Analysis of New Brunswick Asphalt Concrete Mix Design

The update of the volumetric guidelines used in the New Brunswick Department of Transportation and Infrastructure (NBDTI) is fundamental for the future of roads in the province. NBDTI divides their 22,000 km Highway Network into six districts, each with multiple contractors. This study is part of a project that aims to update New Brunswick Asphalt Concrete Specifications according to the present techniques and international standards, as some of NBDTI specifications date more than 20 years ago. A literature review was completed to gather the current specifications and experiences regarding asphalt mix design in several agencies in North America. These specifications were compared with the 2019 NBDTI Asphalt Concrete Specification (Section 261) and the American Association of State Highway and Transportation Officials (AASHTO) SuperpaveTM Volumetric Mix Design Standards M-323 and R-35. It was found that currently NBDTI mix type WMA-B has the same nominal maximum aggregate size (NMAS) as AASHTO SuperpaveTM 19; WMA-C mix has the same NMAS as AASHTO SuperpaveTM 12.5 and, WMA-D mix has the same NMAS as AASHTO SuperpaveTM 9.5. This analysis also showed that New Brunswick specifications have a much broader range in their control points than AASHTO. Mix designs between 2019 and 2021 revealed that even though most of the contractors met the requirements of the provincial specification, some did not comply with the AASHTO standard. Some mixes were selected along with NBDTI considering materials that had shown premature distresses in the past. The next steps in this study will include data gathering from the performance tests as a guide to an improved mix design, along with recommendations for conditioning specimens and testing parameters. The information of this project will contribute not only to the province of New Brunswick, but other agencies that are transitioning and updating their specifications for good-quality roads with higher resistance to common distresses such as rutting and cracking.