Pervious concrete
is a mixture of coarse aggregate, Portland cement, water and
little to no sand. A typical pervious concrete pavement has a
15-25% void structure and allows 3-8 gallons of water per minute
to pass through each square foot.
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.
The result is a very
high permeability concrete that drains quickly. Due to the high void content, pervious
concrete is also lightweight, 1600 to 1900 kg/m3 (100
to 120 lb/ft3).
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.
