Joints in concrete construction are construction, expansion, contraction and isolation joints. These joints are placed in concrete slabs and pavements at regular intervals to prevent development of cracks in concrete.
Types of Joints in Concrete ConstructionsTypes of joints in concrete constructions are:
- Construction Joints
- Expansion Joints
- Contraction Joints
- Isolation Joints
1. Construction JointsConstruction joints are placed in a concrete slab to define the extent of the individual placements, generally in conformity with a predetermined joint layout. Construction joints must be designed in order to allow displacements between both sides of the slab but, at the same time, they have to transfer flexural stresses produced in the slab by external loads. Construction joints must allow horizontal displacement right-angled to the joint surface that is normally caused by thermal and shrinkage movement. At the same time they must not allow vertical or rotational displacements. Fig.1 summarizes which displacement must be allowed or not allowed by a construction joint.
Fig.2: Types of Construction Joints in Concrete Structures
2. Expansion jointsThe concrete is subjected to volume change due to many reasons. So we have to cater for this by way of joint to relieve the stress. Expansion is a function of length. The building longer than 45m are generally provided with one or more expansion joint. In india recommended c/c spacing is 30m. The joints are formed by providing a gap between the building parts. Also Read: Expansion Joint in Concrete – Types and Characteristics
3. Contraction JointsA contraction joint is a sawed, formed, or tooled groove in a concrete slab that creates a weakened vertical plane. It regulates the location of the cracking caused by dimensional changes in the slab. Unregulated cracks can grow and result in an unacceptably rough surface as well as water infiltration into the base, subbase and subgrade, which can enable other types of pavement distress. Contraction joints are the most common type of joint in concrete pavements, thus the generic term "joint" generally refers to a contraction joint. Contraction joints are chiefly defined by their spacing and their method of load transfer. They are generally between 1/4 - 1/3 the depth of the slab and typically spaced every 3.1 - 15 m
4. Isolation Joints
Joints that isolate the slab from a wall, column or drainpipeIsolation joints have one very simple purpose—they completely isolate the slab from something else. That something else can be a wall or a column or a drain pipe. Here are a few things to consider with isolation joints: Walls and columns, which are on their own footings that are deeper than the slab subgrade, are not going to move the same way a slab does as it shrinks or expands from drying or temperature changes or as the subgrade compresses a little.
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