This alley in Washington, D.C., is part of the District of Columbia's Green Alley Program. The use of a 6 mil poly curing sheet was eliminated through the use of a dissipating curing spray.
Photo credit: Photo courtesy of PerviouShield
Forta Ferro-Green is a blend of recycled polypropylene and copolymer macro fibers designed specifically for pervious concrete reinforcement.
Change and improvement are the measuring tools for progress and success. Without change there is no progress; without improvement there is no success. These words could not be more truthful when applied to the pervious concrete industry. So how are we measuring up and how are we responding to the needs of the market? Allow me to report on the advancements that the industry has been making over the past few years.
As a whole, the pervious concrete industry continues to improve, keeping up with the state-of-the-art. And training is no exception. The goal of any pervious concrete certification program is to ensure that knowledgeable pervious concrete installers and ready mix companies are available to maintain high standards. In August 2010, the Text Reference for National Ready Mixed Concrete Association (NRMCA) Contractor Certification was revised to meet this goal.
Several items were expounded on in the revised version including discussion on new admixtures and equipment used for installing pervious. More detailed instructions and methods for using roller screeds were added and many test questions were updated. To date, over 1,900 technicians have been certified with the revised program, and currently there are over 7,000 individuals certified through NRMCA or similar certification programs.
Standards and advancements
Industry standards continue to be developed and refined as well. There are currently four ASTM International standards for pervious concrete, the latest being ASTM C1754 - Standard Test Method for Density and Void Content of Hardened Pervious Concrete. The remaining ASTM standards for pervious concrete are for testing the infiltration rate (ASTM C1701), testing the fresh density and voids (ASTM C1688), and testing the potential resistance to raveling (ASTM C1747).
The American Concrete Institute (ACI) committee on pervious concrete (ACI 522) has followed suit and continues to revise its documents to keep up with improved standards and methods within the industry. As a sneak peek, one such change will be noticed in the revised ACI 522.1 Specification for Pervious Concrete. The requirement to cure with 6-mil poly sheeting will include the phrase “unless otherwise permitted.” This small but powerful revision allows for the use of internal curing methods.
Internal curing is defined as “supplying water throughout a freshly placed cementitious mixture using reservoirs that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation.” This is accomplished by the use of saturated lightweight aggregate sand (LWAS) such as HydroCure by Northeast Solite, or a super absorbent polymer (SAP) admixture such as HydroMax by ProCure. Both internal curing methods maintain higher moisture conditions in a freshly placed mixture allowing better hydration so that the potential properties of the mixture may develop.
Internal curing allows the pervious concrete installer to use traditional primary curing methods without placing and maintaining the thick plastic for seven to 10 days. Such was the case when the District of Columbia’s Department of Transportation (DDOT) started paving with pervious concrete in the Green Alley Program earlier this year. The pervious concrete alleys were internally cured and sprayed with a dissipating curing compound. This curing method proved superior to covering with 6-mil plastic sheeting and has since been specified for all future DDOT pervious concrete projects. Internal curing provides large cost savings over previous curing methods. It also keeps large amounts of plastic out of landfills. This has been somewhat of a suppressed topic among the green community and this new curing method has been well received by those with sustainable goals.
Another exciting advancement in the pervious concrete field that warrants mention is the use of high-dose macro-synthetic fibers for increased toughness. These fibers are not your typical micro fibers dosed at 1 to 2 pounds per cubic yard. No, we are talking about extra heavy-duty structural fibers dosed at 5 to 712 pounds per cubic yard. “Aside from changes in aggregates, cement, proportioning and practice, macro-synthetic fibers, as an integral reinforcement, represent the best opportunity to enhance the performance of pervious concrete and therefore improve its use with confidence in the future,” says Dan Biddle, vice president of Forta Corporation.
Recently I had the chance to work with Forta’s macro-synthetic fibers dosed at 5 pounds per cubic yard on a heavy-duty paving project in Atlanta, Ga. Saying these high-dose macro-synthetic fibers increase toughness is an understatement. These fibers are now being used on several heavy-load, high-traffic-volume projects around the country.
All of these advancements have contributed to the growth of pervious concrete as a whole and make pervious concrete not only more durable in the field, but more durable in the marketplace as well.