Waterproof Roads: How Does Pervious Concrete Work
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Scientists around the world have tried for years to find an affordable solution, struggling to develop a technology that would be easy to implement, cheap and, more importantly, efficient.
Among the results of their work, there’s also the so-called pervious concrete.
If we have a look in the Merriam Webster dictionary, “pervious” is the same thing as “permeable”, which has a pretty self-explanatory name: “having pores or openings that permit liquids or gases to pass through”. But how’s that possible when talking about concrete?
Well, it is possible and pervious concrete is already being used in multiple regions of the world, with an impressive number of organizations encouraging companies and authorities in general, and people in particular, to adopt this new and apparently revolutionary technology.
So what is it? Pervious concrete is, obviously, a new type of concrete that, in essence, lets the water pass through. Okay, but how’s that possible, given the fact that concrete is typically a solid mixture with great strength and with absolutely no openings?
That’s actually the ace up its sleeve. Pervious concrete has been developed with multiple pores that allow the water or any other fluid to freely pass through and thus allow them to seep into the ground.
This apparently complicated product relies on a rather simple mixture. In just a few words and without getting too technical, the final goal is to create a thick coating, somewhat like a paste, that would have the sole purpose of binding together aggregate particles. A permeable content with voids that would allow the water to pass freely is only possible with no sand at all or, in some cases, with a minimum amount of sand, which makes the whole mixture even simpler than typical concrete.
One of the key components of pervious concrete is water and the way the mixture is made is absolutely vital for the end product. In case the workers in charge of making the pervious concrete a stable and uniform surface use too much water, the resulting paste will most likely drain down. On the other hand, insufficient water leads to raveling, so rain won’t be able to pass through the voids.
As said, pervious concrete is already being used around the world, including in the United States, where it is regarded as a more environmentally friendly way to deal with concrete. It can be used for walkways, small parking areas and even in regions with light traffic, but never on large roads such as highways.
Why? Because although pervious concrete has so many advantages, there are also numerous drawbacks that are still breaking the crayons of companies that hope to make a fortune out of this technology.
According to various statistics, a typical pervious concrete mixture has between 15% to 25% voids, which means that’s enough to allow a flow rate of 480 in./hr (0.34 cm/s). Although all these figures can be pushed a lot higher, there’s one word that scares the hell out of everyone: strength.
Since the whole “system” basically enhances groundwater recharge, it’s pretty difficult to make sure that a given construction will resist through the years. There are numerous ways to test the maximum strength of pervious concrete, but none of them has been so far approved by the government. In other words, nobody wants to push pervious concrete beyond its limits and use it on public roads.
Another major problem when it comes to this kind of concrete is maintenance. While typical roads can be cleaned by dedicated and high-end street sweepers, pervious concrete requires much more, let’s say… attention.
The United States Environmental Protection Agency (briefly known as EPA) says the best way to clean pervious concrete is either by using vacuum sweeping or pressure washing, and thus keep the voids clean and let the water seep into the ground. On the other hand, what’s going to happen on winters, when snow and ice cover the road and make cleaning almost impossible?
Last but not least, there's the problem of overall cost. While most companies and organizations claim that using pervious concrete is much more affordable than typical concrete, others beg to differ. Construction, testing and inspection undoubtedly cost a lot more, while cleaning and maintenance definitely bring all these investments to another level.
That being said, it’s still good to see that people are not reluctant to innovations, and as far as we’re concerned, let’s just hope pervious concrete will evolve at a faster pace in the next years. As Neil Armstrong said, “that's one small step for a man, a giant leap for mankind”.
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