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.
