Pervious concrete (also called porous concrete, permeable concrete, no fines concrete and porous pavement) is a special type of

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...

with a high

porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

used for concrete flatwork applications that allows

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

from

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

and other sources to pass directly through, thereby reducing the

runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock market ...

from a site and allowing

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in ...

. Pervious concrete is made using large

aggregate Aggregate or aggregates may refer to: Computing and mathematics * collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...

s with little to no fine aggregates. The concrete paste then coats the aggregates and allows water to pass through the concrete slab. Pervious concrete is traditionally used in parking areas, areas with light traffic, residential

street A street is a public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, ...

s, pedestrian

walkways In American English, walkway is a composite or umbrella term for all engineered surfaces or structures which support the use of trails. ''The New Oxford American Dictionary'' also defines a walkway as "a passage or path for walking along, esp. a ...

, and

greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...

s. Report No. 522R-10. It is an important application for

sustainable Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livin ...

construction Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...

and is one of many low impact development techniques used by builders to protect

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

History

Pervious concrete was first used in the 1800s in Europe as pavement surfacing and load bearing walls. Cost efficiency was the main motive due to a decreased amount of cement. It became popular again in the 1920s for two storey homes in Scotland and England. It became increasingly viable in Europe after WWII due to the scarcity of cement. It did not become as popular in the US until the 1970s. In India it became popular in 2000.

Stormwater management

The proper utilization of pervious concrete is a recognized Best Management Practice by the U.S. Environmental Protection Agency (EPA) for providing first flush

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

control and

stormwater Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...

management. As

regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...

s further limit stormwater runoff, it is becoming more expensive for property owners to develop

real estate Real estate is property consisting of land and the buildings on it, along with its natural resources such as crops, minerals or water; immovable property of this nature; an interest vested in this (also) an item of real property, (more general ...

, due to the size and expense of the necessary drainage systems. Pervious concrete lowers the sites SCS Curve Number by retaining stormwater on site. This allows the planner/designer to achieve pre-development stormwater goals for pavement intense projects. Pervious concrete reduces the runoff from paved areas, which reduces the need for separate stormwater retention ponds and allows the use of smaller capacity

storm sewer A storm drain, storm sewer (United Kingdom, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain ( Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surface ...

s. This allows property owners to develop a larger area of available property at a lower cost. Pervious concrete also naturally filters storm water and can reduce pollutant loads entering into

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from th ...

s, and

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s. Pervious concrete functions like a storm water infiltration basin and allows the storm water to infiltrate the

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

over a large area, thus facilitating recharge of precious groundwater supplies locally. All of these benefits lead to more effective land use. Pervious concrete can also reduce the impact of development on

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s. A pervious concrete pavement allows the transfer of both water and air to root systems to help trees flourish even in highly developed areas.

Properties

Pervious concrete consists of cement, coarse aggregate (size should be 9.5 mm to 12.5 mm) and water with little to no fine aggregates. The addition of a small amount of sand will increase the strength. The mixture has a water-to-cement ratio of 0.28 to 0.40 with a void content of 15 to 25 percent. The correct quantity of water in the concrete is critical. A low water to cement ratio will increase the strength of the concrete, but too little water may cause surface failure. A proper water content gives the mixture a wet-metallic appearance. As this concrete is sensitive to water content, the mixture should be field checked. Entrained air may be measured by a Rapid Air system, where the concrete is stained black and sections are analyzed under a

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

. A common flatwork form has riser strips on top such that the screed is 3/8-1/2 inches (9 to 12 mm) above final pavement elevation. Mechanical screeds are preferable to manual. The riser strips are removed to guide compaction. Immediately after screeding, the concrete is compacted to improve the bond and smooth the surface. Excessive compaction of pervious concrete results in higher compressive strength, but lower porosity (and thus lower permeability). Jointing varies little from other concrete slabs. Joints are tooled with a rolling jointing tool prior to curing or saw cut after curing. Curing consists of covering concrete with 6 mil plastic sheeting within 20 minutes of concrete discharge. However, this contributes to a substantial amount of waste sent to landfills. Alternatively, preconditioned absorptive lightweight aggregate as well as internal curing admixture (ICA) have been used to effectively cure pervious concrete without waste generation.

Testing and inspection

Pervious concrete has a common strength of though strengths up to can be reached. There is no standardized test for compressive strength. Acceptance is based on the unit weight of a sample of poured concrete using

ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...

standard no. C1688. An acceptable tolerance for the density is plus or minus of the design density. Slump and air content tests are not applicable to pervious concrete because of the unique composition. The designer of a storm water management plan should ensure that the pervious concrete is functioning properly through visual observation of its drainage characteristics prior to opening of the facility.

Cold climates

Concerns over the resistance to the freeze-thaw cycle have limited the use of pervious concrete in cold weather environments. National Concrete Pavement Technology Center. Report No. 2006-01. The rate of freezing in most applications is dictated by the local climate. Entrained air may help protect the paste as it does in regular concrete. The addition of a small amount of fine aggregate to the mixture increases the durability of the pervious concrete. Avoiding saturation during the freeze cycle is the key to the longevity of the concrete. Related, having a well prepared 8 to 24 inch (200 to 600 mm)

sub-base In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by v ...

and drainage will reduce the possibility of freeze-thaw damage. Using permeable concrete for pavements can make them safer for pedestrians in the winter because water won't settle on the surface and freeze leading to dangerously icy conditions. Roads can also be made safer for cars by the use of permeable concrete as the reduction in the formation of standing water will reduce the possibility of aquaplaning, and porous roads will also reduce tire noise.

Maintenance

To prevent reduction in permeability, pervious concrete needs to be cleaned regularly. Cleaning can be accomplished through wetting the surface of the concrete and vacuum sweeping.

References

External links

National Pervious Concrete Pavement AssociationPervious Concrete Design Resources
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