Concrete slabs require joints. These joints, in most cases should be filled to prevent edge break-back and bacterial growths.
From: The Concrete Network: 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 in. 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.
Although many building elements are designed and built with joints, including walls and foundations, we'll limit this discussion to joints in concrete slabs. 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)