The use of inflated forms has grown steadily. A single form can be adjusted to build many sizes of culvert arch or other structures such as large-diameter concrete pipe, tunnel linings, and water tanks as well as earth-sheltered buildings.


A key feature of inflated forms is their adaptability. This versatility reduces the contractor's initial form cost because he can do so much with one air bag form. The form can be set vertical to make a silo or a manhole. Shotcreting over a single horizontal form can give a culvert or arch of any desired length up to 60 feet.


Nearly every city, county, or community has a recurring need to provide or replace storm sewers and small bridges. The cylindrical air-supported form can give builders a cost-effective way to meet those needs. The work begins with a reinforced bottom slab or footing, with embedded dowels for tying the arch and footing together. The following steps are relatively simple for a crew to learn:

  1. Inflate the closed-end form after it is tied down with flexible steel straps to control the size and shape of the arch to be built.
  2. Set plastic-tipped bar support chairs or bolsters over the straps to support longitudinal reinforcing bars.
  3. Apply shotcrete, 6 inches or more in one layer.
  4. Deflate the form after the concrete has gained strength.