In this blog post, we will look at the development of concrete from its origins to the present day, and learn about the technological evolution and importance of reinforced concrete and prestressed concrete.
It is very difficult to find a place on earth that has not been touched by concrete. The presence or absence of concrete can even be used to determine whether modern civilization has arrived in a place. Concrete can be found everywhere, including houses, bridges, roads, buildings, and dams. We often see this material as a gray, solid finished product, but it is not easy to understand what materials and processes are involved in its creation. By looking at where and in what form concrete originated in the past and how it has developed through various processes to become what it is today, we can see that concrete has been part of human history throughout the world from ancient times to the present day. But first, let’s find out what concrete actually is.
Concrete is a mixture of cement, sand, gravel, and other aggregates mixed with water. In other words, to understand concrete, you must first understand cement. Cement is a binding agent used in construction and civil engineering to bond materials together. In a broad sense, glue, bond, and even solder can be considered cement, but generally, it refers to an inorganic binding agent used in civil engineering and construction. Cement connects materials, so its role in concrete is to bind aggregates together into a single mass. The answer to why cement acts as a binder lies in the hydration reaction. Hydration is a chemical reaction between cement and water that initially causes a new mineral structure to form, followed by hardening and the development of strength. In simple terms, cement and water mix to form a new material that hardens. The heat generated by this reaction can cause cracks in the concrete.
So, have concrete and cement been together since the beginning? What did concrete look like in its early days? Tracing the origins of concrete, we find the Latin word concretus, which means “solid,” and ancient Rome, where the word originated. The Romans mixed sand and water with lime to make lime mortar, which was the beginning of concrete. However, lime mortar had a tendency to crumble easily when moisture evaporated. Later, pozzolana, which was volcanic ash mixed with lime mortar, was used. This had good hardening properties when mixed with water and was used in numerous structures during the Roman era, such as roads, castle walls, waterways, houses, and palaces. In particular, if you look at the dome of the Pantheon, you can see traces of formwork and aggregate inside, which can be considered the origin of concrete. Concrete began to develop in earnest in the 18th century when British architect John Smeton invented hydraulic lime by heating limestone containing clay.
Later, in 1824, British architect Joseph Aspdin baked clay and limestone together to create the first artificial cement. Every time this cement was made, the mixture overheated and formed hard lumps, which were initially discarded as useless. However, in 1845, Isaac Johnson discovered that grinding these lumps produced a higher quality cement. This is the Portland cement used today. Three advantages—a simple manufacturing process, excellent quality, and readily available raw materials—quickly spread this cement around the world, and concrete made from it became the primary building material.
Concrete is a material that is strong against pressure but weak against tensile force, which is a fatal flaw. Iron is used to compensate for this weakness. Iron is strong against both compression and tension. Consider a long concrete block used as a beam that bends downward in the middle. The upper part of the concrete beam will be able to withstand the pressure, but the lower part may crack due to tensile force. To compensate for this, iron rods are inserted into the bottom. In 1867, French gardener Joseph Monier obtained a patent for a concrete flowerpot reinforced with iron mesh and continued to use reinforced concrete for bridge arches, stairs, and railroad tracks. Later, in 1887, Koen and Weiss of Germany systematized the theory of reinforced concrete structures, and reinforced concrete became the mainstay of the architectural world and the driving force behind the emergence of skyscrapers.
Even after the invention of reinforced concrete, cracks easily formed in buildings due to the weak tensile strength of concrete. This was further accelerated by the weight of the buildings, and rainwater would enter through the cracks, causing moisture and salt to come into contact with the steel bars, leading to corrosion. The durability of buildings remained an issue. Prestressed concrete was created to solve this problem. As the name suggests, it involves applying stress, or force, in advance. By applying stress during the manufacturing process before the building has to bear any load, the fundamental problem of concrete cracking was solved. This was widely used in the post-World War II reconstruction process and became widespread. In addition, ready-mixed concrete was invented, which greatly increased efficiency and usage. This cement, known as “ready-mix” for short, is a homogeneous concrete that is delivered in a non-hardened state, as the name suggests, greatly reducing construction time. This was made possible by the invention of the truck mixer.
The development of concrete continues even today. In addition to steel reinforcement, special concrete containing advanced carbon fibers is used for road and runway pavement, and in Japan, ultra-high-flow concrete has been developed for LNG tanks. Even translucent concrete has been installed at the National Building Museum in Washington, D.C., and concrete that is 30% hollow, allowing water to be absorbed and plants to grow, has also been developed. Its water-absorbing properties make it useful for flood prevention, and it can also be used as an excellent soundproofing and heat insulating material thanks to its air pockets. With its low density and high strength, concrete is now used to build skyscrapers that can withstand earthquakes, and it continues to exceed expectations every day.
