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Is there a problem with steel in concrete? Steel-based concrete is the real foundation of our modern society. Steel inside concrete creates a composite material. In it, concrete provides elasticity against the force of friction, while steel provides elasticity against the force of contraction. However, while steel-based concrete solves one of the biggest limitations of concrete, it creates a completely new problem. So what are we doing to fix this problem? In today's episode, we will look at some improvements in concrete structure. Although steel is not protected, it is easy to be corroded or corroded when submerged in concrete. But there are some factors that often affect the protection of steel. First, the ability to protect clearly when protected from the outside environment with relatively non-water-absorbent materials. Water and pollutants often cannot pass through concrete to steel. The second form of protection is the environment. The high pH of concrete usually creates a thin layer of oxide on steel, helping to protect steel from corrosion. But in some cases, this protection ability is not enough. One of the main sources of corrosion in steel is salt. Whether it is due to contact with salty water near the ocean environment, or the use of anti-frozen salt to ensure a safer path in the winter. These ion chlorides can pass through concrete, corrode steel, and when steel is corroded, it creates a thin layer of oxide that expands inside the concrete. This expansion creates a reaction, sometimes called a kick oxide, and is one of the main causes of concrete corrosion. So, how do we prevent these ion chlorides and other pollutants from reaching steel and causing food poisoning? The first form of protection is coating. Coating is the minimum distance between the outside surface of concrete and steel, and depends on the level of contact and application. Some certain rules specify different amounts of concrete coating, usually from 25 to 75 mm. Coating is one of the reasons why the work of mixing concrete to meet the requirements will require a lot of effort before the concrete appears in the factory. A solid coating and a lot of tightening of all the steel pieces together will ensure that, through all the fallout and confusion that occurs when the concrete is actually poured, the steel is still in the right position to be poured into the final product. Skipping these steps can cause the steel to sink to the bottom of the concrete layer or get too close to the outside surface before the concrete hardens, eventually leading to the steel being eaten up early due to a lack of coating. But even when there is a suitable layer of coating, concrete coating can still cause pollutants and water to come into direct contact with the steel, and you will not be surprised to learn that concrete coating is not rare. Almost all concrete is solid when frozen. This can lead to cracking. The change in temperature can also lead to expansion and solidification, which can lead to cracking. Concrete can also crack under normal conditions due to the way the steel absorbs the reaction in the material. One way to solve this problem is to react the steel first. But today, I would like to introduce another method to reduce these cracks. Concrete coating is almost as accurate as you would expect. This is not a new idea, but understanding and using different types of steel in our concrete still continues to develop. Adding crystal, steel, or composite to concrete can bring many benefits, but one of the most important benefits is controlling cracks. We tested 3 layers of 200mm thick concrete with hydraulic pressurization to check the hardness of each layer and see how it worked. The first thing is that there is only steel as a coating. When you increase the load on the steel, you will see cracks start to appear when the force is applied to about 3 tons. These cracks are formed because the steel expands a little when it absorbs the reaction in the concrete. Hydraulic pressurization is very good and not even close to the crack level, but concrete cannot expand with steel, so it has to crack. You can imagine that these cracks can let water and air come into contact with the steel, and finally make the concrete crack. For the other two layers, I have added fiber to the concrete mixture. One layer has steel fibers and the other has crystal fibers. Steel and fiber combine together to resist the reaction in the concrete. Steel provides a large amount of steel to resist the tensile force on the entire structure, and fiber provides a small amount of steel to resist the tensile force of the concrete. At the level of 3 tons on these layers, you cannot see any cracks. In fact, for these two layers, you will not see any cracks until you almost double that force, and even after that, the cracks will be much smaller. Both layers are buried at the same level as the first layer. The fibers do not really increase the total force for the layers, but you can easily see that they can prevent the concrete from absorbing the reaction. You may ask yourself why we use steel for reinforcement. That's because steel is relatively cheap, has been tested carefully and reliably, but there are many other materials with excellent mechanical properties that do not have this problem. For a high-density environment, sometimes we use epoxy steel or even stainless steel, but there are some new replacement solutions, such as polymer reinforced steel or FRP steel. This is a reinforced material made from basalt, molten molten rock is pressed through small holes to create extremely strong fibers. Such choices often cost less than steel, and in some cases are much more expensive. But the main obstacle to using newer, more creative materials is not just the cost. It is easy to see that these additional costs can be compensated by the increasing age of the concrete. Another simple criticism is that we do not use a lot of material. The slow development of new construction techniques is due to the high impact of the accident. Increasing confidence in a design involves a lot of technical theory, as well as simply looking at how similar designs have worked well in the past. But many technical disasters are not due to poor design, but due to poor maintenance. Therefore, long-term maintenance may be important for safety and supply, like other design criteria. We will definitely see more ways to improve concrete in the future, including the options I mentioned in this video. Thank you for watching and let me know what you think.