Recycled Binder Availability of Virginia RAP Materials and Its Effects on Asphalt Mixture Composition and Performance

About the report

In Virginia, most asphalt mixtures contain reclaimed asphalt pavement (RAP), which may pose some challenges regarding asphalt pavement durability if these mixtures are not properly designed. One of the concerns is the uncertainty in the amount of RAP binder that is available, active, and effectively contributing to the total asphalt content of the mixture. Although the balanced mix design (BMD) approach may help overcome some of these concerns, not all RAP asphalt mixtures produced in Virginia have a BMD framework available. In fact, VDOT’s existing BMD framework still requires mixtures to comply with volumetrics specifications, which may be more challenging for mixtures containing higher amounts of RAP.

The objective of this study was to characterize the asphalt binder availability, activity, and contribution from different RAP materials and asphalt mixtures in Virginia; evaluate the effectiveness of recycling agents (RAs) at activating the available binder for improved blending with virgin binder; and, collectively, assess their effect on asphalt mixture volumetrics and performance. The scope of work included a literature review; characterization of recycled binder availability (RBA) and degree of activity (DoA) of RAP materials; characterization of the recycled binder contribution (RBC) of selected asphalt surface mixtures; laboratory performance tests using VDOT’s BMD and advanced test methods for reference and study mixtures incorporating RBA or RA, or both; and pavement performance simulations.

The literature review revealed knowledge gaps related to the lack of a practical method to estimate RBC, limited comparisons across RBA, DoA, and RBC, as well as limited evaluation of the effect of RAs on binder activation and contribution. The sieve analysis method showed that RBA ranged from 41.4% to 73.5% and an average of 59.5% for nine RAP sources in Virginia, with finer gradations associated with higher RBA values. A strong agreement was observed between RBA from RAP materials and RBC from corresponding mixtures, indicating that the RBA sieve analysis method could be used as a practical, simple, and low-cost method to estimate RBC. Mixture composition analysis showed that assuming 100% RBA overestimates asphalt content, voids in mineral aggregate, and voids filled with asphalt and may incorrectly suggest compliance with the volumetric requirements, especially at higher RAP contents. BMD tests showed that incorporating RBA and/or RA can substantially improve mixture durability and cracking without adversely affecting the rutting resistance. Mechanistic-based pavement performance simulations showed substantial improvement in the fatigue cracking predictions of asphalt mixtures, including RBA and/or RA compared with reference or control mixtures.

This study recommends that VDOT should consider (1) incorporating RBA in the design of dense-graded asphalt surface mixtures with 9.5- and 12.5-mm nominal maximum aggregate size with up to 40% RAP content by total mixture weight; (2) incorporating the sieve analysis method into VDOT’s specification as a practical and low-cost method to quantify RAP materials RBA; and (3) evaluating, along with VTRC, additional RAP stockpiles and corresponding asphalt mixtures with RAP content above 30% to verify RBC consistency among additional mixtures and evaluate the effect of RBA on mixture performance.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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