It’s seen nearly everywhere that you go and you may be wondering how paving asphalt is made. Check out this great video we found that explains the entire process of making paving asphalt. For your convenience, we have provided the video transcript below, as well.

Speaker 1: Asphalt is a black, liquid substance that’s a byproduct of processing crude petroleum. Asphalt is a key component of water-proofing and insulation materials and roofing shingles. But its best known use is for paving roads.

Speaker 1: Asphalt cement is a byproduct of crude oil. The key ingredient they mix with crushed rocks and other minerals to make paving asphalt. So production begins at the paving plant’s quarry, where some 15 meters below ground workers driving heavy machinery collect boulders of granite that have been blasted off the rock walls.

Speaker 1: Trucks transport the rocks to the paving plant, which is right on the quarry site. They dump their cargo into the primary crusher, a machine whose steel jaws crush these big rocks into pieces smaller than 20 centimeters. It takes mammoth force to crush solid rock. The flywheels that amplify the motor’s energy weigh more than six metric tons.

Speaker 1: The primary crusher empties onto a mobile conveyor belt, which transports the crushed rocks to an outdoor storage area. When it’s time to make the asphalt, the rocks travel via conveyor belt from the storage area to a screening building to be classified by size. There, the rocks tumble downward over a series of incline screens whose largest holes are ten centimeters big.

Speaker 1: What’s too large to drop through goes to a secondary crusher that reduces the rocks to ten centimeters or smaller, then sends them to a third re-tertiary crusher that further reduces them to two centimeters or smaller. What’s small enough to pass through the screens bypasses the secondary crusher and goes directly to the tertiary crusher.

Speaker 1: After this last crushing stage, the largest stones are two centimeters in size. Everything smaller than five millimeters goes in one pile. That includes stone dust created by the crushing process.

Speaker 1: Stones ten to fourteen millimeters go into another pile. Stones five to ten millimeters into another. Trucks transfer material from each pile to separate compartments called feed bins.

Speaker 1: Exactly what goes into the paving asphalt depends on what’s being paved. But generally, these are the four ingredients. Sand, stone dust, five to ten millimeter stone, and ten to fourteen millimeter stone. The ingredient proportions vary according to what the paving asphalt will be used for.

Speaker 1: Stones, along with sand and stone dust as fillers, usually make up about 95 percent of the mix. The remainder, added later, will be liquid asphalt cement. Each bin releases a specific amount of material onto a conveyor belt running under it. The belts lead to a main collecting belt that dumps the ingredients combined onto yet another belt that leads to a dryer.

Speaker 1: The drying process, which takes about a minute, removes all traces of humidity. This will enable the materials to bond better with the asphalt cement. Screening equipment then re-separates the dried ingredients making it possible to precisely weigh out the required amount of each one.

Speaker 1: Everything then goes into a mixer. As this demonstration shows, the mixer blends everything thoroughly. Then, it’s time to pump in hot asphalt cement. Oil refineries make asphalt cement from what’s left over after they’ve processed crude oil. The paving mix contains about five percent asphalt cement.

Speaker 1: This is what happens inside the mixer. The hot asphalt cement binds the ingredients in about 30 seconds. The result is ready-to-lay paving asphalt. The mixer empties directly into trucks destined for the paving site. There, a paving machine will spread the hot asphalt on the road bed. Then, a compactor roller will pack it down.

Speaker 1: The asphalt cools and hardens in about one hour, depending on the weather.

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