In the Lab: DDOT’s QA/QC Division Ensures Street Paving Materials Are Up to Spec

An asphalt sample after it has been spun into a cylinder by a gyratory compacter.

An asphalt sample after it has been spun into a cylinder by a gyratory compacter.

DDOT’s Quality Assurance / Quality Control (QA/QC) Division has a universal impact on almost every infrastructure project that DDOT has a hand in.

The QA/QC Division operates as the spine of DDOT’s road management system, shouldering the responsibility of ensuring the safety of the city’s  infrastructure by               ensuring that all materials utilized in DDOT-related construction projects meet the standards established by the District and the Federal Highway Administration (FHWA).

Before DDOT, or DDOT contractors, use any material in the construction projects involving bridges or roadways (eg, asphalt, metal used for beams, concrete) it must first past the muster of a test or review by the QA/QC division. The division serves as DDOT’s auditor of the materials that the agency and its contractors use and ensures that the substance of the city’s infrastructure can stand the test of time.

In addition to testing the materials that the agency and its contractors use, the division conducts geotechnical studies, troubleshoots problems related to roadway and bridge construction projects and resolves citizens’ concerns about roadway vibration and drainage issues.

The Wheat from the Chaff

Several buildings off of the McMillan Reservoir, near Howard University, serve as the QA/QC Division’s laboratory and testing facilities.  One of the structures, a square warehouse fronted by a large garage door, was built by industrious members of the division in the early 1980s, and houses machines that test the dexterity of concrete used in construction around the District.

In this building, engineers test “wet”  samples of concrete that are slated to be used in construction projects, and analyze cylinder-shaped samples of concrete that are usurped from finished roadway and bridge projects. These “core drill” samples are usually taken once every 50 cubic yards to ensure the uniformity of the quality of the concrete used in a project.

Nearby, engineers operate specialized machines that test another ubiquitous material used in construction: asphalt.

As is the practice in the division’s concrete tests, QA/QC engineers test asphalt samples that are taken before and after the materials are installed.

QA/QC engineers place asphalt samples in an ignition oven, which heats the material at 1,000°F.

In the lab, the “aggregate” (asphalt’s rock base) and the “binder” (the oil-based sludge that holds asphalt together) are mixed and subjected to a gyratory compacter that spins the compound to produce a condensed cylinder of material that is comparable to asphalt that is crushed into the street by an asphalt roller (pictured above).  Hot asphalt samples taken from the field are also burned at 1,000°F, to separate the aggregates from the binder, and   subjected to a variety of tests.

These tests–like all of the experiments the QA/QC division performs–ensures that the District is getting an adequate return on what it spends on infrastructure and that DDOT, and its contractors, are using the appropriate materials to keep the District’s streets safe.



About DDOT Blogger

The District Department of Transportation (DDOT) develops and maintains for the District of Columbia a cohesive sustainable transportation system that delivers safe, affordable, and convenient ways to move people and goods - while protecting and enhancing the natural, environmental and cultural resources of the District.
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