Plasticity-based method for the design and analysis of cold recycled pavement layers

Asphalt cold recycling technologies allow the use of up to 100 % reclaimed asphalt pavement (RAP) from an existing asphalt pavement to construct new base layers and new subbase layers. Bituminous stabilized materials (BSM), obtained from cold recycling technologies, are susceptible to traffic-induced accumulation of permanent deformation. In the current design methods, BSM pavement layers are typically assumed to have a linear elastic response under traffic loading application, and this does not account for plasticity initiation and accumulation in the material. This research study provides insight on how to integrate plasticity behavior in numerical simulations of rehabilitated pavement structures with BSM. A BSM mixture prepared with 1.5 % cement by weight of total mixture and 1.5 % foamed asphalt binder content by weight of dry aggregates is characterized in the laboratory. Subsequently, a three-dimensional elastic-perfectly plastic finite element model is developed for the simulation of triaxial shear strength tests. Lab measured force-displacement curves are matched with the numerical simulations at different confining pressures. The calibrated mechanical properties are then used as input parameters in multilayer pavement models for pavement evaluation. Different pavement structures with and without BSM layers are compared in terms of a maximum allowable number of loading repetitions before reaching a 20-mm rut depth on the surface of the pavement. The results indicate that structures with BSM and traditional granular base layers yield comparable results in terms of rutting potential. In addition, the study presents a framework for the design and analysis of cold recycled pavement layers and a method to integrate the plasticity behavior of partially-bonded and unbounded layers for pavement evaluation.