Potholes are a visible and annoying form of pavement distress for highway users. One reason for the short life of pothole repairs is that the commonly used patching mixtures cannot withstand the wet weather and the traffic loading. A comprehensive laboratory investigation was performed to evaluate the engineering properties of hot-mix, cold-laid (HMCL) asphalt concrete patching mixtures. The performance characteristics of patching materials was categorized based on four aspects related to initial stability, in-service durability, water resistance, and workability. The engineering properties of HMCL patching mixes were investigated, including Marshall stability, indirect tensile strength, rutting resistance, pothole simulation, and uniaxial compression. Four binders, one aggregate type, two gradations, and one residual binder content were selected for testing in the laboratory. Test results indicated that curing time, nominal maximum aggregate size, temperature condition, and binder type influenced the performance of maintenance materials. The difference in indirect tensile strength among patching mixtures was shown to be high, and the indirect tensile test appeared to be effective in differentiating patching mixtures. A preliminary criterion of the dynamic stability value of more than 1000 cycles/mm was suggested for maintenance materials for rutting resistance. Patching mixtures subjected to loading cycles of 30 or higher to reach 3-mm rut depth under wet conditions in the pothole test were deemed satisfactory in resistance to moisture-induced damage. The patching mixtures tested exhibited good workability at temperatures of 20°C or higher. Test procedures and acceptance criteria developed in this study could be useful as part of a specification to promote quality of bituminous patching mixtures.
The two primary factors that drive the use of reclaimed asphalt pavement (RAP) are economic savings and environmental benefits. However, highway agencies are concerned about the use of a high percentage of RAP in asphalt pavements. This study addressed issues related to the production, construction, properties, and performance of asphalt pavements that contain high percentages of RAP. Mixtures that contained up to 40% RAP were successfully designed, produced, and constructed after proper procedures were followed and attention to detail was paid during design, production, and construction. A separate drum for drying and heating RAP, called a parallel heating system, was used to produce high RAP content asphalt mixtures in a batch plant. Rejuvenating agents were mixed directly in a surge bin to allow the rejuvenator enough time to diffuse into aged RAP binder. Comprehensive laboratory tests were performed to evaluate the air voids, the resilient modulus, the rut depth, and the Cantabro weight loss of asphalt mixtures with high RAP content. A test road was constructed in 2014 to monitor how high RAP asphalt pavements would perform under real traffic and environmental conditions. An in-depth investigation was conducted of pavement performance, including cracking, friction, and rutting. The engineering properties of plant-produced mixtures and field cores were well correlated with the pavement performance of the test road. Test results indicated that high RAP content asphalt mixtures could perform as satisfactorily as those produced with virgin materials to meet in-service requirements.
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