Determination of Virgin Asphalt Mixture Content in Hot In-Place Recycling Based on Field Rutting Depth Variability

Hot in-place recycling (HIR) technology, 100% recycling reclaimed asphalt pavement (RAP), has been widely used as a sustainable maintenance treatment. However, the inhomogeneity of RAP makes it impossible to securely assume that the produced mixture properties will match the laboratory design. For HIR projects, a virgin asphalt mixture (VAM) is added to modify the gradation of the existing rutted pavement. However, once the quantities of VAM added to areas of rutting are varied along the driving direction, the desired construction quality cannot be maintained. In this paper, a method to estimate the quantities of VAM needed for areas with rutting along the driving direction is proposed. To verify the feasibility of the proposed method and explore the effects of varying VAM content caused by rutting depth (RD) distribution variation on construction quality, performance tests of all samples, including two gradation types of virgin aggregates and five VAM contents, were conducted in the laboratory. Test results indicate that the pavement performance of the recycled mixture with continuously graded virgin aggregates is more stable due to the similar gradation of RAP, while the performance of the recycled mixture with gap-graded virgin aggregates possesses substantial fluctuation. Specifically, when the required VAM content is lower than 15%, namely, all monitored RDs less than 10 mm, gap-graded virgin aggregates are more highly recommended from a high-temperature stability perspective. When the required VAM content ranges from 10% to 15%, namely, all monitored RDs ranging from 5.9 to 10 mm, the continuously graded virgin aggregates should be considered first with respect to low-temperature performance. To improve moisture susceptibility, the continuously graded virgin aggregates are more appropriate.