Monitoring fatigue famage and crack healing by ultrasound wave velocity

This paper presents the possibilities of using a simple ultrasonic method to estimate the fatigue life and crack healing of hot-mix asphalt (HMA). The ultrasound pulse velocity (UPV) was measured on cylindrical HMA specimens prepared using 60/70 asphalt cement and crushed limestone at three different aggregate gradations (maximum nominal aggregate size equal to 12.5, 19.0 and 25.0 mm). The UPV measurements were performed before and after first stage fatigue tests, after rest periods, and after a second stage fatigue tests that followed the rest period. The collected data were analyzed for the possibility of using UPV to predict fatigue life and crack healing of HMA. The results indicated that UPV can be used to predict fatigue life and crack healing especially after a relatively long rest period. The UPV was found to decrease consistently with an increasing number of constant stress fatigue cycles. UPV showed good capability in evaluating crack healing. The relationship between the percent of increase in UPV and the extended fatigue life caused by a rest period was much better than those between UPV and fatigue life before healing or between UPV and the type of aggregate used in preparing the HMA. Increasing of the rest period temperature caused an increase in both UPV and extended fatigue life. However, the percent of increase in UPV may be less than the percent of increase in fatigue life. Also, it can be noticed that the percent increase in UPV due to the use of different aggregate gradations is compatible to the percent increase in fatigue life due to the same reason. UPV was found to be higher in HMA prepared using higher sizes of aggregate. Based on the collected data, statistical models have the capability to predict fatigue life and crack healing in terms of measured UPV, healing temperature, rest period length and aggregate gradation used in preparing HMA were developed.