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The use of high contents of recycled materials in asphalt mixtures has an adverse effect on the low-temperature cracking performance of these mixtures if not accounted for properly due to the high stiffness and poor relaxation properties of the reclaimed asphalt pavement (RAP) binder. This concern has driven some to suggest using recycling agents (RAs) in the asphalt mixture to restore the rheological properties of the RAP binder without compromising the short- and long-term performance of the mixture. However, the relationships between RA type and dosage, virgin and RAP binder characteristics, and low-temperature properties, i.e., creep stiffness and m -value, need to be investigated further to assess the acceptance of RAs. In this study, 26 recycled binder blends from a combination of three virgin binders, four RAP sources, and eight RAs were used to study these relationships. First, the use of a method based on the dynamic shear rheometer to predict low-temperature properties of recycled binder blends successfully is demonstrated. Second, a linear relationship is found to exist between the low-temperature properties and RA dosage of these blends. Third, a parameter based on low-temperature properties is proposed to select an RA that yields a balance in the stiffness and relaxation properties of the recycled binder blends. Fourth, a conceptual framework is proposed to assess the acceptance of RAs based on low-temperature performance-related parameters. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the impact of aging on high polymer (HP)-modified asphalt binders when compared with conventional polymer-modified asphalt (PMA) binders on the basis of rheology- and chemistry-based parameters. An extended asphalt binder aging experiment that considered multiple combinations of PMA and HP binders from different sources was conducted. Long-term oven-aged asphalt binders at multiple temperatures and durations and asphalt binders aged in a pressure aging vessel (PAV) for multiple durations were tested using the dynamic shear rheometer. Several parameters were determined including low shear viscosity and Glover-Rowe parameters at various temperatures. The PAV-aged asphalt binders were further evaluated in terms of critical low temperature difference using the bending beam rheometer. All PMA and HP combinations were evaluated using Fourier transform infrared spectroscopy for characterization of chemical composition and assessment of polymer degradation. Overall, the measures indicated reduced susceptibility to aging of HP binders when compared with PMA binders, shown by a flatter slope with respect to oxidation with the low shear viscosity measures and Glover-Rowe parameters. In addition, the potential of polymer degradation for HP binders when compared with PMA binders was minimal with aging, thus indicating an increased longevity from a chemical-characteristic standpoint. [ABSTRACT FROM AUTHOR]

In recent years, two types of test methods have emerged to evaluate the susceptibility of asphalt mixtures to cracking at intermediate temperatures as part of performance-related mix design specifications: the indirect tensile (IDT) test and the semi-circular bending (SCB) test. In parallel, several associated analysis approaches have been utilised to evaluate cracking characteristics of these mixtures. The objective of this paper was to evaluate various cracking indices obtained from IDT and SCB tests in terms of their ability to provide a low-variability and high-discrimination response. In addition, the ranking potential of the considered indices in terms of cracking performance of asphalt mixtures was evaluated and inter-correlated. The cracking indices were able to capture the asphalt mixture performance with the fracture strain tolerance (FST) index and cracking resistance index (CRI) showing better performance when compared to other cracking indices. Generally, the IDT test results better distinguished the cracking performance of asphalt mixtures when compared to the SCB test results. The Ideal-CT index (CTindex) from the IDT test and the flexibility index (FI) from the SCB test demonstrated a fair correlation. Overall, the results demonstrated the suitability of both tests for predicting the cracking performance of asphalt mixtures at intermediate temperatures. [ABSTRACT FROM AUTHOR]

Road agencies are increasingly incorporating performance-related specifications (PRS) in construction contracts to specify quality in terms of parameters related to desired long-term performance. PRS provides a means to account for the value lost or gained by the variances of the designed performance parameters from the specified target values. The use of PRS for pavement preservation treatments (e.g. chip seals) has been generally non-existent. The objective of this paper is to establish a step-by-step procedure for formulating chip seals PRS guidelines. The percent embedment (PE) of aggregates into emulsified asphalt was selected as the acceptance quality characteristic (AQC). Chip seal specimens with varying percent embedment levels were prepared using aggregate and emulsion types in Michigan. Aggregate loss and bleeding were selected as performance indicators. Laboratory tests were conducted to compute PE, aggregate loss and bleeding for the chip seal specimens. Relationships were developed between quality measures, service life, and pay factors. The expected pay curves were developed based on quality measures and were used to establish acceptable and unacceptable quality levels. The pay factors were evaluated to ensure fair payments for the quality of work produced. The work presented will provide the general guidelines for developing PRS for chip seal projects. [ABSTRACT FROM AUTHOR]

Chip seals are mostly designed on the basis of empirical methods, which fail to account for the effect of microstructural factors (i.e. percent embedment of aggregates and aggregate shape) on chip seal performance. Two-dimensional (2-D) viscoelastic Finite Element (FE) analyses coupled with laboratory-based sweep tests as per ASTM D7000 were performed to evaluate the impact of such factors on the performance of chip seals. The factors considered in this study were percent embedment, two different aggregate shapes (cubical and flaky), temperature, and aggregate application rates. The 2-D FE models were developed from actual images of the chip seal specimens with cubical and flaky aggregates. The analyses revealed that the maximum tensile strain at the aggregate-binder interface for the chip seals with cubical aggregates follows an asymptotic trend after the percent embedment level of 50%. The trend was not evident in the case of the chip seals with flaky aggregates. The FE simulations also indicated that the chip seals with cubical aggregates outperformed the chip seals with flaky aggregates, which was also observed through the laboratory tests. Furthermore, it was determined that excess aggregate application rates, i.e. higher than that of the optimum design rates, are detrimental to the chip seal performance. [ABSTRACT FROM AUTHOR]

Use of recycled asphalt pavement (RAP) in highway construction is highly promoted due to recent awareness in sustainable construction practices. The concerns with material brittleness in utilising higher content of RAP are alleviated through addition of rejuvenators to some extent. Inclusion of rejuvenator to the aged binder improves its flexibility and lessens its cracking potential. A study was undertaken to investigate the effectiveness of the impact resonance (IR) testing in determining low-temperature binder properties through mixture testing. To this effect, the presented study consisted of two stages. In stage I, the IR test was conducted on mixes made with different low-temperature grade binders. Stage II consisted of testing pure RAP mixes treated with a rejuvenating agent at different levels using the IR as well as testing blends of recovered RAP binder and rejuvenator and virgin binder using bending beam rheometer (BBR). The IR test was performed at a range of temperatures between and . The results indicate that the IR test can successfully capture the low-temperature properties of binders in virgin mixes as well as RAP mixes incorporating rejuvenator. A very high linear correlation was observed between stiffness from IR testing of the RAP mix and stiffness from BBR testing of the blend of recovered binder and virgin binder and rejuvenator. A good correlation was also observed between phase angle of RAP mixes obtained from IR with the m-value, a relaxation index, from BBR at a range of temperatures for a given rejuvenator content. The results clearly demonstrate the potential of IR to be used for grading and optimisation for the asphalt binder of RAP and rejuvenator content in lieu of the binder recovery method. [ABSTRACT FROM AUTHOR]