1. Column/Beam Concrete Coverage: 2. Concrete Slab Coverage: 3. Footing concrete cover: - "ing" refers to the reinforcing cover in Reinforced Cement Concrete. Cover is defined as the space between the concrete's outside surface and the inserted reinforcement. Why do we give concrete protection? The purpose of protective concrete is to prevent any part of the reinforcement from being exposed, which would likely cause it to be damaged or even destroyed by vehicle traffic or other external forces.
Protective concrete should be at least 1 inch (25 mm) thick. The top surface of the concrete should be flat, smooth, and free of holes. Any loose objects such as rocks or gravel should be removed because they will increase the amount of damage that can be done to the concrete with heavy vehicles.
There are two types of protective concrete: plain and reinforced. With plain concrete, the purpose is simply to provide a smooth surface on which to place the next layer of concrete. With reinforced concrete, the purpose is to provide extra strength through the use of steel bars placed within the concrete.
Columns and beams that are embedded in concrete require special attention when protecting them. These elements are usually inserted into the concrete before it sets, so they cannot be covered once it is set. However, when embedding reinforcement into fresh concrete, care must be taken not to cut any of the strands of wire used for reinforcing the cement mixture.
"In reinforced concrete, concrete cover is the shortest distance between the surface of embedded reinforcement and the exterior surface of the concrete (ACI 130)." The concrete cover protects the reinforcement from corrosion, insulates it from intense heat such as fire, and guarantees that the reinforcement may be actively repositioned. Concrete cover is also important for aesthetic reasons.
The reinforcement used in reinforced concrete consists of bars or wires of metal (usually steel) that are imbedded at regular intervals in the concrete. These reinforcements serve to give strength and support to the concrete, just as the rebars do in a traditional building structure. The amount of reinforcement used depends on the quality of the concrete and its intended use. Low-quality concrete with no reinforcement in itself can be strengthened by using plain concrete in active areas where stress levels are low. Higher-quality concrete with steel reinforcing will require less reinforcement than lower-quality concrete because the additional strength provided by the reinforcement is taken up by the concrete itself.
The concrete cover is applied in two main forms: external and internal. In an external cover, the outer surface of the concrete is exposed. This means that if anything breaks the cover, such as a crack in the sidewalk due to excessive load bearing, water can enter the reinforcement and cause corrosion or other damage. Corrosion can lead to the loss of reinforcement, which could then need to be replaced. Internal covers have an inner layer of concrete that is bonded to the reinforcement beneath it.
Concrete beam and slab reinforcement specifications should clearly indicate the cover to reinforcement, length of reinforcement, curtailment of reinforcement, and quantity and diameter of reinforcement to be given. The concrete producer can specify either continuous or bundled reinforcement. Continuous reinforcement is placed in one operation while bundled reinforcement consists of several strands of wire wrapped around a steel rod. The number of strands in a bundle varies depending on the application but generally ranges from three to eight. Bundled reinforcement is used primarily for heavy duty applications where continuous reinforcement would be impractical due to cost or space limitations.
Slab reinforcement should be limited to critical areas such as at corners or where stress concentrations may occur. If internal reinforcement is required in other than critical areas, two separate trenches should be dug-one for the reinforcement and one for the cement slurry-and the reinforcement placed in each trench separately.
The length of reinforcement required depends on several factors including the type of reinforcement specified, its quality, the density of the concrete, and the load it will have to carry. Concrete producers usually provide guidelines for minimum reinforcement lengths. These lengths vary by product but average about 8 inches for continuous reinforcement and 4 inches for bundled reinforcement.
Rebar is commonly used in concrete structures to provide strength and support.