A slipform paver is a piece of
construction equipment used to place
concrete.
When placing concrete traditionally,
forms are placed, and then filled with concrete. The placement of the forms takes time, and forms cost money. A slipform paver eliminates the in place forms, by pulling the forms along with it. The paver cannot move very quickly, and the concrete must be fairly dry (known as having a low slump). These help ensure that the concrete will stand on its own, and won't just become a puddle on the ground.
Slipform pavers come in all sizes, from small machines barely larger than a lawnmower, used to place curbs, to machines spanning over 50 feet for road and canal construction. Most larger pavers run on crawler treads, although some run on rails. Large slipform pavers also cost in the hundreds of thousands of dollars. This cost is justified by the speed with which concrete can be placed, coupled with the elimination of in place forms.