Black Tar Road
Spend a good amount of time driving, especially in rural areas, and you've probably noticed those messy-looking black squiggles that cut across asphalt road surfaces in what seems like haphazard fashion. But rest assured that they're not simply the result of some sloppy tar work by a road crew that decided to have a few beers before the end of the shift.
Black Tar Road
Instead, what you're noticing is crack sealing. It's a time-honored technique for remedying the damaged road surfaces, without inflicting even more pain upon taxpayers by tearing up and repaving the entire road.
In the arcane, highly technical world of road maintenance, there seem to be as many different types of cracks as there are types of snow in Finland. One of the most unsightly is fatigue cracking, which turns the highway into something resembling an alligator's hide, and which usually requires an extensive repair job. Another type of damage, reflection cracking, results from movement between the road's asphalt and concrete layers, and looks more like a jagged gash. There's also edge cracking, in which rows of wavy, curved cracks parallel the road shoulder.
While the black stuff that you see on the roads looks like tar, these days it's more likely to be some sort of high-performance polymer-asphalt mix, designed to form a bond that's flexible enough to keep the road from cracking even more. Crews apply it to the fissures with a device that looks vaguely like a vacuum sweeper hose.
When I hear "wicked" I think of the Broadway musical. When I heard the Wicked Streatery food truck was in Cape Coral, I flew over the bridge like Elphaba leaving Emerald City. Following the black-tar road, I found grilled cheese with fried green tomatoes and bacon, a dish as glorious as it sounds. The Korean tacos with kimchi slaw and gochujang shrimp will have me skipping back for more. It was that wicked good.
If you've ever found yourself driving down a long stretch of rural highway for any length of time, your eyes have probably wandered. First to the (maybe desolate) landscape. Then to the other cars whose license plates might have meaning. Then, after several hours in the car going slower than you'd like, you find yourself staring at the road: miles and miles of pavement only broken up by dark squiggles of black "tar".
Asphalt (also known as bitumen outside of the US) is a semi-solid petroleum product. It's sticky, black, and highly viscous. About 70% of asphalt is used in road construction in the form of asphalt concrete (commonly referred to simply as asphalt, blacktop, and pavement in the US). It's is also used to pave parking lots, outside basketball courts, as well as bituminous waterproofing products like roofing felt and sealing flat roofs. Asphalt concrete consists of mineral aggregate particles and an asphalt binder.
In Pennsylvania, we're accustomed to road construction and, well, roads that should probably be under construction. Because we have our fair share of roadways, we have more than our fair share of cracks, ruts, swelling, potholes, and weathering. Sometimes just leaving your front door means you're in for a bumpy ride.
There are many causes of road degradation. Pavement may develop cracks from stress, seasonal changes in temperature, design and construction flaws, base erosion, and even the sun. And just as there are many causes of surface failure, there are many different types of cracks and distress. Alligator cracking, block cracking, and edge cracks are quite common sights while on long road trips.
As these cracks develop, it's important to take care of the problem. However, a complete overhaul of the roadway would be very expensive. That's where the crack sealing comes in. Rather than putting down a new overlay surface, crews can seal the cracks. The substance crews use isn't really tar, even though it sure looks like it. Typically, it's a high-performance polymer-asphalt mix specially-designed to form a flexible bond capable of preventing further cracking.
While crack sealing certainly helps prevent cracks from worsening, the process is not without its flaws. For one, it doesn't really make the road any smoother in most cases. In fact, some motorcyclists complain these patches cause both accidents and damage to bikes.
As a temporary fix, highway construction crews fill the cracks with the tar-based sealant. It prevents water from getting into the cracks and it postpones the need for more expensive road repair. The repairs often result in random, windy lines of tar that resemble snakes; hence, the name black-tar snakes.
The most basic way state and local transportation departments can decide whether to pave a road with concrete or to go with asphalt is pretty simple: Asphalt costs less initially, but concrete lasts longer.
The overall trend of rising oil prices since 2000 has raised the price of asphalt and reduced its price advantage over concrete, but 93% of paved roads are still made of asphalt, according to the National Asphalt Pavement Association.
Roadway segments with high turning movements and stopping points also present some disadvantages for asphalt since it is prone to tearing under these stresses. But even this is not a black-and-white matter. Harder oils can be used in asphalt mixes to reduce rutting, but this can also make the asphalt more brittle. Likewise, the wrong oil in an asphalt mixture can lead to cracking in extreme cold and rutting in extreme heat.
Harsh winter conditions present some disadvantages for concrete. The darker asphalt pavement warms up as sunlight hits a plowed roadway, and Mother Nature helps melt away any snow left behind by plows. Salt used for snow removal also can eat away at concrete, so some municipalities opt for a no-salt policy for the first winter or two after a concrete road is built. Read about how high friction pavement treatments increase tire grip around curves during bad weather.
There are trade-offs between concrete and asphalt, as you have identified. Asphalt initially has a very smooth surface and does not provide the textured surface as tined concrete does, thus improving traction. The benefits of concrete in identifying black ice would only be experienced during daylight, thus making this a less viable factor in pavement type selection. Unfortunately poor pavement marking is due to inadequate frequency of re-striping, which is often a budgetary issue. We appreciate your Michigan perspective, Teri.
We recently started a paving company and came across this article. It offers some great insight as to the advantages of going with asphalt versus concrete. For example, here in the Pacific Northwest, salt and crushed cinder get used on the roads in the winter, and the fact that asphalt stand tougher makes it a good selling point to potential customers. Writing about asphalt and making it entertaining while informative is not easy to do.We will reference this article for years to come. You managed to get the job done. Thanks.