subject: Are You Facing With The Problem Of Concrete Shrinkage And Concrete Cracks [print this page] About Concrete Joints- About Concrete Joints-
Before explaining about concrete expansion joints, it is necessary to understand about concrete joints. Concrete is well known for its features of expansion, drying, shrinkage, or contraction after some time. All concrete structures shrinks as it dries due to loss of moisture and both the drying and shrinkage occurs over a long period with thick slabs normally shrinking more slowly than the slim slabs. Concrete enters into a hardened state when it is set initially and thereafter about 30% to 40% shrinkage occurs during the first month. Another 50% of dry shrinkage occurs in the next 11 months and the balance in the second to third year.
During the process of shrinkage, the concrete develops cracks and therefore to minimize the shrinkage process- separations or designed breaks are made in the concrete to allow for its expansion or contraction in order to minimize or control the cracking in a concrete. These separations or designed breaks are known as concrete joints. There are two types of concrete joints and these are classified into-
1)The Concrete Joints that allow movement during the whole life of the material due to contraction and thermal expansion forces, these joints are known as (a) Concrete Expansion Joints and (b) Isolation joints.
2)The Concrete Joints that control cracking due to shrinkage in the process of drying up of concrete are (a) Control Joints (b) Sawn Joints (c) Weakened Plane Joints.
Concrete Expansion Joints and its features-
Concrete expansion joints main role is to allow contraction and expansion of a concrete slab without generating potentially damaging forces within the slab area or its surrounding structures. These joints are fixed to the formwork before the concrete is poured in. They do not have the reinforced mesh or steel running through them. Most of these joints are found put in between servings of the bridges, pathways, pipelines, train tracks and other similar structures.
Types of concrete expansion joints-
These joints are made up of pre-created resilient materials and these materials include-
Cork material: This material is used where there are wet conditions in that area due to water and is often chosen due to its lightweight and its ability to isolate the concrete slab and easy attachment to other structures.
Asphalt: It is mostly used solutions for filling concrete joints and its nature of durability and long lasting nature. It protects the structures very well from water infiltration.
Fiberboard: Used for sealing unsightly cracks in concrete and other surfaces and well known for its elasticity and versatility.
Polyurethane Foam: It is used to be sprayed into cracks where it reacts with water as per its volume and expands up to thirty times its liquid form. This material easily binds with the concrete and has high resistance to solvents.
The type of material to be used depends upon the type and uses of the concrete structure.
