Agenda Packets - 2008/01/28 - Laserfiche WebLink

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Item No. 8B Meeting Date: January 28, 2008 Type of Business: CA WK: Work Session; PH: Public Hearing; CA: Consent Agenda; CB: Council Business City Administrator Review _______ City of Mounds View Staff Report To: Honorable Mayor and City Council From: Greg Lee, Director of Public Works Item Title/Subject: Resolution 7213 Authorizing the Preparation of a Preliminary Feasibility Report and Consultant Selection for the 2008 Street Maintenance Project (Seal Coat Project) Background: Seal Coating is a common preventative maintenance activity in Minnesota, performed by most cities, counties, and rural Mn/DOT districts. It involves spraying asphalt cement on the surface of an existing pavement followed by the application of a cover aggregate. The asphalt cement is usually emulsified (suspended in water) to allow for it to be applied without the addition of extreme heat. The cover aggregate is normally either naturally occurring gravel or crushed aggregate such as granite, quartzite or traprock (basalt). The primary reason to seal coat an asphalt pavement is to protect the pavement from the deteriorating effects of sun and water. 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, which not only slows down the oxidation process, but also helps the pavement to shed water, preventing it from entering the base material. The 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 the 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 course 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.