Introduction
Following my debrief in the previous article about the broad study of materials science and engineering, let us delve into the deeper pieces of it. Perhaps, we can focus on a specific material, such as cement.
A lot may ask, what is so special about cement? Well, cement is one of the most important construction materials as it binds different materials together. Cement is a basic material for building structures, such as houses, roads, bridges, and dams.
Development
Before we break down the cement composition, some essential vocabulary tends to be mixed up when discussing cement. When I took a materials science class at Brown University, my peers and I, when talking about what we had learned in the class, all mixed up cement and concrete in these discussions. Upon hearing these conversations, our professor was livid. She explained that many people in conversation use cement and concrete interchangeably, but this would be wrong. Cement is an ingredient of concrete and makes concrete itself stronger, by binding it together.
Now let’s break down the process of making cement:
To create the ceramic material of cement, there are three primary raw materials needed. They are limestone, clay, and sand. These three materials can be extracted from quarries, usually through blasting and drilling.
Then those raw materials are crushed into smaller pieces for easier handling, and then to ensure a uniform chemical composition, they are pre-homogenized. The process of pre-homogenization is just a safe way to make sure that the raw materials are as uniform as possible.
The next step is called raw meal grinding, where the raw materials are ground into a fine powder. This can be described as the initial state of cement, and it is extremely crucial because it impacts the quality of the cement.
After, the raw meal that has now been created, is heated in a preheater tower at 800-900 degrees Celsius. This is when the chemical decomposition starts, and the moisture is driven off of the materials. Then the process of pre-calcining begins, which further heats the materials to 900-1000 degrees Celsius. It also ensures the carbonates in the raw meal are converted into oxides.
As the process moves along the raw meal gets transferred into a rotary kiln, and as seen before the temperature will just increase at every step, particularly at 1400-1450 degrees Celsius. This will fuse the raw meal to make this dark grey color and it’s called clinker. This step is known as the kiln phase.
Because of how hot the clinker is, there has to be a cooling process, using either air or water. This cooling preserves the desired mineral structure, which keeps the desired strength or durability.
Once the clinker is cooled, it is mixed with a small amount of gypsum, a soft sulfate mineral. Then it will become a fine powder and the gypsum is added to control the setting time of the cement. This resulting product is known as Portland cement. Portland cement is the most used cement in construction.
The finished cement will then be stored in silos before being packed into bags and shipped. Quality control is essential throughout the production process to ensure the cement meets the required chemical composition, fitness, and setting properties.
Altogether, every step of the cement-making process is crucial, because if one step goes wrong the cement cannot be used and therefore it will have to restart. Luckily, because of the technological advancements humanity has made, creating cement has become an easier, and more efficient process which only takes up to a couple of days to complete.