The influence of reclaimed asphalt pavement (RAP) content on the mixture and recovered binder properties of plant-produced hot-mix asphalt (HMA) was examined by studying the complex moduli of RAP mixtures and binders. RAP was added at 15%, 25%, and 40% levels to HMA with PG 64-22 and at 25% and 40% levels to HMA with PG 58-28 binder. In addition, control mixture samples with PG 64-22 and no RAP were also collected and tested for comparison. Compacted specimens were tested to determine the complex dynamic moduli (|E*|) at three temperatures. Complex shear moduli (|G*|) of the binders recovered from these HMA samples, RAP samples, and original binders were determined at the same test temperatures. Low-temperature creep compliance and indirect tensile strength of the mixtures were also determined, and these results were used to estimate the critical cracking temperature of the pavement. Statistical analysis indicated that there were no differences in mean strength and |E*| of the mixtures at the 15% and 25% RAP levels. Some differences between the control mixture and the 40% RAP mixtures were found only at the higher test temperatures.

No abstract

No abstract

History is a dynamic tapestry of facts and perceptions, dates and personalities. This work attempts to capture the events and rationale of those who contributed significantly to the use of gyratory compaction in the design and field management of hot-mix asphalt and discusses the challenges ahead. Throughout the evolution of asphalt mix design several different types of laboratory compaction devices have been developed. In general, the goal of these laboratory devices is to fabricate a specimen for volumetric or physical characterization, or both. Depending on the system, specimens can be cylindrical, trapezoidal, or rectangular and compaction can be achieved through impact, kneading, or vibration. Gyratory compaction applies a kneading effort to fabricate cylindrical specimens. The evolution of gyratory compaction has resulted in several unique devices and a variety of methods.

The Superpave system is being implemented by state highway agencies. Many states implemented the asphalt binder specification during 1997. The volumetric mix design system, however, is being actively implemented. By the end of 1997, more than 200 Superpave projects had been built in the United States. As states consider specification changes necessitated by Superpave implementation, some questions are being raised. Fine aggregate angularity (FAA) requirements, one of the aggregate consensus properties, has generated considerable debate in some areas of the country. Adopting an FAA requirement of 45 percent for high traffic pavements has changed the number of sources available for asphalt mixtures. Superpave also provides a limit on flat and elongated particles. The aggregate properties requirements have increased interest regarding the basis of the specification and the values specified. The results of a limited cooperative study by industry and agencies to evaluate the role of FAA and particle shape on asphalt mixture properties are presented. A Superpave mixture design for high equivalent single-axle loads was evaluated. The fine aggregate used in the mixture design, with an FAA of 48, was replaced by other fine aggregates with lower FAA values. Properties of the mixtures containing the different fine aggregates were evaluated by using the asphalt pavement analyzer, the couch wheel tracker (a variation of the Hamburg rut tester), and the Superpave simple shear tester. A study to evaluate the sensitivity of the Superpave gyratory compactor and the Superpave mixture design system to differences in particle shape also is presented.