Properties of asphalt mixtures containing RAP.
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2009-12-01
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Abstract:A typical NHDOT Hot Mix Asphalt (HMA) concrete mixture contains at least 15% Reclaimed Asphalt Pavement (RAP). The increasing cost of virgin asphalt and aggregate has increased the interest in using higher percentages of RAP in HMA mixtures. The purpose of this research project was to gain a better understanding of how the addition of RAP affects the properties of HMA. The effects of RAP on a particular mixture were evaluated by comparing the dynamic modulus, strength, and volumetric properties of a series of specimens with similar mix designs and materials but containing different percentages of RAP. Additionally, the Mechanistic-Empirical Pavement Design Guide (MEPDG) software was used to evaluate the predicted performance of the mixtures in a pavement surface course.
Two sites were selected for this study. The cores from the first site were taken from the pavement prior to milling and tested to determine the properties of the RAP. Mixtures were designed and tested in the lab with various RAP contents (0%, 15%, 25%, and 40%) using the milled material. A second site was selected where loose plant mix and field cores from the overlay were collected and tested. This provided comparisons of plant mixed – laboratory compacted, and plant mixed – field compacted mixtures at one RAP percentage.
Overall, this research project showed that the percentage of RAP affects the overall properties of the mixture with respect to volumetrics, dynamic modulus, and strength. However, a statistically significant difference from the virgin mixture was only seen at the 40% RAP level. Laboratory compacted specimens were found to have a significantly higher dynamic modulus and strength than field compacted specimens. Using the MEPDG analysis, the predicted performance of the RAP mixtures in a surface course was equivalent to, or better than the virgin mixture with respect to longitudinal cracking, alligator cracking, and rutting.
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