Over the last few years, pervious concrete has become a very relevant topic in the construction industry. More and more specifications call for pervious concrete in different applications. Some of these applications include parking lots, sidewalks and even pavers where in the past these were solely the domain of conventional concrete or black top. The popularity of pervious concrete continues to rise with the increased awareness of environmental protection and preservation. Pervious concrete is recognized by United States Green Building Council (USGBC), which sets the green building rating system known as the LEED program (The Leadership in Energy and Environmental Design). The LEED program is the nationally accepted benchmark for the design, construction, and operation of high performance “green” buildings.
What is Pervious Concrete?
Pervious concrete, sometimes referred to as “no-fines concrete,” is a mixture of hydraulic cement, coarse aggregate of smaller size, admixtures and water. Pervious concrete allows the water to percolate through the concrete into the sub-base and recharge the underground water level. Typically, pervious concrete does not contain any sand and its air void content varies between 15 and 30%. A small amount of sand can be used for compressive strength improvement but air void content will be reduced and permeability lowered. It is important to maintain the proper volume of paste/mortar in the mix design so that the aggregate is equally coated but the excess of paste/mortar does not fi ll the void space within coarse aggregate. Voids within the pervious concrete should be interconnected so they create channels through which water can freely flow.
Creating a Construction Joint in Pervious Concrete.
Compaction of Pervious Concrete by Rolling.
Admixtures for Pervious Concrete
Chemical admixtures play a significant role in paste/mortar quality, which ultimately determines the quality of pervious concrete.
- Water reducing admixtures may be used for lowering w/c ratio and increasing the strength of paste/mortar. View product information on Water Reducers.
- Retarding / Accelerating admixtures allow one to adjust the setting properties of concrete in relation to ambient conditions. View product information on Set Controlling Admixtures.
- Air Entraining Admixtures may be used to improve the freeze/thaw durability of the paste/mortar. View product information on Air Entrainers.
- Other specialty products such as Viscosity Modifying Admixtures (VMA), latex-based admixtures, or water repellents may be used to ease placement, compaction and improve placement speed. Water repellents have a positive impact on overall durability. View product information on Specialty Products.
SikaMix PV-100 is a concrete admixture specifically designed for use in pervious concrete. Sika Mix PV-100 takes the pain out of pervious and provides a number of benefits including:
- Improved workability
- Better bond to the aggregate
- Increased discharge rate of unloading
- Improved compaction
- Ease of placement
- Improved strength
Advantages of Pervious Concrete
More and more attention is being paid to the impact of the construction industry on our living environment. The Clean Water Act (1977) mandates State counties and Municipalities to adopt steps and procedures to reduce the amount of polluted storm water. Since parking lots are generally impermeable surfaces, they contribute significantly to this issue. The use of pervious concrete is well-suited for this application.
- Reduces the size and sometimes the need for storm water runoffs
- Recharges the ground water level
- Allows for the natural treatment of polluted water by soil filtration
- Does not create heat islands due to its light color
- Reduces risk of flooding and top soil wash away
- Improves the quality of landscaping and reduces the need for watering
- Reduces tire noise – Due to open interconnected air void structure, pervious concrete has been found to act as an effective acoustic absorbent. The tire noise generated between tire and pavement is lower with pervious concrete as compared to conventional concrete or blacktop.
- Prevents glare – Pervious concrete allows the water to flow freely through the surface which reduces glare, especially at night when the road is wet.
- Reduces hydroplaning and flooding – When pervious concrete is designed correctly all the precipitation should be absorbed by sub-grade or diverted away from pavement by a drainage system (in case of low absorption sub-grade). This results in reduced fl ooding and a puddlefree surface, eliminating hydroplaning.
Savings and other benefits that come with the usage of pervious concrete are due mostly to the following factors:
- Reduces or eliminates the need for storm sewers or retention ponds
- Increases facilities for parking by reducing water retention areas
- Increases permeable area and may qualify for permeable area credit
- Recognized by Leadership in Energy and Environmental Development (LEED)
- Requires less costly repairs than black top
- Longer service life and lower life cycle cost than asphalt