Pervious concrete is a special type of concrete that has large voids to permit water or air to enter through it. It is permeable type concrete and voids size ranges from 2mm to 8mm, has a void ratio of 18% to 35%. Further, As per ACI 522, this concrete has a compressive strength ranging from 2.8 N/mm2 to 28 N/mm2. It is also known as water permeable concrete and porous concrete.
Porous concrete is often used in pavement construction. It aids refill groundwater, reducing rainwater run-off by allowing it to seep into the ground. As a result, it gives a benefit in resolving critical environmental problems. Hence, a better step in the direction of sustainable development.
This article includes working of Pervious concrete, How to produce pervious concrete, application of Pervious concrete, benefits and drawbacks of pervious concrete.
How does Pervious Concrete Work?
Pervious concrete permits the water to enter through it. The porosity of concrete depends upon the size of voids and percentage of voids in the concrete. Generally, The percentage of voids in hardened pervious concrete is around 15 to 25%.
Pervious concrete does not have fine aggregates. So, it has a granular type surface texture. It gives higher friction to the tires of vehicles. The pervious concrete’s flow rates are appx. 480 inches per hour. Additionally, driving a vehicle on pervious concrete is trouble-free in rain and snow. Also, it does not permit water storing and also provides night-time glare.
Contaminants of the rainwater that clog the voids of the porous concrete. But, the fundamental property of porous concrete permits the water to pass through it. So, design of porous concrete is done by using storm water sediment test data to minimize the issue of clogging. Although, the de-clogging is done by wetting the concrete surface and cleaning with pressure washing or vacuum suction.
How to make Pervious Concrete?
Pervious concrete is produced by using cement, coarse aggregates (size of CA should be 9.5 to 12.5 mm), and water. It does contain little to no fine aggregates. A little quantity of sand added improves the strength. A void ratio of 15% to 25% is permitted in pervious concrete. The w/c ratio in concrete mixture is 0.28 to 0.40. Lesser w/c ratio gives higher strength. But too little water will decrease the concrete strength. So, verify the mix ratio of concrete before placing it into the field.
Crushed aggregates, recycled concrete and old crushed concrete blocks are suitable materials for porous concrete. The pervious concrete’s density ranges between 1420 and 1840 kg/m3.
Additionally, Geopolymers can be used as binding ingredients in the production of pervious concrete. The characteristics of pervious geopolymers concrete are comparable to portland cement pervious concrete.
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Benefits of Pervious Concrete
The main benefit of pervious concrete is that it absorbs the rainwater. Although, it facilitates multiple direct and indirect advantages as well.
- The rainwater seeps through the porous concrete and infiltrates through the ground. It finally goes up to the ground water increasing groundwater level.
- Porous concrete reduces the rainwater run-off because its surface permits water to pass through it.
- Because of reduction in rainwater run-off, the size and requirements of the rainwater sewers reduce. So, providing cost saving in the stormwater sewer system.
- The porous concrete helps in the growth of trees. The rainwater infiltrating through the ground gives sufficient water content. In addition, porous concrete’s voids permit necessary air for roots to breathe.
- The pervious concrete acts as a filter for rainwater. The dirty particles get trapped into the voids of porous concrete, and hence only pure stormwater reaches the lake, pond and stream.
Drawbacks of Pervious Concrete
Some disadvantages of pervious concrete as discussed below.
- Porous concrete can not be used on pavements with heavy traffic vehicle movements.
- Porous concrete needs longer curing time.
- The traditional concrete tests such as slump test and compaction factor tests are not applicable for porous concrete.
- Porous concrete needs specialised construction practices.
- Porous concrete requires regular cleaning to maintain its porosity.
- Porous concrete needs special design consideration.
Application of Porous Concrete
- Road pavements
- Parking area
- Greenhouses
- External walls
- Light traffic vehicle movements
- Walkways of pedestrians
Conclusion
By taking attention towards the advantages of porous concrete, it is a feasible product for city areas. The pervious concrete solves no of problems at once and gives strength to the vision and target of sustainable development.
The cost, durability and strength are comparable to the traditional paving systems. So, pervious concrete is the suitable option. The US EPA (Environmental Protection Agency of US) has involved porous pavement in the best practices of industry.
Refference :
- https://civilwale.com/pervious-concrete/
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