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The process of reclaimed asphalt pavement (RAP) recycling may occur multiple times during the life of the pavement. This study investigates the effect of multiple recycling on binder properties by employing a virgin 3045 PEN grade binder that was aged in the laboratory intended to simulate aging of binders in RAP. The aged binder was rejuvenated using two bio-oils and one softer binder. The doses of the bio-oils and softer binder were determined by matching the continuous high-temperature performance grade (PGH) of the rejuvenated RAP binder to that of the virgin binder. This aging and rejuvenation cycle was repeated three times. Finally, fatigue and rutting performance of the binder was evaluated for the three reuse levels. Results indicate that the material can be reused up to three cycles keeping good performance on fatigue or rutting. However, care should be taken regarding the cumulative effect of bio-oils causing an over-softening effect on the of the RAP. [ABSTRACT FROM AUTHOR]

Warm mix asphalt (WMA) is increasingly recognised as a green paving technology in terms of energy saving and emission reduction. The reduction in mix production temperature associated with the WMA additives is very desirable from the environmental aspect. However, researchers and practitioners desire a comparable performance with hot mix asphalt (HMA). The major issue with WMA is their moisture susceptibility especially in the pavement early life. Therefore, this study aims at investigating moisture susceptibility of WMA using both laboratory characterisation and field performance compared to HMA. Three mixtures were investigated, namely; HMA mixture, foaming and Evotherm WMA mixture. The laboratory tests included; resilient modulus (MR), Indirect Tensile test, and Hamburg wheel tracking test. Test sections on Farm to Market FM 973 Highway near Austin, Texas, were constructed using these three mixtures. The results of field performance monitoring for five years are represented in this paper. Laboratory test results revealed small differences between measured dry and wet tensile strength and MR of HMA and WMA which shows some improvements using antistripping agents. The field performance evaluation showed that the Evotherm WMA mixture had the least transverse and reflected cracks while the HMA performed better in both ravelling and longitudinal cracking. [ABSTRACT FROM AUTHOR]

Abstract: Permeable friction course (PFC) mixtures constitute one of the best options for surface paving, since they offer advantages (as compared to dense-graded hot mix asphalt) in terms of safety, economy, and environment. However, mix design and evaluation of PFC mixtures still require improvement and standardization to further promote the reliable use of these mixtures. This paper summarizes an extensive literature review focused on the basic aspects integrated in the mix design and evaluation of PFC mixtures. Although substantial advances related to these topics were reported since implementation of PFC mixtures in the 1990’s, there is still a need for integration of several of these advances in an improved mix design procedure. The paper also identifies areas that require additional research, including the optimization of the balance between mixture functionality and durability and replacement of the indirect assessment of these important aspects. [Copyright &y& Elsevier]

Durability of porous or permeable friction courses (PFC) is an important aspect to address when designing this type of hot mix asphalt. At present, several agencies perform the mix design of PFC primarily by determining volumetric mixture properties. This approach ensures adequate mixture functionality, but it does not guarantee mixture durability. This paper evaluates the Cantabro loss test, the Hamburg Wheel-Tracking test (HWTT) and the Overlay test (OT) to determine the one most appropriate for mix design and laboratory performance evaluations. The Cantabro loss test, performed in both dry and wet conditions, is recommended for PFC mix design to corroborate the suitability of the optimum asphalt content defined based on volumetric determinations. The HWTT and the OT are not recommended, since the variability of the test results indicated that these tests may not be suitable for PFC mixtures. [ABSTRACT FROM AUTHOR]

Current hot mix asphalt (HMA) mix design procedures used to determine the optimum asphalt content for permeable or porous friction course (PFC) mixtures are based primarily on total air void (AV) content. Durability and functionality of PFC mixtures are also related to the total AV content. However, the connected AV content (defined as the proportion of AV that form connected pathways for air and water transport through PFC mixtures) may provide more insight into the mixture structure in terms of the AV content directly associated with functionality and durability properties and constitute an alternative parameter to conduct PFC mix design and evaluation. This study evaluated two laboratory methodologies (vacuum and dimensional analysis) for determining water-accessible AV content and two types of analysis to compute interconnected AV content based on X-ray Computed Tomography (X-ray CT) and image analysis techniques. Although both the interconnected AV content and water-accessible AV content constitute determinations of connected AV content, different nomenclature was used to differentiate the origin of the calculation. Dimensional analysis with application of vacuum and X-ray CT and image analysis with inclusion of surface AV are recommended for determining water-accessible AV content and interconnected AV content, respectively. Future work should focus on investigating the use of connected AV content as an alternative parameter to integrate in mix design and laboratory and computational evaluation of PFC mixtures. [ABSTRACT FROM AUTHOR]

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The presence of waIn ter in asphalt pavements deteriorates their condition and causes distresses that result in high maintenance costs to state and federal agencies. The objective of this research was to execute dynamic and relaxation tests and evaluate their effectiveness in assessing moisture susceptibility of asphalt mixture specimens with different air void structures determined using X-ray computed tomography (CT) and conditioned using the modified Lottman procedure. The dynamic test consisted of the application of a sinusoidal cyclic compressive load on the specimen while maintaining the strain within a specified range. The relaxation test, performed in both direct tension and compression, consisted of the application of a constant static strain. A statistical analysis was used to study the effectiveness of the tests in evaluating the moisture susceptibility of the asphalt mixtures. The results showed that none of the tests (dynamic or relaxation) were consistent in differentiating between the moisture conditioned and unconditioned specimens or between the responses of the different mixtures within each condition. In addition, the results of the dynamic and relaxation tests were compared after applying different methods to convert frequency-domain data to time-domain data. [ABSTRACT FROM AUTHOR]

A new accelerated pavement testing (APT) tool has recently been developed between relatively inexpensive laboratory testing and expensive but more realistic full-scale accelerated load testing. The one-third scale model mobile load simulator (MMLS3) applies a scaled load on a single tire smaller than a standard truck tire used in full-scale devices and can be used for both laboratory and field applications. For two hypothetical and eight actual pavement structures at a location where both full-scale APT devices and the MMLS3 were used, stress analyses were conducted to: (1) explore the hypothesis of comparable stress distribution; and (2) compare theoretical and measured rutting performance toward validating a performance prediction methodology. For the hypothetical pavement structures, the comparable stress hypothesis was upheld. Theoretically calculated rutting ratios based on stress analyses after correcting for differences in loading and environmental conditions were compared with actual measured field rutting ratios. The results were credible and demonstrated that when all influencing factors are taken into account, rutting performance under full-scale loading can be predicted based on MMLS3 results and stress analysis. [ABSTRACT FROM AUTHOR]

Abstract: The surface free energy (SFE) is a material property that can be used to identify optimum asphalt–aggregate combinations (i.e., interfaces) for improved design of hot mix asphalt (HMA) and to characterize the HMA performance through the use of micromechanical models. Based on SFE measurements, and subsequent calculation of energy indices, this paper compares asphalt–aggregate interfaces formed with asphalt rubber (AR) and polymer modified (PM) asphalt binders (or asphalts) specified for fabrication of permeable friction course (PFC) mixtures in Texas. Six PM asphalts and four AR asphalts with five different aggregates were assessed. Corresponding results suggest that, in terms of the energy indices computed, the fracture resistance, moisture damage susceptibility, and the wettability of the asphalt over the aggregate of AR asphalt–aggregate systems can be comparable to that developed by PM asphalt–aggregate systems. However, this conclusion is restricted by the variability encountered for both asphalt groups analyzed (i.e., AR and PM). Additional research is recommended to analyze the effect of lime in PM asphalts (since PFC mixtures fabricated with PM asphalts often include lime) and the effect of mineral fillers on both PM- and AR-aggregate systems. [Copyright &y& Elsevier]

Permeable Friction Courses (PFC) are asphalt mixtures characterized by high air void contents that are used as surface layers in conventional pavements, principally to achieve safer roads and control noise pollution. This paper summarizes existing information related to the performance of PFC mixtures in the United States (US), including properties of the mixture that determine the durability and functionality of the pavement and mix design methodologies that are currently being used in the US. The objective of this work is not only to analyze this information but also to identify current and future challenges to enhance the performance of PFC mixtures and promote its responsible use. [ABSTRACT FROM AUTHOR]