Project Details

Road pavements in North Carolina have a long history of good performances of unbound base courses often constructed with high quality crushed aggregate materials. The objective of this study was to evaluate rutting potentials of aggregate materials used in pavement base course in North Carolina and develop and calibrate rutting damage models primarily based on laboratory data to use them with mechanistic-empirical (ME) pavement design approaches such as the AASHTO’s Pavement ME Design procedure. A complete suite of characterization tests were conducted on 16 aggregate materials with laboratory samples consistently prepared for a mid-range dense-graded base course gradation. The tests included imaging-based aggregate particle shape analyses, moisture-density, resilient modulus, shear strength, and permanent deformation. The concept of Shear Strength Ratio (SSR), defined as the ratio between applied stress levels and the material’s shear strength (stress/strength), was introduced to examine effects of varying proportions of stress/strength on the permanent deformation behavior. Clearly, the permanent deformation responses of the aggregate materials correlated better to shear strength than the resilient modulus properties. The accumulated permanent strains were found to steadily increase with applied stress levels. When plastic fines existed in the aggregate gradation, the permanent deformation potential was drastically higher. Note that AASHTO’s Pavement ME Design approach could not adequately distinguish between the performances of aggregate materials with similar resilient moduli but with different shear strength and thus the different permanent deformation characteristics. Accordingly, the experimental results were used to establish a consistent database to investigate the permanent deformation trends influenced by aggregate material properties, shear strength, applied stress states and stress/strength ratios, and to develop a new rutting model referred to as the CMT model. Case studies compared the CMT model predictions with those from the Pavement ME Design procedure and evaluated the adequacy of the proposed model. Based on the findings, a practical design approach is recommended for better prediction of aggregate base rutting potentials.