Recently, due to the global scarcity of natural aggregates, alternative materials like foundry sand and steel slag have been explored to replace fines in asphalt production. However, the increasing availability of large volumes of crushed waste glass (CWG) has sparked interest in its potential as a synthetic alternative to fine aggregates in asphalt. This study focuses on understanding fracture growth and damage evolution in asphalt mixes containing 10% crushed waste glass. A state-of-the-art polyaxial rock testing system, combined with an ultrasonic test-setup, was used to apply uniaxial loading in stress-controlled mode on 100 mm cubical asphalt samples until failure. Real-time active damage monitoring was conducted using a pair of 50 kHz ultrasonic sensors with square wave pulsing. The results indicate that the stages of crack initiation and progression can be detected in the samples through the monitoring of ultrasonic wave changes during loading, particularly in parameters such as velocity, acceleration, and energy. Furthermore, a comparison has been made with identical uniaxial loading on conventional asphalt samples without glass, yielding valuable insights into performance differences between the two mix designs.