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What is Pervious Concrete?
Pervious concrete is concrete that water drains right through.
Usually pervious concrete consists of rock, cement & water, everything regular concrete has, minus the sand.
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Pervious concrete has been around for a very long time and about 30 years ago began to be used in the U.S. starting on the East Coast.
Recently the Chinese installed over 2 million square feet of it for the 2008 Olympics.
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Installation by 'Orangestone Construction Technology'.
Pervious concrete can be so much more. Explore our site to see some of the possibilities.
Below is a more technical definition of pervious concrete:
“Pervious Concrete (PC) is a performance engineered pavement with an interconnected void system that allows rainwater to percolate through it. In PC, carefully controlled amounts of water and cementitious materials are used to create a paste that forms a thick coating around aggregate particles. A PC mixture contains little or no sand. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drain quickly. Typically, between 15% and 25% voids are achieved in the hardened concrete, and flow rates for water through PC are typically around 480 in/hr (.34cm/s), which is 5 gal/sqft/min (200L/sqm/min) or higher. Although low mortar content and high porosity reduce strength compared to conventional concrete mixtures, PC has sufficient strength for most pavement applications including parking areas, streets, plazas, and walkways.”
Source: NRMCA - National Ready Mix Concrete Association
What is PerkTop™?
PerkTop™ is beautiful pervious concrete. Regular pervious concrete is typically clunky and whitish with an irregular surface. PerkTop™ is none of these, it is very fine-textured, with rich colors and an extremely consistent surface throughout. Many different patterns can be created using PerkTop™ and literally any color is possible, from any shade of earth-tone to deep purples, fire engine reds, and banana yellows.
PerkTop™ is:
To learn more about beautiful pervious concrete please visit our new site: www.PerviousProducts.com.
PerkTop™ pervious concrete is similar in cost to install as standard interlocking pavers. Incorporating the use of more colors or more involved designs may increase installation costs to around the cost of installing pervious pavers, but without the maintenance issues due to the gravel used in between the pervious pavers.
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EarthCare guarantees our pervious concrete installations against failure from raveling(severe surface rock delamination) for a period of 10 years. We also guarantee that our pervious concrete will be pervious when installed, and as long as basic maintenance steps are followed it will remain pervious for a period of at least 10 years. Keep in mind this is just our guarantee window, your new pervious concrete should remain durable and pervious for many decades to come.
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Now truth be told most of the pervious concrete that has been on the ground in the east for 20 or 30 plus years has received little or no maintenance and it still performs adequately. The reason for this is the high rate of drainage of pervious concrete, as much as 600" of rain an hour can pass through some pervious concrete(PerkTop is more like 'only' 200"/hr). So even if the pervious concrete were to clog up 98% or more, the concrete would still be able to handle any rain event we get in this area of Northern California. Also due to the much smaller voids in our PerkTop™, it makes it much less likely than regular, clunky pervious concrete to get debris clogged in it in the first place.
However we still recommend some basic maintenance practices. How often maintenance is performed will vary considerably depending primarily on how much litter is falling on it fom trees. The pervious concrete could be vacuumed up to twice a year(in the meantime it can be blown & sweept just like regular concrete) and pressure washed about every 5 years. Pressure washing is an effective way to regain porosity of the pervious concrete due to sand or dirt inadvertenly getting on it.
EarthCare can perform this maintenance.
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One of the main concepts of pervious concrete is to allow the rainwater(& sometimes sprinkler water) to infiltrate into the soil below it. In so doing, pollutants that otherwise would have been washed off of the pavement and into the storm drain system are eliminated and the underground aquifers are recharged. The question then becomes how much of the rainwater can be reasonably expected to be captured and percolated into the soil?
The answer to this question varies depending upon the composition of the soil, the slope and the design of the pavement, including its base. The soil composition in most of the Bay Area is clay, some of it very dense, heavy clay. The first consideration is that the structure of the underlying soil is not seriously compromised during the construction of the pervious pavement. Assuming this is the case, then even the heaviest of clay soils around here, they might absorb 1" of water over a 24 hour period. Now we typically design our pavements for driveways to be about 5" of pervious concrete over 5" of crushed drain rock. Considering that the drain rock consists of at least 40% void space, then that means 2" of water can be stored in it while it is being absorbed into the soil below. With these parameters then in a perfectly level driveway, 3" of rain over a 24 hour period could all be maintained onsite by the pervious concrete pavement.
What to do on sites that slope though? Because in heavier rain events and clay soils, all the water can't be absorbed by the soil right away, the excess water will simply settle in the lowest areas. If the drain rock under the pervious concrete is only a consistent 5" thick throughout, then the water will fill the low areas then overflow the system. There are several strategies that can be employed to minimize this situation from occurring on sloped sites, from creating terraced shelfs, to creating berms to providing extra drainage, and even to directing that drainage to another area of the yard. However the degree to which one wants to implement these measures needs to be balanced with a practical consideration of just how much of a % of rainwater you want to capture and maintain on your property in the first place. According to the latest US EPA laws, they require capturing the 'first f'lush' of rain, which is typically the first 1/2".
Another point to keep in mind is that pervious concrete with a properly designed base is almost always more pervious, it will capture & retain more rainwater, than the surrounding softscape, the planting areas.
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