What is a Construction Joint? A construction joint is a type of concrete joint that is used when a new section of concrete is poured adjacent to another concrete section that has already set. The purpose of a construction joint is to allow for some horizontal movement, while being rigid against rotational and vertical movement.
- Construction joints prevent the premature failure of the concrete structure.
- A construction joint is used when a concrete slab that has already set must be joined with a new section of concrete.
- There are several reasons why this may be necessary.
- One is that construction work must pause at some point (e.g., the end of the day), thus one concrete section is inevitably allowed to set before subsequent sets.
When work resumes it is desirable for the new section and the old section to act as similar to one large slab as possible. Construction joints can have several different geometries, including straight wall butt joints and tongue and groove joints. An alternative method to join a concrete slab that is already set with another concrete slab is to place a tie bar through each, thus connecting them together. : What is a Construction Joint?
- 1 What is contraction joint and construction joint?
- 2 What are the types of joints in construction?
- 3 What are construction joints give examples?
- 4 What is a construction joint in a wall?
- 5 What is construction joint in column?
What is construction joint?
Difference between a contraction joint, isolation joint, expansion joint, construction joint, and a cold joint – Q. What is the difference between a contraction joint, isolation joint, expansion joint, construction joint, and a cold joint? A. A contraction joint is formed, sawed, or tooled groove in a concrete structure to create a weakened plane to regulate the location of cracking resulting from the dimensional change of different parts of the structure.
An isolation joint is a separation between adjacent sections of a concrete structure to allow relative movement in three directions and through which all of the bonded reinforcement is interrupted. An expansion joint in a concrete structure is a separation provided between adjacent sections to allow movement due to dimensional increases and reductions of the adjacent sections and through which some or all of the bonded reinforcement is interrupted.
In pavements slabs on ground it is a separation between slabs filled with a compressible filler material. A construction joint is the interface between concrete placements intentionally created to facilitate construction. A cold joint is a joint or discontinuity resulting from a delay in placement of sufficient duration to preclude intermingling and bonding of the material, or where mortar or plaster rejoin or meet.
What is contraction joint and construction joint?
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Slabs crack directly beneath saw cut contraction joints and transfer load between panels by aggregate interlock. The tooled contraction joint is too shallow, so the concrete created its own parallel joint by cracking. This tooled joint was cut too shallow, so the crack only followed the joint on the right side of the perpendicular joint. Wet-cut walk-behind saws are ideal for larger jobs. Husqvarna. Early entry saws cut a contraction joint before the concrete has a chance to begin shrinking. Husqvarna Torpedo groovers allow tooling of long straight joints. Slip Industries. Cracks often form at changes in the surface slope (and therefore the thickness) of a slab, making that a good location for a joint.
Now let’s talk about what are arguably the most important type of joints—certainly the most likely to cause problems. Both isolation and construction joints are formed before the concrete is poured; contraction joints (or control joints) are “placed” in the fresh concrete before it has a chance to create its own joints—also known as cracks. Video: Cut-Off Concrete Saw Time: 04:22 Watch a demo of the cut-off saw and learn about this piece of equipment.
- After concrete is placed it is going to shrink. We can reduce shrinkage with good mixes, but it is always going to shrink and we need to accept that fact and know how to accommodate that shrinkage. A smooth, unrutted subbase and a moisture barrier directly under the slab reduce friction between the slab and the subbase and reduce internal restraint. Contraction joints are formed by saw cutting, by tooling a joint with a grooving tool, or by inserting a plastic strip into the concrete during finishing (zip-strip). Proper timing and depth of cut are essential. If you wait too long, the slab will crack where it wants to rather than where you want it to. And if the joint is not cut deep enough it will not create the plane of weakness needed to guide the crack. Saw cuts can be made with conventional wet-cut or dry-cut saws or with early-entry saws. Using an early-entry saw, saw cuts can be made within 1 to 4 hours, depending on the air temperature—much earlier than with a conventional saw. Only Soff-Cut (now part of Husqvarna) makes a true early-entry dry-cut saw (sometimes called ultra-early-entry saws). The saw-cut is typically 1 inch deep regardless of slab thickness—although even ¾-inch deep early-entry cuts can function properly. Keeping the skid plate and blades in good condition will improve the cut quality (less raveling). There is now an early entry saw made specifically for decorative work. Plastic zipstrips sometimes come with a removable top to create a clean joint. Cardinal Mftr. Co. Conventional wet-cut gas-powered concrete saws can be used to cut joints, typically waiting until the concrete achieves a strength of about 500 psi to prevent raveling of the cut edges during sawing.
- For more information on groovers, and a demonstration video with Bob Harris, click here: Groovers Info & Demo Video,
- Zip-strips are plastic strips embedded into the concrete to create the plane of weaknesses needed to guide the cracks.
- Some come with a capping strip that is removed to leave radius edges or a sealant reservoir in the top part of the joint.
The timing varies depending on the temperature and the relative humidity, but the window is generally 4 to 12 hours after concrete placement. The cut depth should be at least ¼ the thickness of the slab. For decorative work or smaller slabs, a regular dry-cut cut-off saw can be used. Be sure to use a proper respirator—airborne silica is a serious health hazard, leading to silicosis.
Also use eye and ear protection. For a demonstration of using a cut-off saw, check out Bob Harris’s video. There are several methods for tooling a joint into a concrete slab during the finishing operations, but as with a saw cut, the depth of the groove needs to be at least one-quarter the slab thickness to weaken the slab enough to get the crack to follow.
ACI 360 and 302 do not recommend the use of zip-strips to form contraction joints. When a joint tees, a crack frequently forms on the other side of the joint. The jointing pattern may or may not be specified on your job. Take an active role in this plan to assure that joints are properly spaced and in the best locations for your work. For more information, read about Where to Place Control Joints, For an unreinforced slab, control joints should be spaced in feet 2 to 3 times the slab thickness in inches. In other words, for a 4-inch slab, space the joints 8 to 12 feet apart. The spacing is highly dependent on the concrete mix’s shrinkage potential. Read more on low-shrinkage concrete mixes in the Concrete Mix Design section. Low cement content and larger aggregate are key. Jointed panels should be as close to square as possible. Keep the length divided by the width of a panel (aspect ratio) no more than 1.5 (so if the panel is 12 feet long it should be no less than 8 feet wide). Avoid L- and T-shaped panels. Contraction joints should be straight and continuous, never staggered. Try to avoid “re-entrant” corners—inside corners within the slab. You’re likely to have some, though. The best way is simply to locate joints going both ways from a re-entrant corner. You can also place a couple of pieces of rebar diagonally in the slab near the corner. In most cases, do not extend reinforcement through a contraction joint. Although this will provide load transfer, it will also lead to uncontrolled cracks between contraction joints.
What are the types of joints in construction?
The Purpose of Joints in Concrete Slabs – As concrete moves, if it is tied to another structure or even to itself, we get what’s called restraint, which causes tensile forces and invariably leads to cracking. Restraint simply means that the concrete element (whether it’s a slab or a wall or a foundation) is not being allowed to freely shrink as it dries or to expand and contract with temperature changes or to settle a bit into the subgrade (see Subgrades and Subbases ).
- Joints allow one concrete element to move independently of other parts of the building or structure.
- Joints also let concrete shrink as it dries—preventing what’s called internal restraint.
- Internal restraint is created when one part of a slab shrinks more than another, or shrinks in a different direction.
Think how bad you feel when part of you wants to do one thing and another part wants to do something else! Concrete feels the same way. Different joints in concrete slabs all have the same bottom-line purpose of preventing cracks. In slabs, there are three types of joints:
Isolation joints (also sometimes functioning as expansion joints) Construction joints (which can also function as contraction joints) Contraction joints (also sometimes called control joints)
What is construction joint and expansion joint?
Construction Joint Vs Expansion Joint –
|Sr.No.||Construction Joint||Expansion Joint|
|1||A construction joint occurs when there are multiple concrete placements.||An expansion joint is used in concrete and steel.|
|2||It can occur between different days of concrete placements.||An expansion joint allows the concrete or steel to expand or contract with daily temperature variations.|
|3||If you don’t allow this, you may get crake to develop in concrete||If you don’t allow this, you may get buckling, or spalling, or total failures.|
|4||Type of Construction Joint 1. Free Contraction Joints 2. Partial Contraction Joints 2.a. Tied Partial Contraction Joints 2.b. Debonded Partial Contraction Joints||Type of Expansion Joint 1. Free Expansion Joints 2. Reinforced Expansion Joints|
What are construction joints give examples?
What is a Construction Joint? – Definition from Corrosionpedia A construction joint is a type of concrete joint that is used when a new section of concrete is poured adjacent to another concrete section that has already set. The purpose of a construction joint is to allow for some horizontal movement, while being rigid against rotational and vertical movement.
Construction joints prevent the premature failure of the concrete structure. A construction joint is used when a concrete slab that has already set must be joined with a new section of concrete. There are several reasons why this may be necessary. One is that construction work must pause at some point (e.g., the end of the day), thus one concrete section is inevitably allowed to set before subsequent sets.
When work resumes it is desirable for the new section and the old section to act as similar to one large slab as possible. Construction joints can have several different geometries, including straight wall butt joints and tongue and groove joints. An alternative method to join a concrete slab that is already set with another concrete slab is to place a tie bar through each, thus connecting them together. : What is a Construction Joint? – Definition from Corrosionpedia
What is a construction joint in a wall?
A construction joint is a separation provided in a building that allows its component parts to move with respect to each other; a joint where two placements of concrete meet. A construction joint is a deliberate split, or seam in the material, normally used in materials like poured in place concrete.
It is often used as a starting and stopping place between pours. It is also used as a control point to address the normal shrinkage and edge curling that concrete goes through as part of the curing process. Let’s further discuss the different types of Joints in concrete construction These joints are placed in concrete slabs and pavements at regular intervals to prevent development of cracks in concrete.
We shall have a simple study of these joints in concrete. Various types of joints in concrete constructions are: 1. Construction Joints 2. Expansion Joints 3. Contraction Joints 4. Isolation Joints 1. Construction Joints Construction 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.2. Expansion joints The concrete is subjected to volume change due to many reasons, especially due to thermal expansion. 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.3.
- Contraction Joints A 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, sub base 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 drainpipe Isolation 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.
If slabs are connected to walls or columns or pipes, as they contract or settle there will be restraint, which usually cracks the slab—although it could also damage pipes too like stand pipes or floor drains. Expansion joints are virtually never needed with interior slabs, because the concrete doesn’t expand that much—it never gets that hot.
Expansion joints in concrete pavement are also seldom needed, since the contraction joints open enough (from drying shrinkage) to account for temperature expansion. The exception might be where a pavement or parking lot are next to a bridge or building—then we simply use a slightly wider isolation joint (maybe ¾ inch instead of ½ inch).
Blowups, from expansion of concrete due to hot weather and sun, are more commonly caused by contraction joints that are not sealed and that then fill up with non-compressible materials (rocks, dirt). They can also be due to very long unjointed sections. Long unjointed sections can expand so much from the hot sun to cause blow ups, but this is rare.
Isolation joints are formed by placing preformed joint material next to the column or wall or standpipe prior to pouring the slab. Isolation joint material is typically asphalt-impregnated fibreboard, although plastic, cork, rubber, and neoprene are also available.
Isolation joint material should go all the way through the slab, starting at the subbase, but should not extend above the top. For a cleaner looking isolation joint, the top part of the preformed filler can be cut off and the space filled with elastomeric sealant. Some proprietary joints come with removable caps to form this sealant reservoir.
Joint materials range from inexpensive asphalt-impregnated fiberboard to cork to closed cell neoprene. Cork can expand and contract with the joint, does not extrude, and seals out water. Scott Whitelam with APS Cork says that the required performance is what determines the choice of joint materials.
How much motion is expected, exposure to salts or chemicals, and the value of the structure would all come into play—and of course the cost. At columns, contraction joints should approach from all four directions ending at the isolation joint, which should have a circular or a diamond shaped configuration around the column.
For an I-beam type steel column, a pinwheel configuration can work. Always place the slab concrete first and do not install the isolation joint material and fill around the column until the column is carrying its full dead load.
What is construction joint in column?
Beam–column subassemblies with construction joint in columns above and below the beam Key: Open access content Subscribed content Free content Trial content Construction joints in columns are unavoidable in multi-storey reinforced-concrete structures.
According to ACI 224.3R-95, construction joints in columns are to be provided below the beam for lower storey columns and above the floor slab for upper storey columns. A review of the literature reveals that little attempt has been made so far to study the effect of cyclic loading on beam–column subassemblies with construction joints in the column above and below the beam.
In the present paper, one-third scaled beam–column joint specimens were designed as per relevant provisions of the Indian standard code of practice and detailed as per ductile detailing procedures. Flexural strength ratios of the specimens were 1·2, 1·4, 1·7 and 2·0.
- Specimens were cast in stages, providing construction joints in the column as per ACI 224.3R-95 to simulate in situ construction.
- It was observed that ductility, initial stiffness and energy dissipation capacity reduced by 30–44%, 16–19% and 53–64%, respectively, in specimens with double construction joints in the column compared to control specimens.
Show All : Beam–column subassemblies with construction joint in columns above and below the beam
Why do we have construction joints?
What Is the Difference between Construction Joint and Contraction Joint As the name suggests, this joint allows free translation and rotation in all directions. See figure above. It is most often used in the following circumstances: Different types of joints are used to prevent cracks in concrete from occurring due to weather conditions.
- A key joint is a prefabricated device used to make control joints in concrete structures.
- When freshly poured concrete begins to dry, it tends to shrink or contract.
- This contraction can lead to cracks or fractures on the surface of the concrete or in the tiles and other floor coverings installed on the slab.Q.
What is the difference between a contraction joint, an insulating joint, a compensator, a construction joint and a cold seal? One. A contraction joint is formed in a concrete, sawn or ribbed structure with tools to create a weakened plane to regulate the position of cracks resulting from the dimensional change of different parts of the structure.
- An insulating joint is a separation between the adjacent sections of a concrete structure to allow relative movement in three directions and to interrupt all the bound reinforcement.
- An expansion joint in a concrete structure is a separation between adjacent sections to allow movement due to dimensional reductions and reductions of adjacent sections that interrupt some or all of the bonded reinforcement.
In pavement slabs on the ground, it is a separation between the slabs filled with a compressible filling material. A construction joint is the interface between concrete locations that were intentionally created to facilitate construction. A cold compound is a compound or discontinuity resulting from a delay in placement of sufficient time to prevent mixing and bonding of the material, or in which the mortar or gypsum reconnects or meets.
- References: ACI 224.3R-95 Concrete subjects: joints, movement; Concrete bases This type of joint is formed and has no initial space.
- It is intended to be used when the movement only leads to the opening of the joint (see figure above).
- Contraction joints are mainly defined by their distance and how they transfer the load.
They are usually between 1/4 and 1/3 of the depth of the plate and are usually every 3.1 to 15 m (12 to 50 ft) with thinner plates with shorter distances (see Figure 1). Some states use a semi-random joint spacing pattern to minimize their resonance effect on vehicles.
These patterns typically use a repetitive sequence of joint spacing (for example: 9 ft(2.7 m), then 3.0 m (10 ft),then 4.3 m (14 ft.), then 4.0 m (13 ft.). Transverse contraction joints can be cut perpendicular to the direction of circulation flow or at an angle (see Figure 3). Inclined joints are cut at blunt angles to the direction of traffic flow to facilitate load transfer.
When the seal is properly tilted, the left wheel of each axle first passes through the left plate and only one wheel passes through the seal at a time, resulting in lower load transfer voltages (see Figure 4). This term is commonly, but vaguely, used to describe any transverse joint formed, regardless of its structural role and regardless of whether opening or closing movements are expected.
A contraction joint is a groove sawn, shaped or tooled in a concrete slab that creates a weakened vertical plane. It regulates the position of crack formation caused by dimensional changes in the plate. Unregulated cracks can develop and lead to an unacceptable rough surface, as well as water infiltration into the base, basement and basement, which can allow for other types of sidewalk problems.
Contraction joints are the most common type of joint in concrete pavements, so the generic term “joint” usually refers to a contraction joint. This can be 100 mm or more, which goes far beyond the capacity of an orthodox sealant or seal. Choosing a suitable bridge material for such connections can be complicated by the need to adapt to pedestrian or vehicle traffic.
- A compensating joint is placed at a specific location so that the sidewalk can expand without damaging nearby structures or the pavement itself.
- Until the 1950s, it was common in the United States to use simple articulated plates with contraction and expansion joints (Sutherland, 1956).
- However, expansion joints are generally not used today because their gradual closure causes the contraction joints to gradually open (Sutherland, 1956).
Progressive openings or large joints of seasonal contraction result in a loss of load transfer, especially with joints without ankle rods. Most devices have formed from different materials and due to weather conditions that can shrink or expand.Q. What is the difference between a contraction joint, an insulating joint, a compensator, a construction joint and a cold seal? Construction joints are used to connect old and fresh concrete, and it is also called cold joints.
- As we have discussed, building materials are formed from various raw materials.
- Concrete can shrink or expand due to weather conditions.
- Such an articulation may be applicable in circumstances where some expansion may occur, for example due to an increase in temperature – but only if it follows and is smaller in size than the initial contraction.
: What Is the Difference between Construction Joint and Contraction Joint