This blog post reveals the scientific secret behind why it’s called a ‘gift from God,’ exploring the structural advantages of reinforced concrete and the principle of thermal expansion.
You’ve probably seen ready-mix concrete trucks while walking down the street. The sight of those gray cylindrical trucks slowly rotating as they deliver concrete is common anywhere in the city. Have you ever watched a ready-mix truck heading to a construction site and wondered what’s inside? I remember my parents telling me as a child that the truck contained important materials used to build houses. Back then, I was just fascinated by the big rotating drum, but as time passed, I came to understand how crucial concrete is as a building material.
Before explaining the advantages of concrete and why it’s considered a miraculous technology, let’s first understand what concrete actually is. Concrete is a building material made by mixing coarse aggregates like gravel, fine aggregates like sand, water, and cement. Although concrete has been used for thousands of years, its importance has become even more emphasized in modern times. The reason various types of aggregates are used is that the type of concrete produced, along with its strength and density, varies depending on the size and type of aggregate used. Research into mixing cement appropriately with other materials to create better materials has been ongoing for a long time. As a result, concrete has become an essential building material in modern cities. Walking through any city’s streets, you’ll notice that most large buildings are constructed using concrete, specifically reinforced concrete.
This might raise a question: How were ancient structures built without concrete? In fact, materials similar to concrete were used even in ancient Roman times. For example, the Pantheon in Rome, the largest dome structure built with the architectural techniques of its era, was constructed using a special type of concrete mixed with volcanic ash. Considering this historical background, it becomes clear that concrete itself has long been a core material in construction. However, modern concrete has advanced incomparably compared to its ancient counterpart, with its strength and durability greatly enhanced through the technology of reinforced concrete.
So, let’s explore the advantages of reinforced concrete. The most fundamental principle of concrete is its adhesive strength. When water and cement are mixed, they form an extremely strong adhesive bond. This mixture permeates between the aggregate particles, slowly hardening and solidifying. Therefore, ordinary concrete resists compressive forces exceptionally well. This is because the cement paste permeates deeper into the aggregate. However, it often shows surprising weakness against tensile forces. This is because the bonding strength between the aggregate particles is reduced. Reinforcing steel within reinforced concrete compensates for this weakness. By taking on the tensile forces, the steel enables the concrete to withstand any type of load effectively. The drawback is that steel is a relatively expensive material, so reinforced concrete is typically used only for reinforcement in areas where significant tensile forces are expected. For instance, it is essential for critical structures like the foundations of high-rise buildings or the main structures of bridges.
Reinforced concrete also boasts outstanding performance in terms of durability. It undergoes minimal deformation over time and remains relatively safe against natural disasters like fires or earthquakes. This is why many modern structures choose reinforced concrete as their primary material. These advantages of concrete extend beyond being mere building materials; they are crucial elements directly linked to the safety of our lives.
Now, let’s explore why this reinforced concrete is called a gift from God rather than a great human discovery or invention. To understand this, we must first grasp the concept of thermal expansion. Thermal expansion literally refers to the expansion of a material when heat is applied. This occurs because the thermal energy applied increases the kinetic energy of the molecules composing the material. Just as humans move more actively when they have more energy, molecules also move more vigorously when they have more energy, causing the object’s length, width, and volume to increase. This can be observed when a flattened ping-pong ball is placed in hot water, and the flattened part returns to its original shape. The formulas for calculating the increase in these three physical quantities are distinct. However, they share a common feature: they are proportional to a constant known as the object’s specific thermal expansion coefficient. Just as people differ in the situations that energize them and the extent to which they become active after resting, the degree of thermal expansion in molecules varies depending on the surrounding molecules and the current state of the object. Therefore, the thermal expansion coefficient varies depending on the type of material.
This is where the reason why reinforced concrete is called a gift from God comes into play. The reason is that the thermal expansion coefficients of steel reinforcement and concrete are nearly identical. Let’s consider what would happen if the thermal expansion coefficients of steel reinforcement and concrete were not nearly identical. When two objects are stacked together, what happens if the inner object has a higher thermal expansion coefficient and reacts more sensitively to temperature changes? As the temperature rises, the inner object’s volume increases faster, causing the outer object to crack under the force it bears. Conversely, when the temperature drops, the outer object would contract more rapidly. The inner object, strained to withstand this force, would eventually crack. In other words, whenever the thermal expansion coefficients of objects differ, problems arise during temperature changes. Construction materials inevitably experience temperature fluctuations. While not true for every country, temperatures generally change with the seasons. Therefore, if the thermal expansion coefficients of steel and concrete were not identical when constructing reinforced concrete, we could not build houses with this material.
Ultimately, the fact that the thermal expansion coefficients of steel and concrete are identical is not a coincidence but is accepted as a phenomenon akin to a miracle bestowed upon us by nature. Thanks to this fact, discovered by scientists after years of research, we can now build tall buildings and sturdy bridges. Thus, reinforced concrete vividly demonstrates how crucial the harmony between human technology and nature is.
So far, we’ve explained the advantages of reinforced concrete and why it’s such an amazing technology using the concepts of strength and thermal expansion. Concrete, which we might normally pass by without a second thought, is actually a profoundly important technology deeply embedded in our lives. The next time you see a ready-mix concrete truck, I hope you’ll pause to consider the greatness of the technology within and the miraculous harmony it embodies. I’ll conclude by urging you to reflect once more on the advantages of concrete.
