Permeable Concrete or pervious concrete is changing the way public spaces are landscaped.
Concrete is the second most consumed product in the world. And contrary to our belief, its usage is much wider than constructing buildings only. With recent developments in Concrete, it has become an important material for an array of usages. Permeable Concrete is a prime example of development in concrete industry. Although the material itself isn’t new, since it was first used in 1852, it has been attracting renewed attention.
What is Permeable Concrete?
Permeable Concrete is also known as Porous Concrete, Pervious Concrete, Gap Graded Concrete, No-Fines Concrete and Enhanced-Porosity Concrete. Permeable concrete, similar to Normal Concrete, uses a mix of Cement, Water and Coarse Aggregate with little or no sand (Fine Aggregate) in it. The resulting concrete has 15% to 25% voids which ensure a water flow rate of 480 in/hr or more. Although the higher porosity, and lack of mortar paste reduces the strength of pervious concrete as compared to the conventional one but it is sufficient for most of its uses.
What are the Applications of Permeable Concrete
Although Pavement Construction is the major application of Pervious Concrete since it reduces the stormwater runoff and adds to the surface water table. In fact, the usage of Permeable Concrete in Pavement Construction is considered as one of the Best Management Practices (BMP) by the Environment Protection Agency (EPA). The usage of Permeable Concrete in pavements and in other horizontal constructions, depending on the precipitation values of a certain region, can eliminate the need of retention ponds and other precipitation runoff storage facilities. This would result in a more efficient land use especially in urban areas where land is already expensive.
Below are some of the many applications in modern landscaping;
- Residential Roads and Driveways
- Parking Lots
- Pavements with low traffic volume
- Tennis Courts
- Sub-base for conventional concrete pavements
- Artificial Reefs
- Well Linings
- Slope Stabilisation
- Swimming Pool Decks
- Pavement Edge Drains
Production of Pervious Concrete
Production of Permeable Concrete is very similar to Normal Concrete since it uses the same ingredients. However, the amount of ingredients differ. Pervious Concrete is also mix designed and therefore should be designed for the desired purpose.
A general guideline is enlisted in the table.
Table 1 Typical Mix Proportion for Pervious Concrete (Divya Bhavana et al., 2017)
|Material||Quantity (kg/cubic metre)|
|Cement||270 to 415|
|Aggregate (Coarse and Fine)||1190 to 1480|
|Water to Cement Ratio (by mass)||0.27 to 0.34|
|Aggregate to Cement Ratio (by mass)||4 to 4.5|
|Fine to Coarse Aggregate Ratio (by mass)||0 to 1|
This typical guideline is for information only and therefore a trial mix should always be prepared and checked for the desired purpose. Apart from the usual materials, Supplementary Cementitious Materials (SCM) and chemical admixtures are also used as per their dosage mentioned by the manufactures.
Water to Cement Ratio
A lower water to cement ratio is used since higher water to cement ratios would affect the compressive strength of concrete. If desired for a purpose where compressive strength is of no importance, a higher water to cement ratio can be used.
Usage of Fine Aggregate would reduce the permeability of concrete and make it less porous, however the compressive strength would be improved.
Lightweight aggregate, recycled aggregate and other types of aggregate or other techniques like fly ash geopolymer concrete have also been utilized to make Permeable Concrete.
Characteristics of the Concrete
Although it is similar to Normal Concrete in terms of its ingredients, it has a plethora of characteristics that make this concrete different. Enlisted are some characteristics of Hardened and Green (Fresh) Permeable Concrete.
The Permeable Concrete has a textured surface after placement.
In-place densities are usually 1600 kg/m^3 to 2000 kg/m^3
Due to low or no mortar content, Permeable Concrete renders a lower slump value and a stiffer consistency. Slump values are usually less than 20 mm (0.75 inches).
In spite of higher void percentage the Permeable Concrete can render a compressive strength of 3.5 MPa to 28 MPa (500 psi to 4000 psi). Typical values are about 17 MPa (2500 psi).
No Darby, Trowel or Bullfloat is used since they tend to seal the surface of concrete.
7 Benefits of using Pervious Concrete
Permeable Concrete is much more than a way to reduce the stormwater runoff in urban areas. Listed below are some benefits of using Permeable Concrete.
It reduces the pollution by allowing the water to percolate in the ground. The sand chemistry and biology are allowed to treat the water naturally.
Allowing the rainfall to percolate, it recharges ground water and aquifers.
It improves the land use especially in Urban Areas
The light color of Concrete and relatively open pore structure absorb and store less heat respectively when compared to Normal Concrete. This helps in lowering heat in urban areas.
It is difficult for trees planted in parking lots and sidewalks to grow in impervious concrete environments since it makes it difficult for water to reach the roots. Trees benefit from Permeable concrete and further reduce the heat in urban areas.
It eliminates the risk of ponding over the roads over a longer periods of time as observed in some developing countries after rainfall.
The pervious concrete can absorb the noise of the vehicles on the road creating a pleasant environment.
In rainy days, pervious concrete pavements do not have splashes which glisten at night and are dangerous for drivers.
As per recent researches, the permeable concrete can also be used for the purification of sea water.
Related Landscaping Ideas from Red’s Landscaping and Civil Melbourne
References and Further Reading
Divya Bhavana, T., Koushik, S., Uday Mani Kumar, K., & Srinath, R. (2017). Pervious concrete pavement. In International Journal of Civil Engineering and Technology (Vol. 8, Issue 4). https://doi.org/10.3141/2113-02
Park, S. B., Lee, B., Lee, J., & Jang, Y. Il. (2010). A study on the seawater purification characteristics of water-permeable concrete using recycled aggregate. Resources, Conservation and Recycling, 54(10), 658–665. https://doi.org/10.1016/j.resconrec.2009.11.006
Yang, J., & Jiang, G. (2003). Experimental study on properties of pervious concrete pavement materials. Cement and Concrete Research, 33(3), 381–386. https://doi.org/10.1016/S0008-8846(02)00966-3