August 29th, 2012

GET A GRIP

Preserve Infrastructure, by Catherine Higgins.

UDOT is implementing a Quality Management Plan to prevent stripping and improve the durability of asphalt pavement.

In hot mix asphalt pavement, stripping occurs when the asphalt does not adhere well to the aggregate. The result of stripping is pavement that crumbles under the wear and tear of traffic and weather.

Howard Anderson, left, and Clark Allen, manager of UDOT's central lab stand near Hamburg Wheel Tracking equipment

UDOT requires hot mix plants to add lime to the asphalt mix. Lime works as a bonding agent so the asphalt sticks to the aggregate. In the mixing process, the lime is combined with a precise amount of water to make slurry, blended with the aggregate, and then heat-dried before the treated aggregate is mixed hot with the asphalt binder.

Lime added correctly prevents stripping and makes the pavement more durable, especially during the winter and early spring when the freeze-thaw cycle takes its toll, according to Howard Anderson, UDOT Quality Assurance and Aggregate Engineer. Added incorrectly, the pavement is at risk for stripping.

Anderson has been working with Kevin VanFrank, UDOT Engineer for Asphalt Materials, Kleinfelder and Tim Biel of CME to develop a comprehensive plan to ensure that the correct lime-water slurry is used in the mix design.

UDOT’s QMP

When the QMP is fully implemented, UDOT will only accept HMA from certified plants that keep records documenting their processes.  UDOT has also recently required the contractor to use their own Hamburg Wheel Tracking equipment to check their HMA mix designs.  This change allows the region Hamburg Wheel Tracking equipment to be used on field produced material to insure a quality material is delivered to the pavement.

The ultimate goal of the QMP is to extend the life of HMA pavement which is one important way UDOT uses funding efficiently to provide good value to the public.

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