What are control joints in concrete?

Asked By: Zhengyong Granadino | Last Updated: 27th June, 2020
Category: business and finance construction industry
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Contraction/control joints are placed in concrete slabs to control random cracking. When shrinkage is restrained by contact with supporting soils, granular fill, adjoining structures, or reinforcement within the concrete, tensile stresses develop within the concrete section.

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Keeping this in view, what is the purpose of a control joint in concrete?

Control joints are typically used in concrete masonry to reduce the occurrence of shrinkage-related cracking. A control joint is a continuous vertical joint filled with mortar, but with a bond breaker on one side so that tensile stress cannot develop across the joint.

Similarly, where do control joints go in concrete? Control joints are generally placed into the concrete during the finishing process or within 24 hours of being poured.

Control joints are commonly found in concrete:

  1. Garage floors.
  2. Driveways.
  3. Sidewalks.
  4. Patios.
  5. Basement floors.
  6. House slabs.

Accordingly, what is the difference between a control joint and an expansion joint?

A control joint is used to reduce the occurrence of shrinkage in concrete, and it is usually a continuous, vertical joint filled with mortar. An expansion joint is a continuous or horizontal joint.

How many control joints are there in concrete?

Space joints (in feet) no more than 2-3 times the slab thickness (in inches). A 4" slab should have joints 8-12 feet apart. Cut joints deep enough. Cut joints 25% of the depth of the slab.

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Should you seal expansion joints?

Expansion joints must be sealed with a flexible sealant, like QUIKRETE Self-Leveling Polyurethane Sealant or QUIKRETE Non-Sag Polyurethane Sealant (dependent on application), or an expansion joint strip, to prevent water from penetrating the joint and deteriorating the sub-base.

Are expansion joints necessary?

Pavement expansion joints are only needed when: The pavement is divided into long panels (60 ft (18 m) or more) without contraction joints in-between.

Do concrete control joints need to be sealed?

As it cures, standard concrete pavement cracks. Because the sawed crack control joints offer a point of ingress for water and incompressibles into the pavement structure and base, it's perceived by most road agencies that they should be sealed to keep water and debris out of the structure.

How do you control joints in concrete?

How to Make Concrete Control Joints
  1. Step 1 - Pouring. Concrete control joints, also known as expansion joints, are something best added when you're pouring the concrete or before it cures.
  2. Step 2 - Setting in Place. When you pour a concrete path or driveway you'll see slits between areas of concrete.
  3. Step 3 - Trowel.
  4. Step 4 - Cement Saw.

How do you fix an expansion joint?


How to Replace Concrete Expansion Joints
  1. Sweep away any dirt and debris from the area.
  2. Dig out and remove all the old material that's in the joints with a putty knife.
  3. With a wet-dry vacuum, clean out the joints between the slabs very well.
  4. Apply a bonding adhesive, usually epoxy, into the joints with a brush.
  5. Insert foam backer rod.
  6. Cover and seal the joint.

How often should you put expansion joints in concrete?

How Often Do You Need Expansion Joints? Usually, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches). So for a 4 inch thick concrete slab, expansion joints should be no more than 8 to 12 feet apart.

Why do we need expansion joints?

Importance of Expansion Joints in an Architectural Structure. An expansion joint is an assembly that is designed to absorb safely expansion and contraction of different construction materials caused by heat. These joints also absorb vibration and permit movement due to earthquakes and ground settlement.

Why do they put lines in concrete?

To prevent sidewalks from cracking in random spots and breaking apart, builders make lines in sidewalks. The technical term for sidewalk lines is contraction joints. Contraction joints are placed in fresh concrete before the concrete dries and has a chance to create its own joints, which we call cracks.

What is a dummy joint?

dummy joint. [¦d?m·ē ‚jȯint] (engineering) A groove cut into the top half of a concrete slab, sometimes packed with filler, to form a line where the slab can crack with only minimum damage.

How far apart should control joints be?


The joints should be spaced (in feet) 2.5 times the slab thickness (in inches). For example, in a 6-inch-thick (0.15 m) slab, the joints should be no further apart than 2.5 times 6 between joints, which is 15 feet (4.57 m).

Does concrete need expansion joints?

Expansion joints are put in place before the concrete is poured. Expansion joints are used to allow the slab to move and not put stress on whatever it abuts. If your existing concrete driveway, sidewalk, or patio happens to crack over time, there are several things you can do to prolong the life of the pour.

How wide should an expansion joint be?

Expansion joints should be wide enough to prevent portions of the building on either side of the joint from corning in contact, when the structure is subjected to the maximum expected temperature rise. Joints vary in width from 1 to 6 in.

Do you need control joints in stamped concrete?

Decorative concrete flatwork still needs joints to prevent cracking, which will be even less acceptable than in typical gray concrete. Joints can vary in location a few inches or even a foot or two without leading to cracks. Some stamping contractors use custom-fabricated chisels to cut joints into the stamped pattern.

How often do you need an expansion joint in brickwork?

Typically, most expansion occurs within 6 months, but as the process is irreversible, this movement needs to be accommodated by using movement joint fillers, or expansion joint foams. Thermal expansion can cause the bricks/walls to creep and warp, especially during dry cold weather.

What are control joints and isolation joints?


What are control joints and isolation joints? Explain the purpose and typical locations for each in a concrete slab. control joints – intentionally weakened sections through concrete slab. Resist tensile forces caused by concrete drying.

What is a day joint?

Day joints are positions where the screed has been finished on one day and will be carried on the next day. In these positions, to avoid cracking the joint needs to be reinforced with mesh to bond the screed together. Alternatively an expansion joint could be fitted in this position.

When should you use a Sawcut control joint?

Sawcut Timing
In general, saw cut joints should be installed as soon as the concrete is sufficiently hard to resist tearing and raveling and before random cracking occurs.