Concrete's permeability varies significantly depending on its type and composition. While standard concrete is designed to be relatively impermeable, pervious concrete is specifically engineered to allow water to pass through easily.
Pervious concrete is a special type of concrete pavement that contains a large percentage of interconnected voids. These voids allow water to drain through the pavement surface, reducing stormwater runoff and replenishing groundwater.
Permeability of Pervious Concrete
Based on typical characteristics, pervious concrete exhibits high permeability:
- Void Content: Typically, between 15 and 25 percent voids are achieved in the hardened concrete. These interconnected voids are crucial for water flow.
- Flow Rates: Water flow rates through pervious concrete are generally very high, allowing for rapid drainage. According to ACI 2010, these rates can be:
- 2 to 18 gal/min/ft²
- 81 to 730 L/min/m²
- 192 to 1,724 inch/hr
- 488 to 4,379 cm/hr
These high flow rates demonstrate that pervious concrete is extremely permeable, allowing large volumes of water to pass through quickly.
Contrasting with Standard Concrete
In contrast, standard concrete (used for foundations, walls, etc.) is designed to be dense and minimize void space. While no concrete is completely impermeable, standard concrete has significantly lower permeability than pervious concrete. Its permeability depends on factors like the water-cement ratio, curing, and the presence of cracks or pores. Water flow through standard concrete is typically very slow compared to pervious concrete.
Practical Applications
The high permeability of pervious concrete makes it ideal for applications where drainage is critical, such as:
- Parking lots
- Walkways and patios
- Low-traffic roadways
- Sports courts
By allowing water to infiltrate the ground, pervious concrete helps manage stormwater runoff, reduce flooding, and filter pollutants.
In summary, while standard concrete has low permeability, pervious concrete is highly permeable, designed with a significant percentage of voids to facilitate rapid water drainage.
