Pervious Concrete

What Is Pervious Concrete?

Pervious concrete is a type of concrete that consists of cement, coarse aggregates, water, and, if required, admixtures and other cementitious materials (such as silica fume, fly ash, and so on). In this type of concrete, fine aggregates are not typically used in the concrete matrix. As a result, the void content is greater, allowing water to flow through its body.

Pervious concrete is similar to regular paving material except that it contains 15% to 35% open space. The majority of standard concrete has less than 2% open space. This makes it much easier to drain water than a regular solid concrete slab.

It is used for paving purposes only, not for structural purposes like footings and foundations. This is due to the fact that all of those open voids reduce the compressive strength of the concrete. However, it is still strong enough to be used as pavement. 

Pervious concretePervious concrete can absorb storm water at a rate of 3 to 8 gallons of water per minute per square foot of surface area. This is significantly higher than blacktop or solid concrete, and it exceeds the flow rate required to prevent heavy rain runoff. It can be extremely helpful in areas prone to flooding or with poor drainage.

Rainwater draining through the concrete can either seep into the soil surface or be diverted away with pipes or gravel. Since the pavement serves as a water collection area, it helps reduce the amount of polluted runoff that typically happens when impervious pavements, such as tar or concrete-covered roads, are used.

When water passes through it, it acts as a filter. Aerobic bacteria inside the voids of the pavement help break down pollutants and chemicals as the water moves through the cell structure of the pavement. This method can help in the purification of water before it enters the soil.

Pervious Concrete Installation 

Usually, ready-mix trucks are used to transport pervious concrete to project locations. The concrete must first be leveled with a vibratory screed before being compacted with a heavy steel roller to increase strength.

Due to the low water content, the curing process is complicated. Pervious concrete must be misted with water after placement, covered with plastic, and kept damp for at least seven days to allow for adequate hydration. This allows pervious concrete to achieve the desired strength.

What is Pervious Concrete Used For?

Pervious concrete has several applications, the most common of which is for pavement. Since it is weaker than regular concrete, it is generally not used for structural applications. 

Due to its excellent drainage capabilities, pervious concrete is primarily used as a road construction material. It’s extremely high number of pores and voids allows water to drain right through it, which is a massive advantage for a road, driveway, or parking lot. Because water can drain through the road surface, you don’t have to spend as much on expensive storm-water management systems, drains, and pipes.

Pervious concrete is also known as porous or permeable concrete. Porous refers to the large number of pores that run through it, while permeable refers to its ability to permeate (drain) water. 

Pervious concrete is an excellent solution for addressing environmental problems caused by pollution from roadways. Storm water runoff is reduced and groundwater levels can be replenished naturally by allowing storm water to seep into the ground. 

By eliminating retention ponds, drains, pipes, and other storm-water management systems, pervious concrete paved roads allow for more efficient land use. 

Also Read: Concrete Stairs Reinforcement Details | Components of Road Pavement Structure | Different Types of Asphalt Pavement in Construction

Major Pervious Concrete Applications 

  • Residential roads, alleys, and driveways 
  • Pathways and sidewalks 
  • Low-traffic pavements 
  • Parking areas 
  • Low-water crossings 
  • Sub-base for conventional concrete pavements 
  • Tennis courts 
  • Slope stabilization 
  • Groins and seawalls
  • Well linings 
  • Hydraulic systems (where permeability is accepted) 
  • Decks for swimming pools 
  • Pavement edge drains and a tree grate on the sidewalk 

 Advantages of Pervious Concrete

This section will provide an overview of the advantages of using pervious concrete. 

  • Water and air can flow at a rate of 3–8 gallons per square foot per minute through the slab. 
  • Combines paving and drainage, necessitating less storm-water management. 
  • Improves land use by eliminating the need for storm-water runoff management 
  • Aids in replenishing underground water aquifers. 
  • Encourages natural filtration, lowering water pollution caused by hydrocarbons and other contaminants. 
  • Reduces the harmful effects of urban heat islands. 
  • Lowering long-term maintenance costs. 
  • Since sloped drainage is not required, flat roads and parking lots can be constructed.

Disadvantages of Pervious Concrete

Despite the fact that pervious concrete is a great material, there are still some disadvantages, such as: 

  • It cannot be used on heavily trafficked pavements. 
  • Curing time is longer. 
  • It was poured with no slump and a very low water-to-cement ratio, which made it difficult to work with. 
  • It has a lower compressive strength than regular concrete. 
  • Inadequate structural strength for the vast majority of applications 
  • Cleaning is required to maintain permeability. 
  • All of the water drainage can weaken the sub-base.

Issues with Permeable Concrete 

Pervious concrete may become severely clogged as a result of poor maintenance. However, the permeability of porous concrete is unlikely to be affected.

Ravelling  and abrasion
One issue might be abrasion and ravelling. To reduce ravelling, good curing practices and an appropriate w/c ratio (not too low) are extremely important. A finished pavement will always have some loose stones, but severe ravelling is inappropriate. Ravelling may increase with the use of snowplows.

Freeze and Thaw
If the placement were completely saturated, there is a significant risk that the pervious concrete would experience numerous cycles of freezing and thawing if it were exposed to very low temperatures.

The following actions can increase the permeable concrete’s resistance to freeze-thaw: 

  • It can be improved by using fine aggregates to increase strength and slightly reduce voids to around 20%. 
  • By using air-entraining admixtures to entrain air into the paste. 
  • By installing a perforated PVC pipe in the aggregate base to collect all the water and allow it to drain beneath the pavement.