This week at ConExpo/ConAgg, Propex announced the introduction of a completely new class of non-woven geo-textile: PERC Pervious Concrete Infiltration Fabric.
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.
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Thursday, March 24, 2011
Friday, March 18, 2011
Good Observations
Today I had a Producer send me an email about a project that was just completed. It's good to find Producers that care enough to go back and look at the job with the goal of improvement. His observations/comments were as follows:
"Now that the poly has been removed I went and walked the parking area that the installer placed (about 1000 yds. 8" thick). The overall pavement looks very good with the exception of two items: 1) There was a lot of hand work (adding additional material and hand tamping) at the edges (construction joint) of each lane. This left an overall darker appearance highlighting each lane (maybe 18" wide). This area also concerns me for potential raveling as evidenced by some loose aggregate. 2) The saw joints did not originate at the joints in the curb and also were not continuous across pavement. Some of the cuts went through 2 lanes then was offset by several feet and resumed. There is one crack in the lower area of the pavement originating at a sewer manhole cover. This is not an official report, just thought you would be interested. Again the mix looks like it will perform very well and the placing and finishing work looks very good for the main part of the lanes. Maybe some education on treating the construction joints and developing a joint plan is in order."
These are good observations that could probably be seen at many sites around the country, and yes, more education is needed.
I'll address these two issues in upcoming blogs, working edges and installing joints.
"Now that the poly has been removed I went and walked the parking area that the installer placed (about 1000 yds. 8" thick). The overall pavement looks very good with the exception of two items: 1) There was a lot of hand work (adding additional material and hand tamping) at the edges (construction joint) of each lane. This left an overall darker appearance highlighting each lane (maybe 18" wide). This area also concerns me for potential raveling as evidenced by some loose aggregate. 2) The saw joints did not originate at the joints in the curb and also were not continuous across pavement. Some of the cuts went through 2 lanes then was offset by several feet and resumed. There is one crack in the lower area of the pavement originating at a sewer manhole cover. This is not an official report, just thought you would be interested. Again the mix looks like it will perform very well and the placing and finishing work looks very good for the main part of the lanes. Maybe some education on treating the construction joints and developing a joint plan is in order."
These are good observations that could probably be seen at many sites around the country, and yes, more education is needed.
I'll address these two issues in upcoming blogs, working edges and installing joints.
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