NRRA: Validation of Loose Mix Aging Procedures for Cracking Resistance Evaluation in Balanced Mix Design

Status:  Active
Project Start Date:  04/01/2022


Cracking is the primary mode of distress in asphalt pavements in the United States. To address the cracking issues, many state transportation agencies have made modifications to the volumetric mix design system with a goal of improving the cracking resistance and durability of asphalt mixtures. However, the overall effectiveness of those modifications was not very satisfactory, mainly because of the limitations associated with volumetric analysis. Recently, balanced mix design (BMD) has been developed as a new asphalt mix design system that relies on performance testing in addition to (or sometimes in place of) volumetric analysis for mix design approval and production acceptance. Because BMD addresses many of the limitations associated with the volumetric mix design system, it has the potential to yield asphalt mixtures with good performance. Although the concept of BMD has gained significant attention, the development and implementation of a robust BMD specification has challenges. One of them is the selection of appropriate long-term mix aging procedure(s) for use with the BMD cracking tests so that the mixture can be tested at a representative field aging condition. Consideration of the long-term strip aging is critical for the evaluation of cracking resistance for several reasons. Therefore, a robust BMD specification requires an appropriate laboratory aging procedure for conditioning asphalt mixtures prior to cracking tests. This is particularly important for the evaluation of surface mixtures to ensure adequate long-term pavement cracking performance. Over the years, asphalt researchers and practitioners have developed and evaluated different long-term aging procedures. Most notably, the AASHTO R30 procedure requires aging compacted specimens for 5 days at 85°C, which was originally developed in the Strategic Highway Research Program (SHRP) program to simulate 7 to 10 years of field aging in the United States (Bell et al., 1994). However, the National Cooperative Highway Research Program (NCHRP) project 09-52 found that this aging procedure was not severe enough for asphalt mixtures used nowadays as it was only able to simulate up to 3 years of field aging. Furthermore, the compacted specimen aging procedure has limitations including the presence of aging gradient within the mixture specimen and the inability to accommodate elevated aging temperatures due to specimen distortion concerns. Recently, numerous studies have explored loose mix aging as an alternative, yet accelerated, method to simulate the field aging of asphalt pavements. The temperature of these procedures ranges from 95 to 135°C and the duration varies from hours to weeks. Although the loose mix aging procedures show promising results in 3 terms of correlating to field aging, their development has been based on a limited number of field projects and component materials. Therefore, this project is proposed to validate these procedures with a wider range of field projects with various mixture components, pavement ages, and climatic conditions.A two-phase study is proposed to accomplish the objectives of this project by extensively leveraging the ongoing research efforts and findings at the National Center for Asphalt Technology, Texas A&M Transportation Institute, and University of New Hampshire.

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