In a video that has gone viral, at least in the construction industry, Lafarge Tarmac vividly demonstrates the capabilities of its Topmix Permeable Concrete system to absorb large quantities of water in a short amount of time. According to the video, a parking lot constructed of Topmix is able to absorb 4,000 liters of water in less than a minute, with no puddles!
The Topmix system is exactly that, a system. It starts with a layer of permeable concrete, followed by a loose aggregate as a drainage layer, then permeable soil, a pipe system if desired, and/or an impenetrable layer if contaminants may be present in the run-off. The options selected will depend on existing soil conditions and the anticipated run-off amounts and content.
According to the product information, the system can absorb 1,000 liters of water per square meter per minute. The video portrays this splendidly!
Due to the loose nature of the drainage aggregate and the presence of the piping system to redirect water to storm drains or other water retention systems, the system is not recommended for highways or area of heavy traffic. It works well in parking lots, driveways, small streets, and even with paver systems.
Another problem is that it can become clogged with debris, limiting the ability of the system to drain properly. Maintenance and cleaning of the areas paved with this system is important.
In addressing the importance of stormwater management, Tarmac uses the example of the 2007 floods that devastated Great Britain, costing the economy $4.8 billion. Of the 57,000 homes affected by the floods, two-thirds were damaged not by rivers that overflowed, but by stormwater run-off.
In the US, stormwater routinely overwhelms current wastewater systems, causing untreated sewage to be dumped into local waterways. Storm run-off is also a significant source of pollution for rivers, streams, and reservoirs around the globe. Topmix pavement filters pollutants such as motor oil residue, even as it allows water to drain into the ground below.