01-22-07 Item 2B, Five Year CIP Update

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2006 PMP Update 1118/2007 Page 2 becoming brittle and cracking, and also helps keep the water from seeping through the pavement and causing problems to the base material. Mill and Overlay There are several maintenance practices that involve milling. An edge mill typically consists of grinding the old bituminous surface along the outer 8 feet of the street. This helps establish a uniform cross-section, especially in instances where the crown in the street is relatively flat. A full width mill, or resurfacing, is necessary when the upper surface layer of a pavement has deteriorated considerably. Significant surface pavement distresses and more extensive "thermal" cracking need to be removed and/or repaired with a full width and uniform depth milling process. Both edge mills and full-width mills are typically 1.5 to 2 inches thick, but can vary on a project by project basis. Milling creates an even surface to ensure a uniform overall thickness to the new overlay. An asphalt overlay of 1.5 to 2 inches over the entire pavement width forms a smooth crown, renews the street surface, restores structural capacity and proper drainage, and extends the life cycle of the original pavement. Afull depth mill can be used on a street that has already been reconstructed with a good base section, but the pavement has deteriorated to a point where seal coating or a standard mill and overlay is not effective. A pavement section with significant cracking will end up reflecting through the new pavement. The full depth of the pavement is ground up and removed. This process may also involve some subgrade soil corrections and some removal of aggregate base, if it has been contaminated or is sub-standard. The street is paved with the same thickness of new asphalt. Pavement can also be reclaimed, where approximately 8 to ] 0 inches of the existing asphalt and base are ground up in place. This forms a new more stable base without adding new material. The road is then paved with new asphalt. This is only recommended where there is no curb and gutter on the road, since the existing materials stay in place and a higher road elevation is created once the new pavement thickness is added. Reconstruction When a street is fully reconstructed, the existing asphalt and base are completely removed and replaced. Reconstruction may also involve subgrade soil corrections. For streets that do not meet current design standards for width, curb and gutter, and drainage, an upgrade may also be incorporated.