TOPS News:
September 2022 |
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HiMA Inhibits Rutting in Oklahoma
It takes years to know if an overlay, specification, or technique will prove effective in the pavement world. The wait is over in Oklahoma. A decade has passed since the Oklahoma Department of Transportation (ODOT) used mill and overlay with highly modified asphalt (HiMA) on a two-mile stretch of I-40 in Caddo County, 50 miles west of Oklahoma City. The I-40 HiMA concept was based on experience from Oklahoma test sections in the 2009-2012 cycle of the National Center for Asphalt Technology test track in Alabama, in which HiMA was recommended as a repair option for failed test sections.
 This stretch of I-40, approximately 50 miles west of Oklahoma City, received a mill and overlay with HiMA in 2012. Source: Oklahoma DOT.
In the first commercial application of this new technology, ODOT placed several HiMA lifts and topped them with a 0.75-inch open-graded friction course containing PG76-28 OK asphalt binder but no HiMA. Conventional polymer concentration that exceeds 3 percent becomes more difficult to produce in the plant and less workable for the paving crew. However, a unique polymer was used in the Oklahoma I-40 PG76-28 E binder. The product is designed to be used in significantly larger amounts than conventional polymer modifiers—up to 7.5 to 8 percent while retaining workability. The result is a more durable pavement with thinner sections that stand up to truck traffic. While a highly polymerized mix is more expensive, reducing the required thickness can offset the cost and provide a longer-lasting pavement.
The I-40 section endures more than 25,000 vehicles daily, including 7 percent single-unit trucks and 29 percent combo trucks. Ten years after receiving the new overlay, the I-40 span’s International Roughness Index (IRI) averaged 50 inches per mile, which is smooth enough to result in ride quality bonuses for new construction in some states. In Oklahoma, IRI is combined with a Pavement Condition Rating to develop the sections' Pavement Quality Indices (PQI). The PQI averaged 95 out of 100.
TOPS Resources
Looking for more information? Visit the FHWA Targeted Overlay Pavement Solutions (TOPS) website for a variety of resources including case studies, one-pagers, and webinars. Contact TOPS co-team lead Tim Aschenbrener (asphalt) or Robert Conway (concrete).
Check out a TOPS Webinar
The TOPS team has hosted three webinars in recent months including:
Stone Matrix Asphalt and Highly Modified Asphalt Webinar
Learn about SMA and HiMA and hear presentations from Georgia and Florida.
High-Performance Thin Overlays and Crack Attenuating Mixture Webinar
Learn about HPTO and CAM and hear presentations from New Jersey and Texas.
An Overview of Concrete Overlays Webinar
Get an introduction to concrete overlays, understand the challenges and value proposition, learn how to get started, and more.
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