If you’ve ever been on a long car journey, you’ve probably seen wavy black lines covering certain parts of the highway. While these trails may look messy, they’re usually nothing to worry about. Black lines are crack closure material used to patch the road, simply by definition.
The vast majority of modern roads are paved with asphalt, which is basically a sticky, black, semi-solid form of petroleum. Cracks can occur in this material for many different reasons, from wear and tear or constant traffic flowing on it, to temperature changes that cause the material to expand and contract. Water entering through cracks can also cause major problems for the road surface.
Among the many different types of cracking, fatigue cracking often causes cracks to appear and propagate in a wavy, seemingly randomly shaped pattern that looks a bit like alligator skin.
To repair these cracks, road repair workers often use asphalt rubber sealants with added polymers for greater flexibility. The result is a tar-like liquid that spills over the cracks where it seeps and solidifies.
This is done instead of re-paving or resurfacing the entire highway, which would be too costly for city officials. According to an old document from Texas A&M University for the state’s transportation department, one mile (about one mile) of highway pavement costs over $60,000, while crack-filling costs just $2,500 per mile. It should also be noted that these numbers are from 2008 and the cost is probably much higher today.
While most drivers will not have any problems going over crack sealant, some drivers believe they can be dangerous. Calling the pattern “tar snakes,” they argue that the padding can become more fluid and increasingly slippery as it heats up on hot days.
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