Everything You Need To Know About Cement And Concrete

In the modern world, every building and every road is most likely built using concrete. In fact, the only material used more than concrete is water itself. 

Where does cement come into the picture though?

For most people, concrete and cement are synonymous with each other. However, their actual relationship is quite different. Cement (more precisely, Portland cement) is the most important ingredient of concrete. 

That’s just the beginning, though: here’s everything you need to know about the properties of both materials, they’re made, and the factors that impact their quality.

Cement basics

Portland cement is the most common variant of this material, created in 1824 in England by an ingenious stonemason Joseph Aspdin. When compared to the manufacturing process of this material today, its invention seems crude in comparison – Aspdin created it by burning clay and powdered limestone on his stove.

Today, its manufacturing process is a lot more controlled than it was on old Joseph’s stove. 

We can only say that the rest is history, as cement became one of the most important manufactured materials of all time. 

Cement is made through a chemical combination of calcium, aluminum, silicon, and iron. This means that a lot of raw materials can be used for manufacturing it. For example, it’s possible to combine limestone, chalk, marl, or shells with silica sand, iron ore, shale, slate, clay, and blast furnace slag.

Laboratories closely check each step in the creation of this wonder material by frequently testing its physical and chemical properties. Additionally, they also test the finished product to ensure it’s up to industry standards.

Common methods of cement production

There are two methods of manufacturing:

  • Dry method
  • Wet method

The dry method is more popular (and more modern) so we’ll explore it in more detail (don’t worry, we’ll also explain the wet method too). 

It all starts in a quarry where principal raw materials, like limestone or clay, are collected. These materials are then crushed multiple times in crusher machines. In the first stage, the machine is used to crush the rock down to a size of about six inches. Those fragments are then transported into a hammer mill that reduces the rocks down to three inches and even smaller.

The next stop in the manufacturing process occurs in massive cylindrical steel rotary kilns. The inside is lined with firebrick, where all that ground-up rock mixed with other materials like fly ash or iron ore ends up. 

The axis of these kilns is inclined slightly from the horizontal so that the raw materials can get fed into the higher end. The lower end can be simply described as a furnace in which the ingredients are then heated to about 1482 degrees Celsius (2700 Fahrenheit). This blast of flame is produced by a controlled burning process, which includes coal, oil, gas, or alternative fuel.

The raw materials travel through the kiln as certain elements evaporate in the process. Subsequently, the remaining elements combine and form a new substance known as a clinker. These marble-sized balls exit red hot from the kiln and are cooled down with different types of coolers. 

After the cooling process is complete, the clinker gets ground up and mixed with limestone and gypsum, and voila! You’ve got cement that’s ready to be shipped out to concrete companies.

Remember when we mentioned the wet process? Seems like ages ago. Anyway, both methods are quite similar and involve the same steps. The only difference is that in the wet process, materials are first grounded with water before they are fed into the klin.

Concrete basics

Despite its monumental impact on our society, concrete is really a simple mixture. It’s made by combining our old friend Portland cement with water to form a paste that is used to coat the surfaces of sand and rock (aggregate). All the ingredients are bonded together into a solid material known as concrete.

Everything boils down to the chemistry of cement. When it comes into contact with water and forms a paste, it binds together particles of stone and sand. Through the process of hydration, this paste can solidify and gain structural strength.

You might be wondering how this material can be so diverse that it can be used to build so many different types of buildings. The answer lies in a remarkable trait of concrete – plasticity. 

When it’s freshly mixed, it can be formed into any shape you can imagine. However, once it dries and hardens, concrete is one of the strongest and most durable construction materials on the planet.

What determines the quality of concrete?

The durability of concrete depends on how well the ingredients were proportioned and mixed. 

For example, if your mixture has an insufficient amount of paste to fill the small spaces between aggregates, it will be difficult to place. Once it dries off, it will produce concrete that’s porous and has a rough, honeycomb surface. 

On the other side, too much paste will result in a substance that’s considerably easier to place. Even though the surface will be smooth, the concrete will be more likely to crack.

The best concrete is somewhere in between. If you proportion the mixture well, the fresh concrete will be easily workable and the hardened concrete will be strong and durable. By volume, a typical concrete mixture usually contains:

  • 10-15% of cement
  • 60-70% of aggregates
  • 15-20 of water
  • 5-8% of entrained air bubbles

The characteristics of the concrete itself depend on the paste, while the strength of the paste is determined by the water-cement ratio. To produce concrete of the highest quality, it’s important to reduce this ratio as much as possible without negatively affecting its workability. 

As a rule of thumb, less water equates to concrete of a higher quality, assuming the concrete is properly placed, consolidated, and ultimately cured.

It’s also important to note that concrete may also contain additional materials that increase its strength and durability. For example, it can contain fly ash, which is a byproduct of burning coal. Other byproducts that can be used in concrete are slag, which results from manufacturing iron and silica fume that is created when silicon and ferrosilicon metal are being manufactured.

While these are all waste materials, they can play an impactful role in the hydration reaction that creates concrete and makes it even more resistant than it already is. 

Final thoughts 

Look around you and you’ll see concrete. It’s one of the materials that completely changed our lives and helped the growth and survival of human society as we know it. 

It’s an essential part of the reliable infrastructure that we have today, without which large cities wouldn’t be able to come into existence. That’s because concrete is not only robust and affordable, but it’s also easily accessible. Most importantly, it allowed us to envision structures that climb high into the sky and look borderline futuristic – all because it’s strong and can be formed into any shape you can imagine. 

To think it all started with an Englishman experimenting in his kitchen…