Ohio Adopts Smoothseal: A Thin-lift Asphalt P.M. Strategy
Preventive maintenance is a topic of much interest around the country as DOTs do their best to get the most out of aging roads under increasingly tight budgets – and for good reason. A P.M. treatment on a pavement exhibiting surface distress today can prevent the need for more radical measures in the future, and at a fraction of the cost.
For many pavement engineers, microsurfacing and chip seals are the “defaults” when considering preventive maintenance treatments. In Ohio , however, these aren't the only options. In fact the Ohio Department of Transportation is finding that a thin asphalt overlay—or Smoothseal, as the material has come to be known in the Buckeye state - can provide a cost-effective answer to pavement preservation .
ODOT Supplemental Specification 854, Fine Graded Polymer Asphalt Concrete – dubbed “ Smoothseal ” is a non-proprietary material comprised of a blend of high-quality aggregates with a polymer-modified asphalt. Longevity was a primary goal in ODOT's development of Smoothseal and as such polymer modification was a must. Smoothseal can be placed as thin as three-quarters of an inch and has demonstrated the ability to preserve the life and drivability of structurally sound pavements.
Why Smoothseal was added to the Platter of Ohio 's other Preventive Maintenance Treatements -
One answer is cost. In July of last year, ODOT let to bid US Route 23 in Lucas County near the Michigan state line, inviting bids for asphalt and microsurfacing preventive maintenance processes. Gerken Paving, of Napoleon, Ohio submitted a bid for placing a 1-inch thick Smoothseal, which came in 20 percent cheaper than bids for a double-course microsurfacing.
ODOT Smoothseals US Route 23, Lucas County , as part of nighttime paving project.
But cost is not the only reason Smoothseal is being used. Smoothseal improves ride quality by correcting minor rutting and filling in surface depressions. This improvement to ride quality has been duly noted by pavement engineers. Because Smoothseal is a product placed using an asphalt paver free-floating screed, cross-slope is restored and drainage improved.
An advantage of Smoothseal over that of surface treatments is the fact that by adding additional thickness in the form of a thin asphalt overly, you will increase the structural strength of the pavement. This means Smoothseal does more than just solve short-term pavement degradation and ride issues. Albeit the additional thickness the treatment provides is nominal, however it does serve to make the pavement structure last longer and increase its load carrying capacity. The reason for this is simple. As pavement thickness increases, pressure per square inch on the subgrade decreases, thanks to the increased size of the load's footprint.
As previously mentioned, ODOT's objective in developing Smoothseal was to obtain greater surface life. To accomplish this end, polymers have been added to the mix to provide enhanced wear resistance and resistance to weathering. SBR latex asphalt m ix has been used on Ohio highways for the past 30 years, and more recently SBS asphalt mixes have been prevalent. The performance history of these pavements has given ODOT confidence that polymer modified asphalt mixes result in longer surface life.
Smoothseal is a fine-graded material, and it takes advantage of the positive ride attributes associated with asphalt paving. The free-floating screed of the asphalt paver allows the material to compensate for the roughness of the pavement by filling in the low spots and trimming off high spots. The use of polymers and crushed stone in the mixture enhances its stability and stiffness. A silicon dioxide requirement for the sand portion of the mix helps ensure good skid resistance.
Flexible Pavements of Ohio, the trade association for the state's asphalt industry, presented its 2002 “Master Craftsman Award” to a pavement in the City of Shaker Heights . The award was presented for the paving of Shelburne Road – a pavement that was surfaced with Smoothseal and provided 28 years of service. The Master Craftsman Award is the association's highest honor, recognizing projects that demonstrate the best characteristics of asphalt paving, especially those with long service lives. The product used in this project has come to be known as Smoothseal “Type A.”
In 1993, the industry introduced Smoothseal “Type B” on an experimental project in Logan County . Smoothseal “Type B” was designed for both moderate and heavily trafficked pavements. It uses 100 percent two-faced crushed coarse aggregate, which acts to provide internal friction to the mix, and therefore greater stability. PG 76-22M (“M” is an ODOT designation indicating polymer modification), SBS polymer modified asphalt binder or SBR latex rubber polymer is added to improve Smoothseal “Type B” resulting in a toughness superior to finely graded hot mix asphalt.
Cross-sectional cuts of Smoothseal types.
The interest in Smoothseal continues to grow. Last year Flexible Pavements of Ohio sponsored workshops to expose city and county engineers to preventive maintenance using ODOT's Smoothseal product. Since that time local governments in Ohio are adopting the material as another tool in their preventive maintenance toolboxes. The most recent is the City of Wooster which has taken keen interest in the material and constructed projects.
Smoothseal placed in residential application.
City of Englewood, Oh.
Interest in Smoothseal is awakening on a national level as well. Ohio industry leaders are getting requests from other states and the National Asphalt Pavement Association to share Smoothseal's success story with a broader audience.
The Ohio Department of Transportation's Fine Graded Polymer Asphalt Concrete (a.k.a. Smoothseal) is no “silver bullet,” however it has struck a cord with pavement maintenance engineers seeking long-term preventive maintenance fixes.
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