Watching Our Water Ways

3 Responses to “Shooting down excuses to permeable pavement”

1. joe Says:
   June 30th, 2012 at 9:02 pm

   Mr. Dunagan,

   Why use slanted sources? Why not go to directly to the local municipalities that have used this installation? Permeable asphalt is a waste of taxpayer and private development money. Many different mixes have been tried and all of them have shown excessive wear within the first couple of years. When City’s are struggling to repave roads that are 40 years old due to budget cuts how does Ms. stiffler propose to repave permeable asphalt roads after 10 years at best? She is incorrectw when she states that vacuum sweepers can maintain this pavement by sucking up the top couple “millimeters” of dirt. Permeable pavement is approximately 10 centimeters thick and vacuum sweeping or pressure washing doesn’t work.

   Permeable concrete is much stronger but really really expensive.

   Perhaps a better solution would be to use regular HMA (hot mix asphalt) and utilize perferorated pipe under the sub-grade connected to catch basins that would produce the same effect but would actually last.

2. cdunagan Says:
   July 1st, 2012 at 9:38 am

   Thanks for the comments, Joe. The last time I talked to Bremerton engineers, they told me that the few problems they experienced could be attributed to installation issues.

   What I liked about Lisa Stiffler’s discussion was that she linked to what should be reliable sources, so we can all read about the issues for ourselves. For example, she cited “Government Engineering” (PDF) magazine, reprinted from “Hot Asphalt Technology.” The article included this:

   “Porous pavement does not usually cost more than conventional pavement. On a yard-by-yard basis, the asphalt cost is about the same as the cost of conventional asphalt. The underlying stone bed is usually more expensive than a conventional compacted sub-base, but this cost difference is generally offset by the significant reduction in stormwater pipes and inlets…

   “Over time, we have found that the porous asphalt material has held up as well as, or better than, the conventional asphalt, largely due to the solid sub-base provided by the stone storage/infiltration bed… We have found that sufficient asphalt content is essential to pavement durability (5.75 percent to 6.0 percent bituminous asphalt by weight). In sites where a lower asphalt content was used, some surface scuffing and/or raveling can be observed on the pavement surface.”

   Lisa did not include a link to her comments about the success of vacuum methods in reducing surface clogging. Perhaps others can offer links to studies or other documentation, pro or con, on this point. If permeable pavement does not work, we should be able to find studies to support this finding. In a cursory Internet search, I found discussions about clogging and possible remedies but no clear consensus.

3. Mike Says:
   July 2nd, 2012 at 5:50 am

   Porous paving is a promising development for improving environmental sustainability, though, as pointed out above, not without some concerns.

   Just to add to the discussion, Philadelphia is installing porous paving throughout the city in order to improve storm water drainage. It could be a good proving ground to see how well this undertaking works and what its strengths and limitations are for the rest of the world to learn from.

   Hopefully the City of Philadelphia finds that it is worth the investment and other municipalities follow in its footsteps. Time will tell!

   Here is some more info on Philadelphia’s porous paving project:

   http://apconblog.wordpress.com/2012/06/19/nat-geo-report/