Effects of Reclaimed Asphalt Pavement on Mechanical Properties of Base Materials

Abstract

The purpose of this research was to investigate the influence of reclaimed asphalt pavement (RAP) on the mechanical properties of recycled base materials typical of northern Utah. Two sources of RAP, two sources of base, and five RAP contents were evaluated in a full-factorial experimental design in which the California bearing ratio (CBR) test, free–free resonant column test, and tube suction test were used to measure strength, stiffness, and moisture susceptibility, respectively. A fixed-effects analysis of variance was performed on the collected data. The results indicate that, on average, CBR values decrease between 13% and 29% with each 25% increase in RAP. For stiffness testing at the optimum moisture content determined for each blend, the general trend was a decrease in stiffness from 0 to 25% RAP, followed by a steady increase in stiffness as the RAP content was increased from 25% to 100%. Following a 72-h oven-drying period, however, the general trend reversed; an increase in stiffness occurred as the RAP content was increased from 0 to 25%, and a decrease in stiffness was observed for RAP contents above 25%. For the moisture-susceptible base material tested in this study, additions of 25% and 50% RAP actually increased the moisture susceptibility of the recycled material compared with the neat base, although the blended material was classified as non-moisture-susceptible when the RAP content was 75% or higher. Base stabilization may be required in many instances to ensure adequate strength and durability of recycled materials.