Engineering Properties of Asphalt Concrete Patching Mixtures

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 degrees 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.