PROGRESS REPORT ON OHIO'S SUPERPAVE IMPLEMENTATION

The Ohio Department of Transportation, ODOT, continues its pursuit of the Superior Performing Asphalt Pavement (Superpave) letting to contract the last of its initial round of experimental projects. With the sale of this last project, the list has grown to eight pavements.

To date, three of the eight Superpave projects have been fully constructed. These include Delaware US 23, Athens US 33 and

SR 93 in Lawrence and Jackson Counties. A fourth project, Richland US 30, nears completion while the project on Ottawa SR 2 is just beginning, to pave Superpave asphalt.

LESSONS LEARNED

Developing, manufacturing and placing Superpave mixtures has been a learning experience for Ohio's HMA industry. Always up for a challenge, the industry has met Superpave squarely and is working toward its successful implementation.

We've learned Superpave places significant restrictions on the raw materials incorporated into these paving, mixtures. Where

conventional HMA mixtures were able to use locally available aggregate resources, Superpave may require the importing of aggregates. This is in large part due to demands placed on the aggregate to have sufficient angularity to ensure resistance to rutting. The Department, in its most recent update of the Superpave specification, has tightened its requirement for fine aggregate angularity, making the importing of aggregate a reality. This has been done to ensure rounded fine aggregate does not make its way into these mixes resulting in poor rutting resistance. Mixes having a sandy-like gradation and mixes having a coarse gradation have both been produced in Ohio as Superpave surface course mixtures. This has occurred in large part due to the availability of aggregates which yield the desired volumetric mixture properties. The preferred gradation by

Superpave researchers is a coarsely graded mix to maximize the structural strength of the mixture and its resistance to rutting. ODOT's next round of Superpave projects will be governed by new specification parameters which will encourage the use of coarsely graded mixtures.

A portion of the Department's Superpave specification requires side by side quality control testing in the field, during production, using both the Superpave and Marshall compacting apparati. The Marshall compactor is the Department's conventional asphalt mix design apparatus. This side by side testing has generated valuable data as ODOT evaluates the Superpave mix design criteria.

Preliminary information indicates that the Superpave criteria, if left unmodified, will require less asphalt binder in these type mixes. ODOT and the Ohio HMA industry are working to ensure binder contents remain high and pavement durability is enhanced with the implementation of Superpave.

To ensure long term performance, the Department has opted to require the use of polymer modified asphalt in the Superpave surface course mixtures. The use of polymers has a 20+ year history of success in Ohio, primarily with the use of SBR latex and more recently with SBS polymer. This new requirement will be incorporated into the next round of Superpave projects let to contract.

ODOT Superpave Projects

WHERE WE GO FROM HERE

As with any new technology, there will come with the implementation of Superpave the need for occasional modifications to the specification. The ODOT is attempting to act prudently, implementing Superpave in a systematic fashion, addressing all the variables. In addition to the work being performed by ODOT, expert-task-groups (ETGS) have been formed on a national basis to further hone the Superpave specification. Ohio's HMA industry through its Strategic Plan has poised itself to adopt this new technology, and has committed its resources to building today's roads to bear tomorrow's loads, making HMA the pavement of choice of Ohio's motoring public.

FPI Newsletter, Vol. 6, No. 3, Sept. 30, 1997