Experimental Study on Geocell-Reinforced Recycled Asphalt Pavement (RAP) Bases under Static and Cyclic Loading

Abstract

Recycled Asphalt Pavement (RAP) is a removed and reprocessed pavement material containing asphalt and aggregates which can be used as a base course material for pavement applications. Geocells are a three-dimensional interconnected honeycomb type of geosynthetics used to reinforce weak soils and base courses of roads and are ideal for soil confinement. The objectives of this study are to evaluate characteristics of milled recycled asphalt pavement (RAP) collected from a city street in Lawrence, Kansas and to investigate the creep and cyclic behavior of geocell-reinforced RAP bases over rigid subgrade under static loading and over weak subgrade under cyclic loading through laboratory testing respectively. The compaction and CBR curves were obtained for the RAP. The Mohr-Coulomb failure envelopes for RAP and RAP/geocell interface were obtained by direct shear tests. The asphalt binder and the aggregates were extracted from RAP. The extracted aggregates were tested for their properties including gradation, specific gravity, and fine aggregate angularity (FAA). The viscosity of the extracted asphalt binder was also determined. The results indicated that the asphalt content obtained by the ignition method was slightly higher than that by the centrifuge method. Gradation results indicated that the compaction did not change the gradation of the RAP. Fourteen medium-scale laboratory static plate loading tests were conducted on RAP samples under two vertical stresses at different confining conditions to investigate the creep deformation behavior of geocell-reinforced RAP bases. The creep axial strains at different time were estimated for RAP at different confining conditions and vertical stresses. The results indicated that the geocell confinement significantly reduced the initial deformation and the rate of creep of the RAP bases. Six medium-scale plate loading tests at different confining conditions and one unconfined compression test were conducted on RAP samples by applying static loads in increment to understand the pressure-displacement response and evaluate the bearing capacity and stiffness of the unreinforced and geocell-reinforced RAP bases. The results indicated that geocell significantly increased the bearing capacity and stiffness of RAP bases. Nine large-scale laboratory cyclic plate loading tests were conducted on RAP base sections with three different base course thicknesses. The novel polymeric alloy (NPA) geocells were used to reinforce the RAP bases. The behavior of unpaved RAP bases, such as permanent deformation, percentage of elastic deformation, stress distribution, and strains in the geocell walls was investigated. The results indicated that the geocell effectively reduced permanent deformation, and vertical stress at the interface of base and subgrade and increased the stress distribution angle and increased percentage of elastic deformation. The strain measurements demonstrated that the geocell-reinforced RAP bases behaved as a slab.