Pervious concrete — a strong, durable concrete material that is much better for the environment than regular pavement. Rainwater flows through the pervious concrete to replenish ground water supplies. Water penetrates quickly and completely, leaving dry and safe concrete surfaces with no standing water. Use of pervious pavements helps owners and environment

Although pervious concrete has been in use for more than 50 years in a variety of applications, 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 nar-rowly graded coarse aggregate, cementitious materi-als, water, admixtures, and, in some cases, fibers. Little or no fine aggregate is included in the mixture.

Carefully controlled amounts of water and cementi-tious 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/m 3 (100 to 120 lb/ft 3 ).