Many persons make the mistake of treating the cracks in the concrete as proof of poor quality work. Cracking is inevitable. It doesn't matter whether you have used the best quality cement or not. When concrete dries, it contracts.
However, concrete has been mixed and poured in such a manner that it becomes very hard after it dries. This leads to an obvious contradiction.
Something which is very hard cannot have the elasticity to adjust its size when it contracts. The most obvious consequence is the crack. Even the best concrete will show some signs of cracking. You have the option of controlling the cracks or trying to pass on the cracks to those spots where they do not make any difference. This is done with the help of joints.
Is it obvious that relying on concrete to provide the strength to your structure does not make sense unless you make a provision for the cracking at the right spot? Well, the cracking that occurs after the concrete dries is to be sorted out by a set of joints. Further, there will be cracking due to expansion as well. Now, how can concrete expand?
The substance contracts when it dries. However, when it is heated again, it, like all other substances, is going to expand. In such a scenario, you will have to provide for the joint that will absorb the expansion as well. Just as contraction cracking occurs because it is inevitable, expansion will also occur because it is inevitable. However, you can easily prevent the concrete from cracking.
Concrete will crack if it is pushed against another hard surface and if it does not have space for expansion. Does this mean you should leave some empty vacant space in and around the concrete slab or column?
Well, that is not feasible if you are placing concrete blocks one upon the other. Secondly, the empty space is going to lead to infestation of pests, moisture, humidity and it is probably going to crack the concrete open on its own.
Hence, what you need is a substance that will absorb the pressure and yet prevent moisture from coming in. This is the reason why experts make use of elastic substances fitted in the gap that has been provided for the expansion of concrete.
The substance is hard enough to maintain the strength of the structure and is soft or elastic enough to absorb the expansion.
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