Methods and Techniques in Slipform Operation Method of Placement
Concrete is commonly hoisted by cranes, deck-mounted hoists, or pumping. Deck-receiving hoppers take the concrete in where it is distributed to the various locations in the forms by means of hand buggies. Traffic patterns must be worked out as to allow for easy access of concrete and for the storage of rebar, embedments, and openings. Concrete is usually placed in 2 to 12 in. (50.8 to
304.8 mm) layers, with the 12 in. (304.8 mm) layers the most desirable. The slow rate of placement 2 or 3 in. (50.8 or 76.2 mm) layers is used when there is a delay in the process and the concrete isn’t allowed to have any cold joints (silos, bins, and cooling towers).
Vibration of concrete is very important to the quality of the concrete. One inch (25.4 mm) diameter vibrators are normally used unless the wall being poured is thick, in which case large vibrators up to 3 in. (76.2 mm) in diameter can be used. The vibration of concrete should penetrate just the top layer. The deep vibration of concrete could cause a fall-out of concrete from under the form. Care should be taken to vibrate every section of concrete. Honeycombs in concrete are a result of poor vibration effort.