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What's Cooking With GDOT's 'Roadway Chefs'

Thu February 06, 2020 - Southeast Edition #4
Bre Kirkpatrick – SPECIAL TO CEG

OMAT’s mission is to sample, test and inspect all materials to ensure quality and durability in our construction projects.
OMAT’s mission is to sample, test and inspect all materials to ensure quality and durability in our construction projects.
OMAT’s mission is to sample, test and inspect all materials to ensure quality and durability in our construction projects. Physical Testing Lead Technician Remone Kendricks conducts bridge steel tensile strength test. Soils Lab Supervisor Harold Cox performs elutriation test, which separates target minerals based on size, shape and density in order to quickly determine the clay content of the soil. At a temperature of 140 degrees, the “hot house” dries aggregate to 
reduce moisture content for testing. The coring rig is used to take core samples of asphalt and concrete from the roadway for testing.

Did you know that road surfaces throughout the state have a distinct recipe designed for sustainability, preservation and safety? And that every type of material used or installed on Georgia DOT construction and maintenance projects must be tested and approved before use?

Whether it's concrete curing time, steel tensile strength, assessing potential ground contaminants, evaluating new products or everything in between — Georgia DOT's Office of Materials and Testing (OMAT) determines the sweet spot formula for all products to match the unique characteristics of each project. Down to the bolts.

The roadway chefs at OMAT vigorously test and analyze these products and create the recipes to ensure quality and safety. From the type of materials used, like aggregate, to evaluating new products and facilitating the submission process for companies who present their products for use, OMAT provides the official stamp of approval for all materials used on roads and bridges.

Concrete Strength

One such test is a strength test to determine how much force concrete can withstand prior to failing and crumbling. First, the machine operator places a cylinder of concrete mixed for a specific GDOT project number inside a compression machine. The project number is for organizational purposes; each project has different mixes of assigned materials and the team must identify which substance goes where. The machine increases the amount of pressure on the concrete to determine at what point it will fail — usually expressed in a PSI (pounds per square) unit. This is similar to how the tires on your vehicle use PSI to ensure proper inflation for longevity and for safety.

Aggregate Soundness

In this test OMAT applies a magnesium sulfate solution to aggregate to determine its resistance to breaking down. Using the right mix of materials ensures the longevity of the roadway. For example, if a concrete road is expected to last 30 years, the soundness test helps determine whether the aggregate can withstand the beating of tires, traffic volumes, the weight of heavy commercial vehicles, weather extremes and other factors.

Contaminants Testing

The sand equivalent test is an objective quality test that measures the relative proportions of fine dust or claylike material in soils or graded aggregate (GAB). In other words, it determines how "clean or dirty" the sample is. This is important because contaminants can cause undesirable consequences. For example, clay is a contaminant in many GABs. When clay gets moist from rain it can cause the aggregate material to swell or shrink, meaning it's not at optimal strength. This can cause premature failure of the road.


Imagine sand on the beach and think of the difference between when it's dry and when water is poured on top. In the saturation test, an air-dried fine aggregate sample is placed on a rack under a hot light with the goal to further dry out its surface to test its saturation level. Tests are run at different levels to determine how the aggregate behaves under various conditions like weather.

The scientists, engineers and technicians at OMAT conduct many other tests regarding aggregates, soils, steel, concrete, asphalt, molecules and releasing agents. Each requires a specially crafted recipe to ensure that crews use the optimum mixes, the highest standards in construction materials and the latest technology based on the requirements of each project — to keep Georgia's roads in good working condition.

This article originally appeared in MilePost, a publication of the Georgia Department of Transportation.

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