00:00This is one of the most frustrating loads for truck drivers to transport.
00:03It looks like a huge black solid, but it is actually the asphalt we all know.
00:06It is not that it cannot flow, it just flows extremely slowly.
00:10At room temperature, it is hard like a rock.
00:12Once mixed with crushed stone and sand,
00:13it can even withstand heavy trucks weighing dozens of tons rolling over it again and again.
00:17But once it is heated to around 300 degrees Fahrenheit or about 150 degrees Celsius,
00:23it turns into a hot, shiny black liquid that can stretch into strings.
00:26Asphalt comes from the heaviest and stickiest part left after oil refining.
00:30After gasoline and diesel are taken away,
00:32this black, sticky, hard-to-evaporate material is especially suitable for paving roads and waterproofing.
00:36It is suitable for roads not because asphalt itself is extremely hard,
00:40but because it works like black glue, binding the crushed stone skeleton together.
00:44When wheels press down, the stones spread the force while the asphalt cushions,
00:48waterproofs, and slightly flexes with the road as it expands and contracts with temperature.
00:52But this is also what drivers fear most.
00:54When it is hot, it is dangerous.
00:56When it cools down, it becomes sticky and hard.
00:58If the trip takes too long and the temperature drops,
01:01the valves, pipes, and tank can all get blocked, and the whole load may not come out.
01:05So for many long-distance shipments, workers pack asphalt into steel drums
01:08while it is still hot and fluid, then seal it and let it cool.
01:11At room temperature, it does not leak or spill.
01:13When it reaches the job site, the whole drum is heated again in a furnace.
01:17The hardest part about transporting asphalt is this.
01:19It is dangerous when hot, but impossible to unload when cold.
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