Seal Coating of Asphalt Streets
Seal Coating of Asphalt Streets
(OP)
I'm advising a local private community's management on a proposed project to seal coat not only the two small asphalt paved parking lots, but also the approximately 2 miles of paved asphalt streets. I used seal coat on a parking lot project many years ago and have a low opinion of its benefits, other than "looking nice", for a while anyway. I have not been able to find any meaningful recommendations on using seal coat on streets. Its use appears to be intended only for parking lots. Other informed opinions, either for or against using seal coat for this project will be appreciated.






RE: Seal Coating of Asphalt Streets
I found this in NCHRP 523:
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_r...
RE: Seal Coating of Asphalt Streets
"If you have money to spend on seal coating, place it in my pocket and we both will be better off". Seal coating will cause cracks.
I also once sent an e mail message to a Cathodic church council in a town where I lived. "Dear Council: I have a complaint. I see you tore out the whole parking lot and and replaced it recently. You have destroyed the best example that I have had available to developers and architects as to why you should never seal coat asphaltic pavements. Your frequent "seal coating" had caused the cracks to widen and also caused more cracks to develop so that it was very easy to convince the others how bad that is. Of course I do have other examples, so not all is lost"
My reasoning is this: The usual seal coat products are less elastic than the asphalt in the pavement. So, in cold weather the pavement tends to shrink and go into tension and stretches at the same time. The cover on top is more rigid and it does not stretch. The result: it tends to restrict the stitching of the pavement and causes cracks. At that Catholic church the cracks were as wide as an inch and were so numerous that it was a real hazard for persons walking.
If one must add some stuff on top, include some fine gravel to give a fraction wearing surface and a slight bit of more pavement thickness. Also if you want it black, to look new, buy the cheap0est stuff you can find, but plan on more cracks..
Take a look at typical pavement with parking stalls marked. You will see the cracks along-side the stripes, due to the less "stretchable" paint on the surface.
RE: Seal Coating of Asphalt Streets
RE: Seal Coating of Asphalt Streets
A slurry seal coat of asphalt has some protective value and can seal some cracks; however, the seal coat must be designed properly and applied properly.
All seal coats, even "microsurfacing" have limited effective lives, usually less than the hot mix they are protecting.
RE: Seal Coating of Asphalt Streets
RE: Seal Coating of Asphalt Streets
Ron and oldestguy, I value the experience that both of you have in addressing this question. In the presentation that I am preparing for the community's management may even quote oldestguy's statement: "Asphaltic concrete pavements fail from the bottom up. Covering the surface (with seal coat) does nothing to extend life."
I believe that is what is going on here. The pavement is not that old, but has continuing problems because of our constant high water table. Appears that a Contractor has come along with a "sales job" to convinced management that seal coat is a miracle cure all the problems with the pavement. I'll be trying my best to get them to cancel the previously awarded contract for seal coating (and to walk management through cancellation fee negotiations, if necessary). Sure to be an uphill struggle.
Thanks again.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Seal Coating of Asphalt Streets
I've attached a paper I wrote about 20 years ago on design of pavements in high groundwater areas. Hopefully it will help in some way. Convincing a homeowner's association is always difficult, particularly when salesmen sound better lying than we do telling the truth!
RE: Seal Coating of Asphalt Streets
Back in my technology transfer days with the Cornell Local Roads Program, I worked for a guy who had studied sealers. He sealed our parking lot with several different products, and watched their performance over time. Years and years after the black had worn off, the sealed surfaces were notably less porous than the control. The thing was you'd only notice when it was wet, and if you knew what to look for. The person that originally requested the study moved on, so he never published his results.
It never occurred to me to ask what happens with sealer buildup from habitual users, other than filling in the texture and reducing traction.
RE: Seal Coating of Asphalt Streets
RE: Seal Coating of Asphalt Streets
As to Ron's statements about high ground water, my observations show this is also important in freezing areas, easily noticed as contributing to frost heaving in winter. That thawed ground is the situation that controls the Wisconsin pavement design procedures, tied into the Ottawa Road test results as developed by AASHTO. I was lucky enough to be one of the two authors of that Wisconsin method back in the early 50's. Still in use by the way.
AC traffic: a question: Was Jim Spencer there then?
RE: Seal Coating of Asphalt Streets
Funny story: When he retired, he dropped off a lot of materials from his library, including some MUTCDs from the '50s and '60s. Shortly afterwards, I was asked about NY road signs from the period. I sent them a few pages, and received a nice thank you phone call from a woman with a lovely Quebecois accent, saying they were using it for props for the Hanks/DeCaprio movie "Catch Me if You Can."
RE: Seal Coating of Asphalt Streets
RE: Seal Coating of Asphalt Streets
RE: Seal Coating of Asphalt Streets
In checking out Jim Spencer on Internet I see when he was an instructor a summer survey camp he had yet to graduate.
Here is a half hour interview of him taken a year ago.
http://ecommons.library.cornell.edu/bitstream/1813...