Volume 38, Issue 3 (May 2010)
Nondestructive Fatigue Damage Analysis of a Thin Asphalt Concrete Course Using the Wavelet Correlation Method
Stress wave analysis is employed herein as a nondestructive monitoring tool to assess the level of fatigue damage in a thin asphalt concrete (AC) overlay. A frequency-dependent cross-correlation procedure is developed to specify a stress wave at a desired frequency by using a wavelet kernel. This procedure is referred to as the wavelet correlation method (WCM). Once synthetic surface waves are constructed and subjected to simulated disturbances, such as structural damage or nearby frequencies, their phase velocities are computed using the WCM with over 96 % accuracy. The generated stress waves are periodically processed, while laboratory hot-mix asphalt pavements are trafficked by the third-scale model mobile loading simulator. The dispersion curves are then analyzed to validate that a wave of 16 kHz travels mainly within a 40∼60 mm thickness of a surface layer. Fatigue damage levels are quantified at intervals by the phase velocity that represents the AC elastic modulus. Microdamage healing of the AC during rest periods is then indexed and corrected by shifting the damage progress profile. Consequently, an early reduction in phase velocity, which is caused by microcracking, can be visually observed in the surface cracking once the phase velocity is reduced to about 50 % of the initial value regardless of pavement density and aggregate gradation. Thus, the WCM allows the optimal timing and scheduling of the preservation construction of a thin AC overlay by indicating the critical microdamage stage immediately prior to the visual evidence of surface cracking.