What is pervious concrete?
It is a paving material that acts like grass in a special way. It lets water run through it into the soil while filtering out pollutants. Like grass, it lets the ground below it breathes, and allows tree roots and their supporting microbes and fungus to interact. It is a mixture of coarse aggregates, hydraulic cement, cementitious materials, admixtures and water. It contains no sand, but relies on strong, cohesive, hydraulic Portland cement for its integrity. It differs from impervious concrete just like a urethane foam sponge contrasts with solid urethane. Because of its open cell structure it has more strength and crack resistance than an equal weight of impervious, solid concrete when used for paving. Its main applications are parking lots, low traffic roads and driveways and sidewalks.
For more detailed information, see » What is Pervious Concrete?
How does it work?
Pervious Concrete Storm Water ControlConcrete is like a thermoset exothermic plastic compound. (That is, it is workable when first mixed and it gives off heat while it cures) When mixed in the truck or other mixer the ingredients are blended ready to set up when placed in forms. Time is critical in placement as is water content. Once in place, the chemical reaction of hydration turns a flexible mixture into a hard substance that continues to strengthen with age.
Portland cement and admixtures are like an exothermic plastic (IT GIVES OFF HEAT WHILE CURING) that hardens as long as water is present during the curing process. To insure good curing Pervious Concrete must be covered with polyethylene sheeting within 15 to 30 minutes after being placed and roller compacted.
Since it hardens as porous paving material it permits rain and storm water run-off to percolate through it. The top 1-1/2” acts as a filter that traps oil, grease and particulates. The volatiles are evaporated by sunlight, and remaining organic material is consumed by bacteria in the soil below. This allows it to add filtered water to the aquifer under the project site. You can build the parking lot and still have some of the benefits of paradise.
Pervious Concrete is also used on swales and drainage ditches. It permits water to enter the soil while stabilizing the drainage channel. When Pervious Concrete is used in strips along curbing much rain water can be diverted from becoming damaging storm water run-off to recharge the aquifer.
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