From the beginning of asphalt mixture design it was desired to understand the interaction of aggregates, asphalt, and the voids created during their compaction. In asphalt mixture design, guidance is lacking in the selection of the design aggregate structure and understanding the interaction of that aggregate structure and mixture volumetric properties. Asphalt mixture design concepts are presented that use aggregate interlock and aggregate packing to develop an aggregate blend that meets volumetric criteria and provides adequate compaction characteristics. The concepts rely on coarse aggregate for the skeleton of the mixture with the proper amount of fine aggregate to provide a properly packed aggregate structure. The objective is to use aggregate packing concepts to analyze the combined gradation and relate the packing characteristics to the mixture volumetric properties and compaction characteristics. The new concepts presented for asphalt mixture design and analysis include an examination of aggregate packing and aggregate interlock, blending aggregates by volume, a new understanding of coarse and fine aggregate, and analysis of the resulting gradation. These concepts are the result of many years of field experience and are the backbone of the Bailey method for asphalt mix design. These methods are under continued development as the improved method for asphalt mixture design, which will assist with the transition to contractor mix design.

This paper focuses on the design and laboratory performance of asphalt mixtures with a high percentage of reclaimed asphalt pavement (RAP). Special laboratory measures were taken to process RAP material to achieve target volumetrics for the mixtures. Two aggregate sources were used to develop eight asphalt mix designs. The Bailey method of aggregate packing was used to design four asphalt mixtures with 0% (control), 30%, 40%, and 50% RAP for each material source. Apart from evaluating the moisture susceptibility of the prepared mixtures, performance tests, including dynamic modulus, wheel tracking, and beam fatigue, were also conducted. Moreover, in addition to evaluating the effect of the amount of RAP on mixture performance, the effect of binder grade bumping was also investigated. The study concluded that mixtures including RAP could provide equal or better performance in resistance against moisture susceptibility, rutting, and fatigue failure. Because consistent and similar volumetrics were achieved for all tested mixtures, it can be said with certainly that the performance properties of all tested mixtures were a function of only their mechanical properties.

Abstract. Asphalt recycling is a key component of the sustainable practices in the pavement industry. Use of reclaimed asphalt pavement (RAP) minimizes the construction cost as well as consumption of natural resources. Adding RAP, though, is believed to make the asphalt mixtures prone to thermal cracking by increasing their stiffness. A semi-circular bend (SCB) test was conducted to evaluate the low temperature cracking potential of asphalt mixtures with RAP, whereas, a flow number test was conducted to provide some insight into the gained stiffness. Eight asphalt mixtures with a high amount (up to 50%) of RAP were designed using two material sources. Two additional softer binders were used to prepare testing samples in order to evaluate the effect of binder grade bumping. Flow number test data showed significant improvement in potential rutting resistance of asphalt mixtures when RAP was added. However, thermal cracking potential may increase when RAP is added to asphalt mixtures. This effect could be reduced when binder double-pumped grade is used.

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Quality assurance (QA) specifications for asphalt pavement construction measure quality characteristics to adjust payments. The measured quality characteristics are assumed to empirically relate to performance. The validity of this assumption, however, has been questioned in recent years; thus, there has been increased interest in finding ways to more directly evaluate the performance of the as-constructed materials. One proposed method to meet this need involves using the Asphalt Mixture Performance Tester (AMPT) and its associated test methods, which measure fundamental material properties that are then used to calculate the fatigue cracking performance index, Sapp, and a rutting strain index (RSI). These indices can be used in performance-related specification (PRS) or performance-based specification (PBS) frameworks to determine the pay adjustments during the construction of asphalt pavement. While PBS requires measured indices, PRS uses index-volumetrics relationships (IVRs) to predict Sapp and RSI based on conventional acceptance quality. Payment can then be based on a percent within limits (PWL) approach. This paper demonstrates how pay adjustments can be made for a paving project in Indiana following three different QA specification frameworks: the current QA specifications framework in the Indiana Department of Transportation, a PRS framework using IVRs, and a PBS framework that employs measured Sapp and RSI. For each framework, the main elements of the specification were identified and determined. The specification limits for Sapp and RSI and weight factors in composite pay factor equations were determined such that the resulting pay factors are comparable to pay factors obtained from the current QA practices.