Cement holds different material together and is a key ingredient in concrete
Buffalo City Court Building. © Pfohl, Roberts and Biggie/Wikimedia Creative Commons 2.0 Generic license
Engineers use many different materials. Your house is made of cement, wood, and glass, among other things. Now these materials do not magically stick to one another. An engineer must find a material to hold any structure together. For many building projects, this connecting material is cement. Cement is a grey powder made out of limestone and clay which must be mixed with water to harden. Just think of cement as a glue. It holds different materials together.
Concrete and cement have allowed countries to build beautiful structures and durable buildings. These two materials are often confused with one another. It is important to remember that cement and concrete are not the same thing. They do, however, have similarities.
Cement is the main ingredient of concrete
The bricks of this wall are held together with cement mortar. The actual bricks are made of concrete. © kevin brine/Shutterstock
Cement is the main ingredient of concrete. Cement combined with sand, gravel, and water forms concrete. In concrete, the cement binds the materials together.
When first formed, concrete is in a liquid form. It can easily be shaped. Like cement, concrete is a strong building material. Both are durable and have been used since ancient times. Concrete is the most used construction material in the world. Many dams, highways, and bridges are made of concrete. Most concrete contains Portland cement. An exception is roads. They are made of asphaltic concrete. Asphaltic concrete is commonly known as asphalt. It is a mixture of asphaltic cement and other materials, such as sand, stone, and gravel.
Cement is also used in mortar. Mortar is a paste that binds building materials together. We said earlier to think of cement as a glue. Mortar is what allows cement to act as a glue. Mortar is a mixture of cement and crushed stone or sand. Bricks and stones are held together with cement mortar.
Cement was used in Ancient times, but Portland cement is relatively new
Misleadingly low, the Pantheon's exterior dome steps outwards as it meets the uppermost ring of the drum. © Anthony M. from Rome, Italy/Wikimedia Creative Commons 2.0 Generic license
Incredibly old and beautiful structures were built with the help of cement and concrete. The Ancient Egyptians, Greeks, and Romans built with this material. Cement mortar, which pastes stones, bricks, and concrete together, is a very old material. The Coliseum and Egyptian Pyramids are held together with cement mortar.
A major difference between ancient and modern concrete is their cure time. Cure time is how long a material takes to completely harden. The cement ancient Romans used could take up to two years to completely harden. Modern concrete, by comparison hardens in days or even a few hours. This fast curing time helps construction to occur quickly. A downside is that when concrete cools too quickly, it contracts and cracks. These cracks are caused by a type of stress called thermal stress and they make concrete less durable. Thermal stress occurs when a material is heated and cooled too quickly.
Remember that ancient Roman buildings still stand thousands of years later because they are extremely durable. Concrete structures made today will likely not last more than 100 years.
Just as modern concrete is different, cement has changed. In the 1820s, Joseph Aspdin, a British stonemason, wanted to create a better cement. To do this, Aspdin heated limestone and clay on his kitchen stove. He then ground the mixture into a powder. This formed the first hydraulic cement. Hydraulic cement is just a fancy term meaning cement that hardens in water.
Aspdin’s new material, which he named Portland cement, has been a reliable and popular building material. Portland cement is good because it dries hard and quickly. This allows construction to happen quicker.
We often use Portland cement, but we manufacture it in a different way. It is no longer made on a kitchen stove out of limestone and clay.
Raw materials are ground, blended, and heated to make cement
Construction in Tunisia. © Oussama zrafi/Wikimedia Creative Commons Attribution-Share Alike 3.0 Unported license
Modern cement is made in three steps: grinding, blending, and heating. Cement is a combination of many different elements. The necessary elements are found in limestone, sand and clay. These elements are calcium, aluminum, iron, and silicon.
Dry cement and wet cement can be made. In the dry method, the raw materials are first ground into smaller pieces. The pieces are then blended together. Finally, the mixture is heated in a kiln.
In the wet method, water is added to the raw materials before they are ground. Next, they are blended together and heated. The wet process uses more energy. This is because more water must be evaporated from the cement. The dry process is therefore favorable because it requires less energy.
Both dry and wet cement are heated to over 2700℉. At this high temperature, chemical reactions occur, fusing the materials together.
The result is cement clinkers. Clinkers are little grey balls. The clinkers are removed from the kiln and cooled. Then the clinkers and gypsum, a mineral, are ground together into a powder. Each piece of the powder is so small that it could pass through a mesh sieve. This powder is cement.
Cement is durable, and its strength can be controlled
A soldier with 84th Battalion, 30th Brigade, 643rd Company from Schofield Barracks, Hawaii, empties a bag of cement that will be mixed into brick mortar during the Engineering Civic Action Program portion of Exercise Khaan Quest 2011 in Ulaanbaatar, Mongolia, Aug. 1. The purpose of the program is to improve medical care in the area by adding on to the Ayut Family Hospital, a 17,000 sq. ft. urgent care clinic, which will serve the 9th sub-district of khaan-Uul District. Public domain image.
Cement is extremely durable. To recognize how long cement lasts, just look to the Ancient world. The Pantheon in Rome is the world’s largest unreinforced concrete dome. It is over 2000 years old and relies on cement, the key ingredient of concrete.
High Performance Concrete bridges also exhibit this durability. Made of Portland cement, these bridges last for 100 years. They can withstand extreme weather and harmful chemicals.
Unlike its durability, cement’s strength is easily controlled. It is dependent on the amount of water added to it. Maximum strength occurs when 2.8 gallons of water are added to each sack of cement. Such strength, however, has a drawback. At its maximum strength, cement has a high viscosity. Viscosity means the resistance to flow, so something with a high viscosity will not flow easily. For example, honey has a high viscosity, which means that it sticks together and flows slowly. Water has a low viscosity and easily flows.
Cement’s high viscosity makes it difficult to use. When dealing with cement, builders must decide what balance of strength and viscosity is ideal.
Cement can be improved to help the environment
Cement is a strong building material and the key ingredient of concrete. Its impact spans from Ancient Rome to Modern America. This material, however, could be improved.
Cement production releases carbon dioxide - CO2 - into the atmosphere. This is bad for the environment. CO2 is considered a greenhouse gas that contributes to global warming. It also takes a large amount of energy to make cement. Over time, companies have improved their manufacturing process. Eco-cement, for example, absorbs CO2 while it hardens. Such reabsorption is better for the environment and is more energy efficient.
Remember that any building material can be enhanced. Perhaps you will be the one to create a completely environmentally-friendly cement!