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Concrete Footing and Pier Forms
Alternatives to conventional concrete form methods for concrete footings and piers
Tube formed concrete footings. Here are new alternatives to conventional forming methods for concrete footings and piers that are quicker and less expensive. For point footings, there are two approaches: rigid plastic footing forms, and a fabric "bag" footing form. For continuous strip footings there is a specialized fabric form held in place by a temporary structural system.
Typically a standard sono-tube provides the form for a concrete pier. However, a special fabric alternative can also provide a suitable pier form when properly installed and braced.
Plastic rigid footing forms differ mostly in their shape, though there are variable sizes available, as well. Some are similar to the conventional block shape, while others approach the shape of a truncated cone. They all have a circular opening on top to accept the concrete as well as to connect to the pier formed above, using a sono-tube form. Rigid footing forms have ribs to provide extra strength, and some have small holes made specifically to accept reinforcing rods for above ground applications or other structural requirements. The block shape forms also have small holes to release air during the pour. Some rigid form products can be installed on slightly sloped ground.
Fabric "bag" footing forms are exactly what their name implies. They are flexible fabric sacks with a circular hole on top into which concrete is poured. The shape of the fabric form approximates a standard rectangular footing, but all edges are rounded with bowed sides, and the form may be installed on and conform to uneven ground. For footings that require steel reinforcing, there is a form sack which has a zipper to open the top of the "bag" enough to get the reinforcing rods inside the fabric form before pouring the concrete. Also, there is a foundation pier product developed specifically for HUD-code housing that uses footing form bags as a key part of its design.
For large pier pads, a system similar to the fabric forms for strip footings can be used. This system consists essentially of a sufficient area of fabric laid out over the ground with its side walls held in place by a temporary form system of "top-edge boards" and metal stakes, similar to the form described below for the strip footing system.
The fabric strip footing forms can be used for level and step footings, as well as for deep footings. And, they can be installed over uneven ground or rock, if structurally acceptable to do so. A temporary simple form must be built to which the fabric attaches to hold its shape while the concrete cures. This is made with a board for each side that defines the top edge of the form to which the fabric attaches, held at the required height and width by a special "yoke" support system. The major lengths of boards that hold the fabric in place must be stabilized laterally. This is achieved by regularly spaced metal stakes pounded into the ground along either side of the form. Once the concrete sets, the rigid formwork may be removed and reused, while the fabric form remains in place.
Fabric pier form material comes in 120' lengths, with diameters of 8" or larger. They are the shape of a tube with an attachment tab running down their length. Because they are made of a flexible fabric, the forms are flat before filled with concrete. The fabric is easily cut to length.
Article courtesy of:
NAHB Research Center
http://www.nahbrc.org
and
http://www.toolbase.org
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