Town Talk: The reason we seal coat roadways

Studies by the Asphalt Institute and the Asphalt Emulsion Manufacturers Association show that seal coating surface treatments provide low-cost, all-weather surface for light to medium traffic loads. The New Ulm Street Department staff is dedicated to maintaining the streets and alleys in the most efficient manner possible. Therefore, seal coating in conjunction with crack filling has become a routine task performed by the Street Department staff to maintain the asphalt pavement in New Ulm.

These same studies indicate the optimum time to apply a seal coat is every five to seven years. They also state, “For a successful seal coat, an existing pavement must exhibit minimal structural distress.” When an asphalt pavement is exposed to sun, wind and water, the asphalt hardens, or oxidizes. This causes the pavement to become more brittle. As a result, the pavement will crack because it is unable to bend and flex when exposed to traffic and temperature changes. A seal coat combats this situation by providing a waterproof membrane that not only slows the oxidation process but helps the pavement to shed water, preventing it from entering the base material.

A secondary benefit of seal coating is an increase in the surface friction it provides. This is accomplished by the additional texture the cover aggregate adds to the pavement. With time, traffic begins to wear the fine material from an asphalt pavement surface. This results in a condition referred to as raveling. When enough of the fine material is worn off the pavement surface, traffic is driving mostly on the coarse aggregate. As these aggregate particles begin to become smooth and polished, the roadway may become slippery, making it difficult to stop quickly. A seal coat increases the pavement texture and increases the surface friction properties.

During a typical year of seal coating, the Street Department uses about 50,000 gallons of emulsion oil and about 1,700 tons of aggregate. This translates to about 10 miles of streets. Alleys require much less material per block because of the narrow width. The number of alleys that are sealed each year varies, but alleys generally are done in conjunction with the streets.

In order to maximize the useable life of an asphalt pavement, the Street Department’s most important responsibility is to perform the right maintenance at the right time in the life of that pavement. Seal coating is one of the types of maintenance that is so important.

If you have any questions or would like to discuss our seal coating program, call Jeff Hoffmann, Interim Public Works Superintendent, at 359-8296.


Editor’s Note: The City of New Ulm presents a weekly column highlighting activities in different departments in the city government. Once a month the city will answer questions from readers. Questions on New Ulm city issues can be sent to comments@ci.new-ulm.mn.us.


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