A control joint is used to reduce the occurrence of shrinkage in concrete, and it is usually a continuous, vertical joint filled with mortar. An expansion joint is a continuous or horizontal joint. Unlike control joints, expansion joints are left completely free of mortar. They are filled with an electrostatic sealant to keep them free from water.
In concrete construction, it is normal for the material to expand and contract. These effects come about as a result of moisture and temperature differences. The expansion and contraction of building materials can lead to cracks in hardened concrete. To prevent this from happening, provisions are usually made to take care of volume changes.
This is done by positioning control relief joints at predetermined locations. This helps to prevent a concentration of stress forces that lead to cracks on concrete constructions. Another benefit of using control joints is that it helps prevent the occurrence of unsightly surface cracks. If care is not taken, small cracks can pose risks to the entire construction.
It is therefore beneficial to have adequate control relied on joints to prevent such problems from arising. A construction that has well-designed joints won't have unsightly cracks. They gather, dissipate and distribute forces brought about by temperature changes and moisture differences.
The joint is a simple groove cut positioned on the surface of the concrete. It is designed to allow some cracking to occur where there are differences in moisture levels and temperature variations in the atmosphere. This provision makes it possible for the crack to occur without it being visible.
An expansion joint is usually positioned between two separate pieces of concrete. It can also be made between concrete and other material. The main aim of the joint is to allow space for the two pieces to move with ease. It is made by installing a pre-formed material before the concrete is placed.
The material used can be elastic or resilient and its dimensions should be approximately the same size as the concrete. A pre-formed or pre-molded expansion joint is averagely ¼ inch to ½ inch thick. For it to be functional and beneficial to the construction, it should never be less than ¼ inch thick.
The type of material used to make expansion relief joints vary depending on the construction in place. One can choose between fiber, sponge rubber, cork, or plastic composition to make pre-molded or pre-formed joints. These materials are commonly used in large scale projects such as construction residential, industrial, and commercial slabs.
Expansion relief joints are used where concrete material joins with an existing structure such as junctions of sidewalks, sidewalks with a building, sidewalk with a curb, or sidewalk with a driveway. These types of joints are commonly used in a building floor slab where the slab joins with a wall or footing.
When positioning a control joint, care should be taken to make it beneficial in providing quality, serviceable and durable functions to the construction. The construction should be followed up by proper and continuous curing methods. This helps to enhance the strength of the construction and it minimizes the occurrence of cracks.