- 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 SlabsProperly creating and locating joints keeps concrete looking its best
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.
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.