Traffic and Safety

Comprehensive Investigation of Aggregates in Asphalt Mixture Designs and Relationship to Compaction

Compaction is the most crucial factor in constructing durable asphalt pavements. The current asphalt mixture designs use a target of 4% air voids, however, the mixtures are compacted in the field at a target of 7% air voids and in some instances as high as 10% air voids are allowed.


Recent research has shown that a different approach, in which the mixtures are designed at 5% and compacted at 5% in the field, could result in more durable mixtures. The new method is based on changes to the aggregate gradation that make the mixture more workable in the field. In current research at University of Minnesota, a computational tool is being developed to better understand the compaction process.


Building on this current work, it is proposed that aggregates and asphalt mixtures used in asphalt mixture production are collected from projects in Minnesota and are analyzed using various scanning techniques (2D, 3D) as well as X-ray CT (computed tomography) of asphalt mixtures. The materials will include belt samples, extracted, as well as compacted field and laboratory mixtures. The results will be used to develop an aggregate selection process that could be used in the 5/5 method for typical materials used in Minnesota projects.


This proposed study is a companion to "Simple Methods for Verification of Low-Temperature Cracking Resistance of Asphalt Binders and Mixtures" and common materials will be used between the two. It is recommended that they both be pursued as separate projects.


Idea Submitted by : Dave Van Deusen; John Garrity

List your MnDOT Office,District,City, County, Univ. or Other : OMRR

Idea Champion - Who at MnDOT/LRRB? : John Garrity

Why is this a priority and what are the benefits for the State/County/City? :

This is a priority for road owner agencies because asphalt mixture density is the primary factor affecting long-term pavement performance.


Primary benefits are:


1. A better understanding of aggregate materials properties and how they affect the constructability of mixtures they are used in; and


2. Improved mixture design procedure to reconcile differences that currently exist between assumptions made in the lab and reality in the field.

Project Type - MnDOT or LRRB / Research, Implementation or TRS : MnDOT Research

Idea Status (this will be updated by the moderator) : Need Statement #496


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Idea No. 138