Is permeable tarmac possible?

Question

I've been wondering that considering today's high spec materials and manufacturing whether permeable tarmac (or similar) was possible - it probably wouldn't be genuine tarmac, but would serve the same purpose, and would be some new composite material.

I have the idea of a surface using materials technology that would allow water to permeate to the ground while still being hardwearing - a kind of more flexible porous version of our current surfaces. This would go a long way to helping prevent the flooding we've seen that's been blamed on the lack of open land to soak away rainwater.

I'd like to know from those with materials knowledge whether such an idea might be possible, and how? Thanks.

Answer 1

That's a very good idea, and it would actually be helpful. Right now the approach is to make sure water that flows onto your property (from a stream or drainage ditch) can flow through your property. You are often required to build retention basins capable of catching all runoff from whatever you cover with pavement or buildings, and release it slowly downstream. I haven't heard any recommendations of local percolation. I've asked a real estate developer, and I'll edit my answer if I learn something new.

There are two conceptual problems with permeability. First, it won't last forever, and you'll need to design for runoff anyway. Second, water soaking into the pavement can freeze, likely deteriorating the pavement. Still, it's an idea worth pursuit by the paving industry. We'll suggest it to our contacts. Thanks!

--- update ---
Yes, porous asphalt pavement; see National Asphalt Pavement Association. I did see this and talked to the guy from NAPA.

That's the good news. For you, the bad news is that someone beat you to the invention. Sorry about your patent hopes. No joke, that's exactly the kind of idea that can be developed, patented, and marketed, and can be the foundation of a business.

Answer 2

Permeable Tarmac

Answer 3

well, with increased development, surface run off will always increase due to impermeability or decreased permeability of the land, thus flooding will always be more likely...
In terms of the materials which could be used, i dont really have too much of a clue, but i question whether such a proposition is really worth it
I am not sure though if permeable tarmac will enough to be able to store such large quantities of water in order to avoid flooding.
In addition, flooding such as this is caused by incredibly heavy rainfall, which naturally leads to large amoutns of surface run off due to waterlogged soils as a result of the nature of preceptiation, hence i wonder if tarmac will be the same in heavy rain... i.e. the surface layer shall become saturated quickly and water will take time to trickle down deeper into aquifer storage or wherever it is meant to go once into the tarmac, meanwhile water will continue to run off the surface.
I also feel that should such a thing exist, the pores (if the material is porous) may get blocked by fine particles of soot and rubber deposited by cars, or the joints (if the material is pervious) may be more susceptible to erosion from use and thus more vulnerable and weak.

In Short:
Permeable tarmac probably is possible, i dont know what materials would be used, but i question (with my limited knowledge) whether such a thing really is a viable solution?

Answer 4

Bear in mind the difference between "porous" and "permeable". It's one thing getting the water to soak into a porous road surface, but you would need a phenomenal permeability (the rate of flow capable through a material) in order to remove the sort of deluges that we have seen in the last 40 hours. Also, where would the water be carried to, once it had got through the top surface layer?probably into the underlying foul water drainage system. Once the drains have backed up, then assuming the soil is saturated, no amount of permeable road surfaces will prevent flooding.

Another thing to bear in mind is how to prevent the road surface from cracking up if water inside the tarmac freezes in winter.

Most of the recent flooding (aside from localized exceptions) has been caused by the natural river systems inability to cope with the rainfall. This is partly due to the exceptional volumes of rain, but also significantly due to changes in land-use (loss of floodplain and water meadows to alternative agricultural use or development).

In the short term, you can build roads with better drains and cambered surfaces, but the water has to end up somewhere i.e. the river, where it becomes the problem of the next settlement downstream.

One issue that I think needs much greater attention is the peculiarly British practise (lowest cost solution as always!) of designing storm drains that connect into the foul sewerage water system rather than directly into rivers. Under normal circumstances, of course, modest amounts of rain keep the sewage moving and cuts down on the cost of needing pumping stations. But at times like these, the systems cannot cope, indeed are not designed to cope, and so the water backs up ont street level. It's bad enough to be flooded by plain muddy water; quite another to be flooded by sewage.

Answer 5

They did experiment for a while with a type of permeable tarmac (not sure when - 70s I think) but the very fact that it was permeable made it less strong and it therefore could not stand up to the weight of traffic (much less then than now!)

Answer 6

We do have permeable tarmac in use on British roads, A34 Newbury bypass is a good example.

The Germans have specified it for autobahn construction for several years.