Today I bring an article a little more technical than the previous ones but that I think cannot be missing in a blog on this subject. It is concrete, that material that we civil engineers like so much for its excellent resistance properties and relatively low price.
However, as those of you who are involved in the construction world will already know, concrete has a great weakness. The tensile strength of concrete is much lower than its compressive strength, around 10, and limits, in many cases, the use of this material.
How can we alleviate this defect? Here I leave you some brushstrokes of the most common methods to solve this problem so characteristic of concrete.
This article is part of a series on concrete tensile strength. Here you have the other two articles in case you are interested in consulting them:
- Direct tensile tests of concrete
- Indirect tensile tests of concrete
Reinforced concrete
Assembling the concrete is undoubtedly the traditional method par excellence. It is about integrating the properties of "plain" concrete and reinforcing steel. Both materials must work as one, so it is necessary that they be intimately united and interact through the adhesion forces that develop on their contact surfaces.
That is why the surface of the steel must be rough (corrugated steel rods) and the concrete must be vibrated after being placed in the molds.
Steel, unlike concrete, has similar mechanical characteristics both in tension and compression. When faced with tensile stresses, concrete cracks easily, ceasing to resist. The steel prevents collapse from occurring, joining the two "pieces" and resisting those tensions that concrete is unable to resist.
Prestressed concrete
This concept is newer and more complex than that of reinforced concrete. Any beam is subjected to two main loads: its own weight and external loads. As a consequence, some fibers in the section are betrayed and others are compressed.
Due to the characteristics of concrete, the compressed fibers will work properly, on the other hand, the tensile fibers will do so relatively inefficiently (similarly to what happened in the case of reinforced concrete).
To solve this, in the prestressing a state of initial compressive stresses is created in such a way that future tensions are reduced to values that can be assumed by the concrete or simply disappear.
In this way, concrete is subjected to two systems of forces:
- One caused by internal forces caused by prestressing
- Other caused by external loads and own weight
As a final note, it should be noted that the prestressing action is more efficient, it is placed eccentrically with respect to the centroid of the section. But be careful, since an excess of eccentricity could produce the opposite effect and that the concrete would crack on the opposite side only under the force of the prestressing.
Fiber-reinforced concrete
The last method is based on the incorporation of a certain proportion of fibers in the concrete to improve its properties. The fibers improve some characteristics such as toughness, control of the cracking process, and flexural strength.
Therefore, the brittleness of the concrete is reduced and there is a "stitching" effect of the cracks, reducing the opening of the cracks. The most commonly used fibers, in descending order, are steel, glass, and polypropylene.
And this is the most basic of the basics. Without a doubt, an essential in a blog like this. In any case, this is just a contact that I hope will serve the curious or those who are starting in this world.
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1 Comment for "Tension concrete, how to solve it?"
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