What is Pervious Concrete?

Introduction

Pervious concrete is a type of concrete that is designed to allow water to flow through it, rather than being impervious like traditional concrete. It is also known as porous concrete, permeable concrete, or open-graded concrete. It has gained popularity in recent years due to its ability to reduce stormwater runoff and provide a sustainable solution for managing water on-site.

What is Pervious Concrete?

Pervious concrete, also referred to as porous concrete, permeable concrete, or porous pavement, is specifically engineered to allow water or other liquids to pass through its surface and reach the sub-surface easily. Its porous structure is designed to have larger pores than cellular concrete, with the primary goal of facilitating the smooth flow of water to the ground or any adjacent sub-surface.

Composition of Pervious Concrete

Pervious concrete is composed of coarse aggregates, cement, and water. Unlike traditional concrete, it does not contain fine aggregates such as sand. The absence of fine aggregates allows the concrete mixture to have a higher proportion of voids, which are interconnected to create a porous network. The coarse aggregates used are usually angular in shape to ensure that they interlock and create a stable structure. The water-cement ratio is kept low to reduce the amount of paste and increase the porosity of the concrete.

The mixture is also often designed to have a low slump, which means it is less fluid and can be placed without the use of formwork. To achieve this, superplasticizers or other admixtures may be added to the mix. Once the concrete is placed, it is left to cure and harden like traditional concrete.

Advantages of Pervious Concrete

1. Reduced stormwater runoff: It allows water to infiltrate through the pavement and recharge groundwater supplies. This reduces the volume and velocity of stormwater runoff, which can cause erosion, flooding, and contamination of water bodies.
2. Reduced heat island effect: It has a lower surface temperature than traditional concrete, which reduces the urban heat island effect and improves air quality.
3. Improved water quality: The infiltration of water through it filters out pollutants and contaminants, improving water quality.
4. Cost-effective: Such concrete can be a cost-effective solution for managing stormwater on-site. It eliminates the need for additional stormwater infrastructure such as retention ponds, swales, or underground detention systems.
5. Durable: Pervious concrete can be designed to have similar compressive strength as traditional concrete. With proper installation and maintenance, it can withstand heavy loads and frequent use.

Disadvantages of Pervious Concrete

1. Durability: It is less durable than traditional concrete, and it can deteriorate faster due to freeze-thaw cycles, chemical exposure, and heavy traffic.
2. Maintenance: Pervious concrete requires regular maintenance, such as cleaning and vacuuming to prevent clogging of the pores. It can also require periodic sealing to maintain its porosity.
3. Cost: Can be more expensive than traditional concrete due to the specialized materials and installation techniques required.
4. Limited applications: It is not suitable for all applications and is mainly used for sidewalks, parking lots, and other low-traffic areas.
5. Soil compatibility: This type of concrete is not suitable for all soil types and requires a suitable base material to be effective. It may also require additional drainage systems to handle excess water.

Application of Pervious Concrete

Pervious concrete can be used in a variety of applications, including:

1. Parking lots: Such concrete can be used for parking lots, reducing the amount of stormwater runoff generated by the site.
2. Sidewalks and bike paths: Pervious concrete can be used for sidewalks and bike paths, providing a safe and sustainable surface for pedestrians and cyclists.
3. Residential driveways: Can be used for residential driveways, reducing the amount of stormwater runoff generated by the site.
4. Retaining walls: It can be used for retaining walls, providing stability while also allowing water to infiltrate through the wall.
5. Green infrastructure: Can be used in green infrastructure projects such as rain gardens or bioswales, allowing water to infiltrate and recharge groundwater supplies.

Maintenance of Pervious Concrete

Pervious concrete requires regular maintenance to ensure its effectiveness and longevity. The surface should be cleaned periodically to remove debris, leaves, and other organic matter that can clog the pores and reduce infiltration rates. In areas with heavy use, the surface may need to be vacuumed or pressure washed to remove dirt and stains.

Traditional vs Pervious Concrete

Porous concrete differs from conventional, impermeable pavement, as it enables rainwater to freely drain and infiltrate into the ground underneath. As urban areas face increasing issues of flooding and regulations on stormwater management, some cities have experimented with using permeable concrete on low-traffic roads and parking lots. However, its high porosity makes it less durable than the conventional concrete used on larger roads.

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