It literally sucks, and really, really well as it turns out. Topmix permeable concrete, porous concrete, permeable concrete, no-fines concrete, gap-graded concrete, and enhanced-porosity concrete, whatever you wish to call it is impressive stuff. I can't count the number of conservations that inevitably end up musing about concrete. OK, we can, none, but we can but dream.
That would quickly change if we were to ask them a cheeky riddle. "What has an insatiable thirst and can only drink on the floor?" OK, we made that one up, sorry it's pretty "wet". Wink, wink, ok we'll stop. Yes, Topmix permeable concrete of course! Oh, how they would "roll in the aisles". Strange fantasy aside, this is actually a very interesting material. In the following article, we'll take a quick look at this "miracle" concrete. Brace yourself!
Over the last 50 years, our cities have grown exponentially. Large areas of land are being concreted over, usually with impermeable materials. Heavy rainfall over consecutive days has also gradually increased over time. A ticking time bomb, some might say. Could this material be the answer to stopping predicted increases in flooding? Let's have a look.
[Image Source: Tarmac]
Topmix permeable concrete, sometimes termed pervious concrete, is a great solution to traditional concrete to prevent stormwater runoff, amongst other issues. It allows water to permeate through its microstructure to regenerate groundwater and prevent surface water runoff typically associated with hard surfaces. Especially in urban environments. It is so good that the U.S. Environmental Protection Agency (EPA) recommends it as a means of meeting Best Management Practices to meet stormwater regulations.
This stuff is fast draining and allows for stormwater to be quickly directed off streets, parking surfaces, driveways, and walkways. Its ability to do this provides fantastic cost savings for long-term maintenance for local authorities and developers of stormwater management.
Don't believe us? Check out a cement mixer literally gushing water onto a carpark.
It comes highly recommended
Topmix permeable concrete is recommended by the EPA, other agencies and geotechnical engineers across the U.S. And for good reason. Its use allows for the more efficient use of land by rendering retention ponds, swales and other stormwater structures obsolete. This clearly adds further cost savings beyond that of long term maintenance cost savings. Neat eh?
Its development, as we previously mentioned, has been to combat flooding during storms. It can even prevent, well greatly assist, in the prevention of car crashes on wet roads. It can absorb an impressive 4 liters of water per minute. Given its structure freeze-thaw rules it out for very cold places, sorry Canada.
[Image Source: Tarmac]
How topmix permeable concrete works
Carefully controlled amounts of water and cementitious materials are used to make a lovely paste. Aggregate is then carefully coated in this paste. Very little, if any, sand is used in the matrix. This allows for the final product to have a substantial void content, perfect for rainwater permeation. The use of a paste to coat and bind the aggregate together creates a network of interconnected voids that drains quickly.
Topmix permeable concrete typically contains between 15% and 20% void spaces within the hardened concrete. Flow rates tend to be, typically, 0.34 cm/s or 200 L/m2/minute. Impressive they can actually perform better than this. Clearly, the low mortar content and high porosity do reduce the concrete final strength compared to more conventional concrete. It should, on the whole, have sufficient strength for most applications. All of this sits on top of a base of loose rubble.
Applications do need to take a few things into consideration of course. If fully open to subsurface geology the underlying water table must be established. High water table levels will clearly dramatically reduce the efficacy of the concrete. Obviously, underlying permeability should also be established. Plonking this on top of impermeable substrates will likely negate most of its benefits. It's not all bad news though, you can still use it in tandem with storage systems. These need to be integrated into the structural design of the paving solution.
Tarmac is very proud of it
Topmix permeable concrete can be used for many applications. But it's primarily intended for paving. Tarmac, confidently declare it could not only help tackle flash floodings in cities but also help reduce heating during hot weather. Nice a "double whammy".
"Permeable concrete allows surface water to freely drain through the wearing surface to the underlying ground with the ability to act as a reservoir during periods of high downfall." says Tarmac. "During these periods this characteristic can aid in delaying the discharge of surface water into water courses or drainage systems reducing the risk of overwhelming systems and causing flash flooding" Tarmac add.
''During periods of rising temperatures and intense rainfall, water stored within the system evaporates creating a cooling effect reducing surface temperatures.''
[Image Source: Tarmac]
The concept is nothing new. You'll commonly see a similar application used under paving to help with drainage. Tarmac have, however, made some tweaks to the concept. Advances in compaction seem to be one of Tarmac's secrets. It's even able to withstand the constant wear and tear of vehicles. This makes it great as a top surface rather than under paving solution. Tarmac believe it is ideal for large areas like car parks where surface water accumulation can cause headaches.
Pretty cool. We were sold at the video, to be honest. Tarmac may very well have changed the rules of the game in the paving market. It could very well be the answer to the seemingly increased likelihood of frequent flooding in our cities. Topmix permeable concrete might very well become the only application in urban areas in the future. Time will indeed tell.