Aggregate Quality Process - 591-0420-21

Description of Agency

The Michigan Department of Transportation’s (MDOT’s) Aggregate Quality Unit (AQU), regional offices, and transportation service centers share responsibility for ensuring the quality of aggregate material used during construction. Aggregate is a substance composed of mineral crystals or mineral rock fragments used in pavement.

Each aggregate supplier is assigned an Aggregate Source Inventory number and must pass initial aggregate quality tests. For initial aggregate quality tests, samples are obtained from the source (gravel pit) and brought to AQU’s central laboratory for testing. During use in a project, aggregate is required to be quality assurance tested at the start of the project and every subsequent 1,000 tons. As of January 28, 2021, MDOT had 617 aggregate suppliers.

To reduce required testing frequency, aggregate suppliers can apply to become prequalified. To become prequalified, a supplier must have a quality control plan, internal or contracted quality control testing, and qualified staff.

Audit Objectives

1. To assess the sufficiency of MDOT’s efforts to ensure aggregate quality.
2. To assess the effectiveness of MDOT’s efforts to administer the Aggregate Supplier Program.


Estimated Release Date: October 2022

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