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What is Concrete? - Composition & Use in Construction

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

In this lesson, we are going to learn about concrete, its components, and its use in construction. We are also going to talk about the mechanics of the materials in concrete.

Would you rather build your home out of wood? Steel? Concrete? As you can tell, you have many choices of materials and combinations of these choices and other materials can be used to help build your home or any other building. What you'll have surely noticed is that a ton of buildings are built with heavy reliance upon a building material known as concrete. Let's learn more about it and its uses in this lesson.

Concrete

Main Components

Concrete consists of a cement paste, aggregates (fine and coarse), and, in some cases, other materials.

Cement paste refers to a mixture of water and cement, the latter of which is a binding agent that acts like an adhesive, sort of like glue for a mixture. Cement itself is made from ingredients that are full of calcium or silica (silicon dioxide). These ingredients might include clay, limestone, or even cool-looking seashells! Each concrete mixture can contain up to 21% water and up to 15% cement.

Aggregates in concrete mixtures act as fillers and are a combination of fine material, such as finely crushed stone or sand, and coarse aggregates, such as larger crushed stone and gravel. Natural sources of aggregates are the most common ones used in concrete, but artificial ones, like burned clay, are sometimes used as well. Regardless, this aggregate mixture makes up to 75% percent of the volume of a concrete mixture.

Crushed Stone Aggregate
Crushed stone aggregate

Other materials can be added to the concrete mixture to modify its properties. For example, a liquid obtained from animal fats can be used as an air-entraining agent to build up the concrete's resistance to cold environments. Air-entraining agents create lots of microscopic air chambers that give water space to expand into when it freezes. This helps to relieve the internal pressure of concrete stemming from the expanding water and thus minimize its chances of cracking under this pressure.

Quality

The various characteristics and overall quality of concrete is determined by the exact proportioning and mixing of the ingredients used therein. For instance, when a mixture doesn't have enough cement paste, then the empty spaces between the aggregates creates a rather porous concrete that's hard to place and has a rough surface. On the flipside, if you use too much cement paste, then the concrete will be nice and smooth, but it'll crack more easily.

Generally speaking, high-quality concrete is made from as low of a water-cement ratio as possible, as long as the mixture can still be properly worked with, placed, and cured. What's the water-cement ratio? It's the weight of the water used divided by the weight of the cement.

Oh, and by curing we aren't talking about giving the concrete some sort of pill to make it feel better. Curing refers to the hardening of concrete. The reaction which hardens the concrete as well as strengthens it is called hydration. Hydration occurs when the water and cement are combined. The compressive strength of the concrete will increase as the hydration reaction continues for upwards of 28 days. By compressive strength, we mean the resistance the concrete has to being ''squished.''

Use in Construction

Concrete has been used in construction since ancient Rome. Over thousands of years, concrete has been developed for the purpose of construction. Nowadays, concrete is the single most widely used construction material in the world and is used in the construction of buildings, bridges, and mega-structures such as dams, pavements, etc. The reason for this is because the materials used to make concrete are so diverse and readily available; another reason for this is that concrete can be precast or poured into any shape.

The dome of the ancient Roman Pantheon is constructed of concrete.
The Ancient Roman Pantheons dome is made of concrete

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