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The economic benefits from use of RAP materials can provide a great boost to the highway industry by freeing funds for additional highway construction, rehabilitation, preservation, and maintenance. In recent years, the incentive to recycle has grown stronger because of concerns about the environment and sustainability. The general public is becoming more aware of the need to conserve natural resources through recycling. The use of RAP can result in sustainable development and cost savings by reducing the amount of virgin materials required in the production of the new asphalt mixture (1).Benefits notwithstanding, excessive amounts of RAP in a mixture can have detrimental effects on pavement performance. Xiao et al. reported that inclusion of 15% RAP resulted in a significant increase in stiffness of the mixture (2). In recent years, as asphalt prices have continued to escalate, a great deal of interest has been focused on the use of higher contents of RAP. Currently, RAP use varies considerably across the United States, but the average RAP content in asphalt mixtures is estimated to be around 15% (3).The belief that pavements constructed with RAP materials are more prone to cracking than virgin mixtures is generally attributed to stiffening and embrittlement effects induced by attempting to combine weathered, age-hardened materials with virgin materials. A careful RAP mixture design achieves proper binder stiffness by considering the aged binder stiffness, virgin binder stiffness, and the proportions of these two binder components present in the final blend. Extensive research has been directed toward characterization of low-temperature properties of pavements that contain RAP (1).The current study explores the effect of RAP amounts on the lowtemperature fracture properties of asphalt mixtures. Study of the lowtemperature fracture properties of HMA with RAP was conducted in the context of five RAP levels and two virgin binder sources. RAP levels of 10%, 20%, 30%, 40%, and 50% were studied with PG 64-22 and PG 58-28 virgin binders. Disk-shaped compact tension [DC(T)] fracture testing was conducted to determine the fracture energy of the mixtures. In addition to the DC(T) test, the Superpave ® indirect tensile (IDT) test, which is widely used in the prediction of low-temperature performance of asphalt mixtures, was conducted on HMA specimens that contained 20% and 40% RAP.A new testing method that was developed on the basis of the acoustic emissions (AE) phenomenon was employed to evaluate the low-temperature behavior of mixtures. The AE phenomenon refers to the generation of a transient, elastic mechanical wave caused by the sudden release of local stresses (strain energy) in a solid medium. When a material is mechanically or thermally stressed to the point Significant increases in the cost of asphalt paving and increased awareness of the need for sustainable infrastructure in recent years have in turn increased the use of recycled asphalt pavement (RAP) in the manufacture of hot-mix asphalt (HMA). The use of RAP...

Guided longitudinal modes in both low (<200 kHz) and high (2–8 MHz) frequency ranges were invoked to monitor damage in reinforced mortar specimens undergoing accelerated uniform corrosion. The fundamental longitudinal mode, i.e. L(0, 1), and the L(0, 9) mode were invoked for low- and high-frequency testing, respectively. Because of the significant amount of axial displacement at the steel/mortar interface, the L(0, 1) mode was so appreciably attenuated for the particular specimen size used that it is was not detected until after corrosion had initiated and corrosion product accumulation caused mortar cracking. Once detected, the L(0, 1) mode was sensitive to the combined effects of bond deterioration and mortar stiffness reduction. The L(0, 9) mode has negligible radial and axial displacement at the steel/mortar interface. As a result, the L(0, 9) mode is relatively insensitive to the surrounding interface conditions at high frequencies. This allows for changes in the steel cross-sectional area and bar topography to be isolated and monitored from the onset of corrosion up to severe pitting.

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