Pervious Concrete - Advantages, Disadvantages & Application

What Is Pervious Concrete?

Manik Barman:-Pervious concrete has large voids that allow water or air to pass through it. The pores size varies from 2 to 8 mm, has a void content of 18 to 35 percent.

Further, this concrete has a compressive strength of 2.8-28.0 MPa (ACI 522, 2010). It is also known as porous concrete or water permeable concrete.

Consequently, it offers an advantage in resolving critical environmental challenges. Hence, a better effort towards sustainable development.

While the first use of porous concrete dates back to the 1800s in Europe as pavement surface, it gained popularity in the US in the 1970s. Later, the demand for porous concrete increased after WWII as the cement supplies were badly affected. However, India realized the benefits of this concrete in the 2000s.

This article is dedicated to pervious concrete and discusses several aspects. First, we shall understand the advantages and working of this concrete.

The second is the composition, preparation, and execution process. At last, the article concludes with a discussion on the strength and cost of porous concrete.

Advantages Of Pervious Concrete

The primary advantage of pervious concrete is that it absorbs the stormwater. However, it serves multiple direct and indirect benefits as well.

1. Groundwater Recharge

The stormwater seeps through the pervious concrete and infiltrates through the ground. It ultimately adds up to the groundwater increasing groundwater level.

2. Reduction In Surface Run-off

The stormwater run-off reduces as the porous concrete surface lets the water seep through it to the ground. Hence, the surface run-off reduces.

3. Reduction Of Sewers

Due to the reduced stormwater surface run-off, the size and need of the stormwater sewers reduce. Therefore, offering savings in drainage system costs.

4. Development Of Trees

The stormwater infiltrating through the ground provides higher moisture content. Moreover, the voids of the pervious concrete allow the necessary air for roots to breathe. Consequently, offering a healthier environment for roots to grow into trees and plants.

5. Filtering Of Stormwater

The porous concrete act as a filter for the stormwater. The dirt gets trapped into the voids, and hence only clear water reaches the stream, pond, or lake.

Disadvantages Of Pervious Concrete

1. Can not be used in pavements with heavy traffic flow.

2. Requires longer curing time.

3. Difficult to find out water content in fresh concrete.

4. Conventional concrete tests like slump test, compaction factor test are not applicable.

5. Requires specialized construction practice.

6. Special design considerations need to be implemented.

How Does Pervious Concrete Work?

Pervious concrete allows the water to flow through it. The permeability of concrete depends upon the percentage of voids in the concrete, the size of voids. Typically, 15-25% voids are achieved in hardened permeable concrete.

The flow rates of pervious concrete are approximately 480 in./hr (200 L/m2/min). The flow rate can be much higher than the typical values.

This concrete doesn't use fine aggregates; therefore, it has a grainy-textured surface. It offers higher friction to the vehicle tires.

Subsequently, driving on pervious concrete is easier in rain and snow. Also, it doesn't allow water pooling, consequently offering any night-time glare.

The stormwater contains contaminants that clog the voids of the pervious concrete. Hence, inhibiting its' fundamental property of allowing water to pass through it.

Therefore, pervious concrete design uses stormwater sediment test data to minimize the clogging issue. However, the de-clogging is achieved by wetting the concrete and cleaning with vacuum suction or pressure washing.

This concrete has joints to account for changes due to temperature change. The methodology to execute and finish a joint in permeable concrete concrete is similar to conventional .

How To Produce Pervious Concrete?

Cement, coarse aggregate (size should be 9.5 mm to 12.5 mm), and water make up pervious concrete which contains little to no fine aggregates. A small amount of sand added boosts the strength.

A void content of 15 to 25% is desired in pervious concrete. The higher the mortar content, the lesser the voids, hence lesser permeability.

The water-cement ratio in the mixture is 0.28 to 0.40. A correct water-cement ratio is essential as a lesser water-cement ratio offers higher strength. But too little water will weaken the concrete.

Therefore, check the concrete mix ratio before pouring it into the field.

Crushed aggregates, old crushed

concrete blocks, recycled concrete,

clay-brick aggregate are suitable materials for pervious concrete. Using the old concrete reduces the concrete's carbon footprint-also, the concrete density changes due to the aggregate type. The concrete density ranges from 1420 to 1840 kg/m3.

In addition to Portland cement, Geopolymers can be utilized as cementitious ingredients in the production of porous concrete. The qualities of pervious geopolymers are comparable to those of permeable concrete made of Portland cement.

Strength Of Pervious Concrete

The pervious concrete has voids that render lesser strength than the traditional concrete. However, the porous concrete attains enough strength to cater to the driveway and parking loads.

The use of different aggregate materials also affects the concrete strength. For the crushed limestone pervious geopolymer concrete (LS), the compressive strength is in the range of 11.9-13.6 MPa. Recycled concrete (RCA), RBC, and RCB pervious geopolymer concrete yielded lower compressive strengths in 7.0-10.3, 2.8-3.8, and 2.9-6.6 MPa, respectively. 

It is evident from the above data that the porous concrete is strong enough to support cars. However, with special mix designs, we can achieve a strength of up to 20 MPa. The concrete strength can be further increased by adding a subgrade and sub-base layer of coarse and fine aggregate.

The durability of porous concrete is also sufficient. It can stay in place for up to 20-40 years. The key to durability lies in the concrete mix and concrete laying technique. 

Cost Of Pervious Concrete

Even though the installation cost of pervious concrete is often higher than that of regular concrete, it can be a significantly more cost-effective solution over its lifetime.

The higher installation cost is due to the additional concrete. It is laid as a 6-inch thick layer compared to 4 inch thick traditional concrete.

Because pervious concrete reduces the need for additional drainage systems, it can minimize the overall costs of residential and commercial projects.

This concrete allows rainwater to drain directly to the underlying soil, reducing stormwater control requirements.

In addition, compared to other paving solutions, such as asphalt, porous concrete requires lesser repair and upkeep.

As seen in the below chart, the cost of permeable concrete per square foot is comparable to that of porous asphalt. At the same time, the cost of permeable pavers is way higher.

Application

• Road pavement,

• Parking areas,

• Areas with light traffic,

• Residential streets,

• Pedestrian walkways,

• External Walls,

• Greenhouses. 

Conclusion

Keeping the benefits of pervious concrete in mind, it is a viable product for urban areas. The porous concrete solves multiple problems at once and strengthens the vision of sustainable development.

The strength, durability, and lifetime cost are However, the use of permeable concrete in India is still scarce. The main reason for hesitation in using permeable concrete is the unavailability of expertise.

Another reason is the limitation of study material in the Indian context. Once the difficulties are overcome, the use shall increase as the cost is less than the current prevailing permeable paving system.