Cracks in a concrete structure reduce its strength and durability, leading to unplanned repair costs. As explained in Part 1 of this article, cracking is an unavoidable tendency of concrete, in fact there are many reasons why cracks may occur and we explained some of them. Here, we would like to focus on what happens within the concrete structure when a crack occurs, therefore the structure becomes weak and the degradation process is accelerated.
Most cracks are wrinkled for the following reasons:As a result of deformations and variations of hydraulic and thermal parameters, the lips can move away and come closer; a material entering the crack (grains of sand for example) then causes breaks approximately parallel to the surface of the concrete. (fig c). The lips of the cracks can also move (fig d and e) and lead to wrinkles.
The Diagram illustrates the phenomena caused by the presence of cracks, and their effect in increasing the severity of defects and damage to the structure as soon as they appear.
It is easy clear that cracks have considerable impact on the durability of the structure. However, cracks do not only have mechanical effects. In fact, cracks also allow foreign matter and aggressive substances to penetrate the concrete. These may weaken and damage the concrete and the reinforcements. In this case, it is necessary to intervene as quickly as possible in order to avoid a reduction in the service life of the structure and possible structural risks.
The main substances that can penetrate cracks and the processes that can contribute to the degradation of concrete are:
In the third and last part of this article “Why concrete cracks?” we will focus on how to combat cracking and on the most important preventive measures.