Effectiveness of Rejuvenators on Aged Asphalt Concrete using Ultrasonic Non-collinear Subsurface Wave Mixing

Rejuvenators are products that aim to restore the physical and chemical properties of aged bitumen. To evaluate rejuvenators' restorative properties of aged asphalt concrete, artificially oven-aged (for 36 h at 408 K [135 degrees C]) asphalt concrete specimens were coated with a rejuvenator (10% by weight of the binder) and left to dwell for the following prescribed amounts of time: 3 to 6 days in 1-day increments, 1 to 8 weeks in 1-week increments, and 12 weeks. After its dwell time, each specimen was evaluated using non-collinear mixing of critically refracted dilatational ultrasonic waves. The frequency ratio, f(2)/f(1), at which the interaction took place and the normalized nonlinear wave generation parameter, beta/beta(0), were recorded and compared against a reference plot. The reference plot was created using asphalt concrete samples (with no rejuvenator) subjected to increasing levels of oxidative oven-aging. It was observed that the samples with a dwell time of five weeks and greater exhibited material response similar to the reference virgin specimen. From one to four weeks, the nonlinear parameters become closer to the virgin parameters with each successive week. The approach appears to be capable of estimating the rejuvenators' capacity of restoring the material response of the original asphalt concrete with increasing dwell time. Potential application to pavement maintenance is presented and discussed.