Abstract
Recent research developments have indicated that asphalt mixture durability and pavement life can be increased by modifying the Superpave asphalt mixture design method to achieve an in-place density of 95%, approximately 2% higher than the density requirements of conventionally designed Superpave mixtures. Doing so requires increasing the design air voids content to 5% and making changes to the mixture aggregate gradation so that effective binder content is not lowered. After successful laboratory testing of this modified mixture design method, known as Superpave 5, two controlled field trials and one full scale demonstration project, the Indiana Department of Transportation (INDOT) let 12 trial projects across the six INDOT districts based on the design method. The Purdue University research team was tasked with observing the implementation of the Superpave 5 mixture design method, documenting the construction and completing an in-depth analysis of the quality control and quality assurance (QC/QA) data obtained from the projects. QC and QA data for each construction project were examined using various statistical metrics to determine construction performance with respect to INDOT Superpave 5 specifications. The data indicate that, on average, the contractors achieved 5% laboratory air voids, which coincides with the Superpave 5 recommendation of 5%. However, on average, the as-constructed mat density of 93.8% is roughly 1% less than the INDOT Superpave 5 specification. It is recommended that INDOT monitor performance of the Superpave 5 mixtures and implement some type of additional training for contractor personnel, in order to help them increase their understanding of Superpave 5 concepts and how best to implement the design method in their operation.
Highlights
Recent research developments have indicated that asphalt mixture durability and pavement life can be increased by modifying the Superpave asphalt mixture design method to achieve in-place densities of 95%—approximately 2% higher than the density requirements of conventionally designed Superpave mixtures
The Purdue University research team was tasked with observing the implementation of the Superpave 5 mixture design method; documenting the construction; completing an in-depth analysis of the quality control and quality assurance (QC/QA) data obtained from the projects; completing a literature review concerning asphalt mixture lift thickness and its effect on asphalt pavement density; and making recommendations based on the lift thicknesses used by Indiana Department of Transportation (INDOT)
N Overall, the Superpave 5 mixtures were slightly undercompacted with respect to Superpave 5 recommendations, despite previous trial projects having established that 95% density could be achieved without additional compaction effort beyond that used for conventional Superpave mixtures
Summary
Both short- and long-term, is one of the most important factors in determining asphalt pavement performance. The Indiana Department of Transportation’s (INDOT) method of asphalt mixture design and construction of asphalt pavements targets 4% air voids content (Va) in the laboratory compacted specimens, as required by the conventional Superpave mixture design method. Motivated to increase in-place asphalt pavement densities, Hekmatfar et al (2015) successfully modified the standard Superpave asphalt mixture design method to allow contractors to achieve higher in-place density without increasing compaction effort. Known colloquially as ‘‘Superpave 5,’’ this modified method selects the optimum binder content based on 5% laboratory air voids content, rather than at 4%, as does the standard method. In the controlled study done by Hekmatfar et al (2015), it was noted that the Superpave 5 mixture design method produced mixtures that could be compacted to 5% air voids (95% density) in the field without requiring additional compaction effort beyond that used for the standard mixtures
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