The Slipforming Operation

Подпись: Copyright © Marcel Dekker, Inc. All rights reserved.Slipform construction is an extrusion process in which the form,

1.5 to 6 ft (1.07 to 1.83 m) high, is the die and is constantly being raised. Fresh concrete is placed or pumped into the forms. After two to three hours, the concrete reaches the initial set and loses its plasticity and starts supporting the newly fresh concrete above. The rate of movement of the forms is controlled and matches the initial setting of concrete so that the forms leave the concrete after it is strong enough to retain its shape while supporting its own weight. The forms move upward by mean of jacks climbing on smooth steel rods embedded in the hardened concrete and an­chored at the concrete foundation base. These jacks may be hy­draulic, electric, or pneumatic and operate at speeds up to 24 in./ h (609.6 mm/h).

Figure 8.1 shows a slipforming system supported by the jack­ing rods. Yokes are frames that are used to support the lateral loads and transfer the vertical loads to the jack rods. Workers con-

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The Slipforming Operation

The Slipforming Operation

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Figure 8.1 Slipforming system. (Courtesy of Gleibau Salzburg) tinually vibrate the concrete so as to prevent any honeycombing. An upper working platform is attached to the inner form and slides up with it to provide a place from which workers can place concrete and fabricate steel reinforcement. A lower working platform is sus­pended from the outer form to allow workers to apply a curing compound and to repair any honeycombing that may occur.

Подпись: Copyright © Marcel Dekker, Inc. All rights reserved.Setting up slipforming starts by placing the jack rods in the foundation. A grid of steel girders is constructed and supported by these jack rods. From this grid of steel girders, the system of sheathing and decks are placed and supported. This process of setting up the slipform takes 3 to 5 weeks.