Pervious Concrete Pavement



Pervious concrete has been in use for more than 50 years in a variety of applications,however recent EPA regulations are causing many owners, specifiers and architects to reexamine applications of this unique
material. Also referred to as "no-fines concrete" or "porous concrete," this material is comprised of narrowly graded coarse aggregate, cementitious materials, water, admixtures, and, in some cases, fibers. Little or no fine aggregate is included in the mixture. Carefully controlled amounts of water and cementitious materials are used to create a paste that forms a thick coating around aggregate particles without flowing off during mixing and placing. Using just enough paste to coat the particles maintains a system
of interconnected voids on the order of 15% to 35% depending on materials and intended application. The result is a very high permeability concrete that drains quickly: Percolation rates of 100 to 750 liters per minute per square meter (2 to 18 gallons per minute per square foot) are common. Due to the high void content, pervious concrete is also lightweight, 1600 to 1900 kg/m3 (100 to 120 lb/ft3).

Pervious Installation

After placement, pervious concrete resembles popcorn. Its low paste content and low fine aggregate content make the mixture harsh, with a very low slump. The compressive strength of pervious concrete is limited since the void content is so high. However, compressive strengths of 3.5 to 27.5 MPa (500 psi to 4000 psi) are typical and sufficient for many applications.

Pervious concrete is not difficult to place, but is a bit different from conventional concrete placement. It is a very low workability material, so considerable hand work may be necessary for placement. The use of a vibrating screed is important for optimum density and strength. After screeding, this material is usually compacted with a hand roller. There are no bull floats, trowels etc. used in placing pervious concrete. Conventional jointing methods and spacing are recommended. Curing with plastic sheeting must start immediately and continue for at least 7 days. Careful engineering is required to assure structural adequacy, hydraulic performance, and minimum clogging potential.