A pervious concrete mixture contains little or no sand, creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly. Typically, between 15% and 25% voids are achieved in the hardened concrete, and flow rates for water through pervious concrete are typically around 480 in./hr, although they can be much higher. Both the low mortar content and high porosity also reduce strength compared to conventional concrete mixtures, but sufficient strength for many applications is readily achieved.
There are several benefits to using Pervious Cement, here are a few.
Environmental Benefits:
Pervious concrete pavement systems provide a valuable stormwater management tool under the requirements of the EPA Storm Water Phase II Final Rule. Phase II regulations provide programs and practices to help control the amount of contaminants in our waterways. Impervious pavements-- particularly parking lots-- collect oil, anti-freeze, and other automobile fluids that can be washed into streams, lakes, and oceans when it rains. Pervious concrete pavement is a unique and effective way to address important environmental issues and support green, sustainable growth. By capturing stormwater and encouraging it to seep into the ground, porous concrete is helpful in recharging groundwater, reducing stormwater runoff, and meeting U.S. Environmental Protection Agency (EPA) stormwater regulations. In fact, the use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA-- and by other agencies across the country-- for the management of stormwater runoff. This technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices.
By capturing the first flush of rainfall and allowing it to percolate into the ground, soil chemistry and biology can then “treat” the polluted water naturally. Thus, stormwater retention areas may be reduced or eliminated, allowing increased land use. Furthermore, by collecting rainfall and allowing it to infiltrate, groundwater and aquifer recharge is increased, peak water flow through drainage channels is reduced, and flooding is minimized. In fact, the EPA named pervious pavements as a BMP for stormwater pollution prevention because they allow fluids to percolate into the soil.
The light color of concrete pavements absorbs less heat from solar radiation than darker pavements, and the relatively open pore structure of pervious concrete stores less heat, helping to lower heat island effects in urban areas.
Trees planted in parking lots and city sidewalks offer shade and produce a cooling effect in the area, further reducing heat island effects. Pervious concrete pavement is ideal for protecting trees in a paved environment (many plants have difficulty growing in areas covered by impervious pavements, sidewalks and landscaping, because air and water have difficulty getting to the roots). Pervious concrete pavements or sidewalks allow adjacent trees to receive more air and water and still permit full use of the pavement. Pervious concrete provides a solution for landscapers and architects who wish to use greenery in parking lots and paved urban areas.
Economic Benefits:
Alternative to Costly Stormwater Management Methods-
Parking areas paved with pervious concrete reduce the need for large detention ponds, because the pavement itself acts as a detention area. Parking lot owners that use pervious will spend fewer dollars on the labor, construction, and maintenance of detention ponds, skimmers, pumps, drainage pipes, and other stormwater management systems. Expensive irrigation systems can also be downsized or eliminated. In reducing runoff from paved areas, pervious concrete reduces the need for separate stormwater retention ponds and allows the use of smaller-capacity storm sewers. This allows property owners to develop a larger area of available property at a lower cost.
Stormwater Impact Fees-
Many government agencies are now implementing stormwater impact fees for all impervious areas. As regulations further limit stormwater runoff, it is becoming more expensive for property owners to develop real estate, due to the size and expense of the necessary drainage systems. Pervious concrete can reduce these fees for the property owner by helping to minimize demands upon sewer systems.
Developers are using pervious concrete for parking areas in order to increase utilization of commercial properties. The land ordinarily devoted to costly stormwater management practices or compliance with maximum impervious area ordinances can now be developed or preserved, enhancing the bottom line.
Low Life-Cycle Cost-
Concrete pavements have a significantly lower life-cycle cost than alternatives such as asphalt. Although the initial cost of pervious installation may be slightly higher, concrete saves money in the long run due to its superior durability and strength. It requires fewer repairs than asphalt, and has a longer overall lifespan as well.
Pervious concrete is also economical in that it minimizes the need for runoff retainers, reducing property costs. There is very little overproduction since it is made directly on-site and as-needed, and it can be recycled once it has reached the end of its life-cycle. Thus pervious concrete is widely recognized as the lowest life-cycle cost option available for paving.
Specifics where pervious concrete qualifies for LEED Green Building Rating System credits. :
LEED Credit SS-C6.1 Stormwater Design - Quantity Control
LEED Credit SS-C6.2 Stormwater Design – Quantity Control
LEED Credit SS-C7.1 Heat Island Effect – Non-Roof
LEED Credit WE C1.1 Water Efficient Landscaping
LEED Credits MR-C4.1 AND MR-C4.2 Recycled Content
LEED Credit MR-C5.1 AND MR-C5.2 Regional Materials
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