Concrete Joints

Overview

Concrete is an extremely strong material that may not bend or stretch but it does expand and contract from heat and cold. This expansion and contraction from temperature changes is just one reason concrete must have joints. “Joints are used in slab-on-ground construction to limit the frequency and width of random cracks caused by concrete volume changes.” (ACI 460R-10 6.1) In other words, joints help concrete move from the temperature changes without producing unsightly cracks.

Types

There are three types of joints, isolation joints, construction joints, and contraction joints. Decorative joints also exist, like a diamond saw cut pattern, but these are usually contraction joints.

Isolation Joints

Isolation joints have one purpose, to isolate concrete masses from one and other. Consider a driveway connected to a home, the home is sitting on a footer far deeper than the driveway concrete, and the expected movement will be far different.

A formal definition: 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.

A few things to consider when designing isolation joints

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• The isolation joint must completely disconnect the two materials. In other words, the material must run fully between the tw
• Isolation Joints must use preformed material to divide the two slabs.
• A columns, isolation joints should approach from all four directions

Construction Joints

During large placements that must logically be broken up or just the end of the day, a construction joint is a joint that will stop the end of a pour and is created using some type of form like wood. A construction joint breaks up the logical placement and typically uses a system that allows stress to transfer through the joint.

• Construction Joints should be worked into the over all plan of the placement.
• These joint types can be used for equipment failure when a placement must stop.
• The veritical face of the joint should be cured and treated just as the top portion.
• If not load is transferred across the joint, a standard butt style joint is acceptable without dowling.

Contraction Joints

Contraction joints help create breaks in the slab so that the concrete can be forced to crack in an unseen location. This is achieved by cutting with a saw or during installation process, lines around 1/4 the depth of the slab.

See pictures of our flatwork for examples of concrete joints.

• The depth of a standard contraction joint is typically 1/4 the depth of the slab but a minimum of 1 inch.
• Joints are formed by saw cutting, or wet tooling, and typically done on a timed schedule to avoid joint activation.
• Joint activation occurs when the slab has cracking at the jointed site.
• Contraction joints may be specified on the design but if not, they should be square, and 2 to 3 times the distance in inches.

At Felice Construction we also do decorative saw cuts as part of our contraction joints. We will work with you to ensure your site has the desired look and feel you want.