Water Absorbing Pervious Concrete Pavement - CEMEX USA
Although pervious concrete has been used for over 50 years, only recently has its stormwater management potential been recognized. It creates a pavement that allows infiltration of rainwater rather than creating runoff. Because of the infiltration, ground water supplies are recharged and pollutants are treated.
Pervious concrete pavement is a pavement type that allows rainwater and other sources of water to percolate into the base layer below the concrete. Thus allowing the base material to absorb and control the flow rate of the water as it moves off site.
Pervious concrete's mass consists of an interconnected void structure, which allows water to flow through at very high rates. Typically, when cast on a sandy subgrade soil, the pavement will infiltrate stormwater at a higher rate than that of the soil below.
Drainage design of a pervious pavement system should assume the pavement surface is not a limiting factor. The runoff coefficient or curve number of the paved area should be that of the subgrade soils in the compacted state. Over-compaction of the subgrade during construction will prevent necessary infiltration.
Structurally, pervious concrete is weaker than plain concrete with compressive strengths less than 1000 psi. Due to the lower strengths, pervious concrete pavements are acceptable for light duty applications such as car parking facilities, pedestrian areas, and low traffic pavements.
Pervious concrete pavements may require maintenance to preserve the infiltration capacity. To prevent clogging of the pavement: prevent runoff from adjacent bare or landscaped areas, prevent vehicles from tracking soil onto the pavement, and prevent organics from falling onto the pavement surface.
ACI 522 has developed recommendations and specifications for pervious concrete pavements. Typically, pervious concrete pavements can be produced with a variety of coarse aggregates that result in many variations of concrete density. The key elements to pervious concrete pavements are the percent voids, permeability and compressive strength. The typical void content is 15-25% while the permeability is 100-2000 inches of water per hour and the compressive strength requirements range from 500 to 4000 psi.
Pervious pavements are most often used for sidewalks and parking lots around residential and commercial buildings. They are most beneficial when they increase the usable space on a project site as normally required retention ponds can be minimized or eliminated. Additionally, many agencies do not count the full pervious pavement as impervious surface for zoning.
Common applications for the pervious concrete include:
- Retail Shops
Due to durability concerns, this technology should not be used in airport runways, heavy truck facilities, or uncovered athletic facilities.
Product Technical Information
Placement and finishing techniques for pervious concrete are different from plain concrete. Pervious concrete is actually cast from a no-fines concrete mixture, thus it will not flow. It must be placed with specialty equipment to encourage consolidation without collapsing the void structure. Further, the water content of the fresh concrete must be carefully controlled.
Pervious concrete must cure for seven days before opening to traffic. Every member of the project team (engineer, architect, general contractor, paving contractor) must work together to protect the pavement during the curing period.
Because of its porous structure, pervious pavement allows stormwater to percolate into the underlying soil while filtering out harmful sediments. This results in better stormwater quality, complying with new EPA regulations.
Pervious concrete pavement is a "green" product which can be laid next to trees and foliage, protecting root systems that may be beneath the paved areas. This pavement does not create hazardous runoff, nor does it prevent water from reaching roots.
Pervious pavement can double as a parking lot and retention area, maximizing the land that can be developed and lowering construction costs.