Constituent Proportioning in Recycled Asphalt Mix with Multiple RAP Sources

Abstract

In recent years, recycling of old asphalt mixes in pavement structure has gained prominence due to various reasons. Increased environmental awareness, depletion of available resources, preservation of pavement geometrics are some of the reasons. Recently, researchers have proposed a formulation based on linear programming, where the preliminary constituent proportions (between RAP, virgin binder and aggregates) are suggested based on known properties of the RAP and virgin binder and target properties of the recycled mix. The present work proposes further extension of this formulation considering RAP and virgin binders obtained from multiple sources.In the proposed generalized formulation, different RAPs collected from different sources are assumed to contain varying binder contents and viscosities. A suitable viscosity mixing rule (among the binders and the rejuvenator) is assumed, to predict the target viscosity of the recycled binder. From workability and compatibility requirements, upper and lower limits on recycled binder viscosity are imposed. Minimization of total material cost or maximization of RAP quantities is assumed as objective function.It is expected that the proposed approach would save significant effort in the laboratory in terms of recycled mix design with large available options on possible usage of RAP and virgin binders from multiple sources.