How asphalt roads are made
Doubling the weight on a truck axle does 16 times as much damage to the road beneath it.
- stations
- 6
- things upstream
- 3
- raw sources
- 2
- steps from the ground
- 2
The short version
An asphalt road is crushed stone coated in hot bitumen, spread over a compacted base and rolled flat. The stone is dried and heated to around 150 °C, mixed with hot bitumen at a plant, trucked out and laid in layers. Compaction has to happen while the mix is still hot, before the binder stiffens.
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Compact a base course
On site, crews prepare a compacted base of stone under the new surface. Good drainage keeps water out of the base and the soil beneath.
Goes in -
Quarry and crush stone
Gravel and crushed rock make up the bulk of the mix. They are the mineral aggregate that gives the pavement its strength.
Goes in -
Heat and dry the stone
In the hot-mix process, the aggregate is dried to remove moisture and heated to about 150 °C. Polymer-modified mixes are mixed at about 170 °C.
about 150 °C
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Coat it in bitumen
Hot bitumen, at about 93 °C, is blended with the stone until every piece is coated. Bitumen is the sticky, viscous petroleum residue that binds the aggregate together.
Goes in -
Lay the hot mix
Trucks carry the mix to the site and it is spread in layers. Laying has to be done while the asphalt is hot enough to work.
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Roll it flat
Rollers compact the layers while they are still hot. Poor compaction, especially at the longitudinal joint, can cut a pavement's life by 30 to 40%.
Worth repeating
- Edgar Purnell Hooley patented tarmac in 1901 after noticing that spilled tar kept the dust down.
- The damage a vehicle causes is roughly proportional to the axle load raised to the fourth power.
Back to the ground
Follow every input upstream and asphalt road starts as these 2 raw sources.
Open the whole family tree
Keep walking
Sources
Cite this page: "How asphalt roads are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/road