The Science of Concrete: What Makes This Building Material So Unique?

By Cathy Habas

Concrete is a ubiquitous building material that has been in use for thousands of years. The mega structures of our modern world, including skyscrapers, dams and underground tunnels, would not be feasible on such a large scale without a cheap, easy to use, low-maintenance and durable building material.

Humble concrete is the only substance that comes close to satisfying these parameters. What makes this deceptively simple material so useful? Let’s take a look:

1. Concrete does not compress despite bearing heavy loads. It remains rigid and stable, assuming the concrete is set at the correct density for the weight it is expected to carry. The ability of concrete to support heavy weight allows it to hold the enormous pressure of water at sites like the Hoover Dam, to support the weight of skyscrapers and towers, and to ferry thousands of cars and trucks across bridges every day. When combined with steel and special aggregates, the overall strength and utility of concrete is second to none.
2. Concrete is pliable, but at only one point in time. Concrete is easy to install because it is initially in a fluid slurry form, allowing construction crews to transport it in batches, to pour it and spread it into any shape, to easily integrate steel reinforcements within the concrete, and to even customize its color and texture. Once the concrete dries, it never reverts to its slurry state, resulting instead in a solid structure like no other. But without that initial liquid, pliable state, construction would likely consist of placing stones on top of stones, a logistical nightmare for tall or complex structures. Think about the awe-inspiring craftsmanship of the Egyptian pyramids or the Roman aqueduct. Concrete erases the need for such time-consuming labor.
3. The characteristics of concrete can be modified by adding additional materials. The basic properties of concrete remain the same, but it can be used for innumerable purposes thanks to the addition of “admixtures.” Common admixtures include fly ash, calcined shale, calcined clay, silica fume, and slag. These admixtures can make concrete more pliable without requiring additional water and thus potentially altering the drying time and core stability. They can also make concrete easier to work with in adverse weather conditions, or they can simply make concrete more resistant to erosion based on its environmental placement. Concrete that is constantly submerged in ocean water, for example, benefits from some added protections. Engineers are often trained in concrete mix design in order to choose the best admixtures for their projects.
   

How Does Concrete Work?

Concrete is composed of limestone (CaCO3) and clay (specifically, silicon from the clay: SiO2). When heated to a temperature of 1450 degrees Celsius, calcium silicates (C3S and C2S) are formed. These compounds react with water in a process called hydration to form crystals that bind together and glue the other two components of concrete (sand and larger rocks called aggregates) together into a solid, dense structure.

Concrete Has Been Around for Thousands of Years But Continues to Be Developed

The use of concrete can be traced back to around 10,000 years. Thanks to modern technology, it continues to be developed and improved, and new uses for concrete are found all the time. For example, concrete serves as an effective shield against nuclear radiation, and biologists at Delft University of Technology have even discovered a way to use bacteria to automatically repair cracks in concrete structures.

In short, concrete can be considered one of the most important inventions for modern humans, allowing industrialization and urbanization to progress. Its unique properties, combined with the clever curiosity of the scientists who study it, have made it suitable for an astounding number of projects. It’s easy to take concrete for granted because it is absolutely everywhere. and yet society as we know it surely wouldn’t exist without it.
 

About the Author
Cathy Habas is a Louisville-based freelance writer specializing in fashion, health and home improvement. She received her Bachelor of Art's degree from Indiana University Southeast in 2014 and has been writing professionally ever since. In her spare time, Cathy loves to spend time outdoors with her posse of dogs when the weather's nice.

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