2011 NeFSMA Conference - Trust the Curve, Predicting Pervious Concrete

 “Trust the Curve” - Predicting Pervious Concrete Performance; Case Studies, Jereme Montgomery, Executive Director Nebraska Concrete and Aggregate Association

Traditionally, pervious concrete has been promoted to be a mix with 15%-25% void structure. Our industry has accepted these values due to the balance of hydrological and engineering properties. Less than 15% voids and the slab will not drain rapidly, but is considered durable. More than 25% voids and the slab will drain rapidly, but will lose critical properties essential for long term durability. Lack of standard testing procedures has placed a great deal of responsibility on the producer and the concrete contractor to ensure durable pervious concrete pavements with required engineering and hydrological properties. The following information is two case studies of Metropolitan Community College in Omaha, NE and UNL Parking Garage in Lincoln, NE utilizing recommendations and ASTM standards to predict “in place” void content. ASTM standard 1688, standard test method for density and void content of pervious concrete was used along with recommendations and practices to verify engineering properties. The basis for the testing program was derived from Dr. John Kevern’s paper, Predicting performance of pervious concrete using fresh unit weight, submitted and presented to NRMCA Concrete Technology Forum: Focus on Sustainability.

Typical characteristics of pervious concrete are a mixture with little to no fines, relatively single-sized aggregate, with no slump. Public perceptions are skeptical as to freeze thaw durability, clogging, and strength. For a number of years, national focus has been directed at research and development to improve durability. Research has shown that with proper proportioning of the mix design, many pervious mixtures demonstrate durable qualities that still have the proper void content for storm water infiltration. The challenge is producing and placing pervious concrete pavements that results with in-place properties suggested from successful research conducted in various laboratories. Only recently have more standards become available for pervious concrete producers and contractors

Metropolitan Community College and UNL Parking garage are the first two pervious concrete placements in Nebraska, since the release of the new testing standard ASTM 1688. This standard, along with other industry recommendations were used to “predict” in place void content of these two Nebraska projects.

The presentation will consist of:

·         Basics of Pervious Concrete

·         Local Experience with Pervious Concrete

·         Myths of Freeze/Thaw Durability, Clogging, Strength

·         Quality Assurance Program (utilizing ASTM Standards)

Showing test data from two (possibly three) projects: fresh vs hardened