A concrete spacer is a device used to secure the reinforcing steel or re-bar in concrete structures before the actual pouring of the concrete. The spacers are left in place after pouring and become a permanent part of the slab or structure. Concrete spacers are made in several profiles and sizes, but can be categorized based on the material from which they are made.
Concrete spacers must be made of a material that shares expansion and contraction characteristics with concrete so they bond naturally and design so that they hold reinforcing bars firmly in place either horizontally or vertically. When constructing concrete forms, whether it is a slab floor, a load-bearing wall or a bridge, reinforcing bars are placed at certain positions to support the weight of the concrete. The positioning of these bars depends on the volume of concrete required. More reinforcement, or cover, is required for higher volumes of concrete. The building codes that determine what is needed and where are designed to ensure the maximum strength for each application. Spacers are an added security to make sure the re-bar in stays in these positions.
Concrete spacers are made from fiber-reinforced cement. They’re typically categorized as single, double and triple cover spacers. Because they have the same expansion characteristics as the concrete that surrounds them, this type of spacer bonds to eliminate potential weak spots in the finished concrete. Concrete spacers resemble small blocks of concrete, with varying widths and profiles depending on the number of reinforcements they’re securing. Single cover concrete spacers are used primarily in horizontal concrete reinforcement. Double cover concrete spacers are used for vertical and horizontal spacing of reinforcement bars, while triple cover concrete spacers are used primarily in vertical reinforcement, but can also be used in horizontal applications as well. Concrete line spacers, also called bar spacers, look like long, rectangular concrete bars and are laid on the sub-base of the concrete form. These make for faster placement of reinforcements and are typically used to support large amounts of reinforcement in heavy applications.
Plastic spacers are manufactured in several styles that are ideal for different applications. Track spacers, for example, are continuous strips of plastic resembling a track, and are ideal for use as base reinforcement in suspended concrete slabs. Track spacers are typically used on metal decking. Wheel spacers are designed as a clip-on wheel-shaped spacer that is used when reinforcing columns, walls and beams. Pile cage spacers are round as well, but usually have more of a horseshoe shape. This type of plastic spacer is usually used during the manufacture of precast concrete panels.
Wire spacers are typically made of steel and are used to support mesh reinforcement in concrete slabs. Two main types of wire spacers are available. Hoop spacers are large circular devices that are about 3 feet in diameter. Three to four hoops are typically needed per sheet of mesh to provide proper reinforcement. Deckchairs are the other commonly used type of wire spacers. These resemble the base of a chair, and are used to support fabric reinforcement while preventing damage to the polythene membrane used in the slab. Deckchairs are ideal for use in ground floor slabs and can also be used to support dowel bars.