Development of an Advanced Overlay Design System Incorporating Both Rutting and Reflection Cracking Requirements

Selecting appropriate overlay thickness and combinations of aggregates and binder types are important decisions that Texas Department of Transportation (TxDOT) engineers make on a routine basis. However, this selection is a difficult balancing act. To perform well in the field, the asphalt overlay must have a balance of both good rut and crack resistance and must also have sufficient thickness to withstand the traffic loads and environmental conditions. TxDOT already has the Hamburg wheel tracking device (HWTD) to screen out mixtures that are susceptible to rutting and moisture damage. Meanwhile a new device, the upgraded overlay tester (OT), has been developed for TxDOT engineers to characterize the reflection cracking resistance of asphalt mixes. The main objectives of this research study were to: 1) propose and demonstrate a balanced mix design concept where proposed mixes meet both rutting and refl ection cracking requirements, and 2) develop an asphalt overlay thickness design and analysis system where lab-measured properties can be used to predict overlay performance.