Pervious concrete is awesome, kind of zen

Pervious concrete is, basically, just concrete that allows water to flow through it. This has some benefits and detriments for urban environments, as explained on NPR's Science Friday. Frankly, though, it's kind of pleasant to just sit back and watch this patch of pervious concrete absorb 1500 gallons in five minutes.


  1. How do they plan to backflush it when the pores get glogged with the sediment that is filtered out? I’m guessing that 1500 gallons in five minutes becomes 15 gallons in five minutes pretty fast.

  2. Assuming there isn’t a clogging problem, this would awesome for reducing runoff. Next time I need to repave my driveway, I’m looking into this.

  3. A few freeze-thaw cycles would destroy it. You might say “well, the water will go through it and into the ground before freezing.” But if the ground is saturated (think heavy rains), then the water will not be able to run off, and so will freeze while still in the concrete matrix.

    Also, this would probably make a fantastic environment for mold and bacteria to grow in.

    Also, as others have pointed out, this would just cause roads to wash out the dirt beneath them. Maybe if you built channels below the pervious concrete, so that it is diverted into drain pipes and such, then this specific problem might not be serious.

  4. Cool. If I understand this correctly, there is no filtering: Anything large enough to get absorbed is large enough to pass trough.
    I might be wrong, I’m on my fourth glass of wine.

  5. @ spazzm, really? I haven’t even had lunch yet! (The food kind, not the liquid kind)

    I hate to be obtuse here, but where does the water go when it’s passed? Like… a flood to your downhill neighbor’s yard? Is it really absorbed into the ground?

  6. Concrete getting silted up is a major problem – I’m not sure how you can prevent this once the silt enters below the surface. Porous asphalt works in a similar way; in the UK it is a problem to specify it on site for these reasons. It’s also much more expensive.

  7. I second all the above mentioned drawbacks. I look forward to listening to the show tomorrow to see how and if these problems can be addressed. Fascinating video to watch though.

    Some years I went to an exhibit at the National Building Museum about concrete and the “future of concrete” section got me very interested in materials science. Translucent concrete anyone?

  8. Okay, here is some more interesting information. A deep bed of gravel is laid underneath the concrete so it acts like a infiltration pond in addition to a paved surface.

    The consistency of the stuff sounds like a Rice Crispy Treat. Large aggregate thinly coated in binder with plenty of void to allow flow of water.

  9. The same sort of thing is used in Texas (Austin anyways) but in asphalt/black top form. No worry of prolonged freeze and TDOT says that traffic rolling over it at highway speeds helps keep it porous for water abatement. First I saw popped up a couple years ago. An added benefit is that the tire noise is drastically reduced.

    Detractors think it won’t stand up to traffic for too many years, but major road surfaces are refreshed every few years anyway.

    1. > “Detractors think it won’t stand up to traffic for too many years, but major road surfaces are refreshed every few years anyway.”

      Not in this economy, it ain’t.

    2. Actually, although Porous Asphalt has been specified in the UK for use on the motorways in the past it’s use is frowned upon.

      1. It is not the most whole life economic way of paving roads. It deteriorates quicker than other current paving materials due to the void type nature of its make up.

      2. Further, once it start’s to deteriorate, you can patch it with asphalt, but then the reason for laying it is now crippled and you end up with patchwork of repairs.

      3. Other materials are easier to repair and the majority of roads are now covered in thin surfacings, which unlike traditional hot rolled asphalt employ a negative texture helping reduce road/tyre interaction type noise.

      I believe the M4 in Wales might be one of the few places still to have porous asphalt, but I think it likely that this will soon be replaced.

  10. I’m just thrilled that “pervious” is a word.

    Bring on gruntled, sheveled, chalant, and ept.

    1. Bring on gruntled, sheveled, chalant, and ept.

      “Say… that’s near-fetched, Bill!”

  11. I couldn’t watch the video: does anyone want to list the negatives?

    The only negatives I’ve seen in this thread seem to have been answered: it’s designed not to clog (don’t know if it will or not), and once the water passes through it should just be absorbed into the ground. Were there others?

    It seems like this is a great positive. The huge decrease in permeable surfaces in cities is a big ecological problem. Not only does it affect the water table, but it increases erosion: instead of the water in a storm being absorbed into the earth, it’s channeled into drain sewers and then out to the rivers, greatly increasing the force and volume of the river causing erosion. You can similarly see this erosion to the side of roads without sidewalks: big ditches in the earth caused by the rain.

  12. Good morning, Mrs. Cleaver! Say….didn’t you used to have an inground pool?

  13. I think the main freeway in Italy (the A1, I believe) uses this kind of concrete, because we drove from Rome to Tuscany in one of the worst storms I’ve ever been in, and the road surface was dry-looking and grippy! Pretty neat stuff.

  14. There’s a Safeway near here that’s pretty new and I am pretty sure that they used this in the parking lot there. Driving on it, it seems fine but somehow walking on it, it’s pretty slippery when wet. Or is that just my shoes?

  15. Freeze Thaw is not an issue. Stones and concrete break from freeze thaw because the water expands in a confined space, but the pores in pervious concrete are way to big to be broken. The ice has plenty of room to expand. I also think all the arguments about durability are moot, because just replacing parking lots would be an excellent step even if it is not sufficiently strong for roads, something I am not convinced of. The only argument I have heard against it is that motor oil and all the other gook from cars goes straight into the ground. I don’t see how that is any worse than it getting spread by streams. Both are bad. It is more expensive in terms of money, but can I get a second! that just because something is cheeper in the short term it hasn’t always worked out to be a good idea in the long run. What are a few pennies more for a parking lot if towns aren’t flooding and toxic run off isn’t blighting the mouths of rivers.

  16. It’s being used in central Minnesota just fine. No freeze thaw problems. No clogging or sinkholes.

  17. It’s a “trendy” surface amongst the green crowd – we’ve considered using it on school construction projects where I work…but the reports from other jurisdictions where it has been used report major problems with clogging. We’re in Maryland (USA) on the mid-atlantic and see our share of winter weather. If roads are being treated with sand, cinders and other stabilizers in salt mixtures, clogging will occur. It’s too bad, because it seems like it could really help with run-off and lessen the cost of some of the storm water features that now have to be put in place to preserve water quality. So far, we haven’t taken the plunge.

    1. Crystals – Concrete works because of Calcium Silicate Hydrate crystals growing together from cement particles. “Concrete” is from the latin “Concretus” meaning “Grown together”

  18. If it is less strong than regular concrete that means it would need to be replaced more often, which means more exhaust gases from vehicles idling in construction related traffic jams. Thanks but no thanks. There are other ways to manage runoff from roads. It may be ok for parking lots, though.

  19. Rain on cold porous pavement is trapped as ice. Ice expands. If it was just going to squeeze back out the pores, it would do that in rock crevices too. But it doesn’t. And that’s where little rocks come from. And that’s were broken pavement will come from.

    1. pervious concrete is best utilized in locales with high-volumes of annual rainfall, undersized or outdated storm sewer systems, soils with high infiltration rates, and infrequent winter freezing.

      as for maintenance…it does require some vacuuming to keep the pores clean. vacuum-equipped streetsweeper trucks are a common feature in any public works department fleet.

  20. Freeze-thaw durability is one of the prime considerations in the design of concrete and has been for ages. I have no experience with pervious concrete, and I’m sure it has its downsides—there are always tradeoffs—but the notion that a bunch of commenters on Boing Boing are going to think of things unthought of by researchers who’ve spent their entire professional careers investigating concrete is laughable.

  21. This is my work. Here’s a couple of things:

    Most of the real strength of a slab is in the base (compacted rocks) and sub base (dirt). The best base is even graded, usually an even mix of say 2cm, 1.5cm, 1cm, .5cm. sand, dust, fines etc that is compacted together till it is 95% or more as dense as solid rock. This will not pass water as easily as that porous concrete and will degrade as the fines that lock it together are washed out. Also; the sub base of compacted dirt will weaken when wet and pump under load, destroying the concrete.

    An answer to some of this is to use a thicker open grade base, say 1 & 2cm only and to strengthen a thicker slab of concrete by using rebar (or more rebar) and dovetailing all joints. We should do that anyway but building regulations don’t demand it and contractors can’t stay in business if they have to bid to build a shoddy design and then pay out of pocket to build it right.

  22. Also, if I’m ever walking along a stretch of this with children, I must yell “Hey kids, they paved over SpongeBob!”

    It’ll be okay, they’ll forget they were ever crying, after the concrete soaks up all their tears.

  23. This is what it looks like in dallas when/after it rains. Except it’s 5 minutes of water, rather than just 3:32. If it rains before lunch here, you wouldn’t know that it rained that day walking from your office to your car.

  24. Porous asphalt is great for roads.

    Good: Will stay dry even in heavy rain. Tire noise is absorbed.

    Bad: Wears quicker. When salt is used in freezing weather, the wet salt will drain leaving again ice. This is solved by adding gel forming substances to the salt.

  25. Add to some of the problems mentioned above (although i’d be kinda cool to have a road surface or parking lot draining automatically down to the sewers or a collector for plants) that in, say, the shitty Canadian weather as soon as the left over water INSIDE the concrete freezes the road is gonna look like effed up peanut brittle.


  26. I imagine this will always be less durable than nonporous concrete simply because the idea is younger than the other. With that in mind though, aren’t there plenty of uses where it doesn’t have to be as durable? This still sounds ideal for just about everything except roads.

    I see plenty of footpaths and parking lot trials in these links, does anyone know the proportion of impervious surfaces that aren’t roads?

  27. I just saw this for the first time a few weeks ago in Toronto – they’re using it along Bloor West where they’ve replaced the sidewalks – they’re putting it between the sidewalk and the road, in the at 3 foot wide strip where they plant trees…perhaps its better for roadside trees?

  28. i would be concerned about nasty things leaking into the soil – where they might otherwise be partially held back by the impervious concrete.

    obviously, the choice of where to put this concrete is important. playground, yes. loading dock for a chemical company, probably not without more engineering. superhighway, not so smart.

  29. If the water goes through the road and not run off to the side, where are the birds suppose to bath? WON’T SOMEONE THINK ABOUT THE BIRDS?!

  30. Does anybody have a link to the pdf re: other trans materials? “Transmaterial catalog: Biosteel, pervious concrete, Superblack, corrugated glass, rubber pavements/sidewalks, strawboard, conductive plastic, plasphalt, light-emitting glass, regenerative plastic…”

    It seems to have disappeared and I am quite innerested.

  31. We used to call this “porous flooring” where a top layer of porous material covers an sloped surface that conducts liquid to a drain. Porous flooring was used as swimming pool surrounds as well as shower stall floors. It never became popular due to it’s cost.

  32. Are they using a cement mixer to pour the water? Do they not have water trucks in New Hampshire? Or better yet, since this is a test, couldn’t they have picked a spot near a fir hydrant and use it to pour the water?

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