Environmental sustainability and economic benefits motivate maximum use of recycled asphalt materials (RAM), including reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS), in asphalt mixtures. However, when stiff, brittle, aged materials are added to virgin asphalt-aggregate mixtures, adequate durability (initially and with time) must be maintained by engineering each unique combination of virgin and recycled materials. To maximize durability, state departments of transportation (DOTs) currently limit the RAP and RAS contents and their overall recycled binder ratio (RBR). Strategies for improving binder rheology and mixture durability include utilizing a softer base binder or adding a recycling agent (rejuvenator), but the durability of mixtures utilizing these strategies is unknown. In addition, these types of high RAM content asphalt mixtures are difficult for agencies to accept because no uniform AASHTO practice for their assessment is available.
A comprehensive standard practice is needed that specifically guides the complex task of engineering durable, high RAM content asphalt mixtures within the context of balanced mix design. This practice will promote environmental sustainability of the most recycled product worldwide and realize significant economic benefits.
The objectives of this research are to (1) produce a proposed AASHTO standard practice and associated test methods for design and evaluation of durable high RAM content asphalt mixtures and (2) revise the proposed AASHTO Standard Practice for Characterization of Asphalt Mixtures with High Recycled Materials Contents and Recycling Agents produced in NCHRP Project 09-58 to address mixture durability.
In this research, durability is defined as the ability of an asphalt mixture to withstand traffic and environmental conditions without deterioration evidenced by raveling, surface cracking, pop outs, and damage attributed to moisture. The research shall comprehensively investigate the interaction of material, traffic, and environmental factors that cause deterioration in pavements containing high RAM contents.
Status: The Phase I interim report and proposed Phase II work plan are in review.