Is Pervious Concrete Strong Enough? Thus far it has been difficult to quantify the strength of pervious concrete. We have installed thicknesses of 6" through 10", and have found that with the correct mix and placement it has lasted for many years. We offer a 10 year limited warranty. Ultimate endurance of Pervious Concrete is dependant upon a well compacted porous base, fast, but controlled placement, uniform compaction and correct control joints. These factors control raveling and cracking. (At present Pervious Concrete is not recommended for high speed, high traffic roads.) To understand why Pervious Concrete is so strong, consider that the aggregate used is crushed, not round. This means that under compaction there is more contact between surfaces. The voids are like a honeycomb that creates unusual structural strength. And finally, it is believed that a chemical bond forms between the silicates in cement, some of which are part of its limestone component, and the chemicals in lime rock. (River gravel is not a suitable aggregate in pervious concrete.) Also, since lime rock is somewhat porous it allows penetration by the cement paste. We have more than 25 years working experience with Pervious Concrete, that is why we know it stands up when properly engineered and installed for its intended end use. Properly installed pervious concrete as shown on the right will resist raveling, provide much greater strength and will last. The work on the left by a competitor was not properly screened and compacted.

New Possible Applications For Pervious Concrete 1. Airport Tarmac and Terminal Edge Strips. So much rain water is converted to storm water at airports because of the vast amount of paving for runways, ramps, tarmacs and gate areas. If some of that can be paved with Pervious Concrete, much rain water will reach the aquifer. 2. Curbs, Gutters and Bicycle Path Strips. This is a way that could divert a tremendous amount of water from the storm water sewers. Consider: A 3' wide by 150' long strip of pervious concrete upstream from a catch basin could return over 25,000 gallons of water per hour to the aquifer, diverting it from surrounding bodies of water. This estimate is based upon percolation rate of 1 gallon per minute per square foot. 3. Playground Bases. A well constructed Pervious Concrete system covered with shredded tire mulch can provide a well drained easily maintained playground surface. 4. Drainage Ditch Linings. 5. Sound Absorption Walls For Highways.

©2008 Charger Enterprises, Inc. Florida Contractors Lic Charles Wolfersberger member ICC. and Certified Green Builder

Pervious Concrete Reduces Problems 1. It may reduce or eliminate the need for subterranean storm sewer drains. Pervious concrete not only eliminates much of the run off from pavements, but may also catch the runoff from roofs and return it to the aquifer. 2. Trees are great tools in fighting the greenhouse effect. Unlike impervious pavements, Pervious Concrete lets water and oxygen enter the soil below. This allows tree roots to perform their tasks efficiently. Those tasks include cooling the surrounding air by the evaporation of the captured ground water. This helps reduce air conditioning costs. 3. Finally for the developer or engineer, it makes possible maximum land use for parking lots, roads, and structures. With certified engineering it can reduce the size of retention areas. Storm drains may be eliminated and some curbing as well. For watershed and estuary areas it is an environmental tool to keep these waters clean and cooler. These are ecological as well as dollars and cents issues.

Trees thrive as Pervious Concrete allows rain water to reach their roots. As the water is drawn up to the leaves or blades of grass the miracle of transpiration converts it back to vapor which helps create more rain while cooling surrounding air.

Why is Pervious Concrete superior to other pervious pavement materials? 1. Pervious Asphalt

A. Pervious asphalt is black or grey. It absorbs more of the suns rays and converts them into heat. This heat helps create urban heat islands, which encourages the formation of ozone, nitrogen oxide and smog. B. Pervious asphalt has a tendency to creep at high temperatures. This encourages the formation of ruts from vehicle weight and ridges from vehicle braking. Its asphalt binders will adhere to silt and pollutants and will soon lose porosity. To stabilize it, pervious asphalt is often placed over an impervious base, making its primary advantage noise reduction, not water conservation. C. Pervious asphalt is dependent on oil as a feed stock. After placement, oil byproducts release V.O.C.s (Volatile Organic Chemicals) which pollute the air.

2. Pervious Concrete Paver Blocks.

A. Though these function well in residential driveways, installation is labor intensive. B. The weight of heavy vehicles can cause cracking. C. The weight of heavy vehicles on roadways will also cause settling and shifting. Maintenance issues prohibit installation over sand. If installed over impervious surfaces, they will look better longer, but they will lose their function of channeling rain water to the aquifer. D.Oil and grease seem to be more of a problem than with Pervious Concrete.

These concrete paver blocks were initially used at an intersection in Belleair, Florida. They have since been reinstalled after a few years due to the formation of ruts, accumulation of grease and cracking. 3. Masonry Grass Blocks A. Grass blocks do not allow as much rainwater through because the concrete they are made from is impervious. B. Oil and grease droppings kill grass. C. Mowing and fertilizing are needed. Maintenance cost is higher. Many times grass is replaced with sand. Maintaining grass within grass paver blocks is expensive. The result is that sand eventually takes over and the surface is much less porous than Pervious Concrete.

©2008 Charger Enterprises, Inc. Florida Contractors Lic Charles Wolfersberger member ICC. and Certified Green Builder

Prevention Some critics claim that Pervious gets clogged with oil and debris. It can if not given minimum attention. Some common sense procedures will keep it performing indefinitely. All pavements require some maintenance depending on traffic and location. Pervious concrete usually requires much less. But inspection and some attention will keep it working for many years. As with any pavement don’t blow grass cuttings, mulched leaves or cigarette butts onto it. Even with impervious pavements these items pollute storm water. Be sure the mowing crew is equipped with a blower to propel the cuttings back on to the lawn where they will enhance the fertilizer and not pollute bodies of water nearby. Picture courtesy of Billy Goat Industries.

Any well maintained parking area needs some cleaning. When needed by Pervious Concrete, clean with parking lot vacuums or vacuum sweepers. Sweepers without vacuums do not remove sand from its open cells. Material removed by sweepers should be disposed of as controlled waste. This is true of such material from any vehicle pavement. When streets or large parking lots are designed, they can be best kept clean by street sweepers which combine brushing with

vacuuming. This sweeper the Whirlwind, combines brushing and vacuum functions and it has an extendable vacuum to reach into pervious gutters, without requiring tire intrusion into the gutters. Picture courtesy of Elgin Sweeper Company, Division of Federal Signal Corporation. Visit: http://www.elginsweeper.com Concrete stain removers can be used if needed. Acid-based cleaners should not be used since they will attack portland cement and limestone aggregate. Pressure washing is an acceptable procedure to remove mold or algae. Bleach added in small amounts can keep mold from reappearing for some time. Renew striping as with any concrete. But do not paint Pervious Concrete. It will become Impervious. In heavy traffic areas such as drive-throughs and gas stations, oileating microbes may be included in pavement cleaning. Oil-eating microbes are now available in commercial pavement cleaning products. For best results they should be applied in a liquid carrier and soaked through the pervious concrete to the soil below. Extreme heat will kill them. So you see Pervious Concrete when properly installed is one of the easiest pavements to maintain.

©2008 Charger Enterprises, Inc. Florida Contractors Lic Charles Wolfersberger member ICC. and Certified Green Builder