Friday, November 23, 2012
Green Alley Project of Chicago
Chicago
is already home to the highest number of green rooftops of any city in the
world, including Chicago’s City Hall’s Rooftop Garden. The next initiative
being undertaken by the city is the Green Alley Program. This project is an
expanded approach to Chicago Department of Transportation’s existing alley
program and is designed to improve those alleyways in a sustainable way. The
city contains one of the most extensive networks of alleyways in the world,
covering 1,900 miles with over 3,500 acres of paved, impermeable surfaces. A
number of improvements have been suggested for the Green Alley Program including the use of permeable surfaces, high albedo
pavements, and recycled material.
1) Permeable
Pavement- Permeable
pavement has pores or openings that allow water to pass through the surface and
percolate through the existing subsoil. Permeable pavement comes in the form of
permeable asphalt, permeable concrete, and permeable pavers. In areas where
soils do not drain freely, permeable pavement can be used in combination with
subsurface drainage systems, like pipe underdrains or stormwater infiltration
trenches to slow runoff and reduce stress on the combined sewer system.
Potential Benefits
•
Reduces the rate and quantity of stormwater runoff
• Reduces
stress on the sewer system
•
Recharges ground water
•
Filters silt, pollutants and debris
2) High Albedo
Pavement- High
albedo pavement material is light in color and reflects sunlight away from the
surface. With less sunlight absorbed by pavement, less heat is radiated by the
pavement. High albedo pavement therefore reduces the urban heat island effect.
This reduces cooling costs, helps the survival of urban vegetation, and improves
air quality, which can help reduce the symptoms of some respiratory diseases.
Potential
Benefits
•
Reduces the urban heat island effect
•
Can be used under a wide variety of site conditions
•
Conserves energy by reducing cooling costs
•
Improves air quality
3) Recycled
Construction Materials- Recycled construction materials can be incorporated in a variety
of ways in green alleys. Recycled concrete aggregate can be used in the
concrete mix and as a base beneath surface paving. Also, slag, a by-product of
steel production, can be used as a component of the concrete mix, reducing
industrial waste. Ground tire rubber can be used in porous asphalt and reclaimed
asphalt pavement in non-porous asphalt.
Potential
Benefits
•
Reduces waste hauled to landfills
•
Reduces the need to extract virgin natural resources
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