In this blog post, we will explore the physical properties of steel bars and concrete, their complementary roles, and the scientific reasons why reinforced concrete is widely used in building structures.
Various materials are used in the construction of buildings. Reinforced concrete is one of the most commonly used materials. Reinforced concrete is a material made by adding steel bars to concrete. It is different from ordinary concrete, which is made purely from concrete, and steel bars, which are made purely from steel. Reinforced concrete is a material that combines the two materials to create a new material with new properties.
At first glance, it seems simple to create a new material called reinforced concrete by using steel bars and concrete. It is just a matter of arranging steel bars inside the concrete before it hardens and allowing them to harden together. However, there is a scientific reason why these two materials can be used together. That reason is thermal expansion coefficient. Thermal expansion coefficient is the unique value of a material’s change in volume in response to temperature changes. Reinforcing steel and concrete have almost the same thermal expansion coefficient. In other words, the rate of change in volume due to temperature changes is the same. Therefore, there is no problem in using these two materials together. If the thermal expansion coefficients were different, the two materials would change volume differently, and reinforced concrete, which is a combination of two different materials, could not be used at construction sites.
The use of reinforced concrete has advantages over the use of concrete alone or reinforced steel alone. These advantages arise from the characteristics of each material, reinforced steel and concrete.
There are various types of forces that building materials are subjected to, but the most representative forces are compressive and tensile forces.
When a building is subjected to a load, the materials bend downward, causing compressive force to act on the top of the material and tensile force to act on the bottom. Each material has a different ability to resist compressive and tensile forces. Concrete is resistant to compression but weak against tensile force. Therefore, in the case of concrete, destruction occurs at the bottom where tensile force is applied, as shown in the figure above. On the other hand, steel bars resist both compression and tension well. In other words, the characteristic of reinforced concrete is that steel bars are placed near the area where tensile force occurs in concrete, as shown in the figure above, so that the steel bars resist the tensile force. Therefore, steel bars are basically placed at the bottom of concrete in the figure above, where tensile force acts. As such, reinforced concrete is more resistant to tensile forces than ordinary concrete, which is an advantage in constructing safer buildings.
We have learned above that reinforced concrete is a better material than ordinary concrete. However, it is still unclear whether it is a better material than steel. According to the above facts, steel is strong in both compression and tension, so isn’t it unnecessary to use reinforced concrete? However, even so, reinforced concrete is used rather than steel alone. There are several reasons for this, but the most important reason is to prevent corrosion of the steel. Steel is a metal, so it corrodes when exposed to air. Corrosion weakens the strength of steel. In reinforced concrete, the steel is inside the concrete, so it is not exposed to air, and the concrete prevents the steel from corroding. In other words, using reinforced concrete is still more effective than using steel alone in terms of building stability.
Above, we looked at the advantages of reinforced concrete compared to ordinary concrete and steel. Because of these characteristics, steel and concrete are more often used together as reinforced concrete rather than alone.
