Performance Characteristics of Thin-Lift Overlay Mixtures

Abstract

This study designed and evaluated the performance of thin-lift mixtures that incorporated a high reclaimed asphalt pavement (RAP) content, recycled asphalt shingles (RAS), and a warm-mix asphalt (WMA) technology, both individually and collectively. A Superpave® 9.5-mm mixture was designed with new materials and designated as the control mixture. The same control mixture was developed with 40% RAP, with 5% RAS, and with 35% RAP and 5% RAS. Each of the mixture designs was then repeated at a lower mixing and compaction temperature according to a wax-based WMA technology. The effect of the RAP, RAS, or both on the stiffness of each mixture was measured by using the dynamic modulus. The performance of each mixture was determined by measuring (a) its reflective cracking resistance with an overlay tester, (b) its low-temperature cracking resistance with an asphalt concrete cracking device, and (c) its moisture susceptibility with a Hamburg wheel tracking device. In addition, binder was extracted from each mixture and the performance grade determined. The mixtures that incorporated high RAP content, RAS, or both exhibited higher stiffness, which was confirmed with the extracted binder grading results. The use of RAP, RAS, or both reduced the reflective cracking resistance but did not have a negative impact on the low-temperature cracking resistance of the mixtures. Moisture susceptibility test results indicated that the addition of RAP, RAS, or both improved the mixtures' resistance to moisture failure. The addition of WMA technology to the mixtures provided similar or improved performance in most of the mixture tests.