How does permeable paving work

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Peter Myers. Minh Vu. Jo Skender. Alban Teh-howell. Originally, permeable pavers were made from concrete or brick with gaps between the pavers or bricks to allow water to drain through to the sub-base. These were used in small decorative areas to reduce ponding. Now, however, several types have emerged, including porous asphalt and recycled plastics that are much more permeable than these permeable concrete, asphalt, or interlocking concrete pavers.

These days, a wide variety of types of permeable pavements and surfaces are available, each with its own set of pros and cons. The exact system you choose should depend on the nature of the application and your goals and requirements for the project. Here are a few options:. Permeable concrete has a rougher look than traditional concrete, yet it has the ability to slowly absorb water reducing runoff. Still, this type of paving has limited capacity for water drainage, frequently requires maintenance, has high installation costs, and is more brittle than conventional concrete, resulting in cracks and potholes.

The concrete itself might not be permeable, but the interlocking construction of the paving grid still allows some water absorption until the open areas become clogged over time. The drawbacks of this system are its high price, its decreased permeability over time, and its use being restricted to small residential or light commercial applications.

However, it can be made porous and laid on top of a stone storage bed that allows rainwater to drain into the underlying soil. Despite its ability when new for rainwater to permeate and not pool or run off, the small pore size of porous asphalt can quickly lead to severe clogging, frequent maintenance requirements, and low strength and fragility, which can lead to potholes and ruts.

These grid pavers hug the earth without developing cracks or potholes as it moves. We hope to determine the levels of volume and pollutant reduction achieved by permeable pavement by testing three different types of pavement fig. The following are the specific objectives:. Figure 2. Figure 3. The white study area shown in figure 4 is split equally into three smaller study plots, each receiving similar volumes of runoff from the adjacent parking lot.

These plots will test three types of pavement: permeable pavers, permeable concrete, and permeable asphalt fig. Each plot is equipped with instrumentation to measure reductions in runoff volume water quantity and pollutants water quality. Figure 4. Aerial view of study area showing the locations of equipment and test-plot installations.

Figure 5. Completed installation of test plots: permeable pavers foreground , permeable concrete midground , and permeable asphalt background. Runoff from the parking lot flows toward an existing curb cut, which is equipped with a calibrated flume.

Runoff enters the flume and drains into a concrete structure that divides the runoff into three equal portions, each draining to one of the three test plots fig. The runoff either infiltrates into the permeable subsurface or exits the plot as overflow runoff.

Each test plot is lined with an impermeable membrane, which captures and routes infiltrated runoff through a buried drain tile fig. Runoff that does not infiltrate into the permeable surface is captured by an overflow surface grate.

The test plots are constructed to prevent cross-contamination from adjacent test plots and surrounding soils. Both the drain tile and surface grate are routed into a monitoring facility, where the volume of infiltrated and overflow runoff is captured separately fig.

The monitoring facility accurately measures all inputs and outputs of water using calibrated flumes. Figure 6. Test plot cross-sections showing permeable subsurface materials and runoff flow path.

Illustration created by County Materials Corporation. Figure 7. Monitoring facility used to measure water that both infiltrates through and runs off each test plot. Samples will be tested for concentrations of the following pollutants:.

It can be made using recycled materials, which puts less pressure on the environment to produce materials to build pavements and driveways. There are new techniques that allow manufacturers to use the byproducts, such as slag cement from iron manufacturers, to make concrete that can be used as a component of the green pavement. This helps in reducing landfill space as well. Even in freezing temperatures, the pavement will remain warm and proves to be a safe surface for driving and walking.

The pavement stays cool in the summers due to the circulation of precipitation and water. Additionally, its lighter color also helps in the same. Drawbacks of Permeable Pavement Unfortunately, there are some disadvantages that come along with permeable pavements. They include: It is more expensive to install as compared to traditional pavements. The maintenance requirements of permeable pavement are quite different.