Hoffmann, Inc. commonly uses a slipform technique for the construction of cast-in-place concrete chimneys and other structures. Slipform refers to a method of constructing vertical concrete structures using a mechanical moving platform system enabling continuous placement of concrete. This technique is identified as slipforming, because the deck and wall forms “slip” as the concrete is placed in the moving form. The hydraulic jacking system operates simultaneous to provide vertical movement. Most slips average 12 inches per hour. Once the slipform process begins it continues 24 hours per day unless a controlled stop is planned.
The slipform technique is used to construct cylindrical, square, or irregularly configured concrete structures. Hoffmann’s standard chimney design uses a cylindrical shape. Specific chimney design is based on many requirements from the customer, EPA, FAA, underwriter laboratories, and site specifications. Once the design criterion is defined, Hoffmann then configures the chimney as plumb or tapered while also considering construction costs. Plumb chimneys typically have constant inside diameters with outside wall thickness varying to meet strength requirements. Tapered chimneys have a gradual reduction in diameter and wall thickness to a narrowing top. The reduction in diameter and wall thickness can reduce foundation loads and construction costs in high wind and seismic areas.
Advantages of a slipform structure:
- Versatility with unlimited diameters and configurations
- Expedient construction schedule