Anyone who has an asphalt driveway knows that they must be sealed every couple years to preserve them, inasmuch as moisture/contaminant penetration of the surface leads to accelerated aging, which then may require that the asphalt be “top coated,” or have another layer of asphalt poured on it.
Fine. So, why don’t highway crews periodically * seal * roads and highways, rather than go through the hassle and expense of top coating them every few years? Doesn’t preventive maintenance make more sense? After all, you can top coat only once or twice before the old layers of asphalt have to be bulldozed off and a new, fresh layer is put down.
The state highway department I work for does go out and do crack seals and stuff like that. So do city road crews in some places. If the ones where you live don’t, you should call them up and ask them why, but it’s probably because they’re being penny wise and pound foolish. What I do at work doesn’t have anything to do with pavement maintenance, but maybe I’ll ask around tomorrow and see if any of the engineers there have any idea why some departments don’t do better preventive maintenance.
Asphalt that is constantly rolled over by heavy machinery (i.e. cars, trucks, buses, etc.) does not develop cracks nearly as much as asphalt sitting around and just expanding and contracting with temperature changes. The material has quite a bit of “give” to it, and it adheres to itself. Cracks that form heal themselves when they are rolled over.
Your driveway doesn’t have enough traffic, so cracks form, water gets into the cracks, and will pry the crack open in freezing weather.
I, too, work for a state highway department, testing asphalt of all things.
You may be interested to know that your driveway is paved with the bare minimum thickness of asphalt, containing the absolute minimum percentage of the lowest grade (read: cheapest) of asphalt that the hot plant was able to buy from the refinery. It was mixed with who knows what aggregate gradation, and laid on a non-uniformly compacted base, then rolled just enough to get it to lay down nicely. No wonder it doesn’t last!
Highways, on the other hand, are just the opposite. A good crushed base course is laid down, sometimes with cement added to help it set up. This is compacted until it reaches a specified density (I don’t know what that percentage is, since I don’t have my Standard Specifications at home, but it’s pretty high). The asphalt is composed of strictly controlled aggregate gradations, and about six percent asphalt as a binder. The DOT specifies the grade of asphalt to be used, and that’s what I test. The penalties for providing the wrong grade of binder can get pretty high. We also add hydrated lime to the mix to help prevent water damage, or “stripping”. Asphalt is laid in several “lifts”, or layers, with each one being compacted to a specified density, usually 92% of the theoretical maximum. Remember, all of these things are being checked, and the contractor is being penalized whenever one of the tests fails. After all that, the surface is covered with a chip seal, possibly a fog seal, and then painted. Any cracks that do appear are treated with a rubberized asphalt crack sealer, but usually we get several years before that happens.
All of the above only applies to new construction of course. Generally, the design life of a pavement is ~20 years, but it will probably have to be overlaid at some time in it’s life, also re-sealed.
Anyway, that’s the difference between your driveway and the highway. My first post, and it would have to be about work. Dang y’all anyway.
First, let me apologize for giving my question such a weak subject heading.
So, from what I’ve read, a mandatory spraying of a sealant on asphalt highways/roads is not necessary or would not make much different? What I was imagining was a truck with multiple sprayers that moves down the road and gives it a good sealing that would preserve it longer. Bad idea?
For the record, I wish I had gone with a concrete driveway!
Actually, when the road is fog sealed, or chip sealed, what you describe is what is done. A thin coat of either emulsified or cutback asphalt is sprayed on the surface, and then covered with loose aggregate. This seals the road surface as well as providing a traction course. Usually, it works pretty well, but there are roads out there that have only lasted a few years before they have had to be redone.
From what I’ve been told, sealing a driveway is unnecessary, and basically what you’re doing is painting it. It doesn’t keep it from cracking (although they may not be as noticeable because it’ll be a darker color). Once you start you have to keep doing it or it will look terrible, but if you never seal it you don’t ever have to.
I’ve heard that the roads and highways in the U.S. are not very high quality, and that this is why road crews are constantly making repairs to them.
Anecdotally, I’ve noticed in Germany (10 years ago) that road crews are fairly rare, even on the Autobahn. Despite this, the roads are in very good condtion, this in a climate with widely varying temperatures throughout the year.
If the above is true, are we in the U.S. being “penny wise and pound foolish” in this matter as well? How much money could be saved on maintenance if more money was spent up front for a higher quality road?
To answer robbys hijack – I remember seeing a news segment on this (sorry can’t remember the show) and basically in the U.S. a contractor has to build a road to minimum standards and he is done. In Europe the contractor must build and maintain the road for X years, so they spend more up front to build a better road.
One thing to keep in mind, a road is usually only as good as the money put into it in the beginning. In Akron, Ohio (where I live) there was a debate over concrete vs. asphalt roads.
What it boiled down to was this, if they wanted to put more money up front (concrete requires careful drainage considerations and base compacting), the concrete would be better (that is cheaper) in the long run, but if they didn’t the concrete wpuld shift and break up to fast and asphalt would be cheaper in the long run, though not as cheap overall as if they out more money into it first and did concrete right.
Heck, Tsunami, have it sealed whenever you think that it needs to be sealed. You just need to be aware that it needs to be sealed more often than the highway because it was built to a much lower standard, that’s all.