According to Propex, PERC is specifically designed to assist in the effectiveness of pervious concrete applications with enhanced water flow properties and permeability, but with low pore size to trap soil. Made from 100% recycled PET from soda bottles, the fabric's smaller pores restrict dirt and particulates from contributing to clogs, which reduces maintenance in storm drains.
Most contractors are aware that some sort of fabric is needed to maintain separation between the softer, less compacted soil base and stone filter layer, however, sometimes there is confusion over what fabric to use for pervious concrete applications and where to buy it. Now contractors and installers can order it right from their ready mix supplier and have it delivered to the site.
This is great news for pervious concrete systems but what really excites me are the tremendous growth implications for designers using LID strategies. There have been attempts to use aggregate gradation to maintain structural integrity of the system, which is easy enough to design but impossible to construct. The fabric is engineered to provide structural support to the pavement, while allowing stormwater to infiltrate, but it also has the ability to "wick". Technically this is referred to as "capillary action". It is the same process that allows water to go up a tree to its leaves. For projects that have pour soils, this is big news.
When rain falls on these projects, very little is infiltrated unless the site is perfectly flat (and sites are never flat). Imagine a site with soils that drain at 0.1" (one tenth of an inch) per hour. This is a soil that we would basically call non-porous. Especially when the rain that comes in contact with it runs on down the slope. The trick is getting the water to maintain contact the soil long enough for infiltration to take place. Historically, hard to do, but now, very easy. The fabric will literally pull the water against gravity and spread the stormwater up the hill, maintaining contact with the soil for infiltration over the whole site. That means a site with these poor soils will infiltrate 2.4" per SF over a 24 hour period, even on a slope! I watched a demonstration of this capillary action and saw the water go up a 60% slope!
Use of this fabric will help increase the market for pervious concrete in areas with soils that infiltrate less than ½ inch per hour and the kicker is it is made with 100% post consumer recycled content. Each roll of PERC uses 3,350 plastic soda bottles. And no, color is not added. Green is its natural color.
We are using the PERC fabric beneath about 2500 SF of pervious concrete walkways cast in the Auburn University Arboretum in East Central Alabama. The red clays here don't readily infiltrate water. I'm anxious to see how our pavements behave with this new fabric.
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