Concrete is the world’s most versatile and widely used building material and the second-most used substance on earth after water. Concerning infrastructure of any kind, concrete is present in just about everything. If you were to look around right now, you could probably identify multiple sources made from this solid material. From buildings, swimming pools, roadways, and airport runaways, to doors, staircases, and beams, concrete is everywhere.
What Is Concrete Made Of?
There are many different types of mixtures and grades of concrete, but for now, we’ll focus on its four raw materials:
- Gravel (a coarse aggregate)
- Sand (a fine aggregate)
Water, cement, gravel, and sand are mixed together and left to rest and dry until it hardens (cures) into a stone-like structure. Concrete mix is typically made up of roughly 10% cement, 20% air and water, 30% sand, and 40% gravel. Though the ingredients are simple, what makes concrete so effective is how each ingredient plays its role.
Water and air provide the needed chemical reaction to create workability and hydration. As a general rule of thumb, the more water mixed in, the less strength the hardened mixture will have. Since the amount of water content affects the mixture’s strength, there’s a fine balancing act of water-cement ratio to create the right concrete for the job. Water also has to be clean and free of chlorides to prevent side reactions from occurring, which may weaken the concrete.
The smallest percentage of the mixture is the glue that keeps everything together – cement. Often confused with concrete (more on that later), cement plays a critical role in turning the mixture from liquid to solid. The most common is Portland cement. Cement is the most complex of the ingredients and is made out of a combination of carbonates of lime (limestone, chalk, or marl) and clay. There are many different types of cement depending on the type of concrete needed.
Durable structures cannot come from just cement and water. It needs an aggregate. The other ingredients make concrete into a kind of shapeshifter. And over time, its structure will begin to change shape. However, an aggregate (sand, gravel, rock, etc.) will help concrete to hold its shape much longer.
Aggregates like sand and gravel make up around 70% of the mixture. They fill in spots in the concrete that would otherwise be one too many air pockets. Making up the bulk of concrete’s volume saves cost and improves the structure by increasing strength and reducing shrinkage.
What Is the Difference Between Cement and Concrete?
When recalling the difference between cement and concrete, think of cement as flour and concrete as bread. Cement, like flour, is an ingredient in concrete (bread), but it can also be an ingredient in other things. By definition, cement means something that binds or glues two or more materials together.
To paint the picture more clearly, let’s walk through some common mixtures made with cement:
- Cement paste: cement +water
- Mortuary grout: cement + water + sand
- Concrete: cement + water + sand + stone, gravel or rocks
As the primary binding ingredient in concrete, cement is the most complex and expensive part of the mixture. It’s manufactured through the chemical combination of eight main ingredients, including lime, silica, alumina, magnesia, sulfur trioxide, alkaline, iron oxide, and calcium sulfate.
Fun fact: Did you know the Romans built the earliest concrete structures with a mix of quicklime, pozzolana, and pumice?
What Are the Most Common Types of Concrete?
While the ingredients that makeup concrete are simple, the process of developing a specific concrete mixture by including or excluding certain additives can be somewhat complex. These formulas are known as mix design which is important for ensuring the properties of concrete are proportionate. Different mixing proportions make concrete a reliable and powerful building material. Here are some of the most common types:
- Plain or ordinary: One of the most commonly used types of concrete. You can find it in bed flooring, under the column footings, and in buildings where very high tensile strength is not required.
- Normal strength: A typical foot of concrete combining all the basic ingredients using the 1:2:4 ratio. It is frequently found in pavements or buildings.
- Reinforced concrete: Concrete on its own has high compressive strength; however, the opposite is true for tension. You’ll notice cracks in concrete as a result of too much tension. Reinforcements like wires, steel rods, plastics, or cables are placed inside the concrete before it sets to create a strong bond and help resist tensile forces. This type is widely used in industrial and modern construction.
- Lightweight: Natural and artificial materials with very low thermal conductivity. This type of concrete does a great job protecting steel structures and building long-span bridge decks.
- Heavyweight: Made from high-density crushed rocks and mostly used in atomic power plants and similar concrete structures because it provides protection from radiation.
- Ready-mix concrete: We see cement trucks on the road all the time, but little do most of us know that those trucks are in the process of concrete production. This type is being mixed en route to the construction site, which is key for providing high-precision fresh concrete that’s ready to pour on site.
- Asphalt concrete: Known for its durability, workability, skid resistance, stability, fatigue resistance, flexibility, and permeability, asphalt is a dark mineral frequently used anywhere pavement is needed.
- Polymer: Replaces the cement concrete by using polymers to bind with aggregates increasing strength, adhesion, watertightness, chemical resistance, freeze-thaw durability, and abrasion resistance.
- Air entrained: Primarily used for freeze-thaw resistance, air-entrained concrete has microscopic air bubbles that relieve pressure during a freeze event. Without these voids or air pockets, the water would have nowhere to go, which would lead to cracks and a diminished lifespan.
But we’re only scratching the surface. These are just a few of the dozens of admixtures and components of concrete for specific applications.
The strength of concrete is determined by cement quality, the aggregates’ strength and distribution, and the amount of water in the mix. Curing (hardening) methods also play a fundamental role in the strength that concrete develops.
Depending on the goal, concrete can be fashioned into any shape and create many types of mixtures to build anything from skyscrapers to canoes.
What Are the Benefits of Using Concrete?
When it comes to building construction, there really isn’t a more well-rounded material out there. Because it’s available in a wide range of forms and mixes, it can adapt to form just about any structure, depending on the purpose.
Since concrete is made from simple ingredients, most of which come straight from the earth, it’s a very economical material. Compared to others, it’s downright cheap. But don’t take that to mean it’s not qualified to get the job done.
Concrete is the MVP of building materials because it’s a composite material with many applications.
So why is concrete used twice more than steel, wood, plastics, and aluminum combined? There are many reasons, but it all boils down to concrete being:
- Highly durable
- Low maintenance
- Fire resistant
- Moldable in any size or shape
- Corrosion resistant
- Environmentally friendly
Fun fact: The Hoover Dam, Panama Canal, and Roman Pantheon are some of the world’s largest and most famous structures made with concrete.
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