Numerical Analysis of Hydraulic Conductivity Effect on the Utilization of Recycled Asphalt Pavement in Highway Design

In this paper, the effect of hydraulic conductivity of RAP on drainage time and minimum required thickness of highway base layers was evaluated via DRIP (Drainage Requirement in Pavements), a US FHWA software. Seven RAP materials collected from various places within the state of Maryland were used in the analyses. In addition, their performance as a highway base material were compared with a traditional graded aggregate base material (GAB) and stone no. 57. The time-to-drain approach was employed to evaluate the drainage capability of RAP as well as the control materials. DRIP software helps to categorize the base material as poor, fair, good, and excellent based on the required time for 50% drainage of the infiltrating water. A series of analysis was performed to investigate the influence of drainage percentage U, base thickness H, and hydraulic conductivity k on time-to-drain. The results indicate that the fines content and hydraulic conductivity significantly affect the time to drain, particularly after 40% drainage. Furthermore, increasing the base thickness results in a drastic decrease in time to drain. When compared with the traditional base materials, it can be concluded that RAP materials yield satisfactory results for utilization as a highway base material in terms of drainage capabilities.