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Concrete joints home
Isolation joints
Construction joints
Contraction joints
Where to Locate Joints in Concrete Slabs
Be active in deciding where to place control joints
Joints in commercial floors
Decorative joints: Tips for placing joints in decorative concrete
Special Considerations for Installing Joints
Load transfer- Transferring loads across joints
Sealing joints- Tips for sealing and filling joints
Jointless slabs- Reducing or eliminating joints
Related Information:
How to build high-quality slabs on grade
Grooving tools for forming joints

Joints in concrete can serve both to prevent cracking and as a decorative element.

Concrete is not a ductile material-it doesn't stretch or bend without breaking. That's both its greatest strength and greatest weakness. Its hardness and high compressive strength is why we use so much of it in construction. But concrete does move-it shrinks, it expands, and different parts of a building move in different ways. This is where joints come into play.

Although many building elements are designed and built with joints, including walls and foundations, we'll limit this discussion to joints in concrete slabs. Here's an overview of the types of joints, their function, and tips for locating and installing joints.

Concrete Joint Information

Different joints in concrete slabs all have the same bottom-line purpose of preventing cracks.

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.