Concrete

Concrete is a composite material made from aggregate held together by a special mix that hardens into a solid. It is the most used building material in the world, second only to water. When you mix Portland cement with water and aggregate, it becomes a liquid that can be poured into any shape you like.

Over time, the cement and water react and harden, creating a strong, stone-like material. This process can be changed with special additives to make concrete stronger or set faster. Often, steel bars called rebar are placed inside the concrete to make it even stronger.

Before Portland cement was invented in the early 1800s, people used other types of cement. Today, most concrete uses Portland cement, but there are other kinds too, like asphalt concrete used for road surfaces. Concrete is different from mortar, which is used to hold bricks and tiles together, because concrete contains larger pieces and is used by itself to build structures.

Etymology

The word concrete comes from a Latin word called "concretus". This word means "compact" or "condensed". It comes from an old Latin verb that means "to grow together".

History

Ancient times

Concrete floors were found in old palaces in Tiryns, Greece, from around 1400 to 1200 BC. The people of Greece used special kinds of lime to make strong binders as early as 800 BC. The Assyrian Jerwan Aqueduct, built in 688 BC, used a kind of concrete that could stay strong even when wet.

Long ago, traders called the Nabatean lived in places like southern Syria and northern Jordan. By 700 BC, they had learned how to make a special kind of lime that could harden on its own. They built homes, floors, and secret water storage spaces using this concrete-like material. Some of these buildings still stand today.

Classical era

The Romans used concrete a lot from 300 BC to AD 476. They made their concrete from quicklime, a special kind of ash called pozzolana, and small rocks like pumice. This concrete let them build amazing structures like the Colosseum and the Pantheon, which have the world's largest unreinforced concrete dome.

Roman concrete was very strong, almost as strong as the concrete we use today. But it wasn’t as flexible as modern concrete because it didn’t have steel inside to help it bend. The special rocks and ashes they used in their concrete helped it last a very long time, even near the sea.

Middle Ages

After the Roman Empire, people in places like England kept using lime to make mortar, but the quality wasn’t always very good. They started using better ways to grind and mix the materials in the 12th century, which helped improve the concrete. In places like Mexico, people also used a kind of concrete to build strong buildings.

Early modern period

In the 1600s, people began using a special kind of lime called hydraulic lime to make concrete that could stay strong even underwater. One famous example is the Canal du Midi in France, which was built using concrete in 1670.

A big step forward happened in the 1700s when an engineer named John Smeaton used hydraulic lime to build a lighthouse. He mixed it with small rocks and broken bricks to make a very strong concrete.

Modern period

In 1824, a man named Joseph Aspdin in England invented a new kind of cement called Portland cement. Later, in 1849, another man named Joseph Monier discovered how to make concrete stronger by adding steel inside it. This is called reinforced concrete. In 1928, a French engineer named Eugène Freyssinet invented a way to make concrete even stronger by pulling on it with special cables before it was finished.

Composition

Concrete is a special kind of building material made by mixing things together. It starts with cement, which acts like glue, and pieces of rock or sand, called aggregate. When you mix cement with water and these pieces, it becomes a thick liquid that can be poured into any shape you want.

After a while, the water and cement react together in a special way and harden, turning into a strong, stone-like material. This is why concrete is used for so many buildings and structures — it gets very strong and lasts a long time. Sometimes extra things are added to change how concrete works, like making it stronger or easier to pour. Steel bars are often put inside concrete to make it even stronger.

Production

Concrete production is the process of mixing together water, small rocks or sand, cement, and any extra materials to make concrete. Once mixed, the concrete must be placed before it hardens. Most concrete is made in large factories called concrete plants or batch plants. These plants have big containers for storing ingredients like cement and sand, machines to mix the ingredients, and trucks to carry the mixed concrete to where it is needed.

There are two main types of concrete plants: ready-mix plants and central mix plants. Ready-mix plants blend the dry ingredients, while central mix plants also add water. Central mix plants can make concrete with more precise quality but need to be close to where the concrete will be used.

When concrete is poured, it is often placed into special molds called formwork that hold its shape until it hardens. Sometimes, concrete can be made in factories to create pre-made products like walls or floors.

Workability is how easy it is to pour and shape fresh concrete without losing quality. It depends on how much water is used, the size and shape of the sand and rocks, and the type of cement. Tests like the concrete slump test can measure workability by how much the concrete flows when a cone is lifted off it.

Concrete needs to stay moist while it hardens to become strong and last long. This process, called curing, helps the concrete gain most of its strength in just a few weeks. Keeping the concrete damp during curing prevents cracks and weakness. Methods to keep concrete moist include spraying it with water, covering it with plastic, or using special curing compounds.

Alternative types

Main article: Types of concrete

Main article: Asphalt concrete

Asphalt concrete, also called asphalt or blacktop, is a material used for roads, parking lots, and airports. It is made from rocks mixed with a special kind of tar. People have used it for building roads since the early 1900s.

Main article: Geopolymer concrete

Geopolymer concrete is a special type of concrete that does not use lime, which helps reduce pollution.

Graphene enhanced concretes are regular concrete mixes with a tiny amount of a special material called graphene added during mixing.

Main article: Pervious concrete

Pervious concrete is made with big pieces of rock and little sand. It lets water pass through, which helps keep streets and parking lots from flooding.

Main article: Polymer concrete

Polymer concrete uses special kinds of glue instead of regular cement. It is very strong and does not let water through easily.

Plant fibers and particles can be added to concrete mixes. These materials can make the concrete bend more without breaking, but they can change the concrete’s properties in hard-to-measure ways.

Main article: Sulfur concrete

Sulfur concrete is a special kind of concrete that uses sulfur instead of cement or water.

Volcanic concrete uses rocks from volcanoes instead of limestone. This kind of concrete does not create as much pollution and can help protect the concrete from damage.

Pyroclastic materials like pumice come from volcanoes and have been used in building for thousands of years.

Main article: Waste light concrete

Waste light concrete is a special kind of concrete that uses everyday trash instead of regular building materials. It is not as strong as regular concrete but can be used for roads and buildings.

Recycled aggregate concretes are regular concrete mixes where some of the usual rocks are replaced with old building waste. This can make the concrete a little weaker, but it helps reuse materials and save resources. The strength of this concrete depends on how the old materials are treated and crushed.

Properties

Main article: Properties of concrete

Concrete is very strong when pushed together, but not as strong when pulled apart. To make it stronger in all directions, it is often mixed with steel that is good at pulling. Concrete doesn’t change much shape when force is applied lightly, but it can crack when force grows bigger. It also doesn’t expand much with heat and can shrink as it hardens. Small cracks are normal in concrete because of these changes.

The strength of concrete depends on what it is used for. Very weak concrete might be used for light items, while stronger concrete is needed for big buildings or bridges. Special very strong concrete can be used for important parts like tall building columns.

Concrete can help save energy in buildings. Walls made of concrete keep air from escaping, which helps keep the inside temperature steady and saves energy. Modern buildings often use special concrete walls that are filled with insulation to stay warm in winter and cool in summer.

Concrete buildings are also safer in fires because they don’t catch fire easily and can survive longer in a blaze than buildings made of steel. They are also strong against strong winds and earthquakes when built properly.

Construction

Concrete is one of the strongest and longest-lasting building materials. It stays strong for many years and can resist fire better than wood. People use concrete more than any other man-made material in the world. About 7.5 billion cubic meters of concrete are made every year—that’s more than one cubic meter for every person on Earth!

Reinforced

To make concrete even stronger, people add steel rods or wires called reinforcement inside it before it hardens. This is called reinforced concrete. The steel and concrete work together to hold up buildings, bridges, and many other structures. Reinforced concrete can be built in place or made in a factory and then moved to the building site. It is used for walls, floors, beams, and columns.

Precast

Precast concrete is made in a factory first and then brought to the building site. This way, it can be made in a clean, safe place. Precast concrete saves time and can look very nice because it can be shaped and finished before it is installed.

Mass structures

Very large concrete structures, like dams and big foundations, can create a lot of heat as they harden. To prevent damage from this heat, builders use special cooling methods. They can also use a type of concrete that needs less cooling.

Surface finishes

Raw concrete can look plain and might let water through. People can change how concrete looks and works by using patterns, polishing it, or covering it with other materials.

Prestressed

Prestressed concrete is a special kind of reinforced concrete that is squeezed tightly during building to make it stronger. This helps beams and floors stay up better and can make them lighter.

Placement

After concrete is mixed, it is taken to where it will be used. Big amounts might be poured from trucks, and smaller amounts might be carried in containers or wheelbarrows. Special methods are used when pouring concrete in cold weather or underwater to make sure it hardens properly.

Roads

Concrete roads last longer and use less fuel to drive on. They can also help the environment because rainwater can soak into the ground instead of running off into drains.

Tube forest

Scientists have made concrete that looks like a forest of tubes. This special concrete is much stronger and can resist breaking better than regular concrete by spreading cracks in a controlled way.

Environment, health and safety

Main article: Environmental impact of concrete

Making and using concrete can affect the environment, the economy, and people’s health. When concrete is ground up, it can create dust that is harmful to breathe. This dust can cause health problems like skin irritation and lung issues. Special tools and safety rules help protect workers from this dust.

Concrete also affects the climate. Making cement, a key part of concrete, releases a lot of carbon dioxide, a gas that warms the planet. Every year, the world uses more than 10 billion tonnes of concrete, so finding ways to use less of this gas is very important. Scientists are working on new ways to make concrete that are better for the environment, such as using different materials to mix with cement. These new mixes can help reduce the amount of carbon dioxide released when concrete is made.

Concrete can also affect water and weather in cities. It can change how water flows, sometimes leading to flooding. It also can make cities feel hotter than usual. Even though concrete has these effects, it is very important for building strong and safe structures.

World records

The Three Gorges Dam in Hubei Province, China, holds the record for the largest amount of concrete used in one project. About 16 million cubic meters of concrete were used over 17 years to build this dam.

Other amazing concrete records include pumping concrete to a height of 715 meters during the Parbati Hydroelectric Project in Himachal Pradesh, India, and pouring 32,100 cubic meters of concrete in just 24 hours for the Polavaram dam in Andhra Pradesh. There are also records for the largest continuously poured concrete floor and the largest underwater concrete pour.

Art

Concrete is used as an artistic material. Artists sometimes make paintings and other works that look like concrete surfaces. For example, an artist named Sardoine Mia from the Congo makes canvases that resemble concrete.