Why an Alternate Technical Specification?
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Why does Charger Enterprises, Inc. continue to update and publish its own technical publication PERVIOUS CONCRETE SPECIFICATION UPDATED MARCH 5, 2009 since the American Concrete Institute Committee 522 has published its Specification for Pervious Concrete Pavement (ACI 522.1-08)?
The ACI document is a great achievement. It has created a united voice for a diverse number of companies, Associations, technicians, craftsmen, architects and engineers who are active in promoting Pervious Concrete pavement. That document is an important first, and gives this segment of the concrete industry a stamp of professional credibility. It was written, however, in the format of the Construction Specifications Institute which dictates its terse language and structure. And since it was created by committee, some participants lacking hands-on Pervious Concrete Skills, compromise is apparent. Our specification addresses some of its shortcomings, and questions a few procedures which though even widely accepted, have proven to shorten the service life of Pervious Concrete Pavement.
Our specification seeks to use language and structure that can be easily understood not just by engineers and architects, but by owners, developers, general contractors, installers, inspectors and ready-mix plant operators. The presence of many standard references and submittal requirements in many cases detracts from understanding what makes a good Pervious Concrete Installation. If needed, we defer to the ACI document.
Thus we readily defer to the ACI document when definitions and referenced standards are presented. They are needed when AIA documents may dictate. Our specification may on occasion, and with good reason challenge some requirements within some competing specifications. We have found numerous procedures and tests included in specifications that do not have application to Pervious Concrete or have been replaced or changed. This is why we continue to review and update our specification, which was the first to be referenced in contract documents and posted on the internet.
In the interest of using language that is imperative and terse the ACI Specification is forced to avoid attention to some relative details explanations and placement of some responsibilities. The result is that their document only devotes 4 pages to its installation portion. In our printer friendly concise form our specification addresses far more concerns and responsibilities requiring 14 pages of meat.
For example the ACI document in section 3.5.4 recommends using a short handled shovel or rake to distribute the concrete as it leaves the chute. We agree on the use of come-alongs, but rakes and shovels tend to compact the Pervious, reducing porosity.
In section 3.6 addresses using slipform pavement equipment. We would refuse to use it because the auger component of the equipment compacts the concrete through its entire thickness thus reducing its void structure and porosity. Also it does not provide adequate compression of the surface or edges which leads to unnecessary raveling.
Section 3.10.1 of the ACI Specification states: Secure cover material without using dirt. The alternative most contractors use is the placement of rebar over the plastic. But if there is any wind during the curing process, the plastic will lift slightly creating wind tunnels and bubbles between the plastic and the Pervious Concrete surface. This results in uneven curing. With proper overlaps covering the plastic with a minimal amount of dirt, sufficient to prevent lifting, works the best provided that it is swept off the plastic before it is removed.
The ACI document specifies the use of a roller joint tool to create contraction joints. If you look at the ACI Committee Report: ACI 522R06 in Section 7.4- Jointing in the accompanying picture, Fig. 7-12 notice how this tool starts raveling. Also the radius on either side of the join compacts improperly. This process gives a jumpstart in causing the surface ravel and fail. We comply with section 3.12.3.2 and saw cut when the concrete has hardened after 24 to 48 hours, but before 72 hours.
We have successfully installed long life, well performing Pervious Concrete built to the requirements of our evolving specification for over 30 years. It stands as proof of its years of validity to govern good practices of Pervious installation. Meanwhile, some projects that meet the ACI specification begin to deteriorate after a few months.
We have chosen to not be involved in committees and will probably continue to do so, because we do not intend to be involved in trying to reach consensus on procedure. We have been working smart with Pervious Concrete for over three decades. We know what works, and we warrant our work for 10 years!
New methods, equipment and products continue to flood the market place. Most will pass away, but if something new has promise, and our research and industry communication warrant it we may give it a sample try. But only if its advantages are proven and the product does not suffer will it appear in future updates of our specification.
Unlike some contributors to the ACI specification we regularly get our hands into Pervious Concrete. We don’t just write about it. We don’t compromise what we know for harmony on a committee. We regularly live with our Pervious practices and decisions as a successful, family owned and run business!