In this study, four plant-produced asphalt mixes were considered to evaluate the performance and construction challenges of mixes containing RAP/RAS. Also, asphalt mixes were collected at two different plant-production times for each mix type to monitor the performance variability between lots. A softer base binder (PG 58–22) was used for mixes with RAS compared to the base binder (PG 64–16) used for the control mix (no RAP or RAS) and the mix with only RAP. Use of small dosages of rejuvenators and the softer binder in the RAS mixes were found to show similar performance compared to the control mix with no RAP or RAS. The results obtained from the extracted binders of these mixes indicate that mixes with RAP and RAP/RAS are expected to show higher rutting resistance and slightly lower low-temperature cracking resistance, also shown in the mix rutting and fracture cracking tests. A similar fatigue life was observed for all mixes at low strain levels in the Four-Point Beam test. However, the mix with both RAP and RAS was found to show better fatigue life at high strain levels. Similar performance test results were observed between different lots of the same mix type for most cases. Finally, there were no problems with field mixing, compaction, or finishing of the mixes containing RAP and RAP/RAS.

In the United States, the Superpave Asphalt Binder Performance Grading (PG) system proposed by the Strategic Highway Research Program (SHRP) is the most common method used to characterize the performance-related properties of unmodified and polymer-modified asphalt binders. Dynamic shear modulus (G*) and phase angle (δ) are the two main binder properties and they are measured using a dynamic shear rheometer (DSR) with parallel plate geometry and either a 1-mm or 2-mm gap between the plates. Since these Superpave parameters were developed for binders that do not contain additives or particulates, the California Department of Transportation (Caltrans) does not use them for asphalt rubber binder specifications. Instead, penetration and viscosity are used as acceptance of quality control; however, these parameters do not necessarily provide a satisfactory link between the measured binder properties and potential performance in the field over a range of operating temperatures. In California, current specifications require that crumb rubber particles used to produce asphalt rubber binder in the “wet process” must be smaller than 2.36 mm (i.e., 100 percent passing the #8 sieve), and typically these particles vary in size between 1 mm and 2 mm. Consequently, when the parallel plate geometry is used to test this type of binder, the larger incompletely digested rubber particles can contact the plates. If this occurs, the rubber particle rheology can potentially dominate the results, which in turn may not be representative of the modified binder as a whole. To address this problem, a potentially more appropriate DSR testing protocol using concentric cylinder geometry was investigated in Phase 1 of this study to explore an alternative means of determining the performance properties of asphalt rubber binders. Phase 2 of the study, documented in this report, continued the investigation into the use of the concentric cylinder geometry and alternate parallel plate geometry with a 3-mm gap. The use of these geometries for intermediate-temperature testing and multiple stress creep recovery testing was also investigated, along with modified procedures for short- and long-term aging in the rolling thin-film oven and pressurized aging vessel, respectively, and specimen preparation procedures for bending beam rheometer (BBR) testing. Limited mix testing was also conducted to relate high- and low-temperature mix performance to the performance grades determined for the binders used in the mixes. The concentric cylinder testing approach to measuring the rheological properties of asphalt rubber binders is considered feasible, and that with its use, the edge effects and trimming issues associated with parallel plate testing can be eliminated. However, the concentric cylinder method requires a longer testing time and a larger binder sample than the parallel plate test method. Initial findings from performance grading and related mix testing indicate that the incompletely digested rubber particles, which have different sensitivities to temperature and applied stress and strain than the asphalt binder, appear to dominate the test results. This will need to be factored into analyses and interpretation of rheology and mix performance test results. The proposed modifications to the short- and long-term aging procedures and to the BBR specimen preparation procedures are considered to be more aligned with the original intent of the tests and will likely reduce the variability between replicate specimens during testing. The results from Phase 2 support the continuation of testing, which should be in line with the original workplan and objectives of this research effort. The research should continue to refine the testing procedures on additional field binder sources, assess the repeatability and reproducibility of any proposed test methods, and evaluate the applicability of the results to the actual performance properties of mixes produced with asphalt rubber binders.

This report presents the preliminary results of a study of the effects of pavement structural response on excess fuel consumption (EFCS), which is defined as the additional fuel required to propel a vehicle on an “imperfect” pavement compared to the amount required on an “ideal” pavement. The study compared EFCS for a set of asphalt-surfaced test sections with a pavement with no structural response as well as with the effects of roughness and macrotexture on EFC. EFCS was calculated using three different models for a factorial that included seventeen asphalt-surfaced pavement field sections on the California state highway network with different structure types that were characterized by their viscoelastic properties. The results of the modeling were used to simulate annual EFCS for a factorial of vehicles, traffic flows, speed distributions, and climate regions typical of California. The sensitivity of EFCS to the variables in the factorial was analyzed, and the effects of structural response on EFC were compared with those of roughness and macrotexture to determine whether structural response is sufficiently important to warrant a second phase of the project to validate and calibrate the models using field test sections and instrumented vehicles. It is recommended to complete models for concrete pavements in addition to asphalt-surfaced pavements, to consider multiple layers in the asphalt, particularly near the surface to better evaluate the effects of rubberized asphalt surface materials, and to check the effects of full dynamic pavement modeling (inertial effects in the pavement) on more than the one section analyzed. It is also recommended to begin field validation and calibration of the models and rerun the simulations with the improved and calibrated models for all pavement surface types.