Placement. Compaction is done in two steps in quick succession. First, after the Pervious Concrete is poured from the ready mix chute and and leveled with come-alongs and rakes the first compaction is done with a vibratory screed and then second, with a set of compaction rollers.The screed should never be allowed to idle while more concrete is being placed. That will over work and damage the concrete. But no more than 6′ to 8′ of slab should be placed before compacting with screed. And care must be taken to avoid stepping into the uncompacted concrete. This will reduce porosity under the foot prints.
Using these tools correctly is essential to Pervious Placement! This creates a slab where the top 1½” has smaller voids to trap pollutants which can be removed or which volatize in sunlight. (For example, much oil and grease after volatization, leave inert carbon particulates behind which can be absorbed or filtered by the base and soil below.) This is followed by the curing process.
What does it mean to “cure” concrete? The PCA (Portland Cement Association) explains:
Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Curing Pervious Concrete. Following placement, the Pervious Concrete should be misted with water. Then it needs to be covered with 6 mil, polyethylene film which should be held down securely. Curing time without vehicular traffic is a minimum of seven days. However 28 days must pass before the pervious concrete reaches its maximum strength.
Contractors. Use only qualified placement contractors. Many of the newer Pervious Concrete installation contractors try to compensate for their lack of experience with shortcuts. These involve, as well as others.
- Admixtures which do not work as well as mechanical compaction.
- Roller screeds which vibrate cement cream to the top of the slab, and then smear it to reduce porosity.
- Slipforms which overwork the concrete and reduce porosity.
- Joint rollers with their radiused cutter edge encourage raveling. The use of any of these may reduce the void structure and shorten the life of the Pervious Concrete slab.
Charger Enterprises, Inc. has many successful large and small pervious concrete jobs to its record. Our background includes site preparation work as well. We have engineering contacts throughout the Southeast to support any project, in any way appropriate. We work with the best material suppliers in the area who consistently supply us with the most uniform, high quality pervious mixtures. That’s why we warranty our work for ten years!