Pervious concrete: a sustainable solution for stormwater

Pervious concrete looks like ordinary pavement with a coarser surface. The difference is what it leaves out: most of the fine aggregate. What remains is a network of connected voids that lets water pass straight through the slab.

How the system works

Rainfall drains through the pavement — typically fifteen to twenty percent void space — into an open-graded stone reservoir beneath it. The stone stores the water temporarily and releases it into the subgrade, or into an underdrain where soils infiltrate too slowly.

What it does for a site

• Reduces the runoff volume the site generates, often lowering detention requirements
• Provides water quality treatment as runoff filters through the stone
• Eliminates surface ponding and the sheet flow that carries pollutants to inlets
• Recovers usable area on tight sites by combining pavement and storage in one footprint

Where it fits

Parking stalls, overflow lots, alleys, plazas, and low-speed drive aisles are good candidates. Heavy truck traffic and high-speed roadways generally are not. Infiltration rates from the geotechnical report determine whether the reservoir can discharge to the subgrade or needs an underdrain.

What it demands in return

Pervious concrete is placed and cured differently from conventional concrete, and it needs a crew that has done it before. Once installed, it must be vacuum swept once or twice a year to keep the voids from clogging with fines. Sites that sand for ice or that drain sediment onto the pavement will clog it.

Specified in the right place and maintained on schedule, it is one of the most effective stormwater tools available on a constrained site.