Request for The Permission of the Memorandum from The City Engineer

The purpose of this memo is to request approval from the City Engineer for the final sub-grade preparation and paving of the Gallatin Builders housing development. The following information provides evidence to indicate the subdivision developments are constructed in substantial conformance with the authorized plans and specifications, and where not in substantial conformance, indicates the corrective measures taken to ensure design integrity is met.

PROJECT BACKGROUND AND APPROVED SPECIFICATIONS

The Gallatin Builders housing development has fulfilled all prior project specifications, and the overall design and construction quality has been exceptional.

The only project element not yet approved is the development’s sub-grade preparation and paving. According to provisions in the city specification for paving, pavement lifts must be 4” thick and compacted to 94% of the theoretical maximum density. Secondly, the weather must be dry and at a temperature of 40°F and rising while paving occurs. These standards ensure the necessary strength and durability are met for safety, longevity, and user experience. If compaction standards are not met, the road surface will experience deformation, disintegration, and moisture damage – creating unpleasant and even hazardous driving conditions.

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Compaction tests were conducted in conformance with the approved plans and specifications and met the 94% maximum density specification. There are no discernable issues with the pavement, and the quality appears to be excellent. However, due to unforeseen weather events, the paving had to be performed in weather below 40°F. The paving was performed under sunny, dry conditions; however, the temperature was only 25°F and rising. To eliminate the effects of cold-weather paving, a tarping/heating system was installed to keep the subbase at a temperature above 40°F.

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The subbase temperature was monitored throughout the day, and measurements indicate the temperature never fell below 40°F.

SPECIFICATION MODIFICATION – COLD WEATHER PAVING

According to asphalt researchers and experts, reaching proper density in hot mix asphalt (HMA) pavement is the most important consideration for establishing long term pavement performance. Density is achieved by compacting the mix at the time of placement. To achieve sufficient compaction, the asphalt temperature must be sufficiently high while rolling takes place. The viscosity of the HMA will increase as the mixture cools, making it less compactable. This is the limitation of paving in cold weather: the asphalt layer will cool much faster than it will during warm weather, reducing the time available to compact the material.

The primary factors considered in temperature loss are subbase temperature, lift thickness, initial mat temperature, and air temperature.  Corrective measures were taken to limit the effects of the cold weather. The temperature profile of newly placed pavement indicates that cooling occurs most rapidly at the bottom of the mat (interface of pavement lift and subbase).  A tarping and insulation system was used to keep the subbase temperature above 40°F. By keeping the subbase adequately warm, heat loss in the pavement lift was minimized. The temperature and thickness of the HMA lift control heat dissipation.

Studies conducted by the National Asphalt Pavement Association confirm that paving at temperatures below 40°F incur smaller risk when the lift thickness is greater than 2 inches. For the given environmental and material conditions, the time available to compact is over 60 minutes.  By setting a temperature limit for paving operations, the specification neglects several variables that contribute to the cooling-rate of pavement, and severely limits the available paving season. Pavement placed at low temperatures can perform well, provided that the proper precautions are taken. (1) If the development’s paving was not completed, the lots would not be available for sale until spring, incurring considerable financial expenses.

REQUEST FOR APPROVAL

As the development engineer for Gallatin Builders, I request the development’s sub-grade preparation and paving be approved by the City Engineer. Although the paving was completed in conditions beyond the specification limit, the research conducted on cold weather paving corresponds with the methods used in this project, and the successful compaction tests provide reasonable assurance that the necessary standards for user safety and experience are met.

Updated: Jan 02, 2022
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Request for The Permission of the Memorandum from The City Engineer. (2022, Jan 02). Retrieved from https://studymoose.com/request-for-the-permission-of-the-memorandum-from-the-city-engineer-essay

Request for The Permission of the Memorandum from The City Engineer essay
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