When using concrete for any type of job, there are many elements that go into making sure the final product turns out looking as envisioned and the structures are as sound as possible. One of the most important practices to achieve this goal is the use of joints. There are several types of joints that can be set in concrete depending on the type of job being done. In any case, joints help to ensure the concrete turns out looking great and the integrity of the concrete doesn’t get compromised.
What Are Joints in Concrete?
Concrete is a sturdy material that can be used for various types of jobs, yet it is hardly perfect. When the material dries after being poured, the density will change. This typically results in a slight reduction in overall volume, which will cause random cracking. Joints are put in place to control cracking and to make sure a structure made of concrete stays sound.
One type of joint involves the use of steel reinforcement to prevent the concrete from pulling apart around it. This is usually reserved for vertical structures of concrete where the surface of the concrete is hidden once the whole project is completed. This is because the steel reinforcement method actually makes it more likely for random cracking to occur on the very surface of the concrete.
When laying concrete, the most common type of joint used is a contraction joint. Instead of adding in new materials to the concrete, this method involves creating strategically placed lines on the surface of the concrete to create a weakened plane. When the concrete dries, the concrete will crack at these locations instead of at random spots, keeping the surface aesthetically pleasing. The most common example of the use of this method is on sidewalks where you notice symmetrical lines that span the length of the walkway.
Other types of joints account for more than just the variation in density that occurs when the concrete dries. For very large construction projects involving concrete, the expansion and constriction of concrete based on differences in temperature need to be accounted for. This is especially true in regions with very defined seasons.
This type of joint involves actually separating the pieces of concrete used and making small gaps in between each piece. The gaps are then filled with a more compressible filler material. This allows the concrete structure to expand during especially hot days without crumbling. A common application of this type of joint is on bridges or overpasses.
Isolation joints completely separate pieces of concrete within a given structure, allowing the pieces to move in three dimensions. This type of joint may interrupt all forms of bonding material to complete the necessary function. An application of this type of concrete would be something like a drawbridge.