Guide to select and use the concrete spacer in reinforced concrete structures.
Post date: 03-11-2016
1/ Selection of concrete spacer:
Although the spacers have the similar features, but the selection of the righ type will facilitate the construction and make it more efficient. The selection of spacer will base on the following factors:
The nominal height of spacer is the dimensions of the spacer to form the exact concrete cover for the steel rebar in concrete. This is the most important specification and it must be detemined firstly when order.
With the single spacer, which have the simple shapes such as cube, cylinder, the spacer heights are fixed for using. With the multi-dimension spacer, the heights for supporting the rebars will vary in depend on the position of installation. In a project, where the reinforced concrete structures have various concrete cover thickness, it is practical to select the multi-dimension spacers with the appropriate dimensions (if available) to ease the order and use up the spacer product.
In general, the simple concrete spacers can be used for all structures. However there are some kind of concrete spacer are designed for specific using purposes such as corner-spacer for column/beam, donut-spacer for cylindrical structure.
The donut-shaped spacer usually used in the cylindrical structures such as spun piles, round columns. This kind of spacer can also be used in the normal structures of beam, slab, wall. However, because these spacers must be inserted through the steel rebars before arrangement, it results in some inconvenience and requires the good understanding of workers during their executing.
Donut-shaped spacer used for slab reinforcement
At present, there are many kind of spacers with various shape and use for selection. The users should firstly refer then select the right product in order to obtain the best efficiency.
Concrete spacer products
Find out more information of concrete spacer in Concrete spacer products.
In general, there are 3 basic positions for installation which can affect to the selection of spacer:
- Concrete cover in the horizontal plane of slab, beams.
- Concrete cover in the vertical plane of column, wall.
- Concrete cover at the corner of prismatic structures (column, beam with rectangular section)
Spacer of vertical steel rebar
The spacers are placed under the rebar mesh will be impacted by the above forces such as the weight of steel rebars, workers, equipment. If the contact areas of the spacers with the soil, stone subgrade are not suitable, they can be settled during construction. This condition actually reduces the concrete cover thickness as required.
If capable, the contractor usualy cast the bedding concrete in order to create the flat, clean and firm platform to support the steel rebar. If the subgrade is not firm, the spacers must have the sufficient contact areas. Such kind spacer should be concrete cube or cylindrical blocks.
Spacer cube shaped for slab reinforcement
There are 3 options for connection between spacer and steel rebar:
With the donut-shaped or hook spacers, it is necessary to ensure whether the diameter of the hole or hook fit with the steel rebar insert through them. The spacers with hook are usually designed for a range of rebar diameter. However the user must make sure whether the ready-designed diameter of rebar is suitable or not with the actual requirement.
Because the spacer will stay in and become a part of the reinforced concrete structure, the concrete spacer must have its strength equal or greater than the strength of the structure. This specification will ensure the uniformity of strength and bring good quality for the construction work.
2 / Installation guide:
Spacer installed and fixed with tied-wire