John D'Angelo

Bio: John D'Angelo is an academic researcher from Federal Highway Administration. The author has contributed to research in topics: Asphalt & Viscoelasticity. The author has an hindex of 21, co-authored 43 publications receiving 2076 citations.

Warm-Mix Asphalt: European Practice

Abstract: Warm-mix asphalt (WMA) is a group of technologies that allow a reduction in the temperatures at which asphalt mixes are produced and placed. These technologies tend to reduce the viscosity of the asphalt and provide for the complete coating of aggregates at lower temperatures. WMA is produced at temperatures 20 to 55 °C (35 to 100 °F) lower than typical hot-mix asphalt (HMA). In 2007, a team of U.S. materials experts visited Belgium, France, Germany, and Norway to evaluate various WMA technologies through the Federal Highway Administration’s International Technology Scanning Program. The scan team learned that the benefits of WMA technologies include reduced fuel usage and emissions in support of sustainable development, improved field compaction, which can facilitate longer haul distances and cool weather pavement, and better working conditions. A range of technologies is available to produce WMA. European agencies expect WMA performance to be the same as or better than the performance of HMA. Although several areas need to be addressed as these technologies are adapted to U.S. materials and production practices, the scan team believes that the United States has no long-term barriers to WMA use. With additional research and trials, the team expects that highway agencies will allow WMA as an alternative to HMA.

Revision of the Superpave High Temperature Binder Specification: The Multiple Stress Creep Recovery Test (With Discussion)

Abstract: The inadequacy of the Superpave high temperature specification parameter, G*/sin δ, to correctly grade the superior field performance of modified asphalt binders has been demonstrated by several researchers. A new parameter that is blind to modification type and is performance based is now needed. As a replacement for the existing high temperature binder test (G*/sin δ), the FHWA has developed an easy to use Multiple Stress Creep and Recovery Test (MSCR) that measures fundamental characteristics of asphalt binders. In this study, several binder parameters proposed to replace the existing Superpave rutting parameter were validated using hotmix testing. Several different binder tests were evaluated to determine which would provide a replacement for the Superpave high temperature binder criteria. The new test and criteria will have to be performance related and blind to modification. The results from these binder tests were compared against hot-mix rutting results from the Asphalt Pavement Analyzer, the Hamburg Wheel Tracking, the ALF test sections and actual roadway sites. The results from the mixture rut testing showed that different rut testers will provide completely different ranking of binders. This difference is related to the stress level applied by the different testers. This hot-mix testing indicates that the different binders, specifically the polymer modified binders, have different stress dependencies. The binder criteria currently used to specify the high temperature properties are specifically intended to be run in the linear viscoelastic range and therefore can not determine the stress dependency on binder materials. The multi step creep and recovery test can be run at multiple stress levels and can characterize the stress dependency of polymer modified binders. The MSCR test was developed as a result of these findings and other results from various internal studies conducted by FHWA. A separate sub-study was also conducted in this research to understand the effect of stress and strain on the microstructure of polymer modified binders. It was found that in MSCR data there is a clear relationship between %recovery and %strain in the creep portion of the test. In some cases, at least, this is the dominant relationship. Very high strain causes yield behavior in polymer modified asphalt binders (PMA). After high strain, PMAs still exhibit recovery but the rate of recovery is reduced. At high strain, binder morphology, tensile and shear properties change. A test procedure was developed to run creep and recovery testing on one sample at multiple stress levels (MSCR). This test procedure makes it easy to evaluate how the binder response will change under different stress conditions. A property called non-recoverable compliance Jnr was developed based on the non-recovered strain at the end of the recovery portion of the test divided by the initial stress applied during the creep portion of the test. The Jnr value normalizes the strain response of the binder to stress which clearly shows the differences between different polymer-modified binders.

The Relationship of the MSCR Test to Rutting

Abstract: The Multi-stress Creep and Recovery (MSCR) Test is currently being considered as a replacement for the Superpave high temperature binder criteria G* sinδ. The MSCR test can distinguish between the rutting properties of both neat binders and polymer modified binders. The test is run on the same dynamic shear rheometer test equipment currently used for the current Superpave binder testing and is easy to run. The validation of the MSCR compliance value Jnr to rutting was done through extensive mix testing using laboratory rut testers, large Accelerated Loading Facilities and actual roadway sections. This paper covers the validation of the MSCR test binder compliance value Jnr to mixture rutting for modified and neat binders. Multiple binders and mix types are included in the validation and it is demonstrated that the MSCR test provides a much better correlation to mixture rutting than the existing Superpave binder criteria.

X-ray Tomography to Characterize Air Void Distribution in Superpave Gyratory Compacted Specimens

Abstract: Air void distribution has considerable influence on the mechanical properties of asphalt mixtures. Several factors such as the compaction effort, method of compaction, aggregate gradation, and aggregate shape control the air void distribution. An X-ray computed tomography (CT) system along with image analysis techniques are used in this study for non-destructive characterization of air void distribution in gyratory specimens prepared using different gradations and compaction efforts. The air void distributions in gyratory specimens are quantified using parameters that describe the change in percent and volume of air voids along the horizontal and vertical directions. Air voids are shown to be more concentrated in the top and bottom regions that are in contact with the base plates, as well as in the outer region that is in contact with the mold. The non-uniformity of the distribution increases with an increase in compaction effort. The difference in aggregate gradations used in this study is shown to have ...

Field Evaluation of Witczak and Hirsch Models for Predicting Dynamic Modulus of Hot-Mix Asphalt (With Discussion)

Abstract: The Federal Highway Administration (FHWA) has been evaluating the Simple Performance Tester (SPT) in a field laboratory environment and preliminary findings lead to an investigation of whether the total amount of laboratory testing can be decreased, if appropriate theoretical methods for predicting hot mix performance characteristics are employed. Thus, dynamic modulus, |E*|, values were predicted using the Witczak and Hirsch Models for asphalt mixtures from five pavement construction sites across the United States. |E*| values predicted from equations were then compared to the values measured in the laboratory by the FHWA mobile asphalt laboratory (MATL) to evaluate the predictive capability of the Witczak and Hirsch models. |E*| master curves were generated and the Global Aging System proposed by Mirza and Witczak was evaluated using the |E*| measurements and predictions. Results indicate that both models provide reasonable predictions of dynamic modulus within the scope of this study. It was also found that the binder’s Useful Temperature Range (UTR) calculated by algebraically summing the high and the low continuous PG grade temperatures may be used to accurately predict the activation energy E sub A. The hot-mix shift factors may then be determined using the predicted E sub A and the Arrhenius shift factor equation. Recommendations are made for improvements in the Witczak and Hirsch predictive models. The National Cooperative Highway Research Program (NCHRP) 1-37A pavement design guide software was used to predict the performance of a trial conventional flexible pavement section. Both measured and predicted |E*| data from each site w used as inputs in the design guide software for a Level 1, Level 2, and Level 3 analysis. In general, the subtotal AC rutting results predicted by the design guide were found to be inconsistent at any Level of analysis with the magnitude of differences in the Superpave PG grades of asphalt binders used (from PG58-28 to PG70-22). Suggestions for refinement of the NCHRP 1-37A design guide models for characterizing asphalt materials are discussed.

Evaluation of Sasobit® for Use in Warm Mix Asphalt

Abstract: Several new processes have been developed to reduce the mixing and compaction temperatures of hot mix asphalt without sacrificing the quality of the resulting pavement. One of these processes utilizes Sasobit®, a synthetic long chain Fischer-Tropsch wax. Sasobit® can be blended with the binder at a terminal or in the contractor’s tank, introduced in a molten form, added with the aggregate, or pneumatically blown into a drum plant. A laboratory study was conducted to determine the applicability of Sasobit® to typical paving operations and environmental conditions commonly found in the United States, including the performance of the mixes in quick traffic turn-over situations and high temperature conditions. Superpave gyratory compactor (SGC) results indicated that Sasobit® may lower the optimum asphalt content, so it should be added during the mix design process. Sasobit® was shown to improve the compactability of mixtures in both the SGC and vibratory compactor. Statistics indicated an overall reduction in air voids. Improved compaction was noted at temperatures as low as 190°F (88°C). The addition of Sasobit® does not affect the resilient modulus of an asphalt mix nor does it increase the rutting potential of an asphalt mix as measured by the Asphalt Pavement Analyzer. The rutting potential did increase with decreasing mixing and compaction temperatures, which may be related to the decreased aging of the binder resulting from the lower temperatures as well as from the anti-aging properties of Sasobit. There was no evidence of differing strength gain with time for the mixes containing Sasobit® as compared to the control mixes indicating that a prolonged cure time before opening to traffic is not an issue. The lower compaction temperature used when producing warm asphalt with Sasobit® or any such similar Warm Mix additive may increase the potential for moisture damage. Overall, Sasobit® appears to be a viable tool for reducing mixing and compaction temperatures that can be readily added to hot mix asphalt. Reductions in mixing and compaction temperatures are expected to reduce fuel costs, reduce emissions, widen the winter paving window, and facilitate specialized applications, such as airport runway construction, where rapid opening to traffic is essential.

Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice

Abstract: FOREWORD Recycling asphalt pavement creates a cycle of reusing materials that optimizes the use of natural resources. Reclaimed asphalt pavement (RAP) is a useful alternative to virgin materials because it reduces the need to use virgin aggregate, which is a scarce commodity in some areas of the United States. It also reduces the amount of costly new asphalt binder required in the production of asphalt paving mixtures. This report informs practitioners about the state of the practice for RAP use in the United States as well as best practices for increasing the use of RAP in asphalt pavement mixtures while maintaining high-quality pavement infrastructures. High percentage RAP mixtures are achieved with processing and production practices, resulting in cost and energy savings. Based on an evaluation of pavements containing 30 percent RAP through the Long-Term Pavement Performance (LTPP) program, it has been determined that the performance of pavements containing up to 30 percent RAP is similar to that of pavements constructed from virgin materials with no RAP. This report is of interest to engineers, contractors, and others involved in the specification and design of asphalt mixtures for flexible pavements, as well as those involved in promoting the optimal use of RAP. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report because they are considered essential to the objective of the document. Quality Assurance Statement The Federal Highway Administration (FHWA) provides high-quality information to serve the Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement. Abstract With increased demand and limited aggregate and binder supply, hot mix asphalt (HMA) producers discovered that reclaimed asphalt pavement (RAP) is a valuable component in HMA. As a result, there has been renewed interest in increasing the amount of RAP used in HMA. While a number of factors drive the use of RAP in asphalt pavements, the two primary factors are economic savings and environmental benefits. RAP is a useful alternative to virgin materials because it reduces the use of virgin aggregate and the amount of virgin asphalt binder required in the production of HMA. Using RAP greatly reduces the amount of construction debris going into landfills, and it does not …