What is Pervious Concrete?
Pervious concrete is a structural concrete pavement with a large volume (15 to 35 percent) of interconnected voids. Similar to normal concrete, pervious concrete is made from a mixture of cement, coarse aggregates, and water. However, it contains little or no sand, which results in a porous open-cell structure that water passes through readily.
When pervious concrete is used for paving, it can take in stormwater at a rapid rate of 11 to 19 liters per minute per square foot of surface area, which exceeds the flow rate needed to prevent runoff in most rain events. The rainwater may be stored in a coarse gravel layer underneath the pavement or allowed to percolate into the underlying soil. Because the pavement itself acts as a retention area, it helps to prevent much of the polluted runoff that normally occurs with impervious pavements. The filtration process also helps to purify the water. As the water percolates through the open cells of the pavement, aerobic bacteria in the voids help to break down harmful pollutants and chemicals.
Is Pervious Concrete More Expensive?
Over its lifetime, pervious concrete can be a much more inexpensive option than traditional concrete, even though the installation cost of pervious is typically higher than that of traditional concrete.
Money savings happen because:
- pervious concrete reduces the need for special drainage features.
- Pervious concrete reduces the need for stormwater management as it allows rainwater to drain directly through to underlying soil.
- Pervious concrete also requires less repair maintenance than some other paving options, including asphalt.
Here’s a breakdown of the cost comparisons with pervious concrete installations:
Installation cost: The initial cost of a pervious concrete driveway or parking lot in might be two to three times that of a traditional concrete driveway. This is mainly because pervious concrete is laid thicker — around 15 cm or so, generally, compared to 10 cm for traditional concrete — and more needs to be done to prepare the concrete base for water infiltration. The materials themselves cost about the same, but the difference is in the preparation.
Maintenance cost: The cost of maintaining pervious concrete over time is similar to the cost for traditional concrete. All types of concrete need to be maintained to remain in top shape. However, it should be noted that other types of paving surfaces might cost more over time due to higher maintenance costs. According to the University of California, the upkeep of asphalt over its lifetime “makes it a more expensive choice than permeable pavements, without offering the benefit of water recharge and filtration.”
Cost of other features: If a concrete installation needs to include systems for handling water runoff, pervious concrete can lead to large savings over time. Pervious concrete installations can actually act as water retention systems in many cases, since they handle large amounts of water and allow it to filter deep into the earth. Pervious concrete roadways and parking lots can double as water retention structures, reducing or eliminating the need for traditional stormwater management systems such as retention ponds and sewer tie-ins.
Environmental costs: According to the Environmental Protection Agency, pervious concrete helps to eliminate pollution by helping to filter out pollutants collected by rainwater. The environmental benefits of pervious concrete might not show up on your bill — other than potential savings in stormwater management and treatment, of course — but you’ll still appreciate that your concrete driveway installation is doing good for the environment.