Pervious Concrete Gulps Stormwater

Pervious Concrete Gulps Stormwater

Pervious concrete is a porous pavement that can quickly drain stormwater, saving lives and property from flash floods. Hear about the latest improvements.

Pervious_Concrete_Gulps_Stormwater-Creative_Safety_Supply-220x220For over 30 years, pervious concrete has been made with just aggregate and cement, no sand. The void spaces allow stormwater to flow through a slab into the soil, replenishing ground water. Storm sewers receive less volume and road surface runoff.

In this podcast, Dan Clark tells of a recent pervious concrete improvement by a U.K. company. Dan also compares the new product with the currently-available pervious concrete.


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Dan Clark: Flash flooding overloads drainage systems. It’s a big cause of weather-related deaths in the U.S. Pervious concrete can soak up some of that storm water and increase safety.

Hi, I’m Dan Clark with The Safety Brief. We take on health and safety hazards in today’s demanding industrial and construction worksites, a service of Creative Safety Supply.

Fast draining concrete, also known as porous, permeable or pervious concrete, is a slab that can gulp hundreds of gallons of water. Water that soaks into the soil below instead of a storm drain.

If enough parking lots, driveways, streets and sidewalks were made of pervious concrete, it could save lives. Drainage systems would not be so overloaded, saving people and vehicles from being swept away in a flash flood.

Pervious concrete has been around for a few decades. It’s made with rocks and cement with little or no sand. Cement paste binds the rocks, letting water pass through air gaps. The gaps are called void space. Typical pervious concretes have void space at about 20 percent. Stormwater drains through the void space to a bed of aggregate under the concrete. Gravity then pulls into the soil below allowing groundwater recharge.

Tarmac, a company in the U.K., claims they’ve made a new pervious concrete that’s stronger and capable of absorbing more. Their Topmix Permeable uses a new recipe with a stronger cement bond. Instead of a void space of 20 percent, theirs can go up to 35 percent.

Now, Topmix is not yet available in the United States. Companies in the U.S. say their current pervious concrete formula of 20 percent void space is just fine.


• It can increase safety in areas where people walk. Six inches of fast-moving water is enough to knock a person on their can.

• No black ice. The porous surface is safer for walkways and driveways in winter allowing snow to melt faster, drain away, and not refreeze.

• Expensive storm drains, curbs and large retention ponds are not needed.

• Concrete and aggregate layers filter contaminants such as oil and chemicals before they reach the aquifer.

• Slabs can be poured close to existing trees without sealing them off from water.

• It also reduces the Urban Heat Island [UHI] effect. It’s less dense than traditional concrete and doesn’t store as much heat.


• It can’t withstand the high traffic of busy streets. It’s only appropriate for lower trafficked roadways.

• It also shouldn’t be used in areas where silt could cover the concrete and inhibit drainage.

• It can’t be sanded for winter traction. Grains will clog the void spaces.

• It can’t be used where hazardous materials are loaded, unloaded or stored due to potential spillage and leaching.

Can pervious concrete withstand freezing? It depends on who you ask. U.S. industry groups claim it stands up to the freeze-thaw cycle. Tarmac says their new Topmix Permeable also has great freeze-thaw resistance.


It always comes down to money, doesn’t it? Pervious concrete, per square yard, is more expensive than traditional concrete. But dollars are saved on unneeded storm drains, curbs, gutters and large retention ponds. If installed correctly, pervious concrete can be an efficient way to increase safety and protect the environment in public spaces.

That’s all for this episode, Pervious Concrete Gulps Stormwater. Join me again for more ways to stay safety compliant in today’s always-changing landscape of safety requirements. I’m Dan Clark of The Safety Brief, a service of Creative Safety Supply. Save 10 percent off your entire order at with coupon code BIG10.


Concrete truck and water splash images © 2015 Tarmac Trading Limited

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