Investigation of Asphalt Mixtures Compaction using a Novel Approach based on Tribology

Principal Investigator:

Mihai Marasteanu, Associate Professor, Civil, Environmental and Geo-Engineering

Co-Investigators:

Project Summary:

Over 90 percent of surfaced roads in the U.S. are built with asphalt materials. The hot mix asphalt (HMA) used to build asphalt pavements is produced in a hot mix plant. Aggregates of various sizes are heated and mixed with hot liquid asphalt binder, placed in trucks, and delivered to the construction site. It is then compacted with specialized equipment to reach a target air voids content of 7 percent. Asphalt binder viscosity controls the compaction process; it increases significantly as the temperature of the placed HMA rapidly decreases in field conditions, and this makes further compaction impossible when HMA temperature drops below 175 degrees Farenheit. Insufficient compaction (higher air voids) significantly decreases asphalt pavement's durability. Previous research performed by Le and Marasteanu has shown that the addition of small percentages of a novel material, called graphene nano-platelets (GNP), can significantly reduce the compaction effort required to densify HMA. Surprisingly, this is achieved without reducing asphalt binder viscosity, which indicates that a different mechanism is responsible for this result. This means that the traditional approach, based on rheological experiments and analyses, is not sufficient to understand the complex compaction process of asphalt mixtures. Recent work performed on warm mix additives by Professor Canestrari's research group at Universita Politecnica delle Marche in Italy, in collaboration with Nynas, the largest Swedish manufacturer of specialty naphthenic oils and bitumen products, has shown that a new approach based on the science of tribology--which deals with friction, lubrication and wear of contact surfaces in relative motion--provides a more complete picture of the binder properties that affect the compaction process. The new approach can also explain the results of GNP modification. The main goal of this international collaboration effort is to adopt and advance this novel tribological approach to investigate the lubricity of plain and modified asphalt binders that would allow the research group at the University of Minnesota to move towards a significant different research direction in the broader area of material characterization.

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