A compactor is a heavy, self-propelled construction machine fitted with a large, heavy steel drum (smooth or padded) that compresses soil, gravel, asphalt, or other fill materials to increase their density and load-bearing strength.

 

Using a combination of its own weight and, in most models, drum vibration, it forces air and water out of the material and tightens the particles together, creating a stable, even base for roads, building foundations, airfields, embankments, and landfills.