Cities explore green roadway alternatives
Pervious concrete has gone by quite a few different name. Porous, green, permeable or “thirsty” concrete is an environmentally friendly alternative to traditional concrete for parking lots, driveways, parking lanes, alleys and roadways. It has been used primarily where water collects and takes days to drain. The substance has been improved over the years to endure heavy loads of consistent traffic.
Made of materials that create a permeable texture, pervious concrete allows water to seep through its open pores and be collected in a base below to be reabsorbed into the ground or evaporated. The overflow of rainwater from the base would drain into the public water system, which benefits runoffs and stormwater management.
Southern states that experience constant flooding have invested or plan to invest in this technology. Pervious concrete can absorb up to 1,000 gallons of water in 60 seconds, which allows urban drainage systems to withstand copious amounts of rainfall. The green concrete helps by redirecting water from the already overused drainage system. Cities with older infrastructures have also shown interest in pervious concrete since some areas were built without a drainage system along alleyways.
Chemical discharge from vehicles, fertilizing chemicals from lawns and traditional concrete chemicals can be absorbed by the water and enter the draining system or be evaporated into the air, contaminating the environment. Pervious concrete lacks the potential to contaminate and even filters these pollutants in order to reduce the flow of contaminates into the water system.
Pervious concrete also harbors the ability to reduce heat with its lighter color and open pore structure. It absorbs less heat than the typical concrete that is used in urban areas and diffuses the heat island effect. Trees would significantly benefit from the use of pervious concrete since water and air would have easier access to the roots of the tree. Additionally, the trees can be used as a heat reducer since shade casted along the concrete would create a cooling effect.
In the North
Areas where freezing weather is present have only recently tried utilizing the material, with many continuing to watch small projects to see what can be improved upon. On a world-stage, the Beijing National Stadium caught attention when it was built for the 2008 Summer Olympics in China. For the build, China used copious amounts of pervious concrete, which have held strongly through various weather extremities since 2008. Closer to home, Westmont, Ill., became the first village within the Chicagoland region and five-state area to experiment with pervious concrete on a municipal roadway.
“We’ve known about this technology for many years, but it was used mainly in southern and eastern states,” explained Assistant Director of Public Works and Village Engineer Noriel Noriega. “Closer to 2010, our board of trustees became aware of this technology and thought it’d be great idea to invest in. We were in design for a standard cross section at the time and was requested to use green alternatives. We sort of tested it.”
With Westmont slipping into below freezing temperatures, the care and maintenance for pervious concrete is different from traditional concrete and asphalt. Much more time goes into maintaining pervious concrete and must be cleaned more often as salt would challenge the structural integrity of the roadway. Steel plow blades are also restricted, instead replaced with a rubber blade. These special items along with extra cost in manpower and labor contribute to more attentive responsibility.
“It works better in southern states, but we’re doing our best and being proactive,” commented Noriega. “We definitely have benefits from a political side and feedback by reducing our carbon footprint. Being environmentally friendly goes a long way and salt conservation is another advantage.”
“I would recommend this to others in terms of what they need for their municipality. This mostly exists in parking lots around here. Our roadway was the first in Illinois, definitely a learning process.”
Noriega expressed that there are some difficulties with pervious concrete in a Midwest state. Ensuring that all the staff has proper additional training is a major part of having a successful permeable road. Noriega commented that the village has started investing in other pervious aspects such as alleyways. As progress continues Westmont will always be reviewing and trying out this technology to be more environmentally friendly.
In the South
In areas that don’t dip to freezing temperatures, these kinds of issues wouldn’t occur but southern cities do have another bit of upkeep to maintain in their own ways. Plan Review Engineer Robert Gordon in Wilmington, N.C., has said that pervious concrete must be vacuumed routinely to keep particulates and debris such as leaves, pollen, soil and so forth from eroding the pores within the concrete.
While Wilmington hasn’t publicly invested in pervious concrete beyond small grant projects and extensive private development, the city will be looking into pervious parking lots now that they have the proper equipment. A stable landscape structure with drainage system awareness is also an important factor as the proper flow of debris into the water system prevents clogging the pervious concrete. Most of the maintenance revolves around prevention by keeping clogging materials out of the permeable surface.
“With typical asphalt, you put it in and then you just forget about it,” explained Gordon. “With pervious concrete, if you don’t maintain it and it does get clogged, then it’s shot. That’s the challenge we’ve seen.”
Wilmington plans to use the concrete as a demonstration in public areas for city projects and public education. Some grant projects with pervious concrete have been completed, allowing the city to observe the impact it creates.
Pervious concrete has been present in North Carolina for about 15 years with city and development engineers keeping in touch with new options that are available. It is a widely used material, but maintenance poses a problem for Wilmington, and the cost is more expensive than traditional concrete.
“When you look at the benefit you gain as a space, it becomes a very cost beneficial option,” added Gordon. “I would recommend pervious concrete for municipalities if they have a solid way to maintain it.”
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